Relaxed

Contracting

None of the above

Fully Contracted

Muscle cell

Cardiac Muscle

Motor Neuron

Gland

Calcium

Oxygen

Glucose

ATP

ATPase

Actin

Myosin

Sarcoplasmic reticulum

myofibril

fascicle

motor unit

sarcomere

sarcolemma

sarcoplasm

sarcoplasmic reticulum

transverse tubules

troponin-tropomyosin

sarcomere

sarcolemma

sarcoplasmic reticulum

Neither thin nor thick filaments change in size, although the area of overlap between them increases.

Iron and fats bound to actin play a critical role in muscle cell contraction and relaxation.

Thick filaments stretch, whereas thin filaments stay the same length.

A typical muscle fiber at rest contains enough ATP for millions of contractions.

Thin filaments stretch, whereas thick filaments stay the same length.

It prevents backflow of blood into the atria

It delays the electrical impulse to allow ventricular filling

It serves as the primary pacemaker, initiating the heartbeat

It directly stimulates ventricular contraction

Skeletal muscle does not require calcium for filament sliding, but cardiac muscle does

Only skeletal muscle uses actin and myosin for contraction

Cardiac muscle contraction is involuntary, while skeletal muscle contraction is voluntary

The sliding filament mechanism occurs only in cardiac muscle, not in skeletal muscle