Lecture A

Muscular System

The system responsible for all types of body movement.

Three basic muscle types

Skeletal muscle, cardiac muscle, and smooth muscle.

Skeletal muscle

A type of muscle that is attached to bones, has visible banding, and is subject to conscious control.

Cardiac muscle

A type of muscle found only in the heart, characterized by striations and branching cells.

Smooth muscle

A type of muscle found mainly in the walls of hollow organs, lacking striations and having spindle-shaped cells.

Sarcomere

The contractile unit of a muscle fiber, composed of myofilaments.

Myosin filaments

Thick filaments in a sarcomere composed of the protein myosin, responsible for muscle contraction.

Actin filaments

Thin filaments in a sarcomere composed of the protein actin, anchored to the Z disc.

Sarcoplasmic reticulum (SR)

Specialized smooth ER surrounding myofibrils, responsible for storing and releasing calcium.

Excitability

The ability of muscle cells to receive and respond to a stimulus.

Contractility

The ability of muscle cells to shorten when stimulated.

Neuromuscular junction

The association site of the axon terminal of a motor neuron and a muscle cell.

Synaptic cleft

The gap between the nerve and muscle at the neuromuscular junction.

Sliding Filament Theory

The theory that muscle contraction occurs when myosin heads attach to binding sites on actin filaments and pull them toward the center of the sarcomere, resulting in muscle shortening.