Muscle Tissue Study Notes
Types of Muscle Tissue
Skeletal Muscle: Striated, voluntary control, multinucleated, attaches to bones or fascia.
Cardiac Muscle: Striated, involuntary control, autorhythmic with built-in pacemaker.
Smooth Muscle: Non-striated, involuntary, found in hollow organs and blood vessels.
Functions of Muscle Tissue
Body movement production.
Stabilization of body positions.
Regulation of organ volume via smooth muscle sphincters.
Movement of substances within the body (blood, urine, food).
Heat production (involuntary skeletal muscle shivering).
Properties of Muscle Tissue
Excitability: Response to nerve chemicals.
Conductivity: Propagation of electrical signals.
Contractility: Ability to shorten and generate force.
Extensibility: Ability to stretch without damage.
Elasticity: Ability to return to original shape.
Skeletal Muscle Structure
Composed of muscle fibers, nervous tissue, connective tissue.
Connective Tissue Components:
Epimysium: Surrounds entire muscle.
Perimysium: Surrounds fascicles (bundles of fibers).
Endomysium: Surrounds individual muscle cells.
Tendons (cords) and aponeuroses (flat layers) attach muscle to bone.
Muscle Fiber (Myofiber) Characteristics
Long, cylindrical, multinucleated.
Covered by sarcolemma (cell membrane).
Sarcoplasm contains myofibrils and myoglobin for oxygen storage.
Sliding Filament Mechanism of Contraction
Myosin pulls thin filaments (actin) inward, causing shortening of the muscle fiber.
Contraction Cycle
Steps: ATP hydrolysis, cross-bridge attachment, power stroke, myosin detachment.
Continues as long as ATP and Ca²⁺ levels are sufficient.
Neuromuscular Junction (NMJ)
Connection between nerve and muscle cell.
Acetylcholine (ACh) released at nerve terminal facilitates muscle action potential.
ACh breakdown by acetylcholinesterase leads to muscle relaxation.
Types of Muscle Contractions
Isotonic: Muscle changes length (concentric and eccentric).
Isometric: Muscle tension without length change.
Muscle Fiber Types
Slow Oxidative (Type I): Red, endurance.
Fast Glycolytic (Type IIb): White, power, short bursts.
Fast Oxidative-Glycolytic (Type IIa): Intermediate, both aerobic and anaerobic capabilities.
Muscle Regeneration and Aging
Skeletal muscle fibers cannot divide; growth is by cell enlargement.
Cardiac muscle repairs via fibrosis; smooth muscle can regenerate.
Aging leads to muscle replacement by fat, slower reflexes, and strength decline.
Muscle Disorders
Myasthenia Gravis: Autoimmune disorder affecting ACh receptors.
Muscular Dystrophies: Inherited diseases causing muscle degeneration.
Rigor Mortis: Postmortem muscle stiffness due to Ca²⁺ leakage and ATP depletion.
Muscle Metabolism
ATP sources include creatine phosphate, anaerobic and aerobic respiration.
Fatigue caused by physiological factors like ACh release, oxygen depletion, and lactic acid buildup.
Motor Unit and Muscle Tension Control
Motor unit consists of a motor neuron and the muscle fibers it controls.
Muscle tension depends on the number of activated motor units and their size.
Twitch Contraction: Brief contraction response to motor neuron stimulus.
Abnormal Contractions (
Spasm, cramp, tic, tremor, fasciculation - involuntary muscle movements with varying characteristics.
Types of Muscle Tissue
Skeletal Muscle: Striated, voluntary control, multinucleated, attaches to bones or fascia.
Cardiac Muscle: Striated, involuntary control, autorhythmic with built-in pacemaker.
Smooth Muscle: Non-striated, involuntary, found in hollow organs and blood vessels.
Functions of Muscle Tissue
Body movement production.
Stabilization of body positions.
Regulation of organ volume via smooth muscle sphincters.
Movement of substances within the body (blood, urine, food).
Heat production (involuntary skeletal muscle shivering).
Properties of Muscle Tissue
Excitability: Response to nerve chemicals.
Conductivity: Propagation of electrical signals.
Contractility: Ability to shorten and generate force.
Extensibility: Ability to stretch without damage.
Elasticity: Ability to return to original shape.
Skeletal Muscle Structure
Composed of muscle fibers, nervous tissue, connective tissue.
Connective Tissue Components:
Epimysium: Surrounds entire muscle.
Perimysium: Surrounds fascicles (bundles of fibers).
Endomysium: Surrounds individual muscle cells.
Tendons (cords) and aponeuroses (flat layers) attach muscle to bone.
Muscle Fiber (Myofiber) Characteristics
Long, cylindrical, multinucleated.
Covered by sarcolemma (cell membrane).
Sarcoplasm contains myofibrils and myoglobin for oxygen storage.
Sliding Filament Mechanism of Contraction
Myosin pulls thin filaments (actin) inward, causing shortening of the muscle fiber.
Contraction Cycle
Initiation of Contraction:
Nerve impulse arrives at the Neuromuscular Junction (NMJ), releasing Acetylcholine (ACh).
ACh binds to receptors on the sarcolemma, generating a muscle action potential that propagates along its surface and into the T-tubules.
The action potential triggers the release of Ca from the sarcoplasmic reticulum into the sarcoplasm.
Ca binds to troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin.
Excitation-Contraction Coupling & Cross-Bridge Cycle:
ATP Hydrolysis: Myosin heads hydrolyze ATP into ADP and inorganic phosphate (P$_{ ext{i}}$), becoming energized and in a "cocked" position.
Cross-Bridge Attachment: Energized myosin heads attach to the exposed myosin-binding sites on actin, forming cross-bridges.
Power Stroke: Myosin heads pivot, pulling the thin filaments (actin) towards the M line (center of the sarcomere), releasing ADP and P$_{ ext{i}}$.
Myosin Detachment: A new ATP molecule binds to the myosin head, causing it to detach from actin.
Cycle Repetition: The myosin head re-hydrolyzes ATP, re-energizes, and re-attaches to a new site further along the actin filament, repeating the cycle as long as ATP and Ca are available.
Relaxation:
Nerve impulses cease, and ACh is broken down by acetylcholinesterase.
Ca is actively pumped back into the sarcoplasmic reticulum by Ca pumps.
Tropomyosin moves back to block the myosin-binding sites on actin, preventing further cross-bridge formation, and the muscle fiber relaxes.
Neuromuscular Junction (NMJ)
Connection between nerve and muscle cell.
Acetylcholine (ACh) released at nerve terminal facilitates muscle action potential.
ACh breakdown by acetylcholinesterase leads to muscle relaxation.
Types of Muscle Contractions
Isotonic: Muscle changes length (concentric and eccentric).
Isometric: Muscle tension without length change.
Muscle Fiber Types
Slow Oxidative (Type I): Red, endurance.
Fast Glycolytic (Type IIb): White, power, short bursts.
Fast Oxidative-Glycolytic (Type IIa): Intermediate, both aerobic and anaerobic capabilities.
Muscle Regeneration and Aging
Skeletal muscle fibers cannot divide; growth is by cell enlargement.
Cardiac muscle repairs via fibrosis; smooth muscle can regenerate.
Aging leads to muscle replacement by fat, slower reflexes, and strength decline.
Muscle Disorders
Myasthenia Gravis: Autoimmune disorder affecting ACh receptors.
Muscular Dystrophies: Inherited diseases causing muscle degeneration.
Rigor Mortis: Postmortem muscle stiffness due to Ca leakage and ATP depletion.
Muscle Metabolism
ATP sources include creatine phosphate, anaerobic and aerobic respiration.
Fatigue caused by physiological factors like ACh release, oxygen depletion, and lactic acid buildup.
Motor Unit and Muscle Tension Control
Motor unit consists of a motor neuron and the muscle fibers it controls.
Muscle tension depends on the number of activated motor units and their size.
Twitch Contraction: Brief contraction response to motor neuron stimulus.
Abnormal Contractions
Spasm, cramp, tic, tremor, fasciculation - involuntary muscle movements with varying characteristics.