Human Anatomy and Physiology with Pathophysiology PDF

§ Action Potential Generation: A stimulus reaching threshold triggers depolarization and repolarization. § Propagating Ac...

§ Action Potential Generation: A stimulus reaching threshold triggers depolarization and repolarization. § Propagating Action Potentials: Action potentials travel along the membrane and T tubules, causing muscle contraction. MODULE 5.1: MUSCLES AND MUSCULAR SYSTEM 2. Neuromuscular Junction (NMJ) § The NMJ connects a motor neuron to a muscle fiber, FUNCTIONS OF THE MUSCULAR SYSTEM comprising the presynaptic terminal, synaptic cleft, and motor 1. Body Movement: Skeletal muscles facilitate voluntary end-plate. movements (e.g., walking, running). § Neurotransmitter Release: Acetylcholine (ACh) is released into 2. Posture Maintenance: Skeletal muscles maintain muscle tone the synaptic cleft, binding to muscle fiber receptors and for body stability. causing depolarization. 3. Respiration: Muscles in the thorax assist in air movement during § Acetylcholinesterase: Breaks down ACh to prevent breathing. continuous stimulation. 4. Heat Production: Muscle contractions generate heat to regulate body temperature. 3. Excitation-Contraction Coupling 5. Communication: Skeletal muscles enable facial expressions § Action Potential Propagation: Action potentials travel along and speech. the sarcolemma and T tubules, prompting Ca2+ release from 6. Organ Constriction: Smooth muscles control movement within the sarcoplasmic reticulum (SR). organs and blood vessels. § Calcium Binding: Ca2+ binds to troponin on actin, moving the 7. Heartbeat Regulation: Cardiac muscle drives heartbeats for troponin-tropomyosin complex to expose myosin binding sites. blood circulation. § Cross-Bridge Formation: Myosin heads bind to actin, pulling filaments toward the sarcomere's center, resulting in GENERAL FUNCTIONAL CHARACTERISTICS OF MUSCLE contraction. SKELETAL MUSCLE § Location: Attached to bones 4. Cross-Bridge Cycle § Control: Voluntary § Formation and Movement: Myosin heads attach to actin, pull § Functions: Movement, posture, respiration (power stroke), and release. ATP is needed for each cycle to § Appearance: Striated, multinucleated detach the myosin head and reset it for the next cycle. § Energy Use: ATP is essential for cross-bridge formation and SMOOTH MUSCLE movement. It also allows the myosin head to return to its § Location: Walls of hollow organs and blood vessels original position. § Control: Involuntary § Functions: Movement of substances, regulation of blood flow 5. Muscle Relaxation § Appearance: Non-striated, spindle-shaped § Calcium Reuptake: Ca2+ is actively transported back into the SR, reducing its concentration in the sarcoplasm. CARDIAC MUSCLE § Troponin-Tropomyosin Complex: The complex returns to its § Location: Heart original position, covering the myosin binding sites on actin, § Control: Involuntary and muscle relaxation occurs as a result of decreased cross- § Functions: Pumps blood bridge cycling. § Appearance: Striated with intercalated discs Key Points for Understanding 1. Action Potentials: Initiate muscle contraction. 2. NMJ Function: Transmits nerve signals to muscle fibers. 3. Excitation-Contraction Coupling: Links action potentials to contraction. 4. Cross-Bridge Cycle: Mechanism of contraction. 5. Relaxation: Involves Ca2+ removal and muscle relaxation. FATIGUE TYPES OF FATIGUE 1. Psychologic Fatigue ü Involves the central nervous system (CNS); muscles can function but the individual feels mentally exhausted. ü Mechanism: Psychological factors (stress, motivation, emotional state) affect performance. ü Example: An athlete motivated by spectators FUNCTIONAL PROPERTIES OF MUSCLE TISSUE despite physical exhaustion. 1. Contractility: Ability to shorten forcefully, creating movement. 2. Muscular Fatigue 2. Excitability: Response to stimuli, with skeletal muscles ü Occurs within muscle fibers due to ATP (adenosine responding to nerve signals and smooth/cardiac muscles triphosphate) depletion, impairing contraction. having both autonomic and hormonal responses. ü Mechanism: Low ATP levels hinder the cycling of 3. Extensibility: Ability to stretch beyond resting length. actin and myosin cross-bridges, reducing muscle 4. Elasticity: Ability to return to original length after stretching. tension. ü Example: Muscle fatigue in marathon runners or SKELETAL MUSCLE STRUCTURE swimmers from prolonged exertion. § Components: Muscle fibers, connective tissue, blood vessels, 3. Synaptic Fatigue nerves. ü Happens at the neuromuscular junction (NMJ) § Muscle Fiber Development: Myoblasts fuse to form when action potential frequency exceeds multinucleated fibers; hypertrophy increases fiber size. acetylcholine (ACh) synthesis rate. § Connective Tissue Layers: ü Mechanism: Depletion of ACh in synaptic vesicles ü Endomysium: Surrounds individual fibers. reduces neurotransmitter release, impairing muscle ü Perimysium: Surrounds bundles of fibers (fasciculi). stimulation. ü Epimysium: Surrounds entire muscle. ü Example: Rarely seen under normal conditions, can occur during extreme exertion. PHYSIOLOGY OF SKELETAL MUSCLE FIBERS 1. Muscle Fiber Contraction PHYSIOLOGIC CONTRACTURE AND RIGOR MORTIS § Action Potentials: Nerve cells transmit action potentials to 1. Physiologic Contracture muscle fibers via axons, initiating contraction. ü Muscles cannot contract or relax due to extreme § Ion Channels: fatigue and ATP depletion. ü Ligand-Gated Ion Channels: Open upon ü Mechanism: neurotransmitter binding, allowing Na+ to enter. ATP drops during intense exercise, ü Voltage-Gated Ion Channels: Open with voltage impairing Ca2+ transport into the changes, enabling Na+ and K+ movement. sarcoplasmic reticulum. § Resting Membrane Potential: Muscle cells have a negative Ca2+ accumulates in the sarcoplasm, internal charge due to high K+ concentration inside and low leading to sustained cross-bridge outside. formation between actin and myosin. 33 |AnaPhy Lec  ü Outcome: Muscles remain contracted as cross- ü Slow-Twitch Fibers: Found in muscles used for bridges cannot release. sustained, endurance activities (e.g., chicken leg). 2. Rigor Mortis § Humans: ü Post-mortem muscle rigidity occurring hours after ü Postural Muscles: Higher proportion of slow-twitch death. fibers. ü Mechanism: ü Upper Limb Muscles: Higher proportion of fast- After death, ATP production ceases, twitch fibers. lowering ATP levels in muscle fibers. ü Athletes: Sprinters generally have more fast-twitch Ca²⁺ leaks into the sarcoplasm, leading fibers, while long-distance runners have more slow- to cross-bridge formation. twitch fibers. Lack of ATP prevents cross-bridges from detaching. MUSCLE HYPERTROPHY AND ATROPHY ü Outcome: Muscles remain stiff until tissue § Hypertrophy: Increase in muscle size. degeneration occurs. ü Mechanism: Increased myofibrils, more nuclei from satellite cell fusion, and improved vascularity and ENERGY SOURCES mitochondria. ENERGY SOURCES FOR ATP SYNTHESIS § Atrophy: Decrease in muscle size due to disuse or 1. Creatine Phosphate immobilization. ü A high-energy compound stored in muscle cells. ü Mechanism: Loss of muscle mass and strength; ü Function: Rapidly donates a phosphate group to muscle fibers shrink, and there may be a decrease ADP to regenerate ATP during intense muscle in muscle cell numbers. contraction. ü Reaction: ADP + Creatine phosphate à Creatine + STRENGTH AND ENDURANCE IMPROVEMENTS ATP § Strength: Enhanced by improved neuromuscular coordination ü Duration: Sustains maximal contractions for and reduced fat deposition. approximately 8-10 seconds. § Endurance: Improved by better metabolic efficiency, 2. Anaerobic Respiration increased capillary density, and enhanced cardiac function. ü Occurs in the absence of oxygen; breaks down glucose to produce ATP and lactic acid. HEAT PRODUCTION ü Process: HEAT PRODUCTION BEFORE, DURING, AND AFTER EXERCISE Glucose is broken down into pyruvic 1. Before Exercise acid. ü Preparation Phase: Increased metabolic rate Pyruvic acid is converted to lactic acid. prepares the body, resulting in minimal heat ü ATP Yield: Produces a net gain of 2 ATP molecules production. per glucose molecule. 2. During Exercise ü Duration: Provides ATP for short bursts of intense ü Increased Metabolic Rate: Muscle contractions activity (up to 3 minutes), such as sprinting. significantly raise chemical reaction rates, ü Limitations: Depletion of glucose and creatine producing ATP and heat. phosphate, and accumulation of lactic acid limit ü Heat Production: Heat generated correlates with this process. exercise intensity and duration; vigorous exercise 3. Aerobic Respiration dramatically increases heat. ü Requires oxygen; breaks down glucose to produce Vasodilation: Expands blood vessels in ATP, carbon dioxide, and water. the skin to enhance blood flow and heat ü Process: Pyruvic acid is metabolized in dissipation. mitochondria via the citric acid cycle and electron Sweating: Evaporation of sweat cools transport chain. the body. ü ATP Yield: Produces up to 38 ATP molecules per 3. After Exercise glucose molecule. ü Oxygen Debt and Elevated Metabolism: Increased ü Energy Sources: Utilizes glucose, fatty acids, and metabolic rate continues to generate heat as the amino acids. body restores ATP and converts lactic acid. ü Duration: Supports prolonged, sustained exercise ü Heat Retention: Elevated metabolism helps and resting conditions. maintain body temperature temporarily. ü Advantages: More efficient than anaerobic respiration but slower in ATP production. HEAT PRODUCTION DURING SHIVERING 1. Trigger for Shivering OXYGEN DEBT ü Initiated by a drop in body temperature; involves § The amount of oxygen required to restore normal conditions in rapid, involuntary muscle contractions. the body after intense exercise. 2. Heat Production ü Components: ü Increased Heat Output: Shivering can raise heat Replenishing ATP and creatine production up to 18 times resting levels. phosphate levels. ü Efficiency: Heat generated during shivering may Converting excess lactic acid to pyruvic exceed that produced during moderate exercise, acid and glucose. helping to restore normal body temperature. § Events Leading to Oxygen Debt ü During Exercise: Anaerobic metabolism is used to SMOOTH MUSCLE meet energy demands, leading to temporary STRUCTURE OF SMOOTH MUSCLE oxygen deficit. § Cell Characteristics ü Post-Exercise: Elevated oxygen intake is required ü Smaller than skeletal muscle cells (15-200 µm long, to: 5-10 µm in diameter). Restore ATP and creatine phosphate. ü Spindle-shaped with a single, centrally located Convert lactic acid to pyruvic acid in nucleus. the liver. § Myofilament Organization Replenish glycogen stores in muscle ü Actin and Myosin: Fewer myofilaments than fibers and liver cells. skeletal muscle, with a higher ratio of actin to § Recovery myosin; actin is more prevalent. ü Increased Aerobic Metabolism: Post-exercise, ü Dense Bodies and Areas: Actin is attached to elevated oxygen levels facilitate the restoration of dense bodies and areas on the membrane, metabolic substrates and removal of byproducts. forming an intracellular cytoskeleton. ü Restoration of Glycogen and ATP Levels: Enhanced § Sarcoplasmic Reticulum and Caveolae oxygen consumption supports glucose synthesis ü The sarcoplasmic reticulum is less developed; from lactic acid and replenishes energy reserves. caveolae are shallow invaginations that may function like T tubules. SLOW AND FAST FIBERS DISTRIBUTION OF MUSCLE FIBERS CONTRACTION MECHANISM § Animals: § Calcium Regulation ü Fast-Twitch Fibers: Found in muscles used for quick, ü Ca²⁺ regulates contraction by binding to explosive movements (e.g., chicken breast). calmodulin, activating myosin kinase, which 34 |AnaPhy Lec  phosphorylates myosin heads for cross-bridge formation. § Cross-Bridge Cycling ü The cycling process is slower than in skeletal muscle but uses energy similarly. Myosin phosphatase dephosphorylates myosin, allowing sustained tension with minimal energy. TYPES OF SMOOTH MUSCLE 1. Visceral (Unitary) Smooth Muscle ü Located in digestive, reproductive, and urinary tracts. ü Connected via gap junctions for synchronized contractions; some are autorhythmic, while others contract upon stimulation. 2. Multiunit Smooth Muscle ü Found in blood vessels, arrector pili muscles, and the iris. ü Fewer gap junctions; functions independently, contracting in response to neural or hormonal signals. ELECTRICAL PROPERTIES § Resting Membrane Potential ü Approximately -55 to -60 mV, less negative than skeletal muscle. ü Some cells exhibit slow waves of depolarization leading to contractions. § Action Potentials and Contractions ü Shows slower, sustained contractions in response to action potentials, with multiple potentials potentially leading to prolonged contraction. REGULATION OF SMOOTH MUSCLE § Neural Regulation ü Controlled by the autonomic nervous system; neurotransmitters like acetylcholine and norepinephrine influence contraction. § Hormonal Regulation ü Hormones such as epinephrine and oxytocin can stimulate or inhibit contractions based on the target smooth muscle. § Receptor Mechanisms ü Ligand-gated channels can activate Ca²⁺ channels without significant changes in membrane potential, while other receptors may cause hyperpolarization leading to relaxation. FUNCTIONAL PROPERTIES 1. Autorhythmic Contractions: Some smooth muscles contract rhythmically without external stimuli. 2. Stretch Response: Contracts in response to sudden stretch but not gradual increases. 3. Smooth Muscle Tone: Maintains a constant tension level, adapting to gradual length changes. 4. Amplitude of Contraction: Contraction amplitude remains constant despite changes in muscle length. CARDIAC MUSCLE STRUCTURE OF CARDIAC MUSCLE § Found only in the heart. § Cell Characteristics: ü Typically have a single, centrally located nucleus. ü Cells are branched and interconnected. § Intercalated Disks: ü Specialized cell attachments that join adjacent cardiac muscle cells. ü Contain gap junctions for rapid action potential transmission, enabling coordinated contraction. CONTRACTION MECHANISM § Autorhythmicity ü Cardiac muscle cells are inherently rhythmic and can generate action potentials spontaneously. ü The sinoatrial (SA) node serves as the primary pacemaker, setting the heart's rhythm. § Action Potentials ü Longer duration and refractory period compared to nerve and skeletal muscle action potentials. ü Depolarization involves sodium (Na⁺) and calcium (Ca²⁺) influx across the plasma membrane. § Calcium Regulation ü Calcium ions (Ca²⁺) bind to troponin, initiating actin and myosin interaction for muscle contraction. 35 |AnaPhy Lec  Gastrocnemius: A major calf muscle that enables plantar flexion of the foot and flexion of the knee. Soleus: Located beneath the gastrocnemius, it also aids in plantar flexion but is more involved during standing and walking. MODULE 5.2: MUSCULAR SYSTEM GROSS ANATOMY Sternocleidomastoid: A prominent neck muscle responsible for rotating MUSCLE SHAPES and flexing the head. § Muscles vary in shape and size, influencing contraction degree and force generation. Trapezius: A large muscle in the upper back and neck that helps elevate, § Classes of Muscle Shapes: retract, and rotate the scapula. ü Pennate Muscles: Fasciculi arranged like feather barbs; allows for concentrated force. Pectoralis Major: A thick, fan-shaped muscle that covers the upper chest Unipennate: Fasciculi on one side of the and is responsible for shoulder flexion, adduction, and medial rotation. tendon. Bipennate: Fasciculi on both sides. Serratus Anterior: Located on the lateral side of the thorax, it helps Multipennate: Fasciculi arranged protract and stabilize the scapula. around a central tendon. ü Parallel Muscles: Fasciculi arranged parallel to the Rectus Abdominis: A paired muscle running vertically on each side of the muscle's long axis; can shorten more but generate anterior wall of the human abdomen, it is responsible for flexing the spine. less force. ü Convergent Muscles: Triangular shape, wider base External Abdominal Oblique: The largest and outermost muscle layer of for more force (e.g., deltoid). the abdominal wall, it helps with trunk rotation and lateral flexion. ü Circular Muscles: Fasciculi arranged in a circle; act as sphincters (e.g., orbicularis oris). Flexors of Wrist and Fingers: A group of muscles in the forearm that flex § Specific shapes include quadrangular, triangular, rhomboidal, the wrist and fingers. and fusiform; can have multiple bellies or heads (e.g., digastric, bicipital). Tensor Fasciae Latae: A muscle on the outer thigh that assists in hip flexion and abduction. Vastus Lateralis: One of the four quadriceps muscles, located on the outer side of the thigh, it extends the knee. Rectus Femoris: Another quadriceps muscle, it extends the knee and also helps in hip flexion. Vastus Intermedius: A deep quadriceps muscle that lies beneath the rectus femoris and aids in knee extension. Vastus Medialis: Located on the inner thigh, it also helps in knee extension. MUSCLE NOMENCLATURE Tibialis Anterior: A muscle in the front of the leg responsible for dorsiflexion Muscles are named based on: and inversion of the foot. 1. Location: (e.g., pectoralis in the chest). 2. Size: (e.g., gluteus maximus is large, gluteus minimus is small). Extensor Digitorum Longus: This muscle extends the toes and dorsiflexes 3. Shape: (e.g., deltoid is triangular). the foot. 4. Orientation: (e.g., rectus for straight, oblique for angled). 5. Origin and Insertion: (e.g., sternocleidomastoid originates Fibularis Longus and Brevis: Located on the lateral side of the lower leg, from the sternum). they assist in foot eversion and plantar flexion. 6. Number of Heads: (e.g., biceps has two heads). 7. Function: (e.g., abductor moves structures away from the Quadriceps Femoris: A group of four muscles (vastus lateralis, vastus midline). medialis, vastus intermedius, and rectus femoris) that are primarily responsible for knee extension. ANTERIOR VIEW MUSCLES Facial Muscles: A group of muscles responsible for facial expressions, including movements of the mouth, eyes, and eyebrows. Deltoid: Located on the shoulder, this triangular muscle allows for arm abduction and is crucial for lifting and reaching movements. Biceps Brachii: A two-headed muscle located on the front of the upper arm, involved in elbow flexion and forearm supination. Linea Alba: A fibrous structure that runs vertically down the midline of the abdomen, serving as an attachment point for abdominal muscles. Brachioradialis: A muscle of the forearm that helps flex the elbow, particularly when the forearm is in a neutral position. Retinaculum: A fibrous band that holds tendons in place, particularly around the wrist and ankle. Pectineus: A muscle of the thigh that assists in hip flexion and adduction. Adductor Longus: Part of the adductor group of the thigh, it aids in hip adduction. Gracilis: The most superficial muscle of the inner thigh, it also assists in hip adduction and knee flexion. Sartorius: The longest muscle in the human body, it helps flex, abduct, and laterally rotate the hip. Patella: Also known as the kneecap, it protects the knee joint and improves the leverage of the quadriceps muscle. 36 |AnaPhy Lec  POSTERIOR VIEW MUSCLES Sternocleidomastoid: Same as above; it is also visible in the posterior view, helping with head rotation and flexion. Infraspinatus: Located on the back of the shoulder blade, it assists with shoulder external rotation. Teres Minor: A small muscle below the infraspinatus, it also contributes to shoulder external rotation. Teres Major: Located beneath the teres minor, it aids in internal rotation and adduction of the arm. Triceps Brachii: The large muscle at the back of the upper arm responsible for elbow extension. Splenius Capitis: A muscle in the back of the neck that helps extend and rotate the head. Latissimus Dorsi: A broad muscle of the back that aids in arm adduction, extension, and internal rotation. External Abdominal Oblique: Same as above; it is also visible in the posterior view. Gluteus Medius: Located on the outer surface of the pelvis, it is important for hip stabilization and abduction. Gluteus Maximus: The largest muscle in the buttocks, it is crucial for hip extension, lateral rotation, and abduction. Adductor Magnus: A large muscle in the inner thigh that helps with hip adduction. Iliotibial Tract: A thick band of tissue on the lateral aspect of the thigh that aids in stabilizing the hip and knee. Gracilis: Same as above; it is also visible in the posterior view. Gastrocnemius: Same as above; it is also visible in the posterior view. Soleus: Same as above; it is also visible in the posterior view. Calcaneal Tendon (Achilles Tendon): The tendon connecting the calf muscles to the heel bone, essential for walking, running, and jumping. Extensors of the Wrist and Fingers: Muscles located in the posterior forearm that extend the wrist and fingers. Hamstring Muscles: A group of three muscles (semitendinosus, biceps femoris, semimembranosus) at the back of the thigh responsible for knee flexion and hip extension. Semitendinosus: One of the hamstring muscles, located on the inner side of the thigh. Biceps Femoris: A hamstring muscle with two heads, it is located on the outer side of the thigh. Semimembranosus: The most medial hamstring muscle, it assists in knee flexion and hip extension. Fibularis Longus: Same as above; it is also visible in the posterior view. Fibularis Brevis: Same as above; it is also visible in the posterior view. 37 |AnaPhy Lec