Muscle Anatomy

Epimysium

The connective tissue that wraps around the whole muscle organ.

Perimysium

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

Endomysium

The connective tissue that wraps around an individual muscle fiber.

Sarcolemma

The cell membrane of a muscle fiber.

Myofibril

Rod-like structures inside a muscle fiber that contain myofilaments.

Myofilaments

The actual proteins responsible for muscle contraction, mainly actin and myosin.

Skeletal Muscle

Muscle attached to bones, under voluntary control, striated in appearance, and multi-nucleated.

Smooth Muscle

Muscle located in the walls of hollow organs, under involuntary control, with no striations, and uni-nucleated.

Cardiac Muscle

Muscle found in the heart, under involuntary control, striated and branched, and uni-nucleated.

Sarcomere

The contractile unit of muscle fibers, defined as the segment from one Z-line to the next.

H-Zone

The area in the sarcomere where there is only myosin and no overlapping actin.

I-Band

The area in a sarcomere near the Z-lines that contains only actin.

A-band

The area in the sarcomere that contains the length of the myosin filaments.

M-line

The line located in the center of the sarcomere.

Z-line

The line that demarcates the ends of a sarcomere.

Sliding Filament Theory

The theory that describes how myosin heads pull actin filaments during muscle contraction, causing the H-zone and I-band to shrink.