Lesson Flashcards: Structure of Muscles Biology


A thick filament within a myofibril of a muscle fiber, consisting of long rod-shaped filaments with globular heads that project outward


The cytoplasm of striated muscle cells

Smooth muscle

A type of involuntary muscle tissue that is found in the walls of bodily structures, such as those of the digestive system and arteries

I bands (isotropic bands or light bands)

Regions on a sarcomere where actin and myosin filaments do not overlap, making them appear light in color


A band or bundle of fibrous tissue that can contract and relax to aid movement

Skeletal muscle (striated muscle)

Muscle that is attached to the bones of the skeleton and involved in voluntary movements

Voluntary muscle

Muscle that is under conscious control


A long cylindrical organelle in muscles that is made of protein and specialized for contraction

Sarcoplasmic reticulum

A system of closed saclike membranes involved in the storage of calcium ions in striated (skeletal) muscle cells

Cardiac muscle

A type of involuntary muscle only found in the heart and involved in the regulation of heartbeats

A sarcomere

The functional unit of a myofibril, marked as the distance between two Z lines, which shortens when the muscle contracts


A specialized membrane that surrounds striated muscle fiber cells


A thin filament within a myofibril of a muscle fiber, consisting of two strands twisted around each other

A bands (anisotropic bands or dark bands)

Regions on a sarcomere that contain thick myosin filaments, making them appear dark in color and get particularly darker at their edges as actin and myosin overlap

Z line

A line located at the center of each I band (the distance between two Z lines marks the length of a sarcomere)

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