The Muscular System Flashcards

Comprehensive vocabulary flashcards covering the structural characteristics, microscopic anatomy, cellular contractions, neuromuscular junctions, energy pathways, movements, and terminology of the human muscular system.

Endomysium

A delicate connective tissue sheath that encloses a single muscle fiber.

Perimysium

A coarser fibrous membrane that wraps around a fascicle, which is a bundle of muscle fibers.

Epimysium

A tough connective tissue layer that covers the entire skeletal muscle.

Tendons

Cordlike structures composed mostly of collagen fibers that attach skeletal muscles to bones.

Aponeuroses

Sheetlike connective tissue structures that attach muscles indirectly to bones, cartilages, or connective tissue coverings.

Sarcolemma

The specialized plasma membrane of a muscle cell.

Myofibrils

Long ribbonlike organelles inside a muscle cell that display alternating light (I) and dark (A) bands, giving the cell its striated appearance.

Sarcomere

The contractile unit of a muscle fiber; the structural and functional unit of skeletal muscle located between Z discs.

Myosin filaments

Thick myofilaments composed of the protein myosin that contain ATPase enzymes and possess projections known as myosin heads or cross bridges.

Actin filaments

Thin myofilaments composed of the contractile protein actin anchored to the Z disc.

Sarcoplasmic reticulum (SR)

A specialized smooth endoplasmic reticulum that surrounds myofibrils and stores and releases calcium ions ($\text{Ca}^{2+}$).

Motor unit

A functional structure consisting of one motor neuron and all the skeletal muscle cells stimulated by that neuron.

Neuromuscular junction

The region where the axon terminal of a motor neuron comes into close proximity with the sarcolemma of a muscle cell.

Acetylcholine (ACh)

The specific chemical neurotransmitter released by nerve endings that stimulates skeletal muscle cells.

Synaptic cleft

The fluid-filled gap between the motor neuron axon terminal and the muscle cell sarcolemma.

Acetylcholinesterase (AChE)

The enzyme located in the synaptic cleft that breaks down acetylcholine into acetic acid and choline to end muscle contraction.

Irritability

The ability of muscle cells to receive and respond to a stimulus (also called responsiveness).

Contractility

The ability of muscle cells to forcibly shorten when an adequate stimulus is received.

Extensibility

The ability of muscle cells to be stretched.

Elasticity

The ability of muscle cells to recoil and resume their original resting length after stretching.

Muscle twitch

A single, brief, jerky contraction of a muscle cell that is not a normal muscle operation.

Unfused tetanus

A state of incomplete muscle contraction that occurs when stimulations become more frequent and contractions get stronger and smoother.

Fused tetanus

A state of complete muscle contraction achieved when a muscle is stimulated so rapidly that no relaxation is observed between stimuli.

Direct phosphorylation

An anaerobic ATP regeneration pathway in which creatine phosphate (CP) transfers a phosphate group to ADP, yielding 1 ATP per CP molecule.

Aerobic respiration

A metabolic process occurring in mitochondria that requires oxygen to break down glucose into carbon dioxide and water, yielding approximately 32 ATP per glucose.

Anaerobic glycolysis

A fast metabolic pathway that breaks down glucose without oxygen into pyruvic acid (producing 2 ATP), which is then converted into lactic acid.

Isotonic contractions

Muscle contractions in which myofilaments successfully slide past each other, causing the muscle to shorten and movement to occur.

Isometric contractions

Muscle contractions in which tension increases inside the muscle, but filaments cannot slide against an immovable object and no shortening occurs.

Muscle tone

A state of continuous partial muscle contractions resulting from systematic stimulation of different motor units, keeping the muscle firm and healthy.

Origin

The attachment point of a skeletal muscle to an immovable or less movable bone.

Insertion

The attachment point of a skeletal muscle to a movable bone.

Flexion

A movement that decreases the angle of the joint and brings two bones closer together.

Extension

A movement that increases the angle between two bones.

Rotation

The movement of a bone around its longitudinal axis.

Abduction

The movement of a limb away from the midline or median plane of the body.

Adduction

The movement of a limb toward the midline of the body.

Circumduction

A combination movement of flexion, extension, abduction, and adduction where the proximal end of the bone is stationary and the distal end outlines a circle.

Dorsiflexion

A movement of the ankle that lifts the foot so that its superior surface approaches the shin.

Plantar flexion

A movement of the ankle that points the foot and toes away from the head.

Inversion

A special foot movement that turns the sole of the foot medially.

Eversion

A special foot movement that turns the sole of the foot laterally.

Supination

Forearm rotation laterally so that the palm faces anteriorly and the radius and ulna are parallel.

Pronation

Forearm rotation medially so that the palm faces posteriorly and the radius and ulna cross each other like an X.

Opposition

The unique action of moving the thumb to touch the tips of the other fingers on the same hand.

Prime mover

The muscle that bears the major responsibility for producing a specific body movement.

Antagonist

A muscle that opposes or reverses the action of a prime mover.

Synergist

A muscle that assists a prime mover in a movement or helps prevent unwanted movement.

Fixator

A specialized synergist that holds a bone stationary or stabilizes the origin of a prime mover.