Nerve Junctions

Question 1

What is a neurotransmitter?

Answer 1

chemical that diffuses across cleft of synapse to transmit signal to post synaptic neurone

Question 2

What is a synapse?

Answer 2

junction between 2 or more neurones

Question 3

What are cholinergic synapses?

Answer 3

ones which use acetylcholine as their transmitter substance

Question 4

What is the synaptic knob?

Answer 4

swelling at end of pre synaptic neurone

Question 5

Approximately how wide is the synaptic cleft?

Answer 5

20nm wide

Question 6

What does the presynaptic action potential cause?

Answer 6

the release of neurotransmitter which diffuses across gap to generate new action potential in post synaptic neurone

Question 7

What specialised features does the synaptic knob contain?

Answer 7

many mitochondria (active process using ATP occurs), lots of SER, vesicles of acetylcholine, voltage gated calcium ion channels in membrane

Question 8

How is the post synaptic membrane specialised?

Answer 8

contains specialised Na+ channels that can respond to neurotransmitters, channels are 5 polypeptide mols, 2 mols are receptor with complementary shape to acetylcholine, when it binds the channels open

Question 9

What happens in the synaptic knob before the neurotransmitter can be released?

Answer 9

action potential arrives, voltage gates calcium ion channels open, Ca2+ diffuse in, cause synaptic vesicles to move and fuse with presynaptic membrane

Question 10

How is acetylcholine released? What does it do once released?

Answer 10

By exocytosis, mols diffuse across cleft, bind to receptor sites in post synaptic neurone, Na+ channels open

Question 11

What happens when the sodium ion channels open on the post synaptic membrane?

Answer 11

Na+ diffuse across membrane into post synaptic neurone, generator potential or excitatory postsynaptic potential (EPSP) created, if sufficient generator potentials combine then threshold potential reached = new action potential

Question 12

What is acetylcholinesterase?

Answer 12

enzyme in synaptic cleft, hydrolyses acetylcholine to ethanoic acid and choline

Question 13

What does the breakdown of acetylcholine do?

Answer 13

stops the transmission of signals so synapse does not continue to produce action potentials in the post synaptic neurone

Question 14

What happens to the ethanoic acid and choline?

Answer 14

recycled, re enter synaptic knob by diffusion and recombined into acetylcholine using ATP, stored in vesicles for future use