Molecular physiology of muscle contraction

In the image, what are the small purple dots (D in the legend)?

• Calcium Ions

• Sodium Ions

• Neurotransmitter

• Acetylcholine

What happens that causes calcium channels to open?

• Action Potential on motor neuron

• Depolarization of muscle fiber

• Influx of sodium ions

• Neurotransmitter moves out of the nerve cell.

Answer explanation

When the action potential, (wave of electricity) moves to the end of the nerve cell, this causes the calcium ion channels to change shape and open like doors.

This allows calcium to flow into the cell.

When calcium channels open, what type of transport moves calcium ions (Ca²⁺) into the nerve ending?

• Simple Diffusion

• Facilitated Diffusion

• Active Transport

• Osmosis

Answer explanation

Calcium ions in this case move from a high concentration (outside the nerve ending) to a lower concentration (inside the nerve ending).

This process does not require energy and so must be a form of diffusion.

Because calcium ions cannot cross the membrane and need a channel to move through, it is facilitated diffusion.

What is the effect of calcium ions moving into the nerve ending?

• Sodium ion channels open

• The nerve cell depolarizes

• Synaptic vesicles move to the membrane of the nerve ending.

• The muscle cell depolarizes.

Answer explanation

The effect of calcium ions flowing into the nerve ending is to stimulate synaptic vesicles to move to the membrane of the nerve and release neurotransmitter.

What is the space between the motor nerve and the muscle called?

• Neuromuscular Junction

• Synaptic Cleft

• Chemical Gap

• Motor End Plate

Answer explanation

The space between the neuron and the muscle is called the synaptic cleft.

The neuromuscular junction refers the meeting of the nerve and the muscle, but includes the nerve ending and the muscle.

The motor end plate is specifically talking about the area of the muscle receiving neurotransmitter.

What is structure B in the image?

• Neurotransmitter

• Acetylcholine

• Acetylcholinesterase

• Sodium ions (Na⁺)

Answer explanation

The particles leaving the nerve and moving toward the muscle are chemical signals called neurotransmitter.

Though there are several neurotransmitters in the human body, the neurotransmitter that communicates with muscle is specifically Acetylcholine.

What is structure B in the image?

• Neurotransmitter

• Acetylcholine

• Acetylcholinesterase

• Sodium ions (Na⁺)

Answer explanation

The particles leaving the nerve and moving toward the muscle are chemical signals called neurotransmitter.

Though there are several neurotransmitters in the human body, the neurotransmitter that communicates with muscle is specifically Acetylcholine.

In the image, which structure is acetylcholine going to directly affect?

• Structure C

• Acetylcholine Receptors

• Sodium ion channels

• Sodium ions (Na⁺)

Answer explanation

Acetylcholine will bind to structure C in the image.

Structure C is an acetylcholine receptor, in this case it is also a sodium ion channel.

Acetylcholine acts like a key if the protein were a locked door.

When acetylcholine binds to the receptor, it opens a tunnel allowing sodium ions through.

Which transport process allows acetylcholine to travel across the synaptic cleft?

• Simple Diffusion

• Facilitated Diffusion

• Active Transport

• Osmosis

Answer explanation

Acetylcholine is moving from high to low concentration, so this is a form of diffusion.

Since there is no membrane to cross and there are no proteins to go through this is simple difusion.

What is the effect of sodium ions flowing into the muscle cell?

• the muscle cell is depolarized

• A wave of electricity moves along the muscle cell.

• calcium ions move out of the muscle cell

• acetylcholine receptors close.

Answer explanation

When sodium ions (Na⁺) move into the muscle cell they create a wave of electricity on the muscle cell.

The process of creating this wave of electricity is called depolarization.