💪 Set 2: Cross-Bridge Cycle, Sarcomere & Motor Units

What does calcium bind to?

Troponin.

What happens when calcium binds troponin?

Tropomyosin moves away, exposing myosin-binding sites on actin.

What blocks myosin-binding sites when a muscle is relaxed?

Tropomyosin.

What forms the cross-bridge?

Myosin binds to actin.

What is the power stroke?

Myosin pulls actin toward the center of the sarcomere.

What causes myosin to detach from actin?

ATP binding to myosin.

What re-cocks the myosin head?

ATP hydrolysis to ADP + Pi.

Why does rigor mortis occur?

No ATP is available, so myosin cannot detach from actin.

What are the Z lines?

The ends of a sarcomere.

What is the M line?

The middle of a sarcomere.

Where is only actin found?

I band.

Where is only myosin found?

H zone.

What is the A band?

The entire length of the myosin filament, including overlap with actin.

Which band does NOT change length during contraction?

A band.

What happens to the I band during contraction?

It shortens.

What happens to the H zone during contraction?

It shortens.

What happens to the sarcomere during contraction?

It shortens.

What is a motor unit?

One motor neuron and all the muscle fibers it innervates.

Small motor units are used for what?

Precision movements.

Large motor units are used for what?

Powerful movements.

What is an isotonic contraction?

A contraction in which the muscle changes length while maintaining relatively constant tension.

What is a concentric contraction?

The muscle shortens while contracting.

What is an eccentric contraction?

The muscle lengthens while contracting.

What is an isometric contraction?

The muscle produces force without changing length.