muscular Chapter_009

Muscle tissue

Tissue that enables the body and its parts to move.

Skeletal muscle

Also called striated or voluntary muscle; comprises 40% to 50% of body weight.

Cardiac muscle

Muscle that comprises the bulk of the heart and is characterized by intercalated disks.

Smooth muscle

Also called nonstriated or involuntary muscle; lacks cross stripes and is found in hollow visceral structures.

Striations

Crosswise stripes observed in skeletal muscle tissue under a microscope.

Contractile cells

Muscle fibers that are grouped into bundles and are responsible for muscle contraction.

Sarcomere

The basic functional unit of muscle contraction, separated by Z lines.

Z line

Dark bands that separate sarcomeres in muscle tissue.

Threshold stimulus

The minimum level of stimulus required for a muscle fiber to contract.

All or none response

A muscle fiber contracts completely or not at all upon reaching the threshold stimulus.

Twitch contraction

Quick, jerky responses to a stimulus.

Tetanic contraction

Sustained and steady muscular contractions caused by rapid successive stimuli.

Isotonic contraction

A contraction that produces movement at a joint, with the muscle changing length.

Isometric contraction

Muscle contractions that do not produce movement; the muscle does not shorten.

Prime mover

Muscle whose contraction is mainly responsible for producing a given movement.

Synergist

Muscle whose contractions help the prime mover produce a given movement.

Antagonist

Muscle whose actions oppose the action of a prime mover.

Tonic contraction

A type of muscle contraction that helps maintain body position without producing movement.

Hypertrophy

Increase in muscle size due to regular exercise and increased workload.

Fatigue

Reduced strength of muscle contraction caused by repeated stimulation without adequate rest.

Oxygen debt

Metabolic effort required to restore energy and oxygen reserves after exercise.

Muscle injury

Includes strains and tears resulting from overexertion or trauma.

Muscular dystrophy

A group of genetic disorders characterized by muscle atrophy.

Myasthenia gravis

An autoimmune muscle disease characterized by weakness and chronic fatigue.

Cramps

Painful muscle spasms caused by involuntary twitches.