Muscle Basics - Anatomy and Function

Comprehensive vocabulary flashcards covering basic muscle structure, histology, neuromuscular signaling, biomechanics, contractions, aging, and injury classification from the Western University lecture on Muscle Basics.

Skeletal Muscle

Striated muscle tissue composed of repeating actin and myosin filaments that is under voluntary somatic control and attached to bones via tendons to produce movement.

Cardiac Muscle

Striated muscle tissue located exclusively in the heart that is regulated by involuntary autonomic control.

Smooth Muscle

Non-striated, involuntary muscle tissue found within the walls of hollow visceral organs, blood vessels, and the skin.

Skeletal Muscle Tissue (Histology)

Striated muscle tissue characterized by long, cylindrical, multinucleated fibers with peripherally located nuclei under voluntary control.

Cardiac Muscle Tissue (Histology)

Striated, involuntary muscle tissue characterized by branching fibers, centrally located nuclei, and intercalated discs connecting adjacent myocytes.

Smooth Muscle Tissue (Histology)

Non-striated, involuntary muscle tissue consisting of spindle-shaped cells with a single, centrally located nucleus.

Electrical Excitability

The muscle property of being able to respond to electrical stimuli (e.g., intrinsic pace-making in the heart) or chemical stimuli (e.g., neurotransmitters at the neuromuscular cleft).

Contractility

The ability of muscle tissue to actively shorten and generate tensile force to produce movement when pulling on bones via tendons.

Extensibility

The ability of a muscle to stretch or lengthen within safe limits without sustaining structural damage.

Elasticity

The capacity of a muscle to passively recoil back to its original resting length following contraction or extension; it is greatest in smooth muscle.

Tendon

A dense band of fibrous connective tissue that anchors skeletal muscle to bone to translate mechanical contractile force.

Epimysium

The dense layer of connective tissue situated 'upon' the entire external surface of an individual skeletal muscle ('epi-' means 'upon').

Perimysium

The connective tissue sheath surrounding and grouping individual muscle fibers into bundles called fascicles ('peri-' means 'around').

Endomysium

The delicate connective tissue layer located 'within' a fascicle that envelops each single muscle fiber ('endo-' means 'within').

Fascicle

A distinct bundle of skeletal muscle fibers wrapped collectively by perimysium.

Muscle Fiber

An individual skeletal muscle cell consisting of packed bundles of myofibrils.

Myofibril

A cylindrical intracellular organelle made of longitudinally repeating functional contractile units called sarcomeres.

Sarcomere

The basic functional repeating unit of contraction within a myofibril bounded between two Z-lines, containing actin and myosin filaments.

Actin

The thin protein myofilament of the sarcomere that interacts with myosin cross-bridges during muscle contraction.

Myosin

The thick protein myofilament of the sarcomere that pulls actin inward to generate muscle force.

Fascia

Connective tissue encasing muscles, containing nerves and blood vessels, which limits muscle expansion during contraction to maximize force transferred to bones.

Motor Unit

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

Contralateral Control

The neurological principle where the left side of the brain controls motor functions on the right side of the body, and the right side of the brain controls the left side of the body.

Upper and Lower Motor Neurons

The descending motor pathway consisting of an upper motor neuron traveling from the cerebral cortex through the spinal cord and a lower motor neuron carrying impulses directly from the spinal cord to skeletal muscle.

Origin

The immobile, typically proximal skeletal attachment point of a muscle.

Insertion

The mobile, typically distal skeletal attachment point of a muscle where movement is produced.

Mechanical Advantage

The principle that attaching a muscle farther away from a joint axis produces greater rotational leverage and force at that joint.

Isometric Contraction

A phasic contraction where tension increases within the muscle but the muscle length does not change, resulting in no joint movement.

Isotonic Contraction

A phasic contraction in which the muscle changes length against a constant load to create joint movement, comprising concentric and eccentric forms.

Concentric Contraction

An isotonic contraction where the muscle shortens while generating force as actin and myosin filaments are drawn closer together.

Eccentric Contraction

An isotonic contraction where the muscle lengthens under tension while attempting to shorten, causing actin and myosin filaments to separate.

Agonist

The primary muscle (prime mover) driving a specific joint action by executing a concentric contraction.

Antagonist

A muscle that opposes the prime mover by contracting eccentrically to slow, control, or resist joint motion.

Synergist

An accessory muscle that contracts concentrically alongside the agonist to assist the motion or stabilize the working joint.

Muscle Atrophy

Progressive skeletal muscle wasting that begins around age 30, characterized by loss of motor neurons, reduced conduction speed, loss of muscle fibers, and replacement with fibrous connective tissue and adipose.

Muscle Hypertrophy

The enlargement of overall muscle mass and cross-sectional fiber diameter in response to exercise and functional overload.

Muscle Hypertrophy vs. Atrophy

Opposing structural adaptations of skeletal muscle fibers reflecting increased fiber diameter and myofilament density with exercise (hypertrophy) versus reduced fiber diameter with age or disuse (atrophy).

Strain vs. Sprain

A clinical distinction where acute tearing or overstretching injuries to muscles or tendons are termed strains, whereas damage to ligaments is termed a sprain.

Grade 1 Strain

A mild muscle or tendon injury characterized by stretching or slight microscopic tearing of tissue fibers.

Grade 2 Strain

A moderate muscle or tendon injury characterized by an incomplete or partial structural tear.

Grade 3 Strain

A severe muscle or tendon injury characterized by a complete structural tear or rupture across the tissue.

Muscle Strain Classification

The grading system for muscle injuries ranging from stretching or minor tearing (Grade 1), to partial rupture (Grade 2), to complete muscle fiber disruption (Grade 3).

PRICE Protocol

The standard acute injury management strategy representing Protection, Rest, Ice, Compression, and Elevation.