Synaptic Transmission

Question 1

What is a synapse?

Answer 1

A specialised junction where an axon terminal contacts another neuron or cell type

Question 2

What are the two types of synapse?

Answer 2

Electrical
Chemical

Question 3

What are the features of an electrical synapse?

Answer 3

Linked by gap junctions
These are formed by hemichannels (connexon)
Ionic current in presynaptic membrane flows passively into postsynaptic
Current can pass in both directions (non-rectifying synapse)
OR pass in one direction (rectifying synapse)
Rapid and allow ATP and 2nd messenger exchange
Synchronised activity among neuron populations

Question 4

What is a hemichannel/ connexon?

Answer 4

It is composed of 6 connexin subunits
Connexins rotate to open a pore of the gap junction channel

Question 5

What are the requirements for chemical synaptic transmission?

Answer 5

Mechanisms for:
Synthesising and packing neurotransmitters into vesicles
Causing vesicles to spill contents into cleft after an AP
Producing an electrical/ biochemical response to neurotransmitter in postsynaptic neuron
Removing transmitter from cleft
Must be very rapid!

Question 6

What is the active zone of a chemical synapse?

Answer 6

Presynaptic site of neurotransmitter release
All vesicles wait ready to be activated

Question 7

What is the postsynaptic density of chemical synapses?

Answer 7

The area of the postsynaptic neuron that contains the receptors to translate the extracellular signal into an intracellular signal

Question 8

What ways can synapses be categorised by?

Answer 8

• Connectivity
  Which part of the neuron is postsynaptic to the axon terminal
• synapse Anatomy
  There size and shape

Question 9

What are the 4 types of synapses?

Answer 9

Axodendritic/ Axospinous
Axosomatic
Axoaxonic
Dendrodendritic

Question 10

What are the connections of a axodendritic synapse?

Answer 10

Postsynaptic membrane is on the dendrite of another neuron
30% of neurons in CNS

Question 11

What are the connections of an axosomatic synapse?

Answer 11

Postsynaptic membrane is on the cell body of another neuron
6% of neurons in CNS

Question 12

What are the connections of an axoaxonic synapse?

Answer 12

Postsynaptic membrane is on the axon of another neuron
Rare

Question 13

What are the connections of a dendrodentritic synapse?

Answer 13

Dendrites synapse with each other
Very rare

Question 14

Describe Grays type l synapse

Answer 14

Postsynaptic membrane is thicker than the presynaptic membrane
Thought to be due to more receptors on the post
Usually excitatory

Question 15

Describe Grays type ll synapse

Answer 15

Postsynaptic and presynaptic membranes similar thicknesses
Usually inhibitory

Question 16

What are neurotransmitters?

Answer 16

Molecules released by the presynaptic neuron
Means of communication at a chemical synapse

Question 17

What determines whether a signal is excitatory or inhibitory?

Answer 17

Neurotransmitters are specific to the receptors they bind to
One receptors will let in positive charge (Na+)
Another will let in negative charge (Cl-)

Question 18

Name the different small molecule neurotransmitters that can be used

Answer 18

Glutamate
GABA
Acetylcholine
Dopamine
Noradrenalin
Adrenaline
Histamine
Serotonin

Question 19

Name the purine/ neuro peptides that are used as neurotransmitters

Answer 19

ATP - cotransmitter (purine)
Substance P ]
Metenkephalin ] Neuropeptides
Opioids ]

Question 20

What drugs use the GABAa receptor as their site of action?

Answer 20

Barbiturates
Benzodiazepines
Alcohol

Question 21

What are the two methods of action for G protein coupled channels?

Answer 21

1) opening ion channels
2) activating enzymes that synthesise second messenger molecules

Question 22

What are self regulating neurotransmitters?

Answer 22

At some synapses transmitters activate receptors on the terminal from which they are released as well as receptors on the postsynaptic membrane

Question 23

What are the steps once the transmitter has left the presynaptic membrane?

Answer 23

Diffusion across the cleft
Enzyme degradation in the synapse
Presynaptic re-uptake followed by degradation or recycling
Uptake by glial cells
Uptake by postsynaptic neuron
Desensitisation

Question 24

What are the two types of summation?

Answer 24

Spatial - occurs when stimuli are applied at the same time, but in different areas, with a cumulative effect upon membrane potential. Spatial summation uses multiple synapses acting simultaneously.
Temporal - occurs when multiple action potential signals fire down the axon hillock of a single neuron to be received by the synapse of another neuron. The impulses reach the postsynaptic neuron one at a time, accumulating enough voltage to produce an effective charge.

Question 25

What is shunting inhibition?

Answer 25

It is the inward movement of Cl- anions that will negate the flow of positive ions