Exercise Physiology Chapter 1 Terms

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Actin
A thin protein filament that acts with myosin filaments to produce muscle action
Action Potential
A rapid and substantial depolarization of the membrane of a neuron or muscle cell that is conducted through the cell
Adenosine Triphosphatase (ATPase)
An enzyme that splits the last phosphate group off ATP, releasing a large amount of energy and reducing the ATP to ADP and P
Adenosine Triphosphate (ATP)
A high-energy phosphate compound from which the body derives its energy
Alpha-Motor Neuron
A neuron innervating extrafusal skeletal muscle fibers
Cachexia
A loss of body weight (wasting) accompanied by muscle atrophy, weakness, and fatigue
Concentric Contraction
Muscle shortening
Dynamic Contraction
Any muscle action that produces joint movement
Eccentric Conctraction
Any muscle action in which muscle lengthens
Endomysium
A sheath of connective tissue that covers each muscle fiber
Epimysium
The outer connective tissue that surrounds an entire muscle, holding it together
Excitation-Contraction Coupling
The sequence of events by which a nerve impulse reaches the muscle membrane and leads to cross-bridge activity and thus muscle contraction
Fascicle (Fascicules)
A small bundle of muscle fibers wrapped in a connective tissue sheath within a muscle
Motor Unit
The motor nerve and the group of muscle fibers it innervates
Muscle Fiber
An individual muscle cell
Musculoskeletal System
Body system composed of the skeleton and skeletal muscles that allows, supports, and helps control human movement
Myofibril
The contractile element of skeletal muscle
Myosin
One of the proteins that form filaments that produce muscle action
Myosin Cross-Bridge
The protruding part of a myosin filament; it includes the myosin head, which binds to an an active site on an actin filament to produce a power stroke that causes the filaments to slide across each other
Nebulin
A giant protein that coextends with actin and appears to play a regulatory role in mediating actin and myosin interactions
Perimysium
The connective tissue sheath surrounding each muscle fascicules
Plasmalemma
Plasma membrane, the selectively permeable lipid bilayer coated by proteins that composes the outer layer of the cell
Power Stroke
The tilting of the myosin head, caused by a strong intermolecular attraction between the myosin cross-bridge and the myosin head, that causes the actin and myosin filaments to slide across each other
Principle of Orderly Recruitment
The theory that motor units generally are activated on the basis of a fixed order of recruitment, in which the motor units within a given muscle appear to be ranked according to the size of the motor neuron
Rate Coding
Refers to the frequency of impulses sent to a muscle; increased force can be generated through increase in either the number of muscle fibers recruited or the rate at which the impulses are sent. Also called frequency coding.
Sarcolemma
A muscle fiber's cell membrane
Sarcomere
The basic functional unit of a myofibril
Sarcoplasm
The gelatin-like cytoplasm in a muscle fiber
Sarcoplasmic Reticulum (SR)
A longitudinal system of tubules that is associated with the myofibrils and that stores calcium for muscle action
Satellite Cells
Immature cells that can develop into mature cell types, such as myoblasts
Single-Fiber Contractile Velocity (Vo)
The rate at which an individual muscle cell can shorten and develop tension
Size Principle
Principle asserting that size of the motor neuron dictates the order of motor unit recruitment, with small-sized motor neurons being recruited first
Sliding Filament Theory
A theory explaining muscle action: a myosin cross-bridge attaches to an actin filament, and then the power stroke drags the two filaments past one another
Static (Isometric) Contraction
Action in which the muscle contracts without moving, generating force while its length remains static (unchanged)
Summation
The summing of all individual changes in a neuron's membrane potential
Tetanus
Highest tension developed by a muscle in response to stimulation of increasing frequency
Titin
A protein that positions the myosin filament to maintain equal spacing between actin filaments
Transverse Tubules (T-Tubules)
Extensions of the sarcolemma (plasma membrane) that pass laterally through the muscle fiber, allowing nutrients to be transported and nerve impulses to be transmitted rapidly to individual myofibrils
Tropomyosin
A tube-shaped protein that twists around actin strands, fitting into the groove between them
Troponin
A complex protein attached at regular intervals to actin strands and tropomyosin
Twitch
The smallest contractile response of a muscle fiber or a motor unit to a single electrical stimulus
Type II (Slow-Twitch) Fiber
A type of muscle fiber with a low oxidative capacity and a high glycolytic capacity; associated with speed or power activities
Type I (Slow-Twitch) Fiber
A type of muscle fiber that has a high oxidative and a low glycolytic capacity, associated with endurance-type activities