Skeletal, Smooth, and Cardiac Muscle Structure and Function

Comprehensive vocabulary flashcards covering the structure, physiology, and types of muscle tissue (skeletal, smooth, and cardiac) as described in the Chapter 9 lecture outline.

Endomysium

A thin, delicate layer of connective tissue (CT) that wraps each individual muscle fiber (cell).

Fascicles

Groups of bundled muscle fibers.

Perimysium

A second layer of connective tissue made of collagen that wraps each fascicle.

Epimysium

A layer of dense, fibrous connective tissue that covers each skeletal muscle (formed by bundles of fascicles).

Deep fascia

A very tough fibrous layer of connective tissue that covers each skeletal muscle and may extend into a tendon or aponeurosis to attach muscle to bone, cartilage, or other muscle.

Myofibrils

Structures that compose each muscle fiber, made up of thick (myosin) and thin (actin) protein filaments.

A-Band

The dark area of striations caused by the overlapping of thick and thin filaments.

I-Band

The light area of striations composed of thin filaments alone.

Sarcomeres

Units that divide the length of each myofibril and meet at an area called the Z-line.

Myosin heads (cross bridges)

Globular heads on thick filaments that interact with active sites on thin filaments to form linkages.

Tropomyosin

A rod-shaped protein that spirals around the actin backbone to stabilize it and block myosin binding sites in a resting muscle cell.

Troponin

A complex of three polypeptides that binds to actin, tropomyosin, and calcium ions to help control actin's interaction with myosin.

Sarcoplasmic reticulum (SR)

A network of membranous channels surrounding each myofibril that stores high concentrations of calcium ions.

Transverse tubules (TT)

Membranous channels continuous with the sarcolemma that extend deep into the muscle cell and are filled with extracellular fluid.

Triad

A structure formed by one Transverse Tubule (TT) running between two enlarged portions of the SR called cisternae.

Neuromuscular Junction (NMJ)

The site where a motor nerve ending and a skeletal muscle fiber meet; also known as a synapse or synaptic cleft.

Acetylcholine (ACh)

The specific neurotransmitter released from a motor nerve ending that causes stimulation of the muscle fiber sarcolemma.

Motor Unit

Consists of one motor neuron and all the skeletal muscle fibers it stimulates.

Motor End Plate

The specific part of the muscle fiber's sarcolemma located directly beneath the Neuromuscular Junction (NMJ).

Excitation-Contraction Coupling

The sequence where a muscle impulse triggers the SR to release calcium ions, which bind to troponin and expose myosin binding sites on actin.

Sliding Filament Model

The theory stating muscle contraction involves thin filaments (actin) sliding past thick filaments (myosin), decreasing the distance between Z-lines.

Acetylcholinesterase

An enzyme present in the NMJ that immediately destroys acetylcholine to prevent continuous muscle contraction.

Creatine Phosphate (CP)

A molecule stored in muscle that couples with ADP to regenerate ATP, providing about $10\,\text{seconds}$ of energy.

Oxygen Debt

The amount of oxygen needed to convert lactic acid to glucose, resynthesize ATP and CP, and restore O2 levels to pre-exercise states.

Muscle Fatigue

A physiological inability to contract, often resulting from an ATP deficit and the accumulation of lactic acid which decreases pH.

Threshold Stimulus

The minimal strength of stimulation required to cause contraction; in skeletal muscle fibers, this is a depolarization of $+30\,mV$ (from $-100\,mV$ to $-70\,mV$).

Twitch

A single contraction lasting a fraction of a second followed by relaxation.

Latent period

The delay between the application of a stimulus and the beginning of a muscle contraction.

Staircase Effect (treppe)

A phenomenon where a series of stimuli result in successive contractions that increase slightly in strength due to excess calcium and muscle warming.

Summation

The process where the force of individual twitches combines because the muscle cannot completely relax between successive stimuli.

Tetanic contraction

A sustained contraction that lacks even slight relaxation.

Muscle tone

A certain amount of sustained contraction occurring in fibers even when the muscle is at rest; important for maintaining posture.

Isotonic contraction

A type of contraction where the muscle shortens and its attachments move.

Isometric contraction

A type of contraction where the muscle becomes taut but the attachments do not move.

Slow-Twitch Fibers (red fibers)

Fibers containing myoglobin and many mitochondria that generate ATP quickly enough to contract for long periods without fatiguing.

Fast-Twitch Fibers (white fibers)

Fibers with less myoglobin and fewer mitochondria that contract rapidly but fatigue easily due to lactic acid accumulation.

Multiunit smooth muscle

A type of smooth muscle found in the irises and blood vessel walls that exhibits rapid and vigorous contraction.

Visceral smooth muscle

Smooth muscle found in hollow organ walls that displays rhythmicity and peristalsis (wave-like motion).

Intercalated discs

Specialized cell junctions in cardiac muscle that contain gap junctions and join cells end-to-end.

Syncytium

The functional term for the all-or-nothing, coordinated contraction of cardiac muscle tissue.