04 Skeletal Muscle Physiology (copy)

Muscle Cell (Myocyte)

The contractile unit in muscular tissue, also known as muscle fiber in skeletal muscle.

Sarco- or Myo-

Prefixes commonly associated with muscle nomenclature, such as sarcolemma, sarcoplasm, and sarcoplasmic reticulum.

Striated Muscle

Muscular tissue with cross-striations at right angles to the long axis, classified as either voluntary (skeletal muscle) or involuntary (cardiac muscle).

Neuromuscular Junction (NMJ)

The site where a motor neuron innervates a skeletal muscle cell, leading to the release of Acetylcholine (Ach) and muscle fiber depolarization.

Myofibril

Composed of myosin and actin filaments, the structural unit of a muscle cell responsible for contraction.

Thick Filaments

Large molecular weight proteins called myosin, consisting of heavy and light chains with globular heads that bind to actin and hydrolyze ATP.

Thin Filaments

Composed of actin, tropomyosin, and troponin, with tropomyosin blocking myosin-binding sites on actin at rest.

Troponin

A complex of three globular proteins (troponin T, I, C) that regulate muscle contraction by binding to tropomyosin and Ca2+.

Sarcomere

The basic contractile unit of a muscle, delineated by Z disks and containing thick (myosin) and thin (actin) filaments.

Sliding Filament Model of Contraction

Describes the mechanism of muscle contraction where sarcomeres shorten as thin filaments slide past thick filaments.

Transverse (T) Tubules

Extensions of the muscle cell membrane that carry depolarization deep into the muscle fiber, connecting with the sarcoplasmic reticulum.

Triad

The close apposition of two terminal cisternae of the sarcoplasmic reticulum against a T tubule, important for muscle cell function.

Sarcoplasmic Reticulum (SR)

Internal tubular structure in muscle cells responsible for storing and releasing Ca2+ for muscle contraction.

Transverse Tubules

Structures in muscle cells that are in contact with the sarcoplasmic reticulum and play a role in excitation-contraction coupling.

Ca2+ ATPase (SERCA)

Enzyme located in the sarcoplasmic reticulum membrane that pumps Ca2+ ions from the muscle fiber into the SR, maintaining low intracellular Ca2+ levels at rest.

Ryanodine Receptor (RyR)

Ca2+ release channel in the sarcoplasmic reticulum named after the plant alkaloid that activates it.

Calsequestrin

Low-affinity, high-capacity Ca2+-binding protein in the sarcoplasmic reticulum that helps maintain low free Ca2+ concentration inside the SR.

Muscle Twitch

A single contraction-relaxation cycle of a muscle fiber.

Sarcomere

Basic unit of muscle contraction, composed of actin and myosin filaments.

Calcium Ions

Key ions involved in muscle contraction, binding to troponin to initiate muscle contraction.

Cross-Bridges

Connections formed between myosin and actin filaments during muscle contraction.

Tetanus

Sustained muscle contraction due to repeated stimulation without relaxation.

Fiber Recruitment Summation

Activation of more motor units to increase muscle force.

Length-Tension Relationship

Relationship between muscle length and tension production.

Isometric Contraction

Muscle contraction where the muscle length remains constant, generating tension without changing length.

Passive Tension

Tension generated by stretching non-muscular, elastic elements within the whole muscle.

Total Tension

The sum of active tension from crossbridge cycling and passive tension from stretching the muscle.

Optimal Length (Lo)

Muscle length where maximum active tension occurs due to optimal overlap between thin and thick filaments.

Sarcomeres

Structural units of muscle fibers where muscle contraction occurs.

Isotonic Contraction

Muscle contraction where the muscle shortens as the force of contraction matches the load.

Afterload

The weight attached to the muscle that the muscle must overcome during contraction.

Isotonic Contractions

Muscle contractions where the muscle changes length, resulting in movement.

Preload

The load on a muscle in a relaxed state, prior to contraction.

Force-Velocity Relationship

Describes the velocity of shortening when the force against which the muscle contracts, the afterload, is varied.

Slow-twitch fibers

Muscle fibers that contract slowly and are more resistant to fatigue.

Fast-twitch fibers

Muscle fibers that contract quickly but fatigue quickly.

Muscle Fiber Types

Different types of muscle fibers with varying properties such as contraction velocity and fatigue resistance.

Muscle Metabolism

The process by which muscle fibers generate ATP for muscle contraction.

Creatine Phosphate

A molecule that releases stored energy to convert ADP to ATP, providing energy for muscle contraction.

ATP

Adenosine triphosphate, the immediate source of energy for muscle contraction.

Anaerobic Glycolysis

The process of generating ATP without oxygen, producing lactate from pyruvate.

Aerobic Metabolism

The process of generating ATP with the use of oxygen, mainly through oxidative phosphorylation in mitochondria.

Muscle Hypertrophy

The increase in size of skeletal muscle through growth in the size of its component cells.

Muscle Atrophy

The decrease in mass of the muscle, which may or may not involve cell death.

Sarcomeres

The basic unit of muscle contraction, the arrangement of which affects the force-generating capacity of a muscle fiber.

Muscle Remodeling

The process of muscle adapting to its level of use, involving changes in the number of contractile proteins, enzymes, and mitochondria.