Skeletal Muscle Anatomy and Myofilament Structure

A set of flashcards focusing on the vocabulary related to skeletal muscle anatomy and myofilament structure.

Sarcoplasmic Reticulum (SR)

Smooth endoplasmic reticulum tubules surrounding each myofibril, storing and releasing Ca²+.

T Tubules

Tubes formed by the protrusion of the sarcolemma deep into the cell interior at A-I band junctions.

Triad

A structure formed by the terminal cistern of a sarcomere, a T tubule, and the terminal cistern of a neighboring sarcomere.

Light I Band

Regions of a muscle fiber that lack myosin.

Dark A Band

The muscle fiber that contains myosin.

Z Disc

Structural boundary that separates adjacent sarcomeres and anchors thin filaments.

Myofilaments

The contractile proteins within muscle fibers, including thick (myosin) and thin (actin) filaments.

Thick Filaments

Made of myosin that contains 6 polypeptide chains

Thin Filaments

Filaments made of actin, which is intertwined to form two strands.

F-Actin

Strands are made of kidney-shaped 'G actin' (globular) subunits, which have active sites for myosin head attachment

G-Actin

Globular subunits of actin that make up F-actin and have active sites for myosin head attachment.

Tropomyosin

A regulatory protein that binds to actin and blocks the active sites during muscle relaxation.

Troponin

A regulatory protein complex that binds to tropomyosin and controls myosin-actin interactions.

Myosin Head

The part of the myosin molecule that projects outward and can bind to the active sites on actin.

M Line

The center line of a sarcomere that anchors thick filaments.

Elastic (titin) Filaments

Filaments that provide elasticity to muscles by attaching thick filaments to the Z discs.

Sarcomere

The smallest functional unit of muscle fibers containing organized myofilaments.

H Zone

The central region of the A band where there is no overlap between thick and thin filaments.

Fascicles

Bundles of muscle fibers grouped together within a muscle.

Muscle Fibers

Cells that make up the fascicles, containing myofibrils and specialized organelles.

Myofibrils

Densely packed, rodlike contractile elements within muscle fibers.

Endomysium

Thin connective tissue surrounding each muscle fiber.

Perimysium

Connective tissue that surrounds each fascicle within a muscle.

Epimysium

Dense connective tissue that surrounds the entire muscle.

Glycosomes

Organelles that store glycogen for energy during muscle contraction.

Myoglobin

Oxygen-binding protein in muscle cells similar to hemoglobin in blood.