Muscle Physiology Notes
Muscle Physiology
Sarcolemma
The cell membrane of a muscle fiber, which plays a crucial role in conducting electrical signals that stimulate muscle contraction.
Sarcoplasmic Reticulum
An elaborate network within muscle fibers that stores, releases, and retrieves calcium ions (Ca^{2+}). This regulation of calcium concentration is essential for initiating and controlling muscle contractions.
T-tubules (Transverse Tubules)
Invaginations of the sarcolemma that penetrate into the cell's interior, allowing rapid conduction of action potentials to the sarcoplasmic reticulum. This ensures coordinated muscle fiber contraction.
Terminal Cisternae
Enlarged regions of the sarcoplasmic reticulum that flank the T-tubules. These cisternae are primary sites for Ca^{2+} storage and release, forming a triad structure with the T-tubules.
Triad
A structural unit composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. This arrangement facilitates the rapid and efficient release of Ca^{2+} to initiate muscle contraction.
Myofilaments
The contractile proteins, actin and myosin, organized into thin and thick filaments. Their interaction drives muscle contraction through the sliding filament mechanism.
Myofibrils
Long, cylindrical structures within muscle fibers composed of organized myofilaments. These are the fundamental units responsible for muscle contraction.
Cytosol
The intracellular fluid surrounding the myofibrils, containing essential ions, proteins, and nutrients required for muscle function.
Mitochondria
The powerhouses of the muscle cell, responsible for generating ATP through aerobic metabolism, providing the energy needed for muscle contraction and relaxation.
Endomysium
A delicate layer of connective tissue that surrounds each muscle fiber, providing support and insulation.
Motor Neuron
A nerve cell that transmits signals from the central nervous system to muscle fibers, initiating muscle contraction.
Axon Terminal
The distal end of a motor neuron's axon, where it forms a neuromuscular junction with a muscle fiber.
Synaptic Vesicle
Small vesicles within the axon terminal that store neurotransmitters, such as acetylcholine (ACh), which are released into the synaptic cleft to transmit signals to the muscle fiber.
Acetylcholine (ACh)
A neurotransmitter released at the neuromuscular junction that binds to ACh receptors on the sarcolemma, initiating muscle fiber depolarization and contraction.
ACh Receptor
Receptor proteins on the sarcolemma that bind acetylcholine (ACh), triggering the opening of ion channels and initiating muscle fiber depolarization.
Synaptic Cleft
The narrow gap between the axon terminal of a motor neuron and the sarcolemma of a muscle fiber, across which neurotransmitters diffuse to transmit signals.
Motor End Plate
A specialized region of the sarcolemma at the neuromuscular junction, characterized by numerous folds and a high density of ACh receptors. This structure enhances the muscle fiber's sensitivity to ACh.
Voltage-Gated Ca^{2+} Channel
Ion channels in the axon terminal that open in response to membrane depolarization, allowing calcium ions to enter the axon terminal. This influx of calcium triggers the release of acetylcholine into the synaptic cleft.
Sarcomere
The basic contractile unit of a muscle fiber, delineated by Z discs. It contains the organized arrangement of actin and myosin filaments responsible for muscle contraction.
Z Discs
Protein structures that form the boundaries of the sarcomere, serving as attachment sites for actin filaments. They help maintain the structural integrity of the sarcomere during muscle contraction.
A Band
The region of the sarcomere that contains the entire length of the thick filaments (myosin). Its length remains constant during muscle contraction.
I Band
The region of the sarcomere that contains only thin filaments (actin). The I band shortens during muscle contraction as the actin filaments slide toward the center of the sarcomere.
H Zone
The central region of the A band that contains only thick filaments (myosin). The H zone shortens during muscle contraction as the actin filaments slide inward, reducing the space between the myosin filaments.
M Line
A protein structure in the center of the H zone that anchors and aligns the thick filaments (myosin), helping to maintain the structural organization of the sarcomere.
Zone of Overlap
The regions of the sarcomere where thick and thin filaments overlap. These zones are the sites of cross-bridge formation between actin and myosin during muscle contraction.
Thick Filament (Myosin)
Composed of myosin protein, with heads that bind to actin and generate force for muscle contraction. These heads contain ATPase activity, which hydrolyzes ATP to provide energy for the power stroke.
Thin Filament (Actin)
Composed of actin, tropomyosin, and troponin. Actin contains myosin-binding sites, while tropomyosin and troponin regulate the interaction between actin and myosin in response to calcium ions.
Tropomyosin
A protein that covers the myosin-binding sites on actin molecules in the resting muscle, preventing cross-bridge formation.
Troponin
A protein complex that binds to actin, tropomyosin, and calcium ions. When calcium binds to troponin, it causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin, allowing cross-bridge formation and muscle contraction.
Oxidative Phosphorylation
The primary mechanism for ATP production in muscle cells, occurring within the mitochondria. It involves the complete oxidation of glucose, fatty acids, or amino acids to generate a high yield of ATP.
Anaerobic Glycolysis
A metabolic process that breaks down glucose into pyruvate in the absence of oxygen, producing ATP and lactic acid. It provides a rapid but less efficient source of energy for muscle contraction.
Creatine Phosphate
A high-energy compound stored in muscle cells that can quickly regenerate ATP from ADP. It provides a short-term energy buffer during intense muscle activity.
Isotonic Contraction
A type of muscle contraction in which the muscle changes in length while maintaining constant tension. It can be either concentric (muscle shortens) or eccentric (muscle lengthens).
Isometric Contraction
A type of muscle contraction in which the muscle develops tension but does not change in length. It occurs when the force generated by the muscle is equal to the resistance, such as holding a heavy object in a fixed position.
Type I Fibers (Slow Oxidative)
Muscle fibers that are specialized for endurance activities. They have high oxidative capacity, fatigue resistance, and are rich in mitochondria and myoglobin.
Type II Fibers (Fast Glycolytic)
Muscle fibers that are specialized for short bursts of high-intensity activity. They have high glycolytic capacity, fatigue quickly, and generate more force but with less efficiency.
Cardiac Muscle
Found in the heart, characterized by striated cells connected by intercalated discs, which contain desmosomes and gap junctions. It has a long refractory period preventing tetanus.
Skeletal Muscle
Attached to bones, responsible for movement. It consists of long, cylindrical, striated fibers with multiple peripheral nuclei.
Smooth Muscle
Found in the walls of internal organs and blood vessels, characterized by non-striated, spindle-shaped cells with a single central nucleus. It is involved in involuntary movements such as peristalsis and vasoconstriction.
Muscle Physiology
Sarcolemma
The cell membrane of a muscle fiber, which plays a crucial role in conducting electrical signals that stimulate muscle contraction.
Sarcoplasmic Reticulum
An elaborate network within muscle fibers that stores, releases, and retrieves calcium ions (Ca^{2+}). This regulation of calcium concentration is essential for initiating and controlling muscle contractions.
T-tubules (Transverse Tubules)
Invaginations of the sarcolemma that penetrate into the cell's interior, allowing rapid conduction of action potentials to the sarcoplasmic reticulum. This ensures coordinated muscle fiber contraction.
Terminal Cisternae
Enlarged regions of the sarcoplasmic reticulum that flank the T-tubules. These cisternae are primary sites for Ca^{2+} storage and release, forming a triad structure with the T-tubules.
Triad
A structural unit composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. This arrangement facilitates the rapid and efficient release of Ca^{2+} to initiate muscle contraction.
Myofilaments
The contractile proteins, actin and myosin, organized into thin and thick filaments. Their interaction drives muscle contraction through the sliding filament mechanism.
Myofibrils
Long, cylindrical structures within muscle fibers composed of organized myofilaments. These are the fundamental units responsible for muscle contraction.
Cytosol
The intracellular fluid surrounding the myofibrils, containing essential ions, proteins, and nutrients required for muscle function.
Mitochondria
The powerhouses of the muscle cell, responsible for generating ATP through aerobic metabolism, providing the energy needed for muscle contraction and relaxation.
Endomysium
A delicate layer of connective tissue that surrounds each muscle fiber, providing support and insulation.
Motor Neuron
A nerve cell that transmits signals from the central nervous system to muscle fibers, initiating muscle contraction.
Axon Terminal
The distal end of a motor neuron's axon, where it forms a neuromuscular junction with a muscle fiber.
Synaptic Vesicle
Small vesicles within the axon terminal that store neurotransmitters, such as acetylcholine (ACh), which are released into the synaptic cleft to transmit signals to the muscle fiber.
Acetylcholine (ACh)
A neurotransmitter released at the neuromuscular junction that binds to ACh receptors on the sarcolemma, initiating muscle fiber depolarization and contraction.
ACh Receptor
Receptor proteins on the sarcolemma that bind acetylcholine (ACh), triggering the opening of ion channels and initiating muscle fiber depolarization.
Synaptic Cleft
The narrow gap between the axon terminal of a motor neuron and the sarcolemma of a muscle fiber, across which neurotransmitters diffuse to transmit signals.
Motor End Plate
A specialized region of the sarcolemma at the neuromuscular junction, characterized by numerous folds and a high density of ACh receptors. This structure enhances the muscle fiber's sensitivity to ACh.
Voltage-Gated Ca^{2+} Channel
Ion channels in the axon terminal that open in response to membrane depolarization, allowing calcium ions to enter the axon terminal. This influx of calcium triggers the release of acetylcholine into the synaptic cleft.
Sarcomere
The basic contractile unit of a muscle fiber, delineated by Z discs. It contains the organized arrangement of actin and myosin filaments responsible for muscle contraction.
Z Discs
Protein structures that form the boundaries of the sarcomere, serving as attachment sites for actin filaments. They help maintain the structural integrity of the sarcomere during muscle contraction.
A Band
The region of the sarcomere that contains the entire length of the thick filaments (myosin). Its length remains constant during muscle contraction.
I Band
The region of the sarcomere that contains only thin filaments (actin). The I band shortens during muscle contraction as the actin filaments slide toward the center of the sarcomere.
H Zone
The central region of the A band that contains only thick filaments (myosin). The H zone shortens during muscle contraction as the actin filaments slide inward, reducing the space between the myosin filaments.
M Line
A protein structure in the center of the H zone that anchors and aligns the thick filaments (myosin), helping to maintain the structural organization of the sarcomere.
Zone of Overlap
The regions of the sarcomere where thick and thin filaments overlap. These zones are the sites of cross-bridge formation between actin and myosin during muscle contraction.
Thick Filament (Myosin)
Composed of myosin protein, with heads that bind to actin and generate force for muscle contraction. These heads contain ATPase activity, which hydrolyzes ATP to provide energy for the power stroke.
Thin Filament (Actin)
Composed of actin, tropomyosin, and troponin. Actin contains myosin-binding sites, while tropomyosin and troponin regulate the interaction between actin and myosin in response to calcium ions.
Tropomyosin
A protein that covers the myosin-binding sites on actin molecules in the resting muscle, preventing cross-bridge formation.
Troponin
A protein complex that binds to actin, tropomyosin, and calcium ions. When calcium binds to troponin, it causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin, allowing cross-bridge formation and muscle contraction.
Oxidative Phosphorylation
The primary mechanism for ATP production in muscle cells, occurring within the mitochondria. It involves the complete oxidation of glucose, fatty acids, or amino acids to generate a high yield of ATP.
Anaerobic Glycolysis
A metabolic process that breaks down glucose into pyruvate in the absence of oxygen, producing ATP and lactic acid. It provides a rapid but less efficient source of energy for muscle contraction.
Creatine Phosphate
A high-energy compound stored in muscle cells that can quickly regenerate ATP from ADP. It provides a short-term energy buffer during intense muscle activity.
Isotonic Contraction
A type of muscle contraction in which the muscle changes in length while maintaining constant tension. It can be either concentric (muscle shortens) or eccentric (muscle lengthens).
Isometric Contraction
A type of muscle contraction in which the muscle develops tension but does not change in length. It occurs when the force generated by the muscle is equal to the resistance, such as holding a heavy object in a fixed position.
Type I Fibers (Slow Oxidative)
Muscle fibers that are specialized for endurance activities. They have high oxidative capacity, fatigue resistance, and are rich in mitochondria and myoglobin.
Type II Fibers (Fast Glycolytic)
Muscle fibers that are specialized for short bursts of high-intensity activity. They have high glycolytic capacity, fatigue quickly, and generate more force but with less efficiency.
Cardiac Muscle
Found in the heart, characterized by striated cells connected by intercalated discs, which contain desmosomes and gap junctions. It has a long refractory period preventing tetanus.
Skeletal Muscle
Attached to bones, responsible for movement. It consists of long, cylindrical, striated fibers with multiple peripheral nuclei.
Smooth Muscle
Found in the walls of internal organs and blood vessels, characterized by non-striated, spindle-shaped cells with a single central nucleus. It is involved in involuntary movements such as peristalsis and vasoconstriction.