Muscle Contraction and Muscle Types – Vocabulary

Vocabulary flashcards summarizing essential structures, proteins, ions, and physiological concepts involved in human muscle contraction and muscle types.

Motor Unit

A motor neuron together with all the skeletal muscle fibers it innervates; the basic functional unit for producing muscle force.

Myofibril

Cylindrical bundle inside a muscle fiber composed of repeating sarcomeres that houses actin and myosin filaments.

Sarcomere

The repeating structural and contractile unit of a myofibril, bordered by Z-lines and containing thin and thick filaments.

Sarcoplasmic Reticulum

Specialized endoplasmic reticulum that surrounds myofibrils and stores/releases Ca2+ required for contraction.

Sarcoplasm

The cytoplasm of a muscle cell, containing organelles, glycogen, and myoglobin.

Sarcolemma

The plasma membrane of a muscle fiber capable of propagating action potentials; invaginated by T-tubules.

T-Tubule

Invagination of the sarcolemma that carries action potentials deep into the muscle fiber to trigger Ca2+ release.

Sliding Filament Model

Explanation of muscle contraction in which thin filaments slide past thick filaments, shortening the sarcomere in an all-or-nothing manner.

Troponin

Calcium-binding protein on thin filaments that moves tropomyosin to uncover myosin-binding sites on actin.

Tropomyosin

Rod-shaped protein that blocks myosin-binding sites on actin until shifted by Ca2+-bound troponin.

Myosin Head (Cross-bridge)

Globular part of the myosin molecule that binds actin, performs the power stroke, and hydrolyzes ATP.

Power Stroke

The pivoting motion of the myosin head that pulls actin toward the sarcomere center, generating contraction.

Neuromuscular Junction

Synapse where a motor neuron releases acetylcholine to stimulate a skeletal muscle fiber.

Acetylcholine (ACh)

Neurotransmitter released at the neuromuscular junction that depolarizes the sarcolemma.

Calcium Ion (Ca2+) in Contraction

Ion released from the sarcoplasmic reticulum that binds troponin, enabling cross-bridge formation.

ATP in Muscle Contraction

Energy molecule that detaches myosin from actin and re-cocks the myosin head after hydrolysis to ADP + Pi.

Rigor Mortis

Post-death condition where lack of ATP leaves myosin bound to actin, causing sustained muscle contraction.

Motor Unit Recruitment

Progressive activation of additional motor units to increase muscle force as stimulus intensity rises.

Submaximal Stimulus

A stimulus below maximal intensity that activates only some of the available motor units.

Maximum Stimulus

Highest stimulus intensity that recruits all motor units within a muscle.

Skeletal (Striated) Muscle

Voluntary muscle with striations and multiple peripheral nuclei that contracts via sarcomeres.

Cardiac Muscle

Striated, involuntary heart muscle with one or two central nuclei and interconnected by intercalated discs.

Intercalated Disc

Specialized junction between cardiac muscle cells containing gap junctions that synchronize contractions.

Smooth Muscle

Involuntary, non-striated muscle with a single central nucleus that contracts without sarcomeres and is controlled by the autonomic nervous system.

Muscular Pump

Action of skeletal muscle contractions squeezing blood and lymph vessels to aid circulation.

Thin Filament

Actin-based filament in a sarcomere that interacts with myosin during contraction.

Thick Filament

Myosin-based filament in a sarcomere responsible for force generation through cross-bridge cycling.

Autonomic Nervous System

Portion of the peripheral nervous system that regulates involuntary functions and controls smooth and cardiac muscles.

Mitochondrial Abundance (in Muscle Cells)

High density of mitochondria, especially in cardiac muscle, providing ATP for sustained contraction.