Chapter 9-17: Appendicular and Joint Anatomy PDF

Chapter 9: The Appendicular Skeleton The Shoulder Girdle - Composed of: - Bones found in the upper and lower limbs: humerus, ulna, radius, carpal bones, bones of the hand, femur, tibia, fibula, patella, tarsal bones, bones of the foot. - Bones that attach the limbs to the axial skeleton: - Shoulde...

Chapter 9: The Appendicular Skeleton The Shoulder Girdle - Composed of: - Bones found in the upper and lower limbs: humerus, ulna, radius, carpal bones, bones of the hand, femur, tibia, fibula, patella, tarsal bones, bones of the foot. - Bones that attach the limbs to the axial skeleton: - Shoulder girdle: clavicle and scapula - Pelvic girdle: os coxae Timeline of Skeletal Development Embryonic week 4: Limb development begins. Bones form from a hyaline cartilage model. Embryonic week 12: Ossification of bones begins. Birth: Bones have an ossified diaphysis and cartilaginous ends. Childhood: Bones are mostly ossified with cartilaginous epiphyseal plates. Onset of puberty approximately 11 years: Epiphyseal plate ossification begins. The lesser trochanter is the first to fuse. Approximately age 16-19: Epiphyseal plate ossification completes. The limbs cannot grow longer. Approximately age 25: The clavicle, which is the only appendicular bone to form by intramembranous ossification, completes its ossification process. - Appendicular skeleton development begins before birth and continues through early adulthood. - Completion occurs around age 25. Anatomy of a Limb - Mammals have similar limb construction: - Single, strong bone close to the trunk. - A hinge joint connecting two distal bones. - A complex joint made of a series of short bones. - A hand, foot, or wing made of rows of small bones. Bones of the Shoulder Girdle - The clavicle and scapula compose the shoulder girdle. - They anchor the upper limb to the axial skeleton. - They facilitate movement of the upper limb. - They serve as attachment sites for muscles that move the shoulder and arm. Clavicle - Also known as the collarbone. - Loosely anchored, S-shaped bone. - Articulates medially with the manubrium of the sternum, forming the sternoclavicular joint. - Articulates laterally with the acromion of the scapula, forming the acromioclavicular joint. Scapula - Located on the posterior of the shoulder. - Glenoid cavity articulates with the head of the humerus, forming the glenohumeral joint. - Coracoid and acromion processes. - Scapular spine. - Supraspinous, infraspinous, and subscapular fossae. Bones found in the Arm - Humerus - Ulna - Radius - Carpal bones - Metacarpal bones of the hands - Phalanges of the fingers Humerus - Head of the humerus articulates with the glenoid cavity of the scapula at the shoulder. - Multiple sites for muscle attachment. - Distal end forms the elbow. - Trochlea and olecranon fossa articulate with the ulna. - Capitulum articulates with the radius. Additional Bony Markings of the Humerus - Anatomical neck - Surgical neck (common site of fractures) - Greater and lesser tubercles - Intertubercular (bicipital) groove - Body (shaft) of the humerus - Medial and lateral epicondyles - Coronoid and radial fossae Ulna - Medial bone of the antebrachial region. - Proximal end resembles the shape of the letter "C". - Olecranon and coronoid processes form the trochlear notch. - Articulates with the trochlea of the humerus at the elbow. - Allows hinge-like motion of the forearm. Radius - Lateral bone of the antebrachial region. - Head articulates with the capitulum of the humerus at the elbow. - Rotates around the ulna to allow pronation and supination of the forearm. - Interosseous membrane is between the radius and ulna. - Distal end articulates with the carpal bones. Supination and Pronation - Movements that occur as the radius rotates around the ulna. - When the elbow is flexed: - Pronation occurs as the palm faces inferiorly. - Supination results in the palm facing superiorly. Bones of the Wrist: Carpals - Eight bones arranged into two rows: - Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform. - Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate. Bones of the Hand: Metacarpals and Phalanges - Five metacarpals in the palm of the hand. - Fourteen phalanges found in fingers (three in each finger, two in the thumb). - Named according to relative position: proximal, middle, and distal phalanges. - Thumb only has proximal and distal phalanges. Fractures of Upper Limb Bones - Usually occur as a result of breaking a fall. - Outstretched hand sends force through the upper limb. - Force may result in fracture. - Surgical neck, transverse, supracondylar, and intracondylar fractures of the humerus. - Colles' fracture of the radius. Chapter 10: Joints Classification of Joints - Sites where bones and cartilage form a connection. - Also known as an articulation or arthrosis. - Two ways to classify joints: - Structural: based on the structure that connects the articulating surfaces of bones. - Functional: based on the amount of movement between articulating bones. Structural Classification - Based on the structure of the articulating surfaces: - Fibrous: joined by fibrous connective tissue. - Cartilaginous: joined by cartilage (hyaline cartilage or fibrocartilage). - Synovial: joined within a fluid-filled joint cavity (most common joint). Functional Classification - Based on the extent of joint mobility: - Synarthrosis: little to no movement (example: sutures of the skull). - Amphiarthrosis: slight movement (examples: pubic symphysis, intervertebral discs). - Diarthrosis: significant movement (three categories based on axes of motion): - Uniaxial: movement in one plane (example: elbow). - Biaxial: movement in two planes (example: metacarpophalangeal joints). - Multiaxial: movement in three or more planes (example: hip and shoulder). Structural and Functional Relationship - The structure of a joint determines which types of movement are possible. - Fibrous and cartilaginous joints are functionally synarthroses or amphiarthroses. - Synovial joints are functionally diarthroses. Characteristics of Fibrous Joints - No joint cavity. - Bones held together by dense (fibrous) connective tissue. - Synarthroses. - Permit little to no movement. - Types: sutures, syndesmoses, gomphoses. Types of Fibrous Joints: Sutures - Joins the bones of the skull. - Classified as synarthroses. - Some may allow slight movement. - Convoluted shape prevents movement between bones. - Form when skull bones completely ossify during early childhood. The Newborn Skull - Newborn skull contains wide areas of connective tissue between bones called fontanelles. - Provide flexibility to the skull during birth. - Allow for rapid growth of the brain after birth. - Fontanelles ossify over time. Types of Fibrous Joints: Syndesmoses - Joins two parallel bones using fibrous connective tissue. - Space between bones may be narrow or wide. - Wide spaces are filled by an interosseous membrane. - Functionally classified as amphiarthroses. - Found between the radius and ulna of the forearm and between the tibia and fibula of the leg. - Interosseous membrane anchors parallel bones to each other. - Interosseous membrane between radius and ulna is more mobile. Types of Fibrous Joints: Gomphoses - Anchors teeth to the maxilla (upper jaw) and mandible (lower jaw). - Made of numerous short bands of dense connective tissue called periodontal ligaments. - Classified as synarthroses. Cartilaginous Joints - Bones joined by hyaline cartilage or fibrocartilage. - Synchondroses: joined by hyaline cartilage. - Symphyses: joined by fibrocartilage. Type of Cartilaginous Joint: Synchondroses - Cartilaginous joint using hyaline cartilage. - Found in every long bone early in life to allow an increase in skeletal size. - Allows the epiphyseal plate to increase in size, leading to an increase in bone length. - Classified as synarthroses. - Examples: epiphyseal plates, costal cartilage. Type of Cartilaginous Joint: Symphyses - Cartilaginous joint formed using fibrocartilage. - Permit strong attachment while allowing limited movement. - Classified as amphiarthroses. - Examples: pubic symphysis, intervertebral symphyses. Synovial Joints - Contain a joint cavity. - Bones do not directly touch. - Articular capsule forms the walls of the cavity. - Ligaments attach bones. - Synovial membrane secretes synovial fluid, which lubricates the joint and nourishes cartilage. - Articular cartilage (hyaline cartilage) at the ends of bones. - Classified as diarthroses. Supporting Structures - Ligaments: strong bands of fibrous connective tissue that strengthen and support the joint by anchoring bones together. - Extrinsic ligaments are located outside of the articular capsule. - Intrinsic ligaments are incorporated into the wall of the articular capsule. - Intracapsular ligaments are located inside of the articular capsule. - Tendons: connective tissue structure that attaches muscle to bone. Cushioning Structures - Articular discs and menisci: pads of fibrocartilage between bones that provide shock absorption and help smooth movements. - Bursae and tendon sheaths: prevent friction between bone and tendons or skin. - Fat pads: provide cushioning. Types of Synovial Joints - Pivot joint: rounded portion of a bone enclosed in a ring, allowing rotation around one axis (uniaxial joint). Example: Atlantoaxial joint (formed between C1 and C2 vertebrae). - Hinge joint: convex end of one bone articulates with the concave end of another, allowing bending and stretching along one axis (uniaxial joint). Examples: elbow, knee, ankle, and interphalangeal joints. - Condyloid joint: shallow depression at the end of one bone articulates with a rounded structure from a nearby bone or bones, allowing bending and straightening, anterior-posterior movements (biaxial joint). Example: metacarpophalangeal joints. - Saddle joint: both articulating surfaces have a saddle shape, allowing almost circular movement (biaxial joint). Examples: first carpometacarpal joint, sternoclavicular joint. - Plane joint: surfaces of the bones are mostly flat, allowing bones to slide past each other during motion (limited motion, but multiaxial joint). Examples: intercarpal joints, intertarsal joints, acromioclavicular joint. - Ball-and-socket joint: rounded head of one bone fits into the bowl-shaped socket of another, allowing a great range of motion (multiaxial joint). Examples: hip joint, shoulder joint. Joint Damage - Arthritis: inflammation of a joint, leading to pain, swelling, stiffness, and reduced mobility of the joint. - Most common form is osteoarthritis, caused by degeneration of articular cartilage. - Other causes include gout, autoimmune conditions, and injuries. Hip Replacement - Severely arthritic joints may require surgery to alleviate pain. - Surgery replaces the articular surfaces of the bones with artificial materials. - Hip replacement surgery replaces the head and neck of the femur and the acetabulum of the pelvis. Movements at Synovial Joints - Flexion: reduces the angle of the joint from the resting position. - Extension: returns the joint to the resting position. - Hyperextension: increases the joint angle beyond 180 degrees. - Lateral flexion: bending of the neck or body toward the left or right side. - Abduction: moves a limb, finger, toe, or thumb away from the midline of the body. - Adduction: moves a limb, finger, toe, or thumb toward the midline. - Circumduction: movement in a circular motion (combination of flexion, adduction, extension, and abduction at a joint). - Rotation: twisting movement. - Medial rotation: moves the anterior of a limb toward the midline. - Lateral rotation: moves the anterior of a limb away from the midline. - Supination: moves the palm toward facing posteriorly. - Pronation: moves the palm toward facing anteriorly. - Dorsiflexion: moves the top of the foot toward the anterior leg. - Plantar flexion: lifts the heel away from the ground or points toes toward the ground. - Inversion: movement that turns the bottom of the foot toward the midline. - Eversion: movement that turns the bottom of the foot away from the midline. - Protraction: jaw is pushed forward (mandible) or shoulder moves forward (scapula). - Retraction: returns jaw to resting position (mandible) or scapula pulled posteriorly and medially (scapula). - Depression: downward movement (mandible or scapula). - Elevation: upward movement (mandible or scapula). - Opposition: moves the tip of the thumb in contact with a finger. - Reposition: returns the thumb to its anatomical position. Temporomandibular Joint - Mandibular condyle articulates with the mandibular fossa of the temporal bone. - Hinge joint. - Allows depression/elevation, excursion, and protraction/retraction of the mandible. Shoulder Joint - Head of the humerus articulates with the glenoid cavity of the scapula. - Ball-and-socket joint. - Large range of motion. - Allows flexion, extension, hyperextension, abduction, adduction, medial and lateral rotation, and circumduction. Elbow Joint - Formed by articulation of the humerus, radius, and ulna. - Hinge joint. - Allows flexion and extension of the forearm. - Strengthened by radial collateral and ulnar collateral ligaments. Hip Joint - Formed by articulation of the acetabulum and head of the femur. - Ball-and-socket joint. - Lesser range of motion than the shoulder. - Favors strength and stability. - Allows flexion, extension, abduction, adduction, medial and lateral rotation, and circumduction. Knee Joint - Condyles of the femur articulate with the condyles of the tibia. - Also involves articulation of the femur and patella at the patellar surface. - Medial and lateral meniscus provide support and cushioning. - Anterior and posterior cruciate ligaments help hold the femur and tibia together. - Hinge joint. - Allows flexion and extension of the leg. Chapter 11: Muscle Tissue Functions of Muscle Tissue - Movement of the body and movement of internal materials - Posture maintenance - Stabilization of joints - Protection of internal organs - Temperature regulation Characteristics of Muscle Tissue - Excitability: Responds to changes in electrical potentials across the cell membrane. - Involuntary: Unconsciously controlled (smooth and cardiac muscle). - Voluntary: Consciously controlled (skeletal muscle). - Extensibility: Can stretch or extend. - Elasticity: Can stretch and return to its original shape. - Contractility: Can pull on its attachment site and shorten. Muscle Tissue Cells - Skeletal Muscle: - Long, multinucleated cells. - Cylindrical shape. - Striated. - Cardiac Muscle: - One or two nuclei. - Shorter, branching cells. - Striated. - Smooth Muscle: - One nucleus. - Spindle-shaped (football-like appearance). - Non-striated. Three Types of Muscle Tissue (Figure 11.1) - Skeletal Muscle: Associated with bones. - Smooth Muscle: Found within the walls of internal organs. - Cardiac Muscle: Found in the walls of the heart. Connective Tissue (CT) Coverings of Skeletal Muscle - Epimysium: Surrounds the entire muscle. - Fuses with tendons to link muscle to bone for movement. - Fascia = additional layer of CT external to the epimysium. - Perimysium: Surrounds fascicles. - Fascicles = bundles of muscle cells. - Endomysium: Surrounds individual muscle cells. Structure of Skeletal Muscle Cells (Figure 11.2) - Sarcolemma: Cell membrane. - Sarcoplasm: Cytoplasm. - Sarcoplasmic Reticulum (SR): Endoplasmic reticulum that stores calcium. - Transverse Tubules (T-tubules): Extensions of the sarcolemma. - Myofibrils: Cylinders of contractile proteins. Muscle Cell Components (Table 11.1) - Specialized terms for muscle cell components: sarcolemma, sarcoplasm, sarcoplasmic reticulum. Many are rooted in the Greek prefix sarco- meaning "flesh." Anatomy of a Skeletal Muscle Cell - Endomysium covers individual muscle cells. - Sarcolemma is the plasma membrane of the muscle cell. - Skeletal muscle cells have multiple nuclei. - Multiple mitochondria produce ATP for muscle contraction. - Contractile proteins are arranged into myofibrils. The Sarcomere (Figure 11.3) - Contractile unit of skeletal muscle. - Made of contractile proteins. - Thick filament made of myosin. - Thin filament made of actin. - Associated with regulatory proteins troponin and tropomyosin. - Arrangement of proteins gives skeletal and cardiac muscle a striated appearance. - Z discs anchor thin filaments. - Sarcomere spans Z disc to Z disc. The Neuromuscular Junction (NMJ) (Figure 11.4) - Point of contact between skeletal muscle and the motor neuron that controls it. - Motor end plate = region of the sarcolemma at the NMJ. - Excitatory signals from the motor neuron lead to skeletal muscle contraction. Skeletal Muscle Cell Contraction and Relaxation - The Sliding Filament Model of Muscle Contraction (Figure 11.5) - Describes how a sarcomere shortens. - Thin filaments slide past thick filaments toward the M line. - Steps: 1. Calcium released from the SR binds to troponin. 2. Shape change moves tropomyosin. 3. Myosin heads on the thick filament bind to the thin filament (cross-bridge formation). 4. Myosin heads use the power of ATP to pull the thin filament toward the M line. 5. Myosin heads "re-cock" and continue to pull as long as ATP is available and binding sites are exposed. 6. Z discs move closer together and the sarcomere shortens. - Muscle Contraction - Troponin and tropomyosin regulate cross-bridge formation between thick and thin filaments. - Tropomyosin wraps around the thin (actin) filament and covers myosin (thick filament) binding sites. - Troponin moves tropomyosin to expose myosin binding sites on the actin filament. - This occurs when calcium ions bind to troponin. - Excitation-Contraction Coupling - Connects the muscle action potential and the muscle fiber contraction. - Leads to the release of calcium ions from the sarcoplasmic reticulum (SR). - Nervous system uses membrane potentials to control skeletal muscle: - Membrane potentials = differences in electrical charge across the cell membrane. - Created by the movement of ions across the sarcolemma. - Resting membrane potential = difference across the membrane when the cell is at rest. - Action potential = change in membrane potential that activates the muscle cell. - Leads to contraction. - Measuring Membrane Potential (Figure 11.6) - A voltmeter can be used to measure membrane potential. - The inside of the cell is usually more negatively charged than the outside. - Due to the activities of sodium/potassium pumps. - Membrane potential changes as ions move. - Events at the Neuromuscular Junction - The action potential of the motor neuron causes the release of the neurotransmitter acetylcholine (ACh) from the motor neuron. - ACh diffuses across the synaptic cleft and binds to receptors on the motor end plate of the muscle fiber. - Receptors open and sodium ions (Na+) enter the muscle cell. - The resting membrane potential becomes positive (depolarization). - Electrical Sequence of an Action Potential (Figure 11.7) - Resting membrane potential is -90 mV. - Sodium channels open and sodium enters the cell. - Membrane potential becomes +30 mV (depolarization). - When slow potassium channels open, potassium diffuses out of the cell and the membrane potential becomes more negative (repolarization). - Events Along the Sarcolemma - Voltage-gated channels respond to changes in membrane potential. - Voltage-gated sodium channels: open quickly in response to depolarization at the motor end plate. Sodium ions continue to flow into the cell. Conducts the muscle action potential throughout the entire muscle. - Voltage-gated potassium channels: open more slowly. Allow potassium ions (K+) to exit the cell. Involved in repolarization of the skeletal muscle cell. - End Plate Potential (Figure 11.8) - The muscle action potential begins when sodium ions enter through receptors at the end plate. - Adjacent voltage-gated sodium channels open in response to the change in membrane potential. - The action potential spreads along the entire sarcolemma and down the T-tubules. - Potassium voltage-gated channels slowly open to allow potassium to diffuse out of the cell (repolarization). - Events at the Sarcomere - The muscle action potential travels through the T-tubules. - Causes the release of calcium from the SR. - Calcium binds to troponin, causing a shape change. - Shape change exposes myosin binding sites on thin filaments. - Cross-bridge formation occurs. - The power of ATP is used to pull the thin filament across the thick filament. - Continues as long as ATP and calcium are available. - Steps in Muscle Contraction (Figure 11.9) 1. Action potential arrives at the motor neuron axon terminal. 2. Acetylcholine is released and binds to receptors on the motor end plate. 3. Sodium ions enter the muscle cell, resulting in depolarization to generate a muscle action potential. 4. Depolarization spreads along the sarcolemma into the T-tubules leading to calcium release. 5. Calcium release into the cytosol leads to exposure of myosin binding sites on actin resulting in cross-bridge formation. 6. Sarcomere shortening (contraction) leads to muscle contraction. - ATP and Muscle Contraction - Cross-bridge forms. - ADP and phosphate release leads to the power stroke. - A new ATP molecule binds. - Myosin heads detach. - Myosin heads remain attached if the amount of ATP is insufficient leading to rigor mortis. - ATPase breaks down ATP, releasing energy. - The myosin head returns to the ready position. - Sarcomere Shortening (Figure 11.10) - The length of myofilaments will remain the same. - There is an increase in the overlap between the myofilaments. - The I band and H zone are eliminated because of increased overlap during sarcomere shortening. - Skeletal Muscle Cell Relaxation (Figure 11.11) - The motor neuron stops releasing ACh and acetylcholinesterase breaks down ACh at the NMJ. - Without ACh, ACh receptors close. - Calcium ions are pumped back into the SR. - Tropomyosin moves back into its original position, covering myosin binding sites. - Prevents cross-bridge formation and the muscle relaxes. Skeletal Muscle Metabolism - Sources of ATP (Figure 11.12) - Creatine phosphate - Glycolysis - Lactic acid - Aerobic respiration - Creatine Phosphate - Resting muscle builds up stores of creatine phosphate. - Donates phosphate to ADP. - Quickly regenerates ATP. - Short-lived source of ATP (only lasts about 15 seconds). - Glycolysis - Breaks down glucose to yield ATP and pyruvate. - Energy from bonds in glucose is used to bind phosphate to ADP. - Generates ATP slower than creatine phosphate. - If oxygen is available, pyruvate is used for aerobic respiration. - If oxygen is not available, pyruvate is converted to lactic acid. - Lactic acid can be broken down by the liver. - Produces ATP for approximately 1 minute of muscle activity. - Aerobic Respiration - Occurs in mitochondria and produces large quantities of ATP. - Requires oxygen. - Myoglobin stores oxygen in muscle cells for use by mitochondria. - Glucose is also stored by muscle cells as glycogen for use by mitochondria. - Pyruvate is broken down to generate approximately 36 ATP. - Supplies the majority of ATP used by muscle cells. - Muscle Fatigue - Occurs when the muscle can no longer contract. - Multiple causes: 1. Depletion of ATP. 2. Lactic acid and ADP buildup. 3. Impaired ion movement. 4. Inadequate release of calcium from the sarcoplasmic reticulum. Three Types of Muscle Fibers (Figure 11.13) - Muscles are a blend of three different types of muscle fibers: 1. Slow oxidative (SO) 2. Fast glycolytic (FG) 3. Fast oxidative (FO) - Differ in speed of contraction and ATP production. - Slow Oxidative (SO) Muscle Fibers - Contract slowly. - Weakest strength of contraction of the three types of muscle fibers. - Produce ATP via aerobic respiration. - Red due to the presence of myoglobin. - Fatigue slowly. - Maintain posture and stabilize joints. - Fast Glycolytic (FG) Muscle Fibers - Fast contractions. - Produce the strongest contractions. - Produce ATP via glycolysis. - Store glycogen in higher amounts. - Fatigue quickly. - Used for fast, powerful movements. - Fast Oxidative (FO) Muscle Fibers - Also known as intermediate fibers. - Possess characteristics of both SO and FG fibers. - Contract quickly. - Produce ATP via glycolysis and aerobic respiration. - More fatigue-resistant than FG fibers. - Used for movements like walking. Muscle Tension - Force generated by contraction of the muscle. - Tension can be used to move an object (load). - Isometric Contraction: Muscle contracts, but does not move a load. - Isotonic Contraction: Moves a load. - Concentric Contraction: Muscle shortens to move a load. - Eccentric Contraction: Muscle lengthens to move a load. Types of Muscle Contractions (Figure 11.14) - Concentric Isotonic Contraction: Muscle shortens and moves a load. - Eccentric Isotonic Contraction: Muscle lengthens and moves a load. - Isometric Contraction: Muscle contracts but does not move a load. Length-Tension Range of a Sarcomere (Figure 11.15) - Thick and thin filaments must overlap for the sarcomere to shorten. - The amount of overlap influences the strength of contraction. - Insufficient or excessive overlap = weaker contractions. - Sufficient overlap optimizes the strength of contraction. Myogram of a Muscle Twitch (Figure 11.16) - Twitch: Singular contraction of a muscle cell. - Myogram: Displays the amount of tension produced by a twitch over a period of time. - Latent Period: Action potential is propagated along the sarcolemma and calcium ions are released from the SR. No contraction occurs during this phase. - Contraction Phase: Cross-bridges have formed and sarcomeres shortened. Peak of tension. - Relaxation Phase: Calcium ions are pumped back into the SR and cross-bridge cycling stops. Tension decreases. Summation and Tetanus (Figure 11.17) - Each action potential produces a singular twitch contraction. - Summation: A series of action potentials that sustain muscle contraction. - Tetanus: Occurs when action potentials occur quickly and lead to sustained maximal contraction. Muscle Tone - Skeletal muscles are rarely fully relaxed (flaccid). - Muscle tone is maintained by a small amount of contraction within the muscle fiber. - The nervous system activates a few groups of muscles at a time. - Rotating muscle groups prevents fatigue. - Control of motor units helps maintain muscle tone. Motor Units (Figure 11.18) - A motor unit consists of a motor neuron and all the skeletal muscle fibers it controls. - Each motor unit consists of only one fiber type. - All muscle fibers in a motor unit contract at the same time. - Additional motor units can be recruited if more strength is required (recruitment). Characteristics of Cardiac Muscle (Figure 11.19) - Located in the walls of the heart. - Striated fibers like skeletal muscle. - Sarcomere is the functional unit. - Shorter, branching fibers. - Intercalated discs attach fibers. - Allow for fast communication between cells. - Involuntarily controlled. Cardiac Muscle Cells (Figure 11.20) - Branching shape. - Striated in appearance. - Cells connected by intercalated discs. - Desmosomes firmly attach cardiac muscle cells to each other. - Gap junctions allow for the action potential to move from one cell to another. Characteristics of Smooth Muscle (Figure 11.21) - Found in internal organs. - Non-striated. - Thick and thin filaments are present, but not regularly arranged. - Spindle-shaped cells. - Wide in the middle and tapered at each end. - Single nucleus. - Involuntary. Contraction of Smooth Muscle (Figure 11.22) - Thin filaments anchored by dense bodies. - Dense bodies are connected by intermediate filaments. - Calcium comes from the sarcoplasmic reticulum and extracellular fluid. - Binds to calmodulin and activates myosin kinase. - Activated myosin heads bind to and pull thin filaments. - The ends of the cell are pulled toward the center as it contracts (corkscrew motion). Smooth Muscle Innervation (Figure 11.23) - Innervated by singular neurons with multiple varicosities. - Varicosities = bulges that store/release neurotransmitters. - Single-unit smooth muscle: Multiple cells that contract as a unit. - Contain gap junctions. - Stress-relaxation response. - Multi-unit smooth muscle: Cells contract individually. Chapter 12: The Muscular System Interactions of Skeletal Muscles in the Body - Muscles may have multiple sites of attachments. - Tendons attach muscle to bone. - Tendons pull on periosteum causing bone to move. - Origin: point of attachment that does not move. - Insertion: point of attachment that moves. - Prime mover: principal muscle involved in an action. - Other muscles may be involved in the movement as well. - Example: Biceps brachii is the prime mover for flexion of the elbow. Synergists and Fixators (Figure 12.1) - Synergists: assist the prime mover in accomplishing a movement. - Example: Brachioradialis and Brachialis during flexion of the elbow. - Fixators: stabilize insertion points during a movement. Agonists and Antagonists (Figure 12.2) - Agonist: primarily responsible for an action; also known as the prime mover. - Antagonist: muscle that produces the opposite movement of an agonist. - Triceps brachii is the antagonist of the biceps brachii. - Alternately, the biceps brachii is the antagonist of the triceps brachii. Patterns of Fascicle Organization (1 of 3) - Fascicle: a bundled group of muscle fibers. - Surrounded by perimysium. - Fascicle arrangement: arrangement of fascicles in skeletal muscle. - Influences force generated and range of motion of muscle. Patterns of Fascicle Organization (2 of 3) (Figure 12.3) - Parallel: fascicles arranged in the same direction as the long axis of the muscle. - Fusiform: parallel arrangement with a large muscle belly in the middle and narrowing ends. - Circular: fibers wrap in a circle. - Convergent: fascicles unite on a singular, narrow insertion point. Muscle Bellies (Figure 12.4) - Muscle bellies of fusiform muscles enlarge when the muscle contracts. - Forms an even larger muscle belly. Patterns of Fascicle Organization (3 of 3) (Figure 12.3) - Pennate: fascicles blend into the tendon in the center of the muscle. - Unipennate: fascicles on one side of the tendon. - Bipennate: fascicles on both sides of the tendon. - Multipennate: muscle branches within the muscle to resemble many feathers arranged together. Origins of Skeletal Muscle Names - Many skeletal muscle names are derived from Greek and Latin root words. - Names were based on easily observable characteristics of muscles. - Shape - Size comparison - Orientation of fibers - Number of origins - Action of muscle - Attachment location - Grouping of muscle Characteristics Used to Name Skeletal Muscles (1 of 2) - Muscle shape: named for their resemblance to a shape. - Muscle size: muscles in a group are sometimes named for their size relative to other muscles in the group. - Location: named for the region where they are located. - Orientation of fibers: orientation of the muscle fibers and fascicles is used to describe some muscles. Characteristics Used to Name Skeletal Muscles (2 of 2) - Number of origins: number of origins a muscle has can differentiate it from other nearby muscles. - Action: named for the action the muscle achieves. - Attachment: attachment location can appear in a muscle name. - Origin is always first. - Grouping: some muscles exist in groups. Words that Pertain to Muscle Size (Table 12.1) - Greek and Latin words that describe muscle size include: - Maximus - Medius - Minimus - Brevis - Longus - Major - Minor - Longissiumus Some Muscles are Named for Their Shape (Figure 12.5) - Rhomboid muscles of the back resemble the shape of a rhombus. - Deltoid muscle of the shoulder resembles an upside-down Greek letter delta. Prefixes That Indicate Number (Table 12.2) - Greek and Latin prefixes that indicate number: - Uni = 1 - Bi/Di = 2 - Tri = 3 - Quad = 4 - Multi = many Anatomy of a Muscle Name - Biceps brachii: - “Bi” = Latin for 2 - “Ceps” derived from Latin for “head” - Brachii refers to the brachium region. - Flexor carpi ulnaris: - Flexor derived from action; flexes the wrist. - Carpi derived from wrist. - Ulnaris due to location on ulna. Muscle Actions (Figure 12.6) - Muscle actions are predictable based on their location. - Lateral side of joint: - Abduction of limbs - Lateral flexion of the trunk or neck - Medial side of joint: - Adduction - Anterior portion of joint: - Flexion - Posterior portion of joint: - Extension Axial Muscles - Section 12.3 - Learning Objectives 12.3.1–12.3.2 Muscles of Facial Expression (Figure 12.7) - Originate on bones of the skull and insert on the skin. - Orbicularis oculi - Orbicularis oris - Occipitofrontalis - Buccinator - Zygomaticus major - Zygomaticus minor Muscles of Facial Expression (Table 12.3) Muscles That Move the Eyes (1 of 2) (Figure 12.8) - Originate outside of the eye and insert on the outer surface of the eye. - Superior and inferior obliques - Lateral, medial, inferior, and superior rectus Muscles That Move the Eyes (2 of 2) (Figure 12.8) - Muscles of the eye and movements that they allow. Muscles of Eye Movement (Table 12.4) Muscles That Move the Lower Jaw (Figure 12.9) - Allow for mastication (chewing). - Masseter - Temporalis - Pterygoid muscles Muscles of Mastication (Table 12.5) Muscles That Move the Tongue (Figure 12.10) - Aid in speech, mastication, and swallowing. - Extrinsic muscles: originate outside of the tongue. - Genioglossus, styloglossus, palatoglossus, hyoglossus - Intrinsic muscles: originate inside the tongue. Muscles That Move the Tongue (Table 12.6) Muscles of the Anterior Neck (Figure 12.11) - Assist in swallowing (deglutition) and speech. - Suprahyoid muscles: originate above the hyoid bone. - Digastric, stylohyoid, mylohyoid, geniohyoid - Infrahyoid muscles: originate below the hyoid bone. - Omohyoid, sternohyoid, thyrohyoid, sternothyroid Muscles That Move the Head (Figure 12.12) - Head is balanced, moved, and rotated by neck muscles. - Sternocleidomastoid: lateral flexion and rotation of the head. - Scalenes: synergists of sternocleidomastoid. Muscles That Move the Head (Table 12.7) Muscles of the Posterior Neck and the Back (Figure 12.13) - Lateral flexion, extension, and rotation of the head. - Splenius capitis, splenius cervicis - Extension of the vertebral column. - Erector spinae group: Iliocostalis, longissimus, spinalis - Transversospinalis muscles - Quadratus lumborum muscles Muscles of the Posterior Neck and Back (Table 12.8) Anterior Muscles of the Abdomen (Figure 12.14) - External oblique - Internal oblique - Transversus abdominis - Rectus abdominis - Enclosed by rectus sheaths of linea alba. Posterior Muscles of the Abdomen (Figure 12.15) - Help form the posterior wall of the abdomen. - Stabilize the body and maintain posture. - Psoas major - Iliacus - Quadratus lumborum Muscles of the Abdomen (Table 12.9) Muscles of the Thorax (Figures 12.16 and 12.17) - Diaphragm: divides abdominal and thoracic cavities. - Major muscle involved in breathing. - Intercostal muscles: - External, internal, and innermost. - Located between ribs. - Assist in breathing. Muscles of the Thorax (Table 12.10) Muscles of the Pelvic Floor (Figure 12.18) - Pelvic diaphragm: forms the base of the pelvic cavity. - Levator ani - Consists of pubococcygeus and iliococcygeus. - Forms anal and urethral sphincters. - Ischiococcygeus Muscles of the Perineum (Figure 12.19) - Perineum: space between the pubic symphysis and the coccyx. - Urogenital triangle: anterior of the perineum. - Includes external genitalia. - Anal triangle: posterior perineum. - Includes the anus. Appendicular Muscles Shoulder Muscles (Figure 12.20) - Anterior shoulder muscles: - Subclavius, pectoralis minor, serratus anterior. - Pull scapula forward (protract). - Posterior shoulder muscles: - Trapezius, rhomboid major, rhomboid minor. - Pull scapula back (retract). Shoulder Movements (Figure 12.21) - Movements possible at the shoulder include: - Retraction - Protraction - Flexion - Extension - Abduction - Adduction - Internal rotation - External rotation Muscles That Move the Humerus (1 of 2) (Figure 12.22) - Pectoralis major and latissimus dorsi. - Prime movers of the humerus. - Convergent muscles. Muscles That Move the Humerus (2 of 2) (Figure 12.22) - Muscles that originate on the scapula. - Deltoid, subscapularis, supraspinatus, infraspinatus, teres major, teres minor, coracobrachialis. - Rotator cuff: formed by tendons of subscapularis, supraspinatus, infraspinatus, and teres minor. - Give structure and stability to the shoulder joint. Shoulder and Brachial Muscles (1 of 2) (Table 12.11) Shoulder and Brachial Muscles (2 of 2) (Table 12.11) Muscles That Move the Forearm (1 of 2) (Figure 12.23) - Allow flexion and extension of the elbow, supination, and pronation. - Elbow flexion: biceps brachii, brachialis, brachioradialis. - Elbow extension: triceps brachii, anconeus. Muscles That Move the Forearm (2 of 2) (Figure 12.23) - Pronation: pronator teres, pronator quadratus. - Supination: supinator. The Carpal Tunnel (Figure 12.24) - Many extrinsic muscles of the hand originate on the humerus. - Long tendons pass through the carpal tunnel to connect to the hand. - Retinacula: surround tendons at the wrist. - Flexor retinaculum on the palmar surface. - Extensor retinaculum on the dorsal surface. Movements of the Forearm, Wrist, and Fingers (Figure 12.25) - Forearm: flexion, extension, pronation, and supination. - Wrist: radial and ulnar deviation, flexion, extension, pronation, and supination. - Fingers: flexion, extension, hyperextension, abduction, adduction, circumduction. Muscles That Move the Wrist, Hand, and Fingers (1 of 2) (Figure 12.23) - Superficial muscles: - Anterior muscles: most cause flexion of the hand or fingers. - Flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis. - Posterior muscles: most cause extension of the hand or fingers. - Extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris. Muscles That Move the Hand, Wrist, and Fingers (2 of 2) (Figure 12.23) - Deep muscles: - Anterior muscles: cause flexion of fingers. - Flexor pollicis longus, flexor digitorum profundus. - Posterior muscles: cause extension and abduction of the thumb. - Abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis. Intrinsic Muscles of the Hand (Figure 12.26) - Originate and insert within the hand. - Allow precise movements of fingers. - Thenar muscles: abductor pollicis brevis, opponens pollicis, flexor pollicis brevis, adductor pollicis. - Hypothenar muscles: abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi. - Intermediate muscles: lumbricalis, palmar interossei, dorsal interossei. Forearm, Wrist, and Hand Muscles (1 of 3) (Table 12.12) Forearm, Wrist, and Hand Muscles (2 of 3) (Table 12.12) Forearm, Wrist, and Hand Muscles (3 of 3) (Table 12.12) Movements of the Hip (Figure 12.27) - Movements of the thigh that occur at the hip include: - Abduction - Adduction - Flexion - Extension Gluteal Region Muscles That Move the Femur (Figure 12.28) - Most originate on the pelvis and insert on the femur. - Iliopsoas group: psoas major, iliacus. - Gluteus maximus, gluteus medius, gluteus minimus. - Tensor fascia latae. - Adductor longus, adductor brevis, adductor magnus. - Pectineus. Thigh Muscles That Move the Femur, Tibia, and Fibula (Figure 12.28) - Medial compartment: adduct the femur. - Adductor longus, adductor brevis, adductor magnus, pectineus, gracilis. - Anterior compartment: flex the thigh, extend the knee. - Quadriceps femoris: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius. - Posterior compartment: extend the thigh, flex the knee. - Hamstrings: Semitendinosus, semimembranosus, biceps femoris. Muscles of the Hip and Thigh (1 of 2) (Table 12.13) Muscles of the Hip and Thigh (2 of 2) (Table 12.13) Muscles That Move the Feet (1 of 2) (Figure 12.29) - Anterior compartment: dorsiflex the foot. - Tibialis anterior, extensor hallucis longus, extensor digitorum longus. - Superior extensor retinaculum and inferior extensor retinaculum anchor tendons during contraction. - Lateral compartment: eversion and plantar flexion of the foot. - Fibularis longus, fibularis brevis. Muscles That Move the Feet (2 of 2) (Figure 12.29) - Posterior compartment: plantar flexion of the foot. - Gastrocnemius, soleus, plantaris, popliteus, flexor digitorum longus, flexor hallucis longus, tibialis posterior. - Superficial muscles insert on the calcaneal tendon. Muscles That Move the Toes (Figure 12.30) - Sole supported by plantar aponeurosis. - Dorsal group: Extensor digitorum brevis. - Plantar group: Flexor digitorum brevis, abductor hallucis, abductor digiti minimi brevis, flexor hallucis brevis Chapter 13: Organization and Functions of the Nervous System The Functions of the Nervous System - Sensation: Receiving information from the environment through sensory receptors. - Integration: Processing and interpreting sensory information, often combining it with higher cognitive functions. Association areas within the brain are responsible for this function. - Response: Initiating and carrying out motor functions through effectors (muscles or glands) via both conscious and unconscious nervous pathways. The Central and Peripheral Nervous Systems (Figure 13.1) - Central Nervous System (CNS): - Consists of the brain and spinal cord. - Housed within the cranial cavity and vertebral cavity, respectively. - Protected by bone. - Peripheral Nervous System (PNS): - Consists of nerves outside of the brain and spinal cord. - Not protected by bone. - Nervous Tissue: - Both the CNS and PNS are composed of nervous tissue. - Neurons: Cells capable of communication. - Glial cells: Cells that provide structure and support to neurons. Functional Divisions of the Nervous System (Figure 13.2) - Sensory: Sends information towards the CNS. This is achieved by afferent (sensory) neurons. - Integration: Occurs in the brain and spinal cord. This function is carried out by interneurons. - Response: Communicates with effectors (muscles or glands) to initiate a response. This is achieved by efferent (motor) neurons. Classification Based on Innervation - Somatic Nervous System (SNS): Responsible for conscious perception and voluntary motor responses. Innervates skeletal muscle. - Autonomic Nervous System (ANS): Responsible for involuntary control of the body, helping to maintain homeostasis. Innervates smooth muscle, cardiac muscle, and glands. Nervous Tissue and Cells Anatomy of Neurons (1 of 2) - Neurons: Responsible for communication within the nervous system. - Cell Body: Contains organelles like the nucleus, nucleolus, ribosomes, and endoplasmic reticulum. - Dendrites: Receive signals from other neurons. - Axon: Begins at the axon hillock and sends signals to other neurons. Anatomy of Neurons (2 of 2) - Synapses: Junctions where neurons communicate with other cells. - Myelin: A fatty substance that wraps around axons, providing insulation. - Neurofibril Nodes: Gaps in myelin that allow for faster conduction of electrical signals. - Axon Terminals: Multiple branches of the axon that allow a single neuron to communicate with multiple cells. Anatomical Classification of Neurons - Unipolar Neuron: Only one process from the cell body that splits into an axon and dendrites. Most sensory neurons are unipolar. - Bipolar Neuron: Two processes, one dendrite and one axon, extend from the cell body. Sensory neurons for smell and vision are bipolar. - Multipolar Neuron: Many dendrites and one axon. The majority of neurons in the body are multipolar. Functional Classification of Neurons - Sensory Neurons: Collect and send information to the CNS. - Interneurons: Integrate and process information from sensory neurons. - Motor Neurons: Communicate with effectors to make them perform an action. Glial Cells - Support cells found throughout the nervous system. - Can multiply and divide. - Glial cells of the CNS: - Astrocytes: Regulate the extracellular environment, make up the blood-brain barrier (BBB). - Oligodendrocytes: Myelinate axons in the CNS. - Microglia: Immune defense and waste removal. - Ependymal Cells: Produce cerebrospinal fluid (CSF). - Glial cells of the PNS: - Satellite Cells: Regulate the extracellular environment, clustering around cell bodies. Similar in function to astrocytes of the CNS. - Schwann (neurilemma) Cells: Myelinate axons in the PNS. Similar in function to oligodendrocytes of the CNS. Myelin (Figure 13.5) - Insulation for axons. - Allows axons to conduct electrical signals faster. - Oligodendrocytes: In the CNS, multiple processes myelinate different areas. - Schwann (neurilemma) Cells: In the PNS, singular cells myelinate each section. Neurophysiology Communication within the Nervous System - Once a stimulus is detected, communication depends on electrical signaling. - This occurs due to the movement of ions. - Ion movement generates action potentials. - Action potentials lead to the release of neurotransmitters, chemicals that relay messages from neurons. Membrane Potentials (Figure 13.6) - The cell membrane is a barrier to ionic movement. - Different charges can build up inside and outside of neurons. - Sodium/potassium (Na+/K+) pumps: Play a key role in maintaining membrane potential. - Pumps three sodium ions out of the cell and two potassium ions into the cell. - Creates a relatively negative internal environment of the neuron. - The membrane becomes polarized, with the inside and outside of the cell having different charges. Resting Membrane Potential - The resting membrane potential of a neuron is -70 mV. - This is established by: - Unequal distribution of Na+ and K+ ions across the cell membrane due to the sodium/potassium pumps. - Negatively charged proteins inside the cell, making the interior more negative. - Exit of K+ ions due to leak channels, further reducing positive charges inside the cell. The Na+/K+ Pump (Figure 13.7) - Plays a critical role in the resting membrane potential of neurons. - Pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell using energy from ATP. - Builds chemical and electrical gradients across the membrane. Changes in Resting Membrane Potential - As ions flow into and out of neurons, membrane potential changes. - Depolarization: Changes that cause the charge difference to decrease. - Hyperpolarization: Changes that cause the charge difference to increase. - Repolarization: Occurs if depolarization is followed by a return to a polarized state. - Ion Channels: Changes in membrane potential can be caused by ion channels that allow ions to move. - Some channels are always open and allow ions to freely move (leak channels). - Some channels open and close in response to various stimuli (ligand-gated, mechanically-gated, and voltage-gated channels). Classes of Membrane Channels - Ligand-gated channels: Open and close due to the binding of a molecule (ligand). - Mechanically-gated channels: Open and close in response to pressure. - Voltage-gated channels: Open and close in response to changes in electrical potential. - Leak channels: Always open or randomly open and close, with no single stimulus influencing their activity. Ligand-Gated Channels (Figure 13.8) - Ligand-gated channels open and close due to the binding of an extracellular messenger molecule (ligand). Mechanically-Gated Ion Channels (Figure 13.9) - Mechanically-gated channels open and close in response to pressure, detected by distortions in the cell membrane. Voltage-Gated Channels (Figure 13.10) - Voltage-gated channels open and close in response to changes in electrical potential. Graded Potentials (1 of 2) - Small changes in resting membrane potential. - Can vary in size. - Caused by mechanically-gated and ligand-gated membrane channels. - Occur along dendrites and the cell body. - Membrane channels open to allow Na+ ions to enter the neuron. - Depolarization occurs as the inside of the neuron becomes more positively charged. Types of Graded Potentials - Postsynaptic potential (PSP): Graded potentials occurring in a neuron that received signals. - Excitatory (EPSP): Moves the membrane toward threshold, depolarizing it. - Inhibitory (IPSP): Moves the membrane away from threshold, hyperpolarizing it. Summation (Figure 13.12) - Spatial summation: Graded potentials occurring at several different synapses over a short timeframe. - Temporal summation: Graded potentials occur at one synapse over a short timeframe. The Action Potential (1 of 3) - Begins at the axon hillock and travels towards axon terminals. - Membrane channels in dendrites and the cell body respond to stimuli, producing graded potentials. - Depolarizing graded potentials allow positively charged sodium ions (Na+) to enter the neuron. - Depolarization occurs as sodium ions make the interior of the neuron more positively charged. The Action Potential (2 of 3) - If graded potentials depolarize the cell body to threshold (-55 mV), an action potential is generated. - Once threshold is reached, voltage-gated sodium and potassium channels open. - Sodium enters rapidly and depolarizes the neuron. - At +30 mV, sodium voltage-gated channels close and potassium voltage-gated channels fully open. - Sodium no longer enters the neuron and potassium begins to exit, initiating repolarization. The Action Potential (3 of 3) - Repolarization: Re-establishes the resting membrane potential. Potassium exits via potassium voltage-gated channels, making the membrane potential more negative. - Hyperpolarization: The membrane may hyperpolarize as excess potassium exits. - Na+/K+ pumps: Bring the membrane potential back to -70 mV by removing sodium from the cell and pumping potassium back into the cell. Conformations of the Na+ Voltage-Gated Channels (Figure 13.11) - Closed: Prior to threshold, Na+ voltage-gated channels are closed. - Open: If threshold is reached, they quickly open, allowing Na+ to enter the cell quickly, leading to depolarization. - Inactivated: Inactivation gates on Na+ voltage-gated channels allow them to quickly close, aiding in repolarization. Refractory Periods (Figure 13.13) - The period after an action potential is generated and before another can begin. - Absolute refractory period: No action potential possible. - Relative refractory period: A second action potential is possible with a strong stimulus. The membrane potential must be between -55 mV and -70 mV. Inactivation of Na+ Voltage-Gated Channels (Figure 13.14) - Na+ voltage-gated channels close when the membrane potential reaches +30 mV. - Inactivation gates stop the inflow of Na+. - This stops depolarization. - Inactivation gates are not required on K+ voltage-gated channels. - K+ exits the cell, leading to repolarization. Propagation of an Action Potential down an Unmyelinated Axon (Figure 13.15) - All or nothing event: An action potential either occurs or it doesn't. - Continuous conduction: Propagation in an unmyelinated axon is continuous. - Na+ ions gather at the axon hillock. - Na+ voltage-gated channels open and Na+ ions flow into the neuron. - Each section of the axon depolarizes in sequence. Action Potential Propagation down a Myelinated Axon (Figure 13.16) - Saltatory conduction: Propagation in myelinated axons is saltatory. - Faster than continuous conduction. - Na+ ions gather at the axon hillock. - Na+ ions move towards the axon terminals. - Only neurofibril nodes depolarize. - Myelinated areas lack voltage-gated channels. - Myelin insulates sections of the axon, preventing the loss of Na+ ions. Speed of Action Potential Propagation (Figure 13.17) - The speed of action potential movement is influenced by: - Myelination: Faster conduction in myelinated versus unmyelinated axons. - Size of electrochemical gradient: Larger axons have less resistance to ion movement, resulting in faster conduction. Synapses (Figure 13.18) - Areas where neurons communicate. - Chemical synapses: Release neurotransmitters. - Electrical synapses: Direct connections where ions move from one cell to another. Less common in the human nervous system. Components of a Chemical Synapse - Presynaptic cell: The neuron sending the signal. - Neurotransmitter: Chemical messenger released by the presynaptic cell. - Synaptic cleft: The space between the presynaptic and postsynaptic cells. - Receptors for neurotransmitter: Located on the postsynaptic cell. - Postsynaptic cell: The cell receiving the signal. - System for clearing neurotransmitter from synapse: Ensures that the signal is not prolonged. Synaptic Events (1 of 2) (Figure 13.19) - Action potential reaches the axon terminal: Calcium voltage-gated channels open. - Ca2+ ions enter the synaptic end bulb: Ca2+ causes synaptic vesicles to fuse with the synaptic end bulb. - Neurotransmitter is released: Diffuses across the synaptic cleft. Synaptic Events (2 of 2) (Figure 13.19) - Neurotransmitter binds to receptors on the postsynaptic neuron: Causes a graded potential. - Neurotransmitter is eliminated from the synapse by: - Diffusion: Moving away from the synapse. - Reuptake: Being taken back up by the presynaptic cell. - Breakdown: Being broken down by enzymes. Anatomy of a Synapse - Events of chemical synaptic transmission: - Action potential arrives at the axon terminal. - Neurotransmitter is released into the synaptic cleft. - Neurotransmitter binds to receptors on the postsynaptic cell. - A postsynaptic potential is generated. - Neurotransmitter is removed from the synaptic cleft. Neurotransmitters (1 of 2) - Each neuron only releases one neurotransmitter. - Categories of Neurotransmitters: - Cholinergic: Acetylcholine. - Amino acids: Glutamate, GABA (inhibitory), glycine. - Biogenic amines: Serotonin, dopamine, epinephrine, norepinephrine. Neurotransmitters (2 of 2) - The effect of a neurotransmitter depends on its receptor. - The same neurotransmitter can have different effects on different cells. Cholinergic Neurotransmitters - Acetylcholine: Released by cholinergic neurons. - Acts on two types of receptors: - Nicotinic receptors: Found at the NMJ, adrenal medulla, and some autonomic synapses. - Muscarinic receptors: Found at autonomic synapses. - Elimination by acetylcholinesterase: Enzyme that breaks down acetylcholine. Biogenic Amine Neurotransmitters - Made from amino acids. - Serotonin, dopamine, norepinephrine, and epinephrine: Each has its own membrane receptors. - Elimination from the synapse by reuptake: Serotonin reuptake can be blocked by selective serotonin reuptake inhibitors (SSRIs), used in the treatment of depression and anxiety. Amino Acid Neurotransmitters - Include glutamate, GABA (gamma-aminobutyric acid), and glycine. - Released by glutamatergic, GABAergic, and glycinergic neurons. - Each has its own receptors. - Eliminated from the synapse by reuptake. - GABA: Leads to IPSPs. Receptors are Cl- channels that hyperpolarize the membrane. Chapter 14: Anatomy of the Nervous System Anatomical Patterns of Nervous Tissue - Gray matter: Unmyelinated regions with mainly cell bodies and dendrites. - Nucleus: A collection of cell bodies. - White matter: Myelinated regions with mainly axons. - Tract: A bundle of axons. The Term "Nucleus" - Nucleus: Used in various ways: - The nucleus of an atom contains protons and neutrons. - The nucleus of a cell contains DNA. - In the brain, a nucleus is a cluster of unmyelinated tissue. Connective Tissue Protection of CNS - Bone: - Cranium protects the brain. - Vertebral column protects the spinal cord. - Membranes: - Meninges protect the brain and spinal cord. - Dura mater, arachnoid mater, pia mater The Meninges of the CNS - Dura mater: Most superficial, thick, and collagen-rich. - Separates into two layers in certain locations. - Arachnoid mater: Deep to dura mater. - Encases the brain, spinal cord, and CSF. - Pia mater: Tightly adhered to the surface of the brain. Meningeal Spaces - Subarachnoid space: - Potential space containing cerebrospinal fluid (CSF). - Cushions the brain and spinal cord. - Subdural space: - Between dura mater and arachnoid mater. - Epidural space: - Between dura mater and cranial or vertebral bones. Dural Venous Sinuses - Thin-walled veins located between layers of dura mater. - Collect venous blood from the brain to the heart. Cranial Dural Septa - Dura mater folds to separate and stabilize the brain within the cranial cavity. - Falx cerebri: Separates the right and left sides of the brain. - Tentorium cerebelli: Forms a "roof" over the cerebellum. - Falx cerebelli: Separates the two halves of the cerebellum. - Diaphragma sellae: Forms a "roof" over the sella turcica. Connective Tissue Protection of PNS - Epineurium: Covers the outer surface of the entire nerve. - Perineurium: Covers fascicles. - Fascicles: Bundles of axons. - Endoneurium: Covers individual axons. Cerebrospinal Fluid (CSF) - Derived from blood. - Produced by ependymal cells in ventricles. - Circulates through ventricles and down into the central canal to protect the spinal cord. Circulation of CSF - CSF is produced in the ventricles. - Lateral ventricles: Located within each cerebral hemisphere. - Interventricular foramen: Drains CSF to the third ventricle. - Cerebral aqueduct: Drains CSF to the fourth ventricle. - CSF from the fourth ventricle drains into the central canal of the spinal cord. Functions of CSF - Delivers some nutrients. - Carries away some wastes. - Provides cushioning and protection to the brain and spinal cord. - Volume of CSF is regulated to prevent excess intracranial pressure. Blood and the Nervous System - Primary delivery mechanism of nutrients. - Blood vessels are found between fascicles of peripheral nerves. - Cell bodies are highly protected. - Satellite cells: Provide additional protection to cell bodies in the PNS. - Astrocytes: Form the blood-brain barrier (BBB) in the CNS. Development of the Nervous System - Neural tube: Forms along the posterior of the embryo. - Neural crest cells: Surround the neural tube and will differentiate into neurons. - Notochord: Becomes the bodies of the vertebrae. - Neural tube: Becomes the brain, eyes, and spinal cord. Development of the Central Nervous System - Neural tube: Forms three vesicles during the first stage of development. - Primary vesicles: Forebrain, midbrain, hindbrain. - Primary vesicles: Become five secondary vesicles. - Forebrain: Becomes the telencephalon and diencephalon. - Midbrain: Becomes the mesencephalon. - Hindbrain: Becomes the metencephalon and myelencephalon. The Brain - Controls conscious experiences. - Regulates homeostasis. - Controls muscle movements. - Four major regions: - Cerebrum - Diencephalon - Brainstem - Cerebellum The Cerebrum - Makes up most of the mass of the brain. - Superficial cerebral cortex: - Gyri: Folds (singular = gyrus). - Sulci: Grooves between folds (singular = sulcus). - Fissures: Deep grooves. - The cerebrum is divided into left and right hemispheres by the longitudinal fissure. The Corpus Callosum - White matter tract that bridges the cerebral hemispheres. - Allows for communication between the two hemispheres. The Cerebral Cortex - Responsible for consciousness. - Hemispheres receive input from and control the opposite side. - Divided into lobes by fissures and sulci: - Frontal lobe - Parietal lobe - Temporal lobe - Occipital lobe - Insula Frontal Lobe - Occupies the anterior cerebral cortex. - Bordered by the central sulcus and lateral sulcus. - Contains areas that plan and initiate muscle contraction. - Involved in decision-making and higher-order cognitive behaviors. - Contains the precentral gyrus, which serves as the primary motor cortex. - The prefrontal lobe is involved in personality, short-term memory, and consciousness. Left and Right Parietal Lobes - Located posterior to the central sulcus. - Primarily involved in body sensations (somatosensation). - Contains the postcentral gyrus, which functions as the primary somatosensory cortex. - Processes senses from the skin and proprioception. Left and Right Temporal Lobes - Located on the lateral/inferior regions of the brain. - Involved with hearing (auditory) and smelling (olfactory). - The insula is deep to the temporal lobes. - Involved with taste (gustatory) sensations. Occipital Lobe - Located on the posterior of the cerebrum. - Processes visual information. - Responsible for visual memories. Brain Functions - Primary areas: Receive input or control output. - Association areas: Link sensory information to memories. - Precentral gyrus: Primary motor cortex. - Moves skeletal muscles. - Premotor area: Helps plan movements. - Postcentral gyrus: Primary somatosensory cortex. - Processes sensation from the skin and proprioception. - Primary visual and visual association areas: Located in the occipital lobe. - Primary auditory and auditory association areas: Located in the temporal lobes. - Primary olfactory and olfactory association areas: Located in the temporal lobes. - Primary gustatory and gustatory association areas: Located in the insula. - Language and Speech: Mainly located on the left side of the cerebrum. - Broca's area: Plans movements and regulates breathing for speech. - Wernicke's area: Recognition and understanding of writing or speech. - Intellect and personality: Involves the prefrontal cortex. - One of the last areas to mature. White Matter Tracts - Deep to the gray matter of the cerebral cortex. - Association tracts: - Arcuate fibers: Within a hemisphere. - Longitudinal fasciculi: Within a hemisphere. - Commissural tracts: Connect the hemispheres. - Corpus callosum: - Projection tracts: Connect the cerebral cortex to regions lower in the nervous system. Basal Nuclei - Located within white matter tracts. - Help control the intensity and appropriateness of muscle movements. - May be involved in the regulation of emotions as well. - Striatum: Composed of the caudate nucleus and putamen. - Globus pallidus: External and internal segments. The Diencephalon - Connects the cerebrum to the rest of the nervous system. - Regions of the diencephalon: - Thalamus: Relays information between the cerebral cortex, periphery, spinal cord, and brainstem. - Hypothalamus: Involved in regulating homeostasis. - Epithalamus: Contains the pineal gland, which secretes melatonin and regulates sleep-wake cycles. - Subthalamus: Contains the subthalamic nuclei. Thalamus - Collection of nuclei. - Relays information between the cerebral cortex, periphery, spinal cord, and brainstem. - Major sensory integration and processing area. - Involved in processing all sensations except smell (olfaction). Hypothalamus - Collection of nuclei involved in regulating homeostasis. - Regulatory center of the autonomic nervous system (ANS). - Regulates blood pressure, cardiac and smooth muscle contractions, and many activities of internal organs. - The "master" endocrine gland. - Regulates hormone secretion of the pituitary gland. - Regulates body temperature. - Regulates hunger and thirst. Brainstem - The three regions of the brainstem from superior to inferior are: - Midbrain - Pons - Medulla oblongata Midbrain - Cerebral peduncles: White matter tracts in the midbrain. - Corpora quadrigemina: Four "bumps" on the midbrain. - Inferior colliculi: Aid in processing auditory stimuli. - Superior colliculi: Combine sensory information with motor output. - Substantia nigra: Inhibits motor neurons to help control smooth motor movements. - Red nuclei: Contribute to the reticular formation to help control attention and the state of wakefulness. Pons - Visible as a bulge on the anterior of the brainstem. - Lies between the midbrain and medulla oblongata. - Bridge between the cerebellum and brainstem. - White matter on the surface. - Deep gray matter. - Continuation of midbrain nuclei. - Controls the rate of involuntary respiration. Medulla Oblongata - Most inferior structure of the brain. - Houses the fourth ventricle. - Pyramidal tracts: Tracts decussate (cross over) leading to contralateral control of muscles. - Nuclei: - Cardiovascular center: Regulates heart rate and blood pressure. - Respiratory center: Responsible for the ability to breathe. - Abdominal and thoracic motor centers: Coordinate swallowing, coughing, and sneezing. The Cerebellum - Outer gray matter cortex, inner white matter tracts. - Tracts form the arbor vitae. - Plans and fine-tunes motor movements. The Reticular Formation - Composed of gray matter in the brainstem, diencephalon, and spinal cord. - Regulates states of wakefulness and sleep. - Functions in various states such as drowsiness as well. - Reticular activating system: Sensory component. - Processes visual, auditory, and touch stimuli. - Motor component: Maintains muscle tone, breathing, and heart rate. The Limbic System - Structures collectively process emotion. - Consists of the hippocampus, amygdala, olfactory bulbs, cingulate gyrus, parahippocampal gyrus, fornix, mammillary bodies, and several nuclei. - Hippocampus: Involved in memory formation and navigation. - Amygdala: Processes the fear response. The Spinal Cord - Divided into regions that correspond to the vertebral column. - Cervical, thoracic, lumbar, and sacral. - Intact spinal cord ends at the first lumbar vertebrae (L1). - Forms the conus medullaris. - Continues as a bundle of nerves called the cauda equina. - Enlargements: Occur where more axons are associated with the limbs. - Cervical enlargement: Associated with the upper limb. - Lumbar enlargement: Associated with the lower limb. Cross-Sectional Anatomy of the Spinal Cord - Anterior median fissure: Deep groove on the anterior surface. - Posterior median sulcus: Shallow groove on the posterior surface. - Dorsal (posterior) nerve root: - Posterolateral sulcus: - Ventral (anterior) nerve root: - Gray matter: - Posterior horn: Contains axons of sensory neurons. - Anterior horn: Contains cell bodies of motor neurons. - Lateral horn: Contains autonomic neurons (sympathetic division). - White matter: - Posterior columns: - Lateral columns: - Anterior columns: Gray Horns - Gray matter of the spinal cord resembles the letter H. - Posterior gray horns: Contain axons of sensory neurons. - Anterior gray horns: Contain cell bodies of motor neurons. - Lateral gray horns: Contain autonomic neurons (sympathetic division). - Only in thoracic, upper lumbar, and sacral regions. White Columns - White matter of the spinal cord arranged into columns. - Ascending tracts: Send sensory information to the CNS. - Descending tracts: Send motor information to muscles. - Posterior white columns: - Anterior white columns: - Lateral white columns: The Peripheral Nervous System - Ganglia: Groups of cell bodies in the peripheral nervous system (PNS). - Sensory ganglia: Contain cell bodies of sensory (afferent) neurons. - Autonomic ganglia: (Discussed in Chapter 16) - Posterior root ganglia: Contain cell bodies of sensory (afferent) neurons. - Nerves: - Cranial nerves: Attach directly to the brain. - 12 pairs in total. - May be purely motor, purely sensory, or a mixture of sensory and motor axons. - Spinal nerves: Attach to the spinal cord. - 31 pairs in total. - Mixture of sensory and motor axons. Cranial Nerves - CN I - Olfactory nerve: Sensory for smell. - CN II - Optic nerve: Sensory for vision. - CN III - Oculomotor nerve: Motor nerve for eye movement. - CN IV - Trochlear nerve: Motor nerve for eye movement. - CN V - Trigeminal nerve: Sensory for the face; motor to muscles of mastication. - CN VI - Abducens nerve: Motor for eye movement. - CN VII - Facial nerve: Motor to facial muscles; sensory for taste. - CN VIII - Vestibulocochlear nerve: Sensory for hearing and balance. - CN IX - Glossopharyngeal nerve: Motor to the pharynx; sensory for taste. - CN X - Vagus nerve: Sensory and motor functions of thoracic and abdominal viscera. - CN XI - Accessory nerve: Motor to the sternocleidomastoid and trapezius. - CN XII - Hypoglossal nerve: Motor to the muscles of the tongue. Spinal Nerves - Connected to the spinal cord. - Contain sensory and motor axons. - Sensory axons: Enter via the posterior root. - Motor axons: Exit via the anterior root. - 31 spinal nerves. - Named for the level where they exit the spinal cord. - C1-C8, T1-T12, L1-L5, S1-S5, one pair of coccygeal nerves. Spinal Nerve Plexuses - Spinal nerves emerge separately from the spinal cord. - They quickly weave together to form plexuses. - Combinations of axons from multiple different spinal nerves. - Named for the regions they innervate. Four Spinal Nerve Plexuses - Cervical plexus: - Brachial plexus: - Lumbar plexus: - Sacral plexus: Major Nerves of the Body - Major nerves arise from plexuses. - Cervical plexus: Phrenic nerve. - Brachial plexus: Radial, axillary, median, ulnar nerves. - Lumbar plexus: Femoral and saphenous nerves. - Sacral plexus: Sciatic, tibial, and fibular nerves. - T2-T11: Do not form plexuses. - Continue as intercostal nerves. Major Spinal Nerves (Table 14.2) Plexus Nerve Rami Motor Innervation Cutaneous Innervation Cervical Plexus: C1-C5 Phrenic Nerve C3-C5 Diaphragm Sensation to the central tendon of the diaphragm Brachial Plexus: C5-T1 Radial Nerve C5-T1 Triceps brachii, posterior compartment of the antebrachium Posterior brachium and dorsal aspect of the hand Axillary Nerve C5-C6 Teres minor and deltoids Lateral shoulder Median Nerve C5-T1 Anterior compartment of the antebrachium and thenar musculature Anterior and lateral aspect of the hand, dorsal and distal digits Ulnar Nerve C8-T1 Flexor carpi ulnaris, flexor digitorum profundus, and intrinsic muscles of the hand Medial aspect of the hand, digits 4 and 5 Lumbar Plexus: L1-L4 Femoral Nerve L2-L4 Anterior compartment of the thigh Branches into the saphenous nerve Saphenous Nerve L3-L4 No motor innervation Anterior surface of the lower leg Sacral Plexus: L4-S4 Sciatic Nerve L4-S3 Biceps femoris, semimembranosus, semitendinosus No sensory innervation Tibial Nerve L4-S3 Muscles of the posterior lower leg and intrinsic foot muscles Skin of the posterolateral side of the leg and the lateral aspect of the foot Fibular Nerve L4-S2 Chapter 15: The Somatic Nervous System Sensory Pathways - Sensory information is processed through a series of neurons: - Sensory receptor/Primary neuron: The dendrites are in an organ and its axon transmits the action potential to the CNS (spinal cord). - Secondary neuron: Synapses in the posterior horn and extends to the thalamus. - Tertiary neuron: Extends from the thalamus to the primary somatosensory cortex in the parietal lobe. - The thalamus processes and edits incoming sensory information. Motor Pathways - Motor responses are carried out by a series of neurons: - Primary neuron: Located in the motor cortex of the parietal lobe, its axon extends through the brain, crossing over to the other side at the medulla oblongata, and synapses with the secondary neuron in the anterior horn of the spinal cord. - Secondary neuron: Has its cell body in the anterior horn of the spinal cord and travels toward the muscle. - Decussation (crossing over) leads to many brain injuries affecting the opposite side of the body. Reflexes - Connections between sensory and motor neurons. - Synapse between neurons occurs within the CNS. - Do not include higher brain centers. - Do not involve conscious or voluntary aspects of movement. Categorizing Reflexes - Spinal: Synapse within the spinal cord. - Cranial: Involve the brain. - Intrinsic: Develop before birth. - Learned: Develop after birth. - Somatic: Effector is skeletal muscle. - Visceral: Effector is smooth or cardiac muscle or a gland. - Ipsilateral: Begins and ends on the same side of the body. - Contralateral: Begins and ends on opposite sides of the body. Simple Spinal Reflex Arc - Reflex starts with a sensory receptor. - Stimulus brings the receptor to threshold. - Action potentials travel along the axon of the sensory nerve and synapse with a motor neuron in the spinal cord. - No higher brain centers involved. - Neurotransmitters are released by the sensory neuron and bind to the cell body of the motor neuron. - Directly leads to an action potential in the motor neuron. - Muscle contraction occurs. Monosynaptic versus Polysynaptic Reflexes - Monosynaptic: One synapse between sensory and motor neurons. - Polysynaptic: More than one synapse. Involves interneurons. Ipsilateral versus Contralateral Reflexes - Ipsilateral: Begins and ends on the same side of the body. - Contralateral: Begins and ends on opposite sides of the body. Functional Classifications of Reflexes - Withdrawal: Painful stimuli directly cause contraction of skeletal muscle. - Stretch: Activation of muscle spindles prevents overstretching of muscles. - Tendon: Golgi tendon organs prevent overstretching of tendons. - Crossed-extensor: Activates the opposite (contralateral) side of the body. Withdrawal Reflexes - Painful stimuli directly cause contraction of skeletal muscle. - Causes the body to withdraw from the painful stimulus. - Polysynaptic. - Sensory neuron, interneuron within the spinal cord, and motor neuron. Tendon Reflexes - Tendons are stretched by muscle contraction. - Interneuron prevents the motor neuron from causing contraction. - Muscle relaxes to prevent overstretching of the tendon. - Polysynaptic. - Sensory neuron synapses with an interneuron. - Interneuron inhibits motor neuron firing. Crossed-extensor Reflexes - Reflexes activate the opposite side of the body. - Usually in response to painful stimuli. - Polysynaptic. - Sensory neuron synapses with interneurons. - Interneurons may synapse at different levels within the spinal cord. Sensory Receptors Anatomy of a Sensation - Receptors can detect a variety of stimuli/sensations. - Different stimuli/sensations activate different receptors. - The primary somatosensory cortex interprets (processes) signals. - Determines the location of the stimulus. - To understand a stimulus, the brain needs three key pieces of information: - Modality: Type of stimulus. - Location: Where the stimulus is coming from. - Intensity: How strong the stimulus is. - Intensity of the stimulus is determined by the frequency of action potentials. Characteristics of Sensory Receptors - Transduce stimuli into an electrical charge interpreted by the brain. - Adaptation: Allows receptors to become less sensitive to stimuli over time. - Phasic receptors: Adapt quickly. - Tonic receptors: Adapt slowly or not at all. - Receptors are found all over your body in different forms. Adaptation - Adaptation allows receptors to become less sensitive to stimuli over time. - Action potential generation slows down. - Phasic receptors adapt quickly. - Tonic receptors do not adapt or do so slowly. Types of Receptors - Based on type of stimuli: - Chemoreceptors: Detect chemical stimuli. - Osmoreceptors: Detect solute concentrations in bodily fluids. - Thermoreceptors: Detect temperature. - Mechanoreceptors: Detect physical stimuli like pressure and vibration. - Baroreceptors: Detect pressure. - Nociceptors: Detect pain. - Photoreceptors: Detect photons of light. Only found in the eye. - Based on source of stimuli: - Exteroceptors: Stimuli from the external environment. - Interoceptors: Stimuli from internal organs and tissues. - Proprioceptors: Moving body parts. - Based on distribution: - General sense receptors: Found all over the body. - Special sense receptors: Limited to the head. Used for vision, taste, hearing, olfaction, and balance. General Senses Categories of General Senses - Can be detected everywhere in/on the body. - Pressure, vibration, light touch, tickle, itch, temperature, pain, and proprioception. - Receptors are throughout the body (skin, muscles, tendons, joints, organs). - Unencapsulated receptors: Dendrites enmeshed by surrounding tissue. - Encapsulated receptors: Dendrites wrapped to enable function. Unencapsulated Receptors - Free nerve endings: Detect pain and temperature. - Merkel cells: In the skin, used for discriminatory touch. - Hair follicle receptors: In the skin, detect movement of hair. - Thermoreceptors: Detect temperature. Also respond to chemicals. - Capsaicin: Activates thermoreceptors. Interpreted as an increase in temperature. Encapsulated Receptors - Lamellated corpuscles: In the dermis, detect deep pressure. - Tactile corpuscles: In the dermis, detect light pressure. - Bulbous corpuscles: Detect stretching of the skin. - Each receptor has a receptive field: Tissue space it receives information from. - Higher density of small receptive fields leads to more acuity: Acuity - how accurately the brain interprets the stimulus. Distribution of Touch Receptors in Skin - Free nerve endings: Detect pain and temperature. - Merkel cells: Used for discriminatory touch. - Hair follicle receptors: Detect movement of hair. - Tactile and lamellated corpuscles: Detect pressure. - Bulbous corpuscles: Detect stretch. Receptive Fields - Each receptor has a receptive field. - Tissue area where sensory receptors are distributed. - Fewer receptors with a larger receptive field decreases acuity. - Fewer signals sent to the CNS. - Greater number of receptors with smaller receptive fields increases acuity. - More signals sent to the CNS. Pain - Prevents further damage to tissues and cells of the body. - Detected by nociceptors. - Somatic pain and visceral pain can share the same pathway. - Referred pain: Occurs when the brain becomes confused as to the origin of the pain. - Phantom pain: Occurs when a limb is lost. Pathway remains intact and the CNS continues to interpret signals. Referred Pain - Somatic pain is perceived when the stimulus is visceral. - Pain originating in the heart may cause pain in the left arm. - Occurs because somatic pain and visceral pain can share the same pathway. Opioids and Pain - Nociceptors release substance P to a secondary neuron to communicate pain. - An inhibitory neuron synapses at the nociceptor to release natural endorphins that bind to opioid receptors on the nociceptor. - Decreases the release of substance P and decreases pain. - Opioids mimic the effect of endorphins to decrease pain. - Opioid receptors are also found in brain centers. Special Senses Vision - Accomplished by photoreceptors located within the eye. - Light is transduced into electrical signals interpreted by the brain. - Light passes through the cornea of the eye. - The iris regulates the size of the pupil to adjust the amount of light entering the eye. - The lens focuses light where it is received with the most acuity. - Photoreceptors transduce photons of light into electrical signals. Eye Anatomy - Orbit, eyelashes, and eyebrows: Protect the eye. - Conjunctiva: Stratified columnar epithelium. - Helps protect and keeps the eye moist. - Lacrimal glands: Produce tears to keep the eye moist. The Nasolacrimal Apparatus - Lacrimal glands: Produce tears. - Tears: Flow medially across the eye and drain into the nasolacrimal duct. - Flow of tears: Flushes away foreign particles. - If tear production outpaces drainage: Leads to crying. Tunics of the Eye - Fibrous layer: Contains the sclera and cornea. - Vascular layer: Rich blood vessels. - Iris: Smooth muscle around the pupil. Controls the size of the pupil and the amount of light entering the eye. - Ciliary body: Alters the shape of the lens for better visual acuity. - Neural layer (retina): Nervous tissue for photoreception. Cavities of the Eye - Anterior chamber: Between the cornea and lens. Contains aqueous humor (watery fluid). - Posterior chamber: Behind the lens, extends to the retina. Contains vitreous humor (jellylike). Retina - Contains cells that transduce light. - Rods and cones: In the posterior layer of the retina, transduce light. - Release neurotransmitters onto bipolar cells: Bipolar cells form synapses with ganglion cells. - Axons of ganglion cells: Form the optic nerve. Comparison of Color Sensitivity - Rods: Contain rhodopsin. Sensitive to a variety of wavelengths. Only detects white and black. - Cones: Contain pigments called opsins. Sensitive to specific wavelengths of light. Used to detect red, green, and blue. Dark and Light Adaptation - Dark adaptation: Decreased vision when moving from a brightly lit environment to a dark environment. - In bright light, rods are highly active and store rhodopsin. - Rods take a few moments to activate in dark space. - Light adaptation: Decreased vision when moving from a dark environment to a brightly lit environment. - Rods and cones send signals initially leading to a glare. - Signals adjust and rods turn off while cones refine their signal. Photoisomerization of Rods - Rods: Contain opsin proteins with retinal inside. - Photons of light: Cause a shape change in retinal called photoisomerization. - Hydrocarbon chain of retinal: Becomes 11-trans-retinal (straight chain). - Leads to visual transduction by the eye: Retinal must return to its original shape (11-cis-retinal) for rods to continue transduction. - Bleaching: Occurs if opsin cannot respond to additional photons. Density of Cones in Retina - Periphery of the retina: Has a higher density of rods. - Proportion of cones in the retina: Increases posteriorly. - Macula lutea: Has a high density of cones. - Fovea centralis: Center of the macula lutea with the highest density of cones. - Lens: Focuses light on the fovea centralis for greatest visual acuity. Pathway of Visual Information - Lateral geniculate nucleus of the thalamus: Edits visual information. - Info then sent to the primary visual cortex in the occipital lobe: Some axons of the optic nerve cross to the opposite side of the brain at the optic chiasm. - Right visual field: Processed by the left side of the occipital lobe. - Left visual field: Processed by the right side of the occipital lobe. Taste (Gustation) - A chemical special sense. - Recognized tastes include: - Sweet, salty, sour, bitter, umami, and fat. - Papillae: On the tongue, contain taste buds. - Taste buds: Contain taste receptors. - Transduce: Chemicals in food into taste. - Basal epithelial cells: Replace damaged taste receptors. Detection of Tastes - Saliva: Dissolves molecules so more chemicals reach taste receptor cells. - Salty: Detected when Na+ ions activate taste cell receptors. - Sour: Detected when H+ ions activate taste cell receptors. - Sweet: Detected when glucose activates taste cell receptors. - Other monosaccharides and artificial sweeteners can activate sweet receptors. - Bitter: Detected by 23 different taste receptors. - Varies with each individual. - Umami: Detected when L-glutamate activates taste cell receptors. - Monosodium glutamate (MSG) can also activate umami receptors. Pathway of Taste Information - Taste information travels to the CNS along cranial nerves: - Glossopharyngeal, Facial, and Vagus nerves. - Nerves converge at the medulla oblongata: Information is next sent to the thalamus. - Thalamus: Sends information to the insula to be processed. Smell (Olfaction) - A chemical special sense. - Odorant molecules: Bind to olfactory receptors in the olfactory epithelium. - Olfactory neurons: Pass through the cribriform plate to form the olfactory bulb. - Axons gather to form the olfactory tract: The olfactory tract projects to different regions of the brain: - Primary olfactory cortex in the temporal lobe, limbic system, and thalamus. External Ear - Hearing: Is the transduction of sound waves into electrical signals interpreted by the brain. - Auricle, ear canal, and tympanic membrane: Make up the external ear. - Auricle and auditory canal (external acoustic meatus): Funnel the sound waves toward the tympanic membrane. - Tympanic membrane: Vibrates in response. Middle Ear - Middle ear: Contains the ossicles: Malleus, incus, and stapes. - Ossicles: Attached to the tympanic membrane, amplify vibrations. - Stapes: Rests against the oval window. - Oval window: Is the door to the inner ear. - Middle ear: Connects to the pharynx via the auditory (Eustachian) tube. The Inner Ear - Inner ear: Within the temporal bone. Consists of the cochlea, vestibule, and semicircular canals. - Cochlea: Involved in hearing. - Vestibule and semicircular canals: Involved in balance. The Function of the Ossicles - Ossicles: Amplify vibrations. - Middle ear: Is an air-filled space. - Inner ear: Is a fluid-filled space. - Vibrations: Must have more force to move fluid through the cochlea. Components of the Inner Ear - Malleus, incus, and stapes: Amplify vibrations of the tympanic membrane. - Oval window: Receives amplified vibrations. - Vibrations: Are transduced into electrical signals by the cochlea. - Cochlea: Scala vestibuli, scala tympani, and cochlear duct are the tubular portions of the cochlea. The Cochlea - Three separate tubes: Rolled together. - Scala vestibuli: Filled with perilymph. - Scala tympani: Filled with perilymph. - Cochlear duct: Filled with endolymph. - Contains spiral organs: That transduce movement of the scala vestibuli. Sound Transduction - Spiral organs: Sit on top of the basilar membrane. - Fluid: Moves through the scala, causing the basilar membrane to move up and down. - Stereocilia of hair cells: Sitting on the basilar membrane, make contact with the tectorial membrane. - Contact between hair cells and the tectorial membrane: Depolarizes hair cells. - This leads to signal transduction: Through the cochlear nerve. The Basilar Membrane - Width of the basilar membrane varies: Causes different locations to move in response to different sound wave frequencies. - Higher-pitched sounds: Move the region close to the base of the cochlea. - Lower-pitched sounds: Move the region close to the tip of the cochlea. - Allows us to detect differences in sound: Like volume, pitch, and tone. Pathway for Auditory Information - Axons of hair cells: Form the cochlear branch of the vestibulocochlear nerve. - Synapses with the cochlear nucleus: In the medulla oblongata. - Axons from the medulla: Synapse in the superior olivary nucleus of the pons. - Signal: Then carried to the midbrain and thalamus. - Primary auditory cortex: In the temporal lobe, ultimately processes information. Equilibrium (Balance) - Maintained by hair cells: Of the vestibule and semicircular canals. - Sensitive to head movement and body position. - Static equilibrium: Sense of head position and acceleration. - Maintained by the vestibule. - Dynamic equilibrium: Rotation of the head or body. - Detected by hair cells of the semicircular canals. - Each semicircular canal detects a different plane Dynamic Equilibrium - Dynamic equilibrium: Rotation of the head or body. - Detected by hair cells of the semicircular canals: Each semicircular canal detects a different plane. - Stereocilia: Extend into a jelly-like cupula on top of the ampulla. - Movement of the head: Causes endolymph to move and the cupula moves in response. - Hair cells in the ampulla: Respond to movements of the cupula. Static Equilibrium - Static equilibrium: Sense of head position and acceleration. - Maintained by the vestibule: Contains two chambers: the utricle and saccule. - Hair cells in the vestibule: Supported by the macula. - Stereocilia: Embedded in the otolithic membrane. - As the head moves: Otoliths (calcium carbonate crystals) cause movement of the otolithic membrane. - Stereocilia of hair cells: Interpret movements of the otolithic membrane. Pathway for Equilibrium - Axons of hair cells: Form the vestibular branch of the vestibulocochlear nerve. - Axons of the vestibulocochlear nerve: Terminate in nuclei within the pons and medulla. - Nuclei: Relay information throughout the CNS. Chapter 16: The Autonomic Nervous System Somatic Nervous System versus Autonomic Nervous System - Somatic Nervous System: Causes contraction of skeletal muscle. Controls voluntary responses. - Autonomic Nervous System: Controls cardiac and smooth muscle and glands. Controls involuntary responses. Helps maintain homeostasis in the body. Characteristics of the Autonomic Nervous System (ANS) - Primarily innervates internal organs. - Two divisions: - Sympathetic Nervous System: Associated with "fight-or-flight" responses. - Parasympathetic Nervous System: Associated with "rest and digest" responses. Most organs receive dual innervation from both divisions. Divisions of the Nervous System - The autonomic nervous system is divided into sympathetic and parasympathetic divisions. Sympathetic Division of the Autonomic Nervous System - Responds to a threat to our homeostasis (stress) or enables survival. - Increases oxygen delivered to skeletal muscle. - Increases sweating. - Blood is shifted away from the digestive system and toward skeletal muscle. - Pupils dilate. - Brain becomes alert. Neurotransmitters of the Sympathetic Nervous System - Acetylcholine (ACh): Used at the synapse of the sympathetic preganglionic and postganglionic neurons. - Norepinephrine: Released by postganglionic neurons onto target cells. - Epinephrine and norepinephrine: Released as hormones from the adrenal gland. Parasympathetic Division of the Autonomic Nervous System - Active when the body is not stressed or under a threat. - Controls "rest and digest" activities: - Salivation - Lacrimation - Urination - Digestion - Defecation - Sexual arousal Anatomy of a Parasympathetic Nervous System Pathway - Cell bodies of preganglionic neurons located in the brainstem and sacral spinal cord. - Long preganglionic axons project to ganglia near or within the target organ. - Short postganglionic axons synapse with cells in the target organ. Neurotransmitters of the Parasympathetic Nervous System - Acetylcholine (ACh): Released by preganglionic and postganglionic neurons of the parasympathetic nervous system. Chemical Components of the Autonomic Responses Synapses of the Autonomic Nervous System - Cholinergic synapses: Acetylcholine (ACh) is the neurotransmitter released. - Adrenergic synapses: Norepinephrine is the neurotransmitter released. Types of Cholinergic Receptors - Nicotinic receptors: Chemically-gated ion channel. - Endogenous ligand - acetylcholine. - Exogenous ligand - nicotine. - Muscarinic receptors: Trigger changes in the cell without allowing ions to pass through the membrane. - Endogenous ligand - acetylcholine. - Exogenous ligand - muscarine. Cholinergic Receptors Receptor Type Location(s) Roles Endogenous Ligand(s) Example of an Exogenous Ligand Nicotinic Receptors Adrenal medulla, all skeletal neuromuscular junctions, postganglionic neurons throughout the ANS, some CNS synapses Depolarizes the postsynaptic cell, causing contraction or a new action potential Acetylcholine Nicotine - A drug in cigarettes and some vaping devices, causes skeletal muscle activation, but the CNS locations lead to addiction Muscarinic Receptors All target tissues of the parasympathetic nervous system Can have excitatory effects or inhibitory effects, but is not an ion channel so does not directly affect membrane potential Acetylcholine Muscarine - A type of mushroom poison; causes salivation, intestinal cramping, slowing of the heart rate Varicosities - Postganglionic synapses in the autonomic nervous system differ from the neuromuscular junction (NMJ). - Synapses occur as swellings along the length of postganglionic axons. - Called varicosities. Adrenergic Receptors - Adrenergic receptors bind to norepinephrine and epinephrine. - Alpha (α)-adrenergic receptors: - α1 - located in skin, GI and pelvic organs, and blood vessels. Cause contraction of smooth muscle. - α2 - found in the pancreas, platelets, brain, and spinal cord. Inhibit insulin release. Promote blood clotting. - Beta (β)-adrenergic receptors: - β1 - found in the heart and kidney. Increase heart rate, force of contraction, and secretion of renin. - β2 - found in blood vessels, lungs, uterus, stomach, and small intestines. Cause relaxation of smooth muscle. - β3 - found in adipose tissue. Stimulate breakdown of lipids. The Cholinergic and Adrenergic Synapses of the ANS - Acetylcholine: Used at cholinergic synapses. Receptors are either nicotinic or muscarinic. - Norepinephrine: Used at adrenergic synapses. Receptors can be activated by norepinephrine or epinephrine. Alpha-1, alpha-2, beta-1, beta-2, and beta-3 receptors. Autonomic Receptors Autonomic Reflexes and Homeostasis Autonomic Reflexes - Help maintain internal homeostasis. - Important in maintaining parameters like: - Blood pressure - Heart rate - Airway diameter - Digestive activity - Components of autonomic reflex arcs are similar to those in somatic reflex arcs. Effectors are smooth or cardiac muscle and glands. The Structure of Reflexes - Afferent branch: A single neuron. Sensory information comes from somatic and special senses and viscera. Some visceral sensations are not consciously perceived. - Efferent branch: Two neurons. Preganglionic neuron synapses with postganglionic neuron in a ganglion. Maintaining Homeostasis - Both divisions of the autonomic nervous system innervate most organs. - Called dual innervation. - Blood vessels, sweat glands, and arrector pili muscles receive only sympathetic innervation. - The divisions usually have opposite effects on an organ. - Parasympathetic dominance: Effects of the parasympathetic nervous system are seen. - Lower heart rate, increased GI activity, pupil dilation, airway constriction, decrease breathing rate. - Sympathetic dominance: Effects of the sympathetic nervous system are seen. - Opposite of parasympathetic effects. Autonomic Tone - Balance between parasympathetic and sympathetic dominance when an organ is at rest. - Different for each organ. - Parasympathetic tone: Dominates the heart at rest. Lowers heart rate to a normal range. - Sympathetic tone: Dominates blood vessels at rest. Adjusts constriction of vessels to maintain blood pressure. Stress - The autonomic nervous system helps the body respond to stress. - Aim is to increase nutrients in the blood and deliver more blood to the head and muscles. - Stress response results in: - Lipid breakdown and increased blood glucose. - Airway dilation for increased oxygen in the blood. - Increased blood flow to skeletal muscles, decreased blood flow to viscera. - Higher blood pressure to increase the speed of delivery to the brain and muscles. - Endocrine hormones also help. Prolonged Stress - Prolonged stress has negative effects on the body. - Chronic high blood pressure and diabetes. - Exercise also initiates a stress response. Changes are considered beneficial. - Parasympathetic dominance after exercise can reverse some effects of chronic stress. Chapter 17: The Endocrine System Internal Communication - The nervous and endocrine systems facilitate long-distance communication. - The nervous system uses electrical signals and neurotransmitters for communication between cells. - The endocrine system uses hormones, which are chemical signaling molecules that travel in the blood, reaching most cells of the body and having widespread effects. Functions of the Endocrine System - Helps maintain homeostasis by regulating: - Use of calories and nutrients - Secretion of wastes - Blood pressure and blood osmolarity - Growth - Fertility and sex drive - Lactation - Sleep Chemical Signaling - Hormones are chemical messengers used by the endocrine system. - Most hormones are released into the blood. - Paracrine signaling: A hormone affects neighboring cells. - Autocrine signaling: A hormone affects the same cell that released it. - Endocrine signaling: A hormone travels through the blood to affect cells throughout the body. - Neurotransmitters: Used by neurons and the nervous system. Endocrine and Exocrine Glands - Chemical secretions exit glands via exocytosis. - Endocrine gland secretion: Releases product into the bloodstream or extracellular fluid. - Exocrine gland secretion: Releases product into a duct that carries product to a body surface. Endocrine Glands - Include the pituitary, thyroid, parathyroid, adrenal, and pineal glands. - Mainly secrete hormones. - Some have non-endocrine functions. - Do not have a duct for secretion. - Secretions enter the blood or interstitial fluid. - Hormones affect target cells, which are cells with receptors for that specific hormone. Other Organs That Have Endocrine Function - Contains cells that have endocrine functions. - Includes the hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, adipose tissue, ovaries, and testes. Target Cells - Hormones travel through the bloodstream and can reach almost any cell in the body. - Hormones only affect target cells, which are cells with a receptor for a particular hormone. - Binding of a hormone to its receptor on a target cell initiates intracellular signaling. Comparison of Nervous and Endocrine Systems - Both nervous and endocrine systems allow control and communication of the body. - They accomplish this in different ways: - Neurotransmitters: Used by the nervous system. - Hormones: Used by the endocrine system. - The nervous system is generally faster to make a change. - The endocrine system has more widespread effects. - Endocrine system effects generally last longer. Hormones Types of Hormones - Based on chemical structure: - Steroid hormones: Cross cell membranes easily. Lipid-based hormones. - Amine-based hormones: Modified amino acids. Water-soluble; cannot cross cell membranes. - Peptide and Protein hormones: Made from chains of amino acids. Water-soluble; cannot cross cell membranes. Steroid Hormones - Produced from cholesterol molecules. - Lipid-soluble hormones. - Can pass through cell membranes. - Require transport proteins to travel in the blood. - Examples include testosterone and estrogens. Amine Hormones - Made from individual amino acids. - Water-soluble hormones. - Cannot freely pass through the cell membrane. - Do not require transport proteins in the blood. - Examples include melatonin, epinephrine, and norepinephrine. Peptide and Protein Hormones - Chains of amino acids. - Water-soluble hormones. - Cannot freely pass through the cell membrane. - Do not require transport proteins in the blood. - Examples include antidiuretic hormone and insulin. Production of Hormones - Steroid hormones: Made on demand by modifying cholesterol molecules. Cannot be stored. Not soluble in blood. Travel bound to transport proteins when in blood. - Peptide hormones: Translated like other proteins. Modified and stored in vesicles until release. Soluble in blood. Travel in a "free" state. Hormone Receptors - Receptors can be intracellular or on the cell surface. - Lipid-soluble hormone receptors: Usually intracellular (cytosol or nuclear). This is because lipid-soluble hormones can pass through cell membranes. - Water-soluble hormone receptors: Usually on the surface of the cell. This is because these hormones are usually unable to cross cell membranes. Intracellular Hormone Receptors - Associated with steroid and thyroid hormones. - Hormone must be lipid-soluble to pass through the membrane. - May be in the cytosol or nucleus. - Results in increased transcription and increased protein synthesis. Membrane-bound Hormone Receptors - Associated with water-soluble hormones (amine and peptide hormones). - Hormone serves as the first messenger in the pathway. - An intracellular second messenger relays the message insid