Kinesiology: Myology (4)

A complete set of vocabulary flashcards defining myology terms, structural organization, fiber types, muscular morphology, functional mechanics, and neuromuscular principles based on lecture notes.

Epimysium

The outermost sheath of dense connective tissue that surrounds an entire muscle bundle.

Perimysium

The layer of connective tissue that surrounds a fascicle, which is a bundle of individual muscle fibers.

Endomysium

The delicate layer of connective tissue located between individual muscle fibers.

Sarcomere

The fundamental contractile unit of a muscle cell composed of myofilaments, lying in series along the muscle length between adjacent Z disks.

A Band

The dark band within a sarcomere containing thick myosin filaments.

I Band

The light band within a sarcomere containing thin actin filaments.

H Band

The region in the center of the A band where thick myosin filaments do not overlap with thin actin filaments.

M Line

The central attachment line located in the middle of the H band that connects thick myosin filaments.

Z Disk

The boundary structure that connects adjacent sarcomeres through thin actin filaments.

Tendon

Non-contractile connective tissue that transmits tensile force directly from muscle to bone.

Aponeurosis

A broad, sheet-like tendon that distributes muscle force over a wider structural area.

Fascia

A continuous sheet of connective tissue integrating epimysium, perimysium, and endomysium to provide support and force transmission throughout the muscular system.

Strap Muscle

A long, thin, flat muscle morphology with parallel fibers of equal length and shorter tendons, characterized by high endurance and limited strength (e.g., sartorius, sternocleidomastoid).

Fusiform Muscle

A muscle morphology with parallel fibers where the muscle belly is wider than its origin and insertion (e.g., biceps brachii).

Triangular Muscle

A muscle morphology with a wide proximal attachment tapering to a single point of insertion, designed for maximum force production (e.g., pectoralis major).

Unipennate Muscle

A feather-like muscle morphology with oblique fibers attaching to one side of a central tendon (e.g., flexor pollicis longus).

Bipennate Muscle

A muscle morphology featuring two sets of oblique fibers sharing attachment to a central tendon in opposing directions (e.g., rectus femoris).

Multipennate Muscle

A muscle morphology with fibers arranged in multiple orientations converging onto a shared central tendon (e.g., deltoid).

Pennation Angle

The angle of orientation formed between muscle fibers and the tendon; an angle greater than zero increases fiber density but reduces force transmission per fiber parallel to the tendon.

Physiologic Cross-Sectional Area (PCSA)

The sum of the cross-sectional area of all muscle fibers within a muscle perpendicular to fiber orientation, measured in $cm^2$, which determines maximum force production.

Sliding Filament Theory

The mechanism of muscle contraction where an action potential releases ACh to open $Na^+$/$Ca^{2+}$ channels, causing $Ca^{2+}$ to bind troponin, move tropomyosin, and allow myosin heads to form cross-bridges and execute power strokes using ATP.

Passive Tension

Tensile force generated purely by stretching muscle tissue, elongating both parallel and series elastic connective tissues without active contraction.

Type I Muscle Fiber

A slow-twitch muscle fiber characterized by slow contraction time, high oxidative capacity, small diameter, high fatigue resistance, and small force output.

Type IIA Muscle Fiber

An intermediate fast-twitch muscle fiber with fast contraction time, high oxidative capacity, medium diameter, moderate fatigue resistance, and moderate force output.

Type IIX Muscle Fiber

A fast-twitch muscle fiber featuring very fast contraction time, low oxidative capacity, large diameter, small fatigue resistance, and very high force output.

Tonic Muscles

Slow oxidative muscles oriented toward endurance, stability, and postural support, which are prone to tightness or shortening.

Phasic Muscles

Fast glycolytic muscles oriented toward power output and mobility, which are prone to weakness or functional inhibition.

Concentric Contraction

An active muscle contraction during which the muscle shortens while accelerating an external load.

Eccentric Contraction

An active muscle contraction during which the muscle lengthens while decelerating an external load, producing the highest force output.

Isometric Contraction

A muscle contraction in which muscle length remains constant because internal torque matches the external load.

Agonist

The primary muscle or group of muscles directly responsible for executing a specific movement (the prime mover).

Antagonist

A muscle that produces the anatomical movement directly opposite to that of the agonist prime mover.

Cocontraction

The simultaneous activation of agonist and antagonist muscles surrounding a joint to provide joint stability.

Synergist

A muscle that acts in cooperation with the primary agonist to assist in carrying out a desired movement.

Motor Unit

A single alpha motor neuron and all the specific muscle fibers that it innervates.

Henneman's Size Principle

The principle stating that motor units are recruited sequentially from smallest motor neurons (Type I fibers) to largest motor neurons (Type II fibers) as force requirements increase.

Rate Coding

The mechanism of force regulation achieved by altering the firing frequency of action potentials delivered to active motor units.

Tetanus

A state of sustained, smooth maximal muscle contraction produced when stimulation frequency is high enough to eliminate relaxation phases between twitches.

Muscle Spindle

A Group Ia afferent sensory receptor responsive to muscle length and rate of stretch that increases agonist excitability and inhibits the antagonist via reciprocal inhibition.

Golgi Tendon Organ (GTO)

A Group Ib afferent sensory receptor responsive to muscle tension that decreases agonist excitability via autogenic inhibition and increases antagonist excitability.

Reciprocal Inhibition

A neuromuscular reflex where muscle spindle stretch causes the agonist muscle to contract while inhibiting activation of its opposing antagonist muscle.

Autogenic Inhibition

A protective neuromuscular reflex triggered by Golgi tendon organs under high tension that reduces force output in the active muscle to prevent tissue injury.

All-or-None Principle

The principle stating that if a stimulus to a motor neuron fails to reach threshold, no muscle fibers in the motor unit contract; if threshold is exceeded, all fibers contract completely.

Active Insufficiency

The inability of a multi-joint muscle to generate effective tension or force when it is simultaneously placed in a fully shortened position across all crossed joints.

Passive Insufficiency

The structural limitation where a multi-joint muscle lacks adequate length/extensibility to allow full passive range of motion across all crossed joints at the same time.

Sarcopenia

The age-related loss of muscle mass, fiber count, and motor unit function, accompanied by selective atrophy of Type II fibers.