Anatomy & Physiology - Muscular System PDF

ANATOMY & PHYSIOLOGY MASCULAR SYSTEM The Muscular System Functions Properties of Muscles Movement Contractility Maintain posture the ability of muscle to shorten forcefully, Respiration...

ANATOMY & PHYSIOLOGY MASCULAR SYSTEM The Muscular System Functions Properties of Muscles Movement Contractility Maintain posture the ability of muscle to shorten forcefully, Respiration or contract Production of body heat Excitability Communication the capacity of muscle to respond to a Heartbeat stimulus Contraction of organs and vessels Extensibility the ability to be stretched beyond its Types of Muscles normal resting length and still be able to Skeletal contract attached to bones Elasticity striated the ability of the muscle to recoil to its voluntarily controlled original resting length after it has been Cardiac stretched located in the heart Skeletal Muscle Structure Striated muscle striated Skeletal muscle, or striated muscle, with its involuntarily controlled associated connective tissue, constitutes Smooth approximately 40% of body weight. Located in blood vessels, hollow organs Skeletal muscle is so named because many Non-striated of the muscles are attached to the skeletal involuntarily controlled system. Some skeletal muscles attach to the skin or connective tissue sheets. Skeletal muscle is also called striated muscle because transverse bands, or striations, can be seen in the muscle under the microscope. Individual skeletal muscles, such as the biceps brachii, are complete organs, as a result of being comprised of several tissues: muscle, nerve, and connective tissue. Connective Tissue Coverings Epimysium Each skeletal muscle is surrounded by a connective tissue sheath called the epimysium. Fascicles A skeletal muscle is subdivided into groups of muscle cells, termed fascicles. Perimysium Each fascicle is surrounded by a connective tissue covering, termed the perimysium. Endomysium Each skeletal muscle cell (fiber) is surrounded by a connective tissue covering, termed the endomysium. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Muscle Fiber Structure The Muscle Fiber A muscle fiber is a single cylindrical cell, with several nuclei located at its periphery. Muscle fibers range in length 1 cm to 30 cm and are generally 0.15 mm in diameter. Skeletal muscle fibers contain several nuclei that are located at the periphery of the fiber. Sarcolemma The sarcolemma (cell membrane) has many tubelike inward folds, called transverse tubules, or T tubules. Transverse Tubules T tubules occur at regular intervals along the muscle fiber and extend into the center of the muscle fiber. Tubelike inward folds Sarcomere Sarcoplasmic Reticulum The sarcomere is the basic structural and The T tubules are associated with enlarged functional unit of a skeletal muscle portions of the smooth endoplasmic because it is the smallest portion of a reticulum called the sarcoplasmic skeletal muscle capable of contracting. reticulum. Z disks The sarcoplasmic reticulum has a relatively Z disks form a network of protein fibers that high concentration of Ca2+, which plays a both serve as an anchor for actin major role in muscle contraction. myofilaments and separate one sarcomere from the next. Triad A sarcomere extends from one Z disk to the T tubules connect the sarcolemma to the next Z disk. terminal cisternae to form a muscle triad. Actin & Myosin myofilaments The organization of actin and myosin Terminal Cisternae myofilaments gives skeletal muscle its The enlarged portions are called terminal striated appearance and gives it the ability cisternae. to contract. The myofilaments slide past each other, Sarcoplasm causing the sarcomeres to shorten. The cytoplasm of a muscle fiber is called Each sarcomere consists of two light- the sarcoplasm, which contains many staining bands separated by a dark- bundles of protein filaments. staining band. I band Myofibrils Light bands, consist only of actin, and are Bundles of protein filaments are called called I bands that extends toward the myofibrils. center of the sarcomere to the ends of the Myofibrils consist of the myofilaments, myosin myofilaments. actin and myosin. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM A bands Resting Membrane Potential Dark staining bands are called A bands, The resting membrane potential exists because of: that extend the length of the myosin The concentration of K+ being higher on the myofilaments. inside of the cell membrane and the Actin and myosin myofilaments overlap for concentration of Na+ being higher on the some distance on both ends of the A band; outside this overlap causes the contraction. The presence of many negatively charged Actin myofilaments are made up of three molecules, such as proteins, inside the cell components: that are too large to exit the cell ▪ Actin The presence of leak protein channels in the ▪ Troponin membrane that are more permeable to K+ ▪ Tropomyosin than it is to Na+ Troponin molecules have binding sites for Na+ tends to diffuse into the cell and K+ tends Ca2+ (calcium ion). to diffuse out. Tropomyosin filaments block the binding In order to maintain the resting membrane sites on myosin myofilament and actin potential, the sodium-potassium pump myofilaments. recreates the Na+ and K+ ion gradient by Myosin myofilaments, or thick pumping Na+ out of the cell and K+ into the myofilaments, resemble bundles of tiny golf cell. clubs. Myosin heads have ATP binding sites, ATPase and attachment spots for actin. Skeletal Muscle Fiber Action Potential To initiate a muscle contraction, the resting membrane potential must be changed to an action potential. Changes in the resting membrane potential occur when gated cell membrane channels open. In a skeletal muscle fiber, a nerve impulse Excitability of Muscle Fibers triggers gated Na+ channels to open and The electrical charge difference across the Na+ diffuses into the cell down its cell membrane of an unstimulated cell is concentration gradient and toward the called the resting membrane potential. negative charges inside the cell. Muscle cells (fibers) have a resting The entry of Na+ causes the inside of the membrane potential but can also perform cell membrane to become more positive action potentials. than when the cell is at resting membrane The resting membrane potential is due to the potential. inside of the membrane being negatively charged in comparison to the outside of the membrane being positively charged. Action potentials are due to the membrane having gated channels. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Depolarization Ion Channels and Action Potentials This increase in positive charge inside the cell membrane is called depolarization. If the depolarization changes the membrane potential to a value called threshold, an action potential is triggered. An action potential is a rapid change in charge across the cell membrane. Depolarization during the action potential is when the inside of the cell membrane becomes more positively charged than the outside of the cell membrane. Near the end of depolarization, the positive charge causes gated Na+ channels to close and gated K+ channels to open. Nerve Supply Motor Neuron A motor neuron is a nerve cell that Repolarization stimulates muscle cells. Opening of gated K+ channels start Neuromuscular Junction repolarization of the cell membrane. A neuromuscular junction is a synapse Repolarization is due to the exit of K+ from where the fiber of a nerve connects with the cell. muscle fiber. The outward diffusion of K+ returns the cell Synapse to its resting membrane conditions and A synapse refers to the cell-to-cell junction the action potential ends. between a nerve cell and either another In a muscle fiber, an action potential results nerve cell or an effector cell, such as in a in muscle contraction. muscle or a gland. Presynaptic Terminal A presynaptic terminal is the end of a neuron cell axon fiber. Synaptic Cleft A synaptic cleft is the space between the presynaptic terminal and postsynaptic membrane. Postsynaptic Membrane The postsynaptic membrane is the muscle fiber membrane (sarcolemma). Synaptic Vesicle A synaptic vesicle is a vesicle in the presynaptic terminal that stores and releases neurotransmitter chemicals. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Neurotransmitters Muscle Contraction Neurotransmitters are chemicals that 1. An action potential travels down motor stimulate or inhibit postsynaptic cells. neuron to presynaptic terminal causing Ca2+ Acetylcholine channels to open. Acetylcholine is the neurotransmitter that 2. Ca2+ causes synaptic vesicles to release stimulates skeletal muscles. acetylcholine into synaptic cleft. Neuromuscular Junction 3. Acetylcholine binds to receptor sites on Na+ channels, Na+ channels open, and Na+ rushes into postsynaptic terminal (depolarization). 4. Na+ causes sarcolemma and t-tubules to increase the permeability of sarcoplasmic reticulum which releases stored calcium. 5. Ca2+ binds to troponin which is attached to actin. 6. Ca2+ binding to troponin causes tropomyosin to move exposing attachment sites for myosin. 7. Myosin heads bind to actin. 8. ATP is released from myosin heads and heads bend toward center of sarcomere. 9. Bending forces actin to slide over myosin. Function of the Neuromuscular Junction 10. Acetylcholinesterase (enzyme breaks down acetylcholine) is released, Na+ channels close, and muscle contraction stops. Skeletal Muscle Excitation ANATOMY & PHYSIOLOGY MASCULAR SYSTEM ANATOMY & PHYSIOLOGY MASCULAR SYSTEM ATP and Muscle Contractions Contraction phase Energy for muscle contractions is supplied The contraction phase is the time during by ATP which the muscle contracts and the Energy is released as ATP → ADP + P Relaxation phase ATP is stored in myosin heads relaxation phase is the time during which the ATP helps form cross-bridge formation muscle relaxes. between myosin and actin The new ATP must bind to myosin before cross-bridge is released Rigor mortis will occur when a person dies, and no ATP is available to release cross- bridges ATP Breakdown and Cross-Bridge Movement Summation and Recruitment Summation In summation, individual muscles contract more forcefully. ▪ Tetanus is a sustained contraction that occurs when the frequency of stimulation is so rapid that no relaxation occurs. Recruitment Recruitment is the stimulation of several motor units. Multiple-Wave Summation Muscle Twitch A muscle twitch is a single contraction of a muscle fiber in response to a stimulus. A muscle twitch has three phases: 1. latent phase, 2. contraction phase, and 3. relaxation phase. Latent phase The latent phase is the time between the application of a stimulus and the beginning of contraction. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Skeletal Muscle Fiber Types Mechanisms of fatigue include: Slow twitch fibers Acidosis and ATP depletion due to either an contract slowly increased ATP consumption or a decreased fatigue slowly ATP production have a considerable amount of myoglobin Oxidative stress, which is characterized by use aerobic respiration the buildup of excess reactive oxygen are dark in color species (ROS, free radicals) used by long distance runners Local inflammatory reactions Fast twitch fibers Types of Contractions contract quickly There are two types of muscle contractions: fatigue quickly Isometric use anaerobic respiration The isometric contraction has an increase energy from glycogen in muscle tension, but no change in light color length. Isotonic used by sprinters The isotonic contraction has a change in o A muscle has a blend of types, with one type muscle length with no change in tension. dominating. Humans have both types of Concentric contractions are isotonic fibers contractions in which muscle tension o The distribution of fibers is genetically increases as the muscle shortens. determined Eccentric contractions are isotonic contractions in which tension is Energy for Muscle Contractions maintained in a muscle, but the opposing Muscle fibers are very energy-demanding resistance causes the muscle to lengthen. cells whether at rest or during any form of Muscle Tone exercise. Muscle tone is the constant tension This energy comes from either aerobic (with produced by body muscles over long O2) or anaerobic (without O2) ATP periods of time. production Muscle tone is responsible for keeping the ATP is derived from four processes in back and legs straight, the head in an upright skeletal muscle. position, and the abdomen from bulging. 1. Aerobic production of ATP during most Muscle tone depends on a small exercise and normal conditions. percentage of all the motor units in a 2. Anaerobic production of ATP during muscle being stimulated at any point in time, intensive short-term work causing their muscle fibers to contract 3. Conversion of a molecule called creatine tetanically and out of phase with one phosphate to ATP another. 4. Conversion of two ADP to one ATP and one Smooth Muscle AMP (adenosine monophosphate) during Smooth muscle cells are non-striated heavy exercise small, spindle-shaped muscle cells, usually with one nucleus per cell. Muscle Fatigue The myofilaments are not organized into Fatigue is a temporary state of reduced work sarcomeres. capacity. The cells comprise organs controlled Without fatigue, muscle fibers would be involuntarily, except the heart. worked to the point of structural damage to Neurotransmitter substances, hormones, them and their supportive tissues. and other substances can stimulate smooth muscle. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Cardiac Muscle Cardiac muscle cells are long, striated, and branching, with usually only one nucleus per cell. Cardiac muscle is striated as a result of the sarcomere arrangement. Cardiac muscle contraction is autorhythmic. Intercalated disks Cardiac muscle cells are connected to one another by specialized structures that include desmosomes and gap junctions called intercalated disks. Cardiac muscle cells function as a single unit in that action potential in one cardiac muscle cell can stimulate action potentials in adjacent cells. Skeletal Muscles Skeletal Muscle Anatomy Tendon A tendon connects skeletal muscles to bone. Aponeuroses Aponeuroses are broad, sheetlike tendons. Retinaculum A retinaculum is a band of connective tissue that holds down the tendons at each wrist and ankle. Origin Skeletal muscle attachments have an origin and an insertion, with the origin being the attachment at the least mobile location. Insertion The insertion is the end of the muscle attached to the bone undergoing the greatest movement. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Belly Muscles of Mastication The part of the muscle between the origin Temporalis and the insertion is the belly. Masseter Agonists Pterygoids (two pairs) A group of muscles working together are called agonists. Muscles of Facial Expression and Mastication Antagonists A muscle or group of muscles that oppose muscle actions are termed antagonists. Muscle Attachment Tongue and Swallowing Muscles Nomenclature Muscles are named according to: 1. Location – a pectoralis muscle is located in the chest. 2. Size – the size could be large or small, short or long. 3. Shape - the shape could be triangular, quadrate, rectangular, or round. 4. Orientation of fascicles – fascicles could run straight (rectus) or at an angle (oblique). 5. Origin and insertion - The sternocleidomastoid has its origin on the sternum and clavicle and its insertion on the mastoid process of the temporal bone. 6. Number of heads - A biceps muscle has two heads (origins), and a triceps muscle has three heads (origins). 7. Function - Abductors and adductors are the muscles that cause abduction and movements. ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Deep Neck and Back Muscles Abdominal Wall Muscles Rectus abdominis center of abdomen compresses abdomen External abdominal oblique sides of abdomen compresses abdomen Internal abdominal oblique compresses abdomen Transverse abdominis compresses abdomen Thoracic Muscles Upper Scapular and Limb Muscles External intercostals Trapezius elevate ribs for inspiration shoulders and upper back Internal intercostals extends neck and head depress ribs during forced expiration Pectoralis major Diaphragm chest moves during quiet breathing elevates ribs Serratus anterior between ribs elevates ribs Deltoid shoulder abductor or upper limbs Triceps brachii 3 heads extends elbow Biceps brachii “Flexing muscle” flexes elbow and shoulder Brachialis flexes elbow Latissimus dorsi lower back extends shoulder ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Arm Muscles Forearm Muscles Flexor longus Flexor carpi radialis Flexor carpi ulnaris Flexor digitorum profundus Flexor digitorum superficialis Pronator Brachioradialis Extensor carpi radialis brevis Pelvic Floor Muscles Levator ani Ischiocavernosus Bulbospongiosus Deep transverse perineal Superficial transverse perineal (male) ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Muscles of the Hip and Thigh Muscles of Hips Iliopsoas flexes hip Gluteus maximus buttocks extends hip and abducts thigh Gluteus medius Hip abducts and rotates thigh Muscles of the Thigh Quadriceps femoris is comprised of 4 thigh muscles: Rectus femoris front of thigh extends knee and flexes hip Vastus lateralis extends knee Vastus medialis extends knee Vastus intermedius extends knee Adductors: Gracilis adducts thigh and flexes knee Adductor longus, Adductor magnus Hamstring muscles: Biceps femoris, Semimembranosus, Semitendinosus Hamstring back of thigh flexes knee, rotates leg, extends hip ANATOMY & PHYSIOLOGY MASCULAR SYSTEM Muscles of Lower Leg Tibialis anterior front of lower leg inverts foot Gastrocnemius calf flexes foot and leg Soleus attaches to ankle flexes foot