Muscle Physiology PDF

1. Muscle Types Skeletal Muscle: Striated, voluntary muscle attached to bones. Cells are large, multinucleated, and responsible for conscious movements. Cardiac Muscle: Striated and involuntary. Found only in the heart, with uninucleate, branching cells connected by intercalated...

1. Muscle Types Skeletal Muscle: Striated, voluntary muscle attached to bones. Cells are large, multinucleated, and responsible for conscious movements. Cardiac Muscle: Striated and involuntary. Found only in the heart, with uninucleate, branching cells connected by intercalated discs. Contracts at a steady rate set by a pacemaker. Smooth Muscle: Non-striated and involuntary. Located in the walls of hollow organs (e.g., stomach, blood vessels). Cells are spindle-shaped, uninucleate, and contract slowly and steadily. 2. Connective Tissue in Muscles Endomysium: Surrounds each muscle fiber. Perimysium: Wraps around bundles of muscle fibers (fascicles). Epimysium: Encloses the entire muscle. Fascia: Outer layer connecting the muscle to other structures. 3. Microscopic Anatomy of Muscle Fibers Sarcolemma: Specialized plasma membrane of muscle cells. Myofibrils: Long organelles within muscle cells that give muscles their striated appearance. Sarcomere: The contractile unit within myofibrils, containing thick (myosin) and thin (actin) filaments. Sarcoplasmic Reticulum (SR): Specialized endoplasmic reticulum that stores and releases calcium, essential for muscle contraction. 4. Mechanism of Muscle Contraction (Sliding Filament Theory) Sliding Filament Process: Calcium binds to regulatory proteins on actin, exposing binding sites for myosin heads. Myosin heads attach to actin, pivot, detach, and reattach further along the filament, causing actin filaments to slide toward the center of the sarcomere. Role of ATP: ATP provides the energy for each attachment, pivot, and detachment cycle. Calcium's Role: Triggers the binding of myosin heads to actin filaments, initiating contraction. 5. Nerve-Muscle Communication (Neuromuscular Junction) Motor Neuron: Releases acetylcholine (ACh) across the synaptic cleft at the neuromuscular junction. Action Potential: ACh binds to receptors on the sarcolemma, opening Na+ channels. Na+ influx depolarizes the membrane, leading to an action potential that triggers contraction. Acetylcholinesterase (AChE): Enzyme that breaks down ACh, ending the signal and allowing the muscle to relax. 6. Types of Muscle Contractions  Isotonic: Muscle shortens, and movement occurs (e.g., lifting a weight). Isometric: Muscle tension increases, but the muscle does not shorten (e.g., pushing against an immovable object). 7. Energy Sources for Muscle Contraction Direct Phosphorylation: Creatine phosphate transfers a phosphate to ADP to create ATP. Quick but short-lasting energy. Aerobic Respiration: Glucose + Oxygen → ATP. Provides sustained energy and occurs in the mitochondria. Anaerobic Glycolysis: Glucose → Pyruvic Acid → Lactic Acid + ATP. Quick energy but produces lactic acid, leading to muscle fatigue. 8. Muscle Fatigue and Recovery Causes of Fatigue: ATP depletion, ion imbalances, oxygen deficit, and lactic acid buildup. Recovery: Oxygen deficit is repaid post-exercise by rapid, deep breathing, allowing ATP and oxygen levels to normalize. 9. Effect of Exercise on Muscles Aerobic (Endurance) Exercise: Increases muscle flexibility, stamina, and overall metabolic efficiency. Resistance (Strength) Exercise: Enhances muscle size and strength by increasing individual muscle fiber size.