Question

Place the following events in synaptic transmission at a cholinergic synapse in order:

Answer 1

I believe the correct order is:

D - A nerve signal arrives at an axon terminal;

B - Voltage gated calcium channels open and calcium enters the cell;

C - ACh is released and diffuses across the axon terminal;

E - Ligand gated sodium channels open and sodium enters the cell.

A - A postsynaptic potential is produced;

Explanation:

The dendrites of the presynaptic neurons receive a signal. The signal stimulates the nucleus of the presynaptic neuron to produce an electrical signal that is managed by the axon hillock. the axon hillock again manages and transmits the nerve impulse into the axon towards the axon terminal. The signal is transmitted via saltatory conduction on myelinated axons for faster communication. When the nerve impulse reaches the axon terminal, it causes opening of voltage gated calcium ion channels. This will cause an influx of calcium ions into the presynaptic axon terminal. The influx of calcium ions then stimulates the synaptic vessicles in the presynaptic membrane that contain the neurotransmitter acetylcholine (ACh) to move towards the presynaptic membrane. They then fuse with the membrane and open up releasing all their acetylcholine into the synaptic cleft (space between presynaptic membrane and post synaptic membrane). The ACh will bind to ligand ion channels on post synaptic membrane causing opening of sodium channels and there is an influx of sodium inside the post synaptic membrane producing a membrane potential. The voltage gated calcium ion channels in the presynaptic membrane will then close and no more ACh is released. The cells then return to rest. The acetylcholine in the postsynaptic neuron is either broken down by the enzyme acetylcholinesterase into metabolites that are used by the cell or they are removed as waste into the surrounding glial cells called astrocytes that nourish neurons. They (ACh) also can be stored for future use by the post synaptic neuron.

Level: High School

Subject: Biology

Topic: The nervous system