Skeletal, Cardiac, and Smooth Muscle Anatomy and Physiology Flashcards

A detailed set of vocabulary flashcards defining structural, molecular, and physiological terminology associated with skeletal, cardiac, and smooth muscle tissues.

Excitability

The ability of muscle tissue to respond to a stimulus by changing its electrical membrane potential.

Conductivity

The property of muscle tissue that involves sending an electrical change down the length of the cell membrane.

Contractility

The ability exhibited when myofilaments slide past each other, enabling the muscle cell to cause movement.

Elasticity

The ability of a muscle cell to return to its original length following a lengthening or shortening.

Extensibility

The ability of a muscle cell to be stretched.

Epimysium

A layer of dense irregular connective tissue that wraps around the whole skeletal muscle.

Perimysium

A layer of dense irregular connective tissue wrapping a muscle fascicle that houses blood vessels and nerves.

Endomysium

An delicate layer of areolar connective tissue wrapping an individual muscle fiber that provides electrical insulation, capillary support, and binding of neighboring cells.

Tendon

A cordlike structure of dense regular connective tissue that attaches muscle to bone, skin, or another muscle.

Aponeurosis

A thin, flattened sheet of dense irregular connective tissue that attaches muscle to bone, skin, or another muscle.

Deep fascia

A sheet of dense irregular connective tissue located external to the epimysium that separates different muscles while binding them together.

Superficial fascia

A layer composed of areolar and adipose tissue located superficial to the deep fascia that separates muscles from skin.

Myoblasts

Embryonic cells that fuse together during development to form a multinucleated skeletal muscle fiber.

Satellite cells

Unfused embryonic myoblasts that remain in adult muscle tissue to assist in support and repair of muscle fibers.

Sarcolemma

The plasma membrane of a muscle cell, containing voltage-gated ion channels and transverse T-tubules.

T-tubules (transverse tubules)

Invaginations of the sarcolemma that extend deep into the muscle cell and conduct electrical signals.

Sarcoplasm

The cytoplasm of a muscle cell containing standard organelles, contractile proteins, and specialized structures.

Myofibrils

Longitudinal bundles of myofilaments enclosed within the sarcoplasmic reticulum that make up most of a muscle cell's volume.

Sarcoplasmic reticulum

An internal membrane complex in a muscle fiber similar to smooth endoplasmic reticulum that stores calcium ions.

Terminal cisternae

Blind sacs at the ends of the sarcoplasmic reticulum that serve as reservoirs for calcium ions and flank central T-tubules.

Triad

A structural unit composed of a central T-tubule flanked by two terminal cisternae of the sarcoplasmic reticulum.

Thick filaments

Contractile structures consisting of bundles of myosin protein molecules, each having two heads and two intertwined tails.

Thin filaments

Contractile structures composed primarily of two twisted strands of fibrous actin (F-actin) alongside troponin and tropomyosin.

F-actin

Fibrous actin consisting of a long strand made of hundreds of connected globular actin (G-actin) subunits.

G-actin

Globular actin molecules that each contain a specific binding site for myosin heads during contraction.

Tropomyosin

A twisted, stringlike regulatory protein that covers myosin binding sites on actin in a noncontracting muscle.

Troponin

A globular regulatory protein attached to tropomyosin that, upon binding calcium ($Ca^{2+}$), pulls tropomyosin off the myosin binding sites on actin.

Myoglobin

An oxygen-storing molecule located within muscle cells that facilitates aerobic ATP production.

Motor unit

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

Neuromuscular junction

The specific region, typically near the mid-region of a muscle fiber, where a motor neuron innervates the muscle.

Synaptic knob

The expanded tip of a motor neuron axon housing synaptic vesicles filled with acetylcholine and voltage-gated calcium channels.

Motor end plate

A specialized, folded region of the sarcolemma that contains numerous acetylcholine (ACh) receptors.

Synaptic cleft

A narrow, fluid-filled space separating the synaptic knob from the motor end plate where acetylcholinesterase resides.

Acetylcholinesterase

An enzyme located in the synaptic cleft that breaks down acetylcholine molecules to terminate muscle stimulation.

Resting membrane potential (RMP)

The electrical charge difference across the sarcolemma of an unstimulated muscle cell, which is approximately $-90\,mV$.

Slow oxidative fibers (type I)

Red muscle fibers with half the diameter of other fibers that produce slower, less powerful contractions but offer high fatigue resistance via aerobic ATP production.

Fast oxidative fibers (type IIa)

Intermediate-sized, light red muscle fibers that generate fast and powerful contractions primarily through aerobic respiration.

Fast glycolytic fibers (type IIb)

The largest and white-colored muscle fibers that produce brief, fast, and powerful contractions using anaerobic cellular respiration.

Hypertrophy

An increase in muscle size resulting from resistance exercise due to increased synthesis of contractile proteins, glycogen reserves, and mitochondria.

Atrophy

A decrease in muscle size and function resulting from a lack of exercise or disuse.

Fibrosis

The process during aging or injury where muscle mass is replaced by dense regular connective tissue, leading to decreased flexibility.

Intercalated discs

Specialized cellular junction structures connecting adjacent cardiac muscle fibers that contain desmosomes and gap junctions.

Caveolae

Flasklike invaginations of the sarcolemma in smooth muscle cells that increase surface area in place of transverse tubules.