Vocab Test 1: Structure & Function of Exercising Muscle

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_i

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

Apoptosis

programmed cell death

Concentric Contraction

muscle shortening

Dynamic Contraction

any muscle action that produces joint movement

Eccentric Contraction

any muscle action in which the 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

a small bundle of muscle fibers wrapped in a connective tissue sheath within a muscle

Force-Velocity Relation

the force generated by a muscle is a function of its velocity. Increasing the velocity of contraction whil shortening reduces force, while faster contraction as the muscle is lengthening increases force

Length-Tension Relation

the tension developed by a muscle is a function of its length. The highest force can be generated when there is optimal overlap between actin and myosin filaments

Motor Unit

the motor nerve and the group of muscle fibers it innervates

Muscle Fibers

an individual muscle cell

Musculoskeletal System

body system composed of the skeleton and skeletal muscles that allows, supports, and helps control human movement

Myofibrils

the contractile element of skeletal muscle

Myosin

one of the proteins that form filaments that produce muscle action

Myosin Cross-Bridges

the protruding part of a myosin fiilament. it includes the myosin head, which binds to an active site on an actin filament to produce a power stroke that cause the filaments to slide across each other

Myosin Heavy Chain (MHC)

contractile protein iso-forms of the sarcomere’s thick muscle filaments

Nebulin

a gaint protein that coextends with actin and appears to play a regulatory tole in mediating actin and myosin interactions

Perimysium

the connective tissue sheath surrounding each muscle fasciculus

Plasmalemma

plasma membrane, the selectively permeable lipid bilayer coated by proteins that composes the outer layer of a cell

Power Stroke

the tilting of the myosin head, caused by a strong intermolecular attraction between the myosin cross-bridge and the myosin head, which causes the actin and myosin filaments to slide across each other

Principle of Orderly Recruitment

the theory that motor units generally are activiated 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 fiber 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

Sacroplasmic Reticulum (SR)

a longitundinal system of tubules that is associated with the myofibrils and that stores calcium for muscle action

Satellite Cells

immature cells that can devlop into mature cell types, such as myoblasts

Single-Fiber Contractile Velocity (V₀)

the rate at which an individual muscle cell can shorten and devlop tension

Size Principle

principle asserting that the 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) Muscle Contraction

action in which the muscle contracts without moving, generating force while its length remains static (unchanged). also know as an isometric action

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 an nerve impulses to be transmitted rapidly to individual myofibrils

Tropomyosin

a tube-shaped protein that twists around actin stands, fitting into the groove between them

Troponin

a complex protein attached at regular intervals to actin stands and tropomyosin

Twitch

the smallest contractile response of a muscle fiber or a motor unit to a single electrical stimulus

Type I Fibers

a type of muscle fiber that has high oxidative capacity and a low glycolytic capacity; associated with endurance-type activities

Type II Fibers

a type of muscle fiber that has a low oxidative capacity and a high glycolytic capacity; associated with speed or power activites