Synapses and Neurotransmission

Question 1

What is signal transduction?

Answer 1

How the messages between cells are converted into biochemical signals.

Question 2

What is the reticular doctrine?

Answer 2

Neurons are hard-wired together to form a continuous network.

Question 3

What is the neuron doctrine?

Answer 3

The neuron is the elementary functional unit of the brain, which communicates through chemicals and not continuity.

Question 4

What is synaptic transmission?

Answer 4

The process of information transfer between neurons.

Question 5

Why is there no measurable delay in signal propagation across an electrical synapse?

Answer 5

Depolarisation spreads very quickly across gap junctions, which couples together neurons.

Question 6

Does information flow in one or both directions at an electrical synapse?

Answer 6

Both directions (bidirectional).

Question 7

Does information flow in one or both directions at a chemical synapse?

Answer 7

One direction (unidirectional).

Question 8

Describe the process of neurotransmitter synthesis in the axon terminal.

Answer 8

1. The precursor molecule interacts with an enzyme in the cytosol at the terminal region and is converted into neurotransmitter.
2. Neurotransmitter is packaged and stored in synaptic vesicles.

Question 9

Describe the process of neurotransmitter synthesis in the soma.

Answer 9

1. Precursor peptide is synthesised in the RER.
2. In the Golgi apparatus, the new peptide is sorted, activated and packaged.
3. Secretory granules “bud” away from the Golgi apparatus.
4. The granules are transported to the terminal via axoplasmic transport.

Question 10

Which molecules traffics vesicles to the active zone?

Answer 10

Actin.

Question 11

How do SNAREs facilitate fusion and exocytosis of a vesicle?

Answer 11

1. An action potential causes an influx of calcium ions.
2. Calcium binds to synaptotagmin (a calcium sensor).
3. This stimulates the v- and t-SNAREs to combine into an alpha-helical-shaped complex.
4. The SNARE complex forces the two membranes together (fusion).
5. It then pulls the membranes apart to spill the vesicle contents into the synaptic cleft (exocytosis).

Question 12

How do neurotoxins inhibit exocytosis?

Answer 12

Neurotoxins interfere with the SNARE proteins that mediate vesicle fusion with the presynaptic membrane, thereby inhibiting exocytosis.