6.2.2 Synaptic Transmission

Question 1

Structure of a synapse

Answer 1

Pre-synaptic neurone:
-axon
-vesicles contain neurotransmitter
-voltage gates Ca channels
-axon terminal

Synaptic cleft

Post-synaptic neurone:
-receptor and Na ion channel

Question 2

What are cholinergic synapses

Answer 2

Synapses that use acetylcholine (ACh) as a neurotransmitter

Question 3

Transmission across a cholinergic synapse

Answer 3

Pre-synaptic:
-depolarisation of pre causes opening of voltage gated Ca channels, Ca diffuse in
-causing vesicles containing ACh fuse with pre membrane releasing ACh into cleft via exocytosis

Post:
-ACh diffuses across cleft and binds to specific receptors on post
-causing Na channels to open, Na diffuses into post causing depolarisation.
-if threshold is met action potential is initiated

Question 4

What happens to ACh after transmission

Answer 4

It’s hydrolysed to acetylcholinesterase

Products are absorbed by pre

Stops over stimulation

Question 5

How are synapses unidirectional

Answer 5

Neurotransmitter is only released form the pre

Receptors are only on post

Question 6

What is summation of synapses

Answer 6

Addition of a number of impulses converging on a single post neurone

Causing rapid build up of neurotransmitter

So threshold is more likely to be met to generate an action potential

Question 7

Spatial summation

Answer 7

Many pre share 1 post

Collectivley release sufficient neurotransmitter to reach threshold to release an action potential

Question 8

Temporal summation

Answer 8

1 pre released neurotransmitter many times over a short time

Sufficient neurotransmitter is met to reach threshold to trigger an action potential

Question 9

Inhibition by inhibitory synapses

Answer 9

Inhibitory neurotransmitter hyperpolarise post as:
-Cl- channels open so Cl- diffuse out
-K+ channels open so K diffuses out

Inside of axon has a more negative charge than outside (below resting potential)

More Na required for depolarisation

Reduces likelihood of threshold being met

Question 10

Structure of a neuromuscular junction

Answer 10

Very simmilar to neurons except:
-receptors are only muscle fibre sarcolemma instead of post.
-muscle fibres form clefts to store enzymes (AChsterase) to break down neurotransmitter

Question 11

Compare transmission form cholinergic and neuromuscular

Answer 11

Chol:
-neurone to neurone
-transmitters can be inhibitory or excitatory
-action potential may be imitated by post

Neuro:
-motor neurone to muscle
-always excitatory
-action potential propagates along sarcolemma down T tubes

Question 12

Effect of drugs on synapses

Answer 12

Some stimulate - more action potentials:
-simmilar shape to neurotransmitters
-stimulates release

Some inhibit -less action potentials:
-inhibit release of neurotransmitter
-Ca ion channels don’t open
-block receptors by mimicking shape of neurotransmitter