Muscle Physiology

These flashcards cover key concepts in muscle physiology, including types of muscle fibers, conduction mechanisms, and physiological properties of skeletal, smooth, and cardiac muscle.

Skeletal muscle fibers

The three types of skeletal muscle fibers are slow-twitch (Type I), fast-twitch (Type IIa), and fast-twitch (Type IIb), each differing in speed, endurance, and metabolic properties.

Muscle spindle

A sensory receptor located in the belly of muscles that detects changes in muscle length and adjusts sensitivity to stretch.

Extrafusal fibers

The muscle fibers outside the muscle spindle that are responsible for muscle contraction and are innervated by alpha (α) motor neurons.

Intrafusal fibers

The specialized muscle fibers within a muscle spindle that help adjust the sensitivity of the spindle to stretch and are innervated by gamma (γ) motor neurons.

Golgi tendon organs (GTOs)

Sensory receptors located in tendons that detect passive tension or stretch in muscles and contribute to reflex inhibition.

Smooth muscle

Involuntary muscle found in internal organs and blood vessels, characterized by its spindle shape, non-striated appearance, and muscle contraction controlled by the autonomic nervous system.

Single-unit smooth muscle

A type of smooth muscle where fibers contract as a single unit due to connections by gap junctions; found in organs like the intestinal tract.

Multi-unit smooth muscle

A type of smooth muscle where fibers act independently, requiring individual innervation; found in locations like the large airways and arteries.

Cardiac muscle

Striated muscle found only in the heart that is involuntary and regulated by pacemaker cells and the autonomic nervous system.

Excitation-contraction coupling

The physiological process by which an action potential triggers muscle contraction, involving calcium ions and regulatory proteins.

Calmodulin

A calcium-binding protein that plays a key role in the contraction of smooth muscle by activating myosin light-chain kinase.

Myosin light-chain kinase (MLCK)

An enzyme that phosphorylates myosin, enabling crossbridge cycling and muscle contraction in smooth muscle.

Crossbridge cycling

The process by which myosin heads bind to actin filaments, causing muscle contraction.

Bursts of spontaneous depolarizations

Spontaneous changes in membrane potential of pacemaker cells in smooth muscle that lead to rhythmic muscle contractions.

Striations

The alternating light and dark bands found in skeletal and cardiac muscles due to the organized arrangement of myofibrils.

Voluntary control

The conscious control over muscle movement primarily associated with skeletal muscle.

Involuntary control

Unconscious control of muscle movement mainly seen in smooth and cardiac muscle types.

Refractory period

The period after an action potential during which a muscle fiber is unable to respond to a new stimulus.

Pacemaker cells

Specialized cardiac muscle cells that generate electrical signals, initiating contractions in the heart.