Chapter 9: Muscles and Muscle Tissue Review

A comprehensive set of vocabulary flashcards covering skeletal and smooth muscle anatomy, physiology, and pathology based on Chapter 9 lecture notes.

Excitability

The ability of muscle tissue to receive and respond to stimuli.

Contractility

The ability of muscle tissue to shorten forcibly when stimulated.

Extensibility

The ability of muscle tissue to be stretched.

Elasticity

The ability of muscle tissue to recoil and resume resting length after stretching.

Epimysium

Dense irregular connective tissue surrounding an entire skeletal muscle.

Perimysium

Connective tissue sheath surrounding a fascicle.

Endomysium

Fine areolar connective tissue surrounding each muscle fiber.

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber, containing glycosomes and myoglobin.

Sarcoplasmic reticulum (SR)

Specialized smooth endoplasmic reticulum that stores and releases calcium ($Ca^{2+}$) in muscle fibers.

T tubule

An extension of the sarcolemma that carries electrical signals deep into the muscle fiber.

Sarcomere

The smallest functional contractile unit of skeletal muscle, extending from one Z disc to the next.

A band

The dark region of a sarcomere containing the full length of the thick filaments.

I band

The light band containing thin filaments and the Z disc.

H zone

The lighter central region of the A band where only thick filaments are present.

M line

The middle anchoring line of the H zone.

Z disc

A protein structure that anchors thin filaments and marks the boundary of a sarcomere.

Myosin

The motor protein that forms the thick filament; its heads bind to actin during contraction.

Actin

The contractile protein that forms the thin filament; it contains active sites for myosin binding.

Tropomyosin

A regulatory protein that blocks actin active sites when a skeletal muscle fiber is relaxed.

Troponin

A regulatory protein on thin filaments that binds calcium in skeletal muscle to move tropomyosin.

Titin

An elastic filament protein that holds thick filaments in place and contributes to muscle recoil.

Dystrophin

A protein that links thin filaments to the sarcolemma and stabilizes the muscle fiber.

Sliding filament model

The model stating that thin filaments slide past thick filaments to shorten the sarcomere; the filaments do not shorten.

Acetylcholine (ACh)

The neurotransmitter released by motor neurons at the neuromuscular junction to stimulate muscle fibers.

Acetylcholinesterase

The enzyme that breaks down ACh in the synaptic cleft to end the signal.

End plate potential

A local depolarization of the sarcolemma produced when ACh opens chemically gated ion channels.

Excitation-contraction coupling

The process by which an action potential triggers calcium release and initiates contraction.

Cross bridge

The connection formed when a myosin head binds to actin.

Power stroke

The step of the cross bridge cycle in which the myosin head pivots and pulls the thin filament toward the M line.

Motor unit

One motor neuron and all the muscle fibers it innervates.

Muscle twitch

A brief, single contraction response of a muscle fiber to one action potential.

Latent period

The first phase of a twitch where excitation-contraction coupling occurs but tension is not yet visible.

Temporal summation

An increase in muscle force when stimuli arrive before the muscle fully relaxes; also called wave summation.

Unfused tetanus

A sustained but wavering contraction caused by rapid, repeated stimulation.

Fused tetanus

A smooth, maximal sustained contraction without any evidence of relaxation.

Recruitment

The increase in muscle force by activating additional motor units.

Size principle

A recruitment pattern in which smaller motor units are activated before larger ones.

Muscle tone

A constant, low-level state of partial contraction that keeps muscles firm and ready.

Isotonic contraction

A contraction in which the muscle changes length and moves a load.

Concentric contraction

A type of isotonic contraction in which the muscle shortens while producing force.

Eccentric contraction

A type of isotonic contraction in which the muscle lengthens while generating force.

Isometric contraction

A contraction in which tension rises but the muscle does not shorten because the load is too great.

Creatine phosphate (CP)

A high-energy phosphate compound that rapidly regenerates $ATP$ in muscle.

Anaerobic glycolysis

An $ATP$-producing pathway that breaks down glucose without oxygen and converts pyruvate to lactate.

Aerobic respiration

A metabolic pathway in mitochondria that provides the most $ATP$ during rest and light-to-moderate exercise.

Excess postexercise oxygen consumption (EPOC)

The extra oxygen required after exercise to restore a muscle to its resting state.

Slow oxidative fibers

Fatigue-resistant fibers specialized for endurance and posture; rich in myoglobin and mitochondria.

Fast glycolytic fibers

Fast, powerful fibers that rely mainly on anaerobic glycolysis and fatigue quickly.

Calmodulin

The calcium-binding regulatory protein used in smooth muscle instead of troponin.

Dense bodies

Anchoring structures in smooth muscle that functionally resemble Z discs.

Unitary smooth muscle

Visceral smooth muscle with gap junctions, spontaneous activity, and coordinated sheetlike contraction.

Multiunit smooth muscle

Smooth muscle with few gap junctions and independent fiber control; found in large airways, large arteries, and the iris.

Myasthenia gravis

An autoimmune disease in which antibodies attack ACh receptors, causing muscle weakness.

Duchenne muscular dystrophy (DMD)

A severe inherited muscle-destroying disease caused by defective dystrophin.

Rigor mortis

Postmortem stiffening caused by a lack of $ATP$, preventing cross bridge detachment.