Topic 4 - synapses and neurotransmitters

Question 1

How is an electrical synapse formed?

Answer 1

• formed from gap junctions that allow current to pass directly between neurons.
• have fast communication
• synchronising neurons

Question 2

What was the first evidence of a chemical synapse?

Answer 2

Using two isolated frog hearts that nerves release a chemical which slow the heartbeat. This was done by…

1. Stimulate vagus
2. Heart rate slows
3. Remove fluid sample
4. Add fluid to recipient heart
5. Heart rate also slows in this heart!

Question 3

What are the steps in a chemical synaptic transmission?

Answer 3

1. Package neurotransmitters in vesicles, put them at the pre-synaptic terminal
2. Action potential arrives  voltage-gated Ca2+ channels open
3. Ca2+ influx  vesicles fuse to membrane, neurotransmitters released
   (after fusing, vesicle is taken up by again by endocytosis)
4. Neurotransmitters diffuse across the synaptic cleft, activate receptors on the postsynaptic cell  further signaling
5. Neurotransmitters are removed from the cleft

• They diffuse away
• Actively taken up by transporters for recycling
• They are destroyed in the synaptic cleft by enzymes

Question 4

What are the 2 types of post synaptic receptors that neurotransmitters can bind to?

Answer 4

1. Ligand-gates ion channel - ionotropic receptors -> directly depolarise or hyperpolarise the post synaptic cell.
2. G-protein coupled receptors - metabotropic receptors -> more complex effects.

The neurotransmitter itself does NOT enter the post synaptic cell.

Question 5

What is the differene between electrical and chemical synapses?

Answer 5

ELECTRICAL:

• synapses pass in both directions
• signals are passed directly
• fast (<0.3 ms)

CHEMICAL:

• synapses pass in one direction
• signals can be transformed
• slower (0.3-0.5 ms)

both are ‘plastic’

Question 6

What is the neuromuscular junction and how does the NMJ achieve efficient transmission?

Answer 6

NMJ uses acetylcholine

Has active zones and juntional folds that are precisely aligned.

Question 7

What is the criteria for a neurotransmitter?

Answer 7

• be present in presynaptic terminals
• be released in response to stimulation
• act on postsynpatic neuron
• blocking the neuron should stop synaptic transmission.

Question 8

Name 3 types of neurotransmitters.

Answer 8

1. Amino acids - Glu, GABA and GLY
2. Amines
3. Peptides

Question 9

Compare amino acids and amines to peptides….

Answer 9

AMINO ACIDS AND AMINES:

• small molecules
• stored in synaptic vesicles
• bind ligand gated ion channels or g-protein coupled receptors

PEPTIDES:

• large molecules
• stored in secretory granules
• Only bind to g-protein coupled receptors

Question 10

What is Glutamate?

Answer 10

An amino acid - a common excitatory transmitter