Skeletal Muscle Contraction Lecture Flashcards

This set of vocabulary flashcards covers the macroscopic and microscopic structures of skeletal muscle, the components of thin and thick filaments, the mechanisms of the sliding filament theory, and the processes involving calcium and ATP during muscle contraction and relaxation.

Multiple Sclerosis (MS)

A condition where degeneration in the CNS disrupts control of muscle function, leading to symptoms like muscle weakness and spasms.

Epimysium

The fibrous covering that surrounds the entire skeletal muscle.

Perimysium

The layer of connective tissue that surrounds a fascicle (a bundle of muscle fibers).

Endomysium

The connective tissue that surrounds an individual muscle cell (fiber).

Sarcomere

The contractile unit of a myofibril located between two Z-lines.

Desmin

A structural protein that scaffolds the Z-line.

Titin

A structural protein that anchors myosin to the Z-line.

α-Actinin

A structural protein that anchors actin to the Z-line.

Myomesin

A structural protein that anchors the tail of myosin to form the M-line.

A band

The area of thick filaments in a sarcomere; its length stays the same during muscle contraction.

H zone

The area of thick filaments alone; its length decreases during muscle contraction.

I band

The area of thin filaments alone; its length decreases during muscle contraction.

G-actin

Individual molecules that form F-actin strands, each possessing one myosin binding site.

Troponin T

The subunit of the troponin complex that binds to tropomyosin.

Troponin I

The subunit of the troponin complex that binds to actin to block myosin interaction.

Troponin C (Tp-C)

The subunit of the troponin complex where $Ca^{2+}$ binds to uncover the binding site of actin.

Myosin II

The individual myosin molecule consisting of two heavy chains (rod, hinge, head) and four light chains (alkaline and regulatory).

T-tubules

Invaginations of the muscle membrane that penetrate deep to deliver action potentials to each myofibril.

Sarcoplasmic reticulum (SR)

An internal membrane system that surrounds myofibrils and stores large amounts of $Ca^{2+}$.

Terminal cisternae (TC)

Enlarged regions of the sarcoplasmic reticulum located near the T-tubules.

Triad

A structure in skeletal muscle appearing at the A-I junction consisting of one T-tubule and two terminal cisternae.

Electromechanical coupling

The skeletal muscle connection between calcium channels on the T-tubule sarcolemma and the sarcoplasmic reticulum via mechanical linkage.

Cocked state

The state where the myosin head is extended at a 90 degree position but not yet attached to actin because active sites are guarded.

Power stroke

A conformational change where the myosin head performs a 45 degree tilt toward the arm of the cross bridge, sliding the filaments.

SERCA

The Calcium ATPase pump responsible for taking $Ca^{2+}$ back up into the sarcoplasmic reticulum during relaxation.

CPK (Creatine phosphokinase)

An enzyme that helps transfer Pi from CP (Creatine Phosphate) to ADP to maintain the ATP pool for contraction, yielding creatinine.