Week 2 (Myofiber (Structure-Function Relationships: Membranes, PLasmalemma, T-Tubules &SR)

Sarcolemma

Membrane that covers myofiber, differing from plasmalemma.

Basement membrane

Outer connective layer of sarcolemma that connects to endomysium and serves as scaffolding for muscle development.

Plasmalemma

Inner layer of the sarcolemma, also known as the plasma membrane, composed of phospholipids, proteins, and cholesterol.

Phospholipids

Primary components of plasmalemma that create a lipid bilayer.

Dystrophin

Protein complex that, when missing or mutated, causes muscle degeneration, weakness, and dysfunction.

T-Tubules

Extensions of plasmalemma that conduct action potentials into the myofiber. Forms tube that acts like a membrane tunnel. 2 T-Tubules per sarcomere

Sarcoplasmic Reticulum (SR)

Membrane system that wraps around each myofibril and stores calcium for muscle activation.

Function: Stores, releases, & re-sequesters intracellular calcium (Ca2+) that is used to activate the force-generating proteins (actin & myosin)

Triad

Structure comprising one T-Tubule sandwiched between two opposing SR, critical for muscle activation.

Cytosol

Aqueous portion inside of a cell, also known as intracellular fluid.

Sarcoplasm

Cytoplasm of a myofiber, including fluid, enzymes, and organelles, excluding nuclei.

Troponin

Protein that binds calcium on the thin filament to help regulate force production.

Tropomyosin

Protein on the thin filament that blocks interaction necessary for force production.

Dihydropyridine receptor (DHPR)

Protein in the T-Tubule membrane that activates Ryanodine Receptor (RyR1) in SR upon receiving action potential.