neuromuscular junction and activation

What is the neuromuscular junction?

The site where a motor neuron communicates with a muscle fiber.

What does a motor neuron do?

Carries an electrical impulse toward muscle fibers.

What is the synaptic terminal?

The end of a neuron that releases neurotransmitter.

What is an action potential?

A rapid electrical change that travels along a cell membrane.

What triggers acetylcholine release at the nerve terminal?

An arriving action potential opens voltage-gated calcium channels.

What happens when calcium enters the nerve terminal?

Vesicles release acetylcholine into the synaptic cleft.

What is acetylcholine (ACh)?

A neurotransmitter released by motor neurons.

What is the synaptic cleft?

The small gap between a motor neuron and a muscle fiber.

What is the motor end plate?

The specialized muscle membrane containing ACh receptors.

What happens when ACh binds to receptors on the motor end plate?

Ion channels open, causing depolarization that can trigger a muscle action potential.

Which ion mainly enters to depolarize the muscle membrane?

Sodium (Na⁺).

Does the muscle membrane become more or less negative during depolarization?

Less negative.

Where does the muscle action potential travel?

Along the sarcolemma and down the T-tubules.

What does acetylcholinesterase (AChE) do?

Breaks down acetylcholine in the synaptic cleft.

What happens to choline after acetylcholine is broken down?

It can be taken back up by the nerve and reused to make ACh.

What is a triad in skeletal muscle?

One T-tubule between two terminal cisternae of the sarcoplasmic reticulum.

What happens when an action potential reaches the triad?

The sarcoplasmic reticulum releases calcium.

Where does released calcium bind to start skeletal muscle contraction?

Troponin.

What exposes the myosin-binding sites on actin?

Calcium binding to troponin shifts tropomyosin.