Unit 9

Sarcomere

The smallest functional unit of a muscle from one Z-line to the next.

Actin

The thin filament in the sarcomere responsible for muscle contraction.

Myosin

The thick filament in the sarcomere that has heads resembling golf clubs and interacts with actin.

Z-line

The boundary of one sarcomere, characterized by a zigzag appearance.

Troponin

A protein that binds with calcium and shifts tropomyosin to allow muscle contraction.

Tropomyosin

A protein that covers actin and prevents contraction until calcium is present.

Creatine Phosphate

A fast-acting energy source for muscles that provides energy for about 10–15 seconds.

Anaerobic Respiration (Glycolysis)

The process that breaks down sugar without oxygen, producing lactic acid and resulting in fatigue.

Aerobic Respiration

A process using oxygen to generate a large amount of ATP, suitable for sustained activities.

Rigor Mortis

The stiffening of muscles after death due to a lack of ATP that prevents myosin from releasing actin.

Atrophy

The wasting away of muscle due to lack of use; 'use it or lose it' principle.

Hypertrophy

The enlargement of muscles due to regular exercise and use.

Smooth Muscle

Involuntary, non-striated muscle found in the walls of hollow organs.

Skeletal Muscle

Voluntary, striated muscle attached to bones and responsible for body movements.

Cardiac Muscle

Involuntary, striated muscle found only in the heart, containing intercalated discs.

Origin

The end of a muscle attached to a stationary bone.

Insertion

The end of a muscle attached to a bone that moves during contraction.

Slow-Twitch (Type I) Muscle Fibers

Red muscle fibers with high endurance, rich in mitochondria; ideal for endurance activities.

Fast-Twitch (Type II) Muscle Fibers

White muscle fibers that are powerful and fast but fatigue quickly; suited for sprinting.

All-or-None Law

The principle stating that a muscle fiber will either contract fully or not at all.

Peristalsis

The rhythmic, wave-like contraction of smooth muscle that moves food through the digestive tract.