Synapses

Question 1

Does mylination or axon diameter have a greater effect on speed of an impulse?

Answer 1

Myelination.

Question 2

What are the two types of synapse?

Answer 2

Electrical synapses and chemical synapses.

Question 3

What are the differences between the two types of synapse?

Answer 3

1. Electrical- Pre- and post-synaptic neurones are directly connected by gap junctions (2 nM)
2. Electrical- electrical synapses allow local currents from arriving APs to flow directly across the junction, very rapid
3. Chemical- Pre- and post-synaptic neurones are physically separated by synaptic cleft (20-50 nM)
4. Chemical- Presynaptic neurones release chemical transmitter from their axon terminals
5. Chemical- Transmitter binds to receptors on post-synaptic neurons

Question 4

What are axodendritic synapses?

Answer 4

Between the axon of one neurone and the dendrites of another.

Question 5

What are axosomatic synapses?

Answer 5

Between the axon terminals of one and the cell body of another.

Question 6

What are axoaxonal synapses?

Answer 6

1. Between two axons.

2. another synapses can influence transmission by touching the terminal of another synapse

Question 7

What are the two types of neurotransmitter receptors?

Answer 7

Ligand-gated ion channels and G-protein coupled receptors.

Question 8

How are ligand-gated channels opened?

Answer 8

The neurotransmitter binds to the receptor, activated resulting in a conformational change such that it forms an open channel

Question 9

How are G-protein coupled receptors opened?

Answer 9

A neurotransmitter binding to a receptor that contains and G-protein attached that then binds to an effector protein that sends intracellular messages to a voltage-gated ion channel so that it opens.

Question 10

Where does Ach act?

Answer 10

Muscarinic or nicotinic receptors. Muscarinic are G-protein coupled and nicotinic receptors are ion channel receptors.

Question 11

What enzyme synthesises Ach?

Answer 11

Choline acetyl transferase.

Question 12

What enzyme breaks down Ach?

and where?

Answer 12

acetylcholinesterase, in the cleft

Question 13

How is ACh formed?

Answer 13

Choline and acetyl CoA combining.

Question 14

What are the breakdown products of ACh?

Answer 14

Choline and acetic acid.

Question 15

Why are neuromuscular junctions used as a model synapse?

Answer 15

They are easy to experiment with and study - they are simple as there is only one input and one output.

Question 16

What is temporal summation?

Answer 16

Adding together of action potentials that occur at the same synapse but at different times.

Question 17

What is spatial summation?

Answer 17

Adding together of potentials that occur at different sites on the neurone.

Question 18

How are APs generated in the presynaptic neurone

Answer 18

by graded potentials

Question 19

common features of all synapses

Answer 19

presynaptic terminals have vesicles arranged in active zones, with the others dispersed
post membrane is specialised and contains clusters of neurotransmitter receptors and signalling molecules

Question 20

what defines a neurotransmitter

Answer 20

present in axon terminals along with synthetic material for making it
released in response to depolarisation (calcium dependent exocytosis)
specific receptors in post membrane
mechanism for removal

Question 21

where are nicotinic receptors found?

Answer 21

at neuromuscular junctions of skeletal

Question 22

process of release of neurotransmitter by exocytosis

Answer 22

• vesicles docked at active sites
• arrival of AP causes VGCC to open, calcium ions flow in and allow docked vesicles to fuse with the membrane (some completely fuse and some are recycled by endocytosis)

Question 23

a drug might:

Answer 23

increase leakage of neurotransmitter from a vesicle
increase transmitter release into cleft
inhibit transmitter synthesis
block transmitter uptake
bind to receptor on post-synaptic membrane to block neurotransmitter (agonist)
inhibit or stimulate secondary messenger in post synaptic cell

Question 24

glutamate- excitatory or inhibitory?

Answer 24

generates excitatory postsynaptic potential (EPSP)

Question 25

GABA

Answer 25

Y-aminobutyric acid

generates inhibitory postsynaptic potential (IPSP)

Question 26

What is needed for action potentials to occur?

Answer 26

Graded potentials to reach above the threshold.

Question 27

What are graded potentials

Answer 27

1. Graded potentials are activated by synapses from other neurones
2. Above threshold action potentials are generated