Hole's Human Anatomy & Physiology - Chapter 09 Muscular System

Key vocabulary terms and structural/functional definitions covering the Muscular System from Hole's Human Anatomy & Physiology.

Skeletal muscle

Voluntary muscle tissue attached to bones and skin of the face that is under conscious control.

Cardiac muscle

Involuntary muscle tissue located exclusively in the wall of the heart responsible for pumping blood.

Smooth muscle

Involuntary muscle tissue found in the walls of hollow internal organs, such as those of the digestive tract.

Fascia

A thin covering of connective tissue that surrounds a muscle and is part of a complex network of fasciae.

Tendon

A cord-like mass of connective tissue that connects a muscle to a bone.

Aponeurosis

A sheet-like mass of connective tissue that connects a muscle to a bone, skin, or another muscle.

Epimysium

The layer of connective tissue that surrounds the entire skeletal muscle beneath the fascia.

Perimysium

The connective tissue layer surrounding fascicles, which are bundles of skeletal muscle fibers within a muscle.

Endomysium

The thin layer of connective tissue surrounding individual skeletal muscle fibers within a fascicle.

Compartment syndrome

A painful condition caused by fluid accumulation within an enclosed muscle compartment, leading to elevated pressure and oxygen deficiency.

Sarcolemma

The cell membrane of a skeletal muscle fiber.

Sarcoplasm

The cytoplasm of a skeletal muscle fiber containing nuclei, mitochondria, and myofibrils.

Myofibrils

Long, parallel structures running through a muscle fiber that consist of thin actin filaments and thick myosin filaments.

Sarcomere

The repeating functional contractile unit of a myofibril, joined end-to-end between adjacent Z lines.

Sarcoplasmic reticulum (SR)

The specialized endoplasmic reticulum of a muscle fiber that stores calcium ions.

Transverse tubule (T tubule)

A membranous channel extending inward from the sarcolemma that relays electrical impulses deep into the muscle fiber to the sarcoplasmic reticulum.

Triad

A muscle fiber structure composed of one transverse tubule flanked by two cisternae of the sarcoplasmic reticulum.

I band

The light band of a sarcomere composed strictly of thin actin filaments, centered on a Z line.

A band

The dark band of a sarcomere composed of thick myosin filaments, including overlapping regions of thin actin filaments.

H zone

The central region of an A band composed exclusively of thick myosin filaments.

Z line (Z disc)

The structure located in the center of an I band that anchors thin actin filaments and defines sarcomere boundaries.

M line

The center boundary of a sarcomere and A band that anchors thick myosin filaments.

Neuromuscular junction (NMJ)

A specialized synapse where an axon terminal of a motor neuron interacts with a skeletal muscle fiber.

Motor end plate

The specialized, folded portion of a muscle fiber sarcolemma containing neurotransmitter receptors.

Synaptic cleft

The narrow space separating the motor neuron axon terminal from the motor end plate of a muscle fiber.

Acetylcholine (ACh)

The specific neurotransmitter released by motor neurons to stimulate skeletal muscle fibers.

Myasthenia Gravis (MG)

An autoimmune disorder in which antibodies attack acetylcholine receptors at motor end plates, causing muscle weakness and fatigue.

Dystrophin

A structural muscle protein that binds to the inner side of muscle cell membranes, holding them intact during contraction.

Excitation-contraction coupling

The sequence of events linking muscle impulse generation on the sarcolemma to mechanical cross-bridge action and contraction.

Sliding filament model

The mechanism of muscle contraction where thin and thick filaments slide past each other, shortening sarcomeres without changing filament lengths.

Acetylcholinesterase

An enzyme in the synaptic cleft that rapidly decomposes acetylcholine to stop muscle fiber stimulation.

Creatine phosphate

A high-energy molecule that stores phosphate energy to rapidly regenerate ATP from ADP during muscle activity.

Myoglobin

An iron-bearing pigment in muscle cells that temporarily binds and stores oxygen for aerobic respiration.

Oxygen debt

The volume of oxygen required by liver cells to convert accumulated lactic acid to glucose and restore muscle ATP and creatine phosphate reserves.

Threshold stimulus

The minimal strength of electrical stimulation required to trigger an action potential and prompt muscle fiber contraction.

Twitch

A brief, single contractile response of a muscle fiber to a single impulse.

Latent period

The brief delay between the application of a stimulus and the onset of force contraction in a muscle fiber.

Summation

The combination of forces from individual muscle twitches when stimuli arrive at high frequency, generating sustained contraction.

Tetanus

A sustained, forceful muscular contraction that lacks relaxation between individual stimuli.

Motor unit

A single motor neuron together with all the skeletal muscle fibers it controls.

Recruitment

The increase in the number of active motor units activated by higher stimulation intensity to produce greater contraction force.

Muscle tone (tonus)

A continuous state of partial contraction present in resting skeletal muscles.

Concentric contraction

An isotonic contraction in which a muscle shortens as it generates force greater than the opposing resistance.

Eccentric contraction

An isotonic contraction in which a muscle lengthens because the force it produces is less than the resistance.

Isometric contraction

A contraction in which muscle tension develops without any change in overall muscle length or joint movement.

Slow-twitch (Type I) fibers

Red, fatigue-resistant muscle fibers rich in myoglobin and mitochondria with slow ATPase activity.

Fast-twitch glycolytic (Type IIb) fibers

White, easily fatigued muscle fibers with low myoglobin, rapid ATPase activity, and primary reliance on anaerobic respiration.

Fast-twitch oxidative (Type IIa) fibers

Intermediate pink muscle fibers with quick contraction speeds, moderate myoglobin content, and intermediate fatigue resistance.

Hypertrophy

An increase in the size and total strength of skeletal muscle resulting from exercise.

Atrophy

A reduction in skeletal muscle size and force capacity resulting from non-use.

Multi-unit smooth muscle

Smooth muscle tissue organized as independent, unorganized units found in blood vessel walls and the iris of the eye.

Visceral smooth muscle

Single-unit smooth muscle structured in sheets connected by gap junctions that displays automatic rhythmicity and peristalsis.

Calmodulin

A calcium-binding protein utilized by smooth muscle cells in place of troponin to trigger contraction.

Intercalated discs

Specialized cell junctions connecting cardiac muscle fibers that facilitate direct signal communication so the heart contracts as a unit.

Origin

The immovable or fixed end of a skeletal muscle attachment point.

Insertion

The movable end of a skeletal muscle attachment point pulled toward the origin during contraction.

Agonist

A muscle that actively causes a specified bodily movement.

Prime mover

The primary agonist muscle directly responsible for producing a specific movement.

Synergists

Muscles that contract alongside and assist the action of a prime mover.

Antagonist

A muscle whose contraction directly opposes the action of a prime mover.