Sarcomere Basics

Sarcomere

Smallest functional unit of a muscle fiber;

Z-line

Boundary of a sarcomere;

Actin

Thin filament;

Myosin

Thick filament;

A band

Length of the myosin filament;

I band

Region containing only actin;

H zone

Region containing only myosin;

Sarcomere contraction

Z-lines move closer together;

Nerve impulse

Triggers muscle contraction;

Calcium release

Allows contraction to occur;

Troponin

Protein calcium binds to;

Tropomyosin

Moves to expose actin binding sites;

Cross-bridges

Form when myosin binds to actin;

Power stroke

Myosin pulls actin inward using ATP;

Sarcomere shortening

Actin slides past myosin;

ATP

Provides energy for the power stroke and detaches myosin from actin;

Calcium

Exposes binding sites on actin;

No ATP

Muscle remains contracted (rigor mortis);

No calcium

Muscle cannot contract;

Muscle relaxation

Calcium is pumped back into the sarcoplasmic reticulum;