Muscular System Lecture Flashcards

Vocabulary practice flashcards covering muscular system anatomy, physiology, fiber types, contraction mechanisms, and anatomical movements.

Masseter Muscle

Located in the jaw, it is the strongest muscle in the human body by weight, reaching a maximum pressure of $200\,\text{PSI}$.

Gluteus Maximus

Located in the buttocks, it is the largest muscle in the human body by volume.

Skeletal Muscle

Voluntary, striated, multinucleated muscle tissue controlled by conscious will and governed by the Central Nervous System (CNS) that attaches to the skeleton to produce movement.

Smooth Muscle

Involuntary, nonstriated, spindle-shaped muscle tissue controlled by the Autonomic Nervous System, located in the walls of the digestive and respiratory tracts, blood vessels, and lymph vessels.

Cardiac Muscle

Involuntary, striated, H or Y-shaped muscle tissue found only in the heart.

Irritability (Excitability)

The capacity of muscle tissue to receive and react to a stimulus.

Contractility

The ability of a muscle to contract or shorten, thereby exerting a force.

Elasticity

The ability of a muscle to return to its original shape after contracting.

Extensibility

The ability of a muscle to stretch.

Fascicles

Contractile fibrous tissue arranged in separate parallel bundles that form the whole muscle.

Superficial Fascia

Fascia located just beneath the skin that covers the entire muscular system.

Deep Fascia

Fascia that penetrates deep into tissue to anchor muscle to bone and extends beyond muscle ends as tendons or aponeuroses.

Epimysium

The connective tissue layer that covers the outer surface of an entire muscle.

Perimysium

The connective tissue layer that separates a muscle into bundles of fascicles by wrapping around each fascicle.

Endomysium

The connective tissue layer that separates fascicles into individual muscle fibers (cells) by wrapping around each muscle fiber.

Sarcolemma

The cell membrane surrounding a muscle fiber, situated directly beneath the endomysium.

Myofibrils

Long, slender strands located within muscle fibers that run their full length and contain repeating functional units called sarcomeres.

Sarcomere

The smallest functional unit of a muscle fiber and the basic unit of muscle contraction, containing actin and myosin filaments.

Myosin

The thick protein filament in a sarcomere that makes up nearly $50\%$ of muscle tissue.

Actin

The thin protein filament within a sarcomere that is pulled across myosin during muscle contraction.

Sliding Filament Theory

The mechanism of muscle contraction where actin filaments slide across thick myosin filaments toward the M line, narrowing the I band and bringing Z lines closer together.

Transverse Tubules

A system of channels within the muscle cell containing extracellular fluid that aids in transmitting nerve impulses throughout the cell.

Sarcoplasmic Reticulum

A network of membranous channels within the muscle cell that stores and releases calcium ions to trigger muscle contraction.

Neuromuscular Junction (NMJ)

The junction site where a motor neuron branch and a muscle fiber meet.

Motor Unit

A single motor neuron and all of the individual muscle fibers that it controls.

Acetylcholine (ACh)

The principal chemical neurotransmitter in muscle contraction, released from motor neuron ends to bridge the synaptic gap at the NMJ.

All-or-None Response

The physiological principle stating that if a neural stimulus is sufficient, all muscle cells within a motor unit contract to their fullest extent, or not at all.

Graded Response (Motor Unit Recruitment)

The process by which the nervous system regulates the overall force of a muscle contraction by varying the number of motor units recruited.

Cross-Bridge Cycle

The sequence in which myosin heads attach to exposed actin sites, pivot (power stroke), detach via ATP, and cock back to repeat contraction.

Aerobic Respiration

A cellular respiration process taking place in mitochondria that requires oxygen and glucose to generate ATP for sustained muscular energy.

Anaerobic Respiration

An energy pathway operating without oxygen that breaks down glucose into pyruvic acid and then lactic acid when oxygen is depleted.

Oxygen Debt

The accumulation of lactic acid during intense physical activity that must later be processed by the liver using oxygen to convert lactic acid back to glucose.

Muscle Fatigue

A condition in which a muscle ceases to respond to nerve stimulation, resulting as a by-product of oxygen debt from rapid or prolonged contractions.

Type I Muscle Fibers

Slow-twitch 'red muscle' fibers characterized by high fatigue resistance, slow contraction speed, and abundant myoglobin, capillaries, and mitochondria.

Type II Muscle Fibers

Fast-twitch 'white muscle' fibers that contract $5\times$ to $10\times$ faster than Type I fibers, fatigue easily, and rely on glycogen and creatine phosphate for ATP.

Postural Muscles

Stabilizer muscles with a higher proportion of Type I fibers that support the body against gravity and tend to shorten and tighten when subjected to stress.

Phasic Muscles

Movement muscles containing a higher proportion of Type II fibers that respond quickly and forcefully to stimuli and tend to weaken and become inhibited when stressed.

Fusiform Muscles

A parallel muscle shape in which the belly of the muscle is wider and tapers toward tendons at both ends, such as the biceps brachii.

Pennate Muscles

Muscle structures whose fascicles attach obliquely to a central tendon, categorized into unipennate, bipennate, and multipennate arrangements.

Origin

The muscle attachment site where the tendon anchors to a relatively immovable or more stable skeletal section, usually situated closer to the midline.

Insertion

The muscle attachment site where the tendon anchors to a more moveable skeletal section, where muscle action is expressed.

Functional Reversibility

The phenomenon where muscles temporarily reverse their functional roles of insertion and origin.

Isometric Contraction

A muscle contraction that generates force without changing overall muscle length or creating movement.

Isotonic Contraction

A muscle contraction that produces body movement, altering the distance between the endpoints of the muscle.

Concentric Contraction

A type of isotonic contraction in which the distance between the ends of the contracting muscle decreases.

Eccentric Contraction

A type of isotonic contraction in which the distance between the ends of the contracting muscle increases.

Prime Mover (Agonist)

The chief muscle responsible for executing a specific movement.

Antagonist

A muscle that produces the opposite movement of the agonist, relaxing and lengthening when the agonist contracts.

Synergist

A muscle that assists the agonist to ensure smooth, coordinated, and graceful movement execution.

Fixator

A stabilizer muscle that holds a body part firm so that another muscle can effectively perform an action on an adjacent segment.

Circumduction

A sequential combination of flexion, adduction, extension, and abduction producing circular movement with a fixed proximal end.

Pronation

Medial or inward rotation occurring specifically at the forearm.

Supination

Lateral or outward rotation occurring specifically at the forearm.

Dorsiflexion

Ankle flexion movement that decreases the angle of the joint, lifting the foot upward.

Plantar Flexion

Ankle movement that increases the angle of the joint, pointing the foot downward.