4th, 1+

At rest, what blocks myosin from binding to actin?

Tropomyosin.

What happens when calcium (Ca²⁺) binds to troponin?

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

What do myosin cross-bridges do after the binding sites are exposed?

They attach to actin.

What occurs after the myosin head binds to actin?

The power stroke occurs.

What happens during the power stroke?

Actin slides over myosin, causing muscle contraction.

What are the two areas of control for the Sliding Filament Theory?

Myosin activation/deactivation and calcium (Ca²⁺) regulation.

What are the two binding sites on the myosin head?

An actin-binding site and an ATP-binding site.

How many binding sites on the myosin head can be occupied at one time?

Only one.

What happens when the myosin head binds ATP?

ATP is split into ADP and phosphate (Pi), activating the myosin head.

What does the activated myosin head hold until calcium is available?

ADP and phosphate (Pi).

What causes ADP and phosphate to be released from the myosin head?

Myosin binding to actin.

What happens after ADP and phosphate are released?

The power stroke occurs.

After the power stroke, which direction does the myosin head point?

Toward the M-line.

What happens after the power stroke when ATP binds to the myosin head?

Myosin releases actin.

Why does myosin release actin?

Because ATP binds to the myosin head.

What happens after myosin releases actin?

The cycle resets and myosin is reactivated.

Where is calcium (Ca²⁺) stored in a muscle fiber?

In the sarcoplasmic reticulum (SR).

What causes calcium to be released from the sarcoplasmic reticulum?

A stimulus from the nervous system.

Where does communication between a motor neuron and a muscle fiber occur?

At the neuromuscular junction.

What is the neuromuscular junction?

The site where a motor nerve impulse is transmitted from the nerve ending to the skeletal muscle cell membrane.

What is the bouton (axon terminal)?

The end of the motor neuron where voltage-gated calcium channels open.

What happens when voltage-gated calcium channels open in the bouton?

Calcium enters the axon terminal.

What is the synaptic cleft?

The small gap between the neuron and the muscle cell.

What is acetylcholine (ACh)?

A neurotransmitter that carries signals from a neuron to another cell.

What happens in Step 1 of excitation-contraction coupling?

An action potential arrives at the bouton, opening voltage-gated calcium channels and allowing calcium to enter the synaptic terminal.

What happens in Step 2 of excitation-contraction coupling?

Synaptic vesicles fuse with the presynaptic membrane, and ACh is released into the synaptic cleft by exocytosis.

What happens in Step 3 of excitation-contraction coupling?

ACh binds to receptors on the motor end plate (MEP), creating an electrical signal.

Where does the electrical signal travel after reaching the motor end plate?

Across the sarcolemma and down the T-tubules.

What is the importance of the T-tubules?

They carry the electrical signal deep into the muscle fiber, causing calcium to be released so the muscle can contract.

What happens in Step 4 of excitation-contraction coupling?

The signal travels down the T-tubules to the sarcoplasmic reticulum, causing it to release calcium (Ca²⁺).

What is a synaptic vesicle?

It contains acetylcholine, a neurotransmitter.

What is a motor end plate?

A specialized region of the sarcolemma, contains ACh receptors.