Skeletal Muscle Tissue Comprehensive Study Guide

Comprehensive vocabulary flashcards covering the structural hierarchy, microscopic anatomy, molecular machinery, innervation, and physiology of skeletal muscle tissue based on the lecture series.

Fascicle

A bundle of muscle fibers surrounded by perimysium that makes up skeletal muscle tissue. This layer contains the blood vessels and nerves.

Epimysium

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

Perimysium

Dense irregular connective tissue that wraps indivdual fascicles and houses major neurovascular bundles.

Endomysium

Areolar connective tissue that wraps individual fibers to provide electrical insulation, capillary support, and binding of neighboring cells.

Aponeuroses

Thin, flattened sheets of dense irregular connective tissue used for muscle attachment.

Deep Fascia

Connective tissue that separates and binds different muscles together while housing nerves and lymph vessels.

Myoblasts

Embryonic cells that fuse into a single large multinucleated cell to form a muscle fiber.

Satellite cells

Myoblasts that do not fuse during development and remain in the periphery to assist in support and repair.

Sarcolemma

The plasma membrane of a muscle fiber containing T-tubules that conduct electrical signals deep into the cell.

Sarcoplasmic Reticulum (SR)

An internal membrane complex designed for ion storage, acting as the cell's Calcium bank.

Triad

A structural hallmark consisting of one T-tubule flanked by two terminal cisternae (blind sacs of the SR).

Calmodulin and Calquestrin

Storage proteins used by the Sarcoplasmic Reticulum to maintain high internal concentrations of Calcium.

Sarcomere

The functional unit of skeletal muscle contraction, defined as the distance from one Z-disc to the next.

Thick Filaments

Bundles of Myosin molecules, each featuring two intertwined tails and two heads with actin-binding and ATPase sites.

Thin Filaments

Two strands of Actin (G-actin globules) containing myosin binding sites along with the regulatory proteins Tropomyosin and Troponin.

Tropomyosin

The regulatory protein that acts as a blocker by covering the myosin binding sites on actin.

Troponin

The regulatory protein that acts as a lock, binding $Ca^{2+}$ to move the blocker (tropomyosin) out of the way.

Z-Discs

anchor thin filaments; The zigzag boundaries of a single sarcomere that mark the edges of sarcomeres in skeletal muscle.

I-Bands

Light regions of the sarcomere containing only thin filaments; they narrow or disappear during contraction.

A-Band

Dark region, has thin and thick filaments; the length remains constant during contraction.

H-Zone

The center of the A-band containing only thick filaments; it disappears during contraction.

M-Line

The protein attachment site in the exact center of the thick filaments.

Connectin

A protein extending from Z-disc to M-line that provides springlike passive tension and maintains structural integrity.

Dystrophin

A protein that anchors myofibrils to sarcolemma proteins.

Motor Unit

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

Synaptic Knob

The end of a motor neuron that releases ACh into the synaptic cleft to stimulate muscle contraction.

Acetylcholinesterase

The enzyme residing in the synaptic cleft that acts as a molecular off switch by breaking down Acetylcholine.

Motor End Plate

The folded region of the sarcolemma packed with Acetylcholine (ACh) receptors.

Resting Membrane Potential (RMP)

The electrical state of a fiber at rest, typically $-90\,mV$.

End-plate Potential (EPP)

A local electrical change caused by Acetylcholine binding to receptors and opening chemically gated channels.

Depolarization

The phase where voltage-gated $Na^+$ channels open, shifting the membrane potential to $+30\,mV$.

Repolarization

The phase where $Na^+$ channels close and $K^+$ channels open, letting $K^+$ flow out to return the cell to $-90\,mV$.

Power Stroke

The moment of force in the crossbridge cycle where myosin pulls the thin filament toward the M-line.

Myasthenia Gravis

An autoimmune disease where antibodies attack Acetylcholine receptors, leading to decreased stimulation and rapid fatigue.

Myoglobin

A unique protein used strictly for internal oxygen storage within muscle fibers.

Creatinine Phosphate

A high-energy molecule that acts as the cell's emergency cash by donating a phosphate group to instantly replenish ATP.

Synaptic Cleft

The fluid-filled gap where the enzyme Acetylcholinesterase resides.

Crossbridge Cycle (Mechanical Action)

The series of events that occur when myosin heads attach to actin filaments, pull them toward the center of the sarcomere, and detach, leading to muscle contraction.

Sliding Filament Theory

The theory that explains muscle contraction through the sliding motion of actin and myosin filaments past one another, leading to shortening of the sarcomere.

Acetylcholine (ACh)

A neurotransmitter released at the neuromuscular junction that binds to receptors on muscle cells, triggering muscle contraction.

Acetylcholinesterase (AChE)

An enzyme that breaks down acetylcholine in the synaptic cleft, terminating the signal for muscle contraction.