module 5 - 13.5 synapses

Question 1

what is the synaptic cleft?

Answer 1

a gap that separates the axon of one neurone from the dendrite of the next neurone

Question 2

what is involved in the structure of a synapse?

Answer 2

• synaptic cleft
• presynaptic neurone
• postsynaptic neurone
• synaptic knob
• synaptic vesicles
• neurotransmitter receptors
• voltage gated calcium ion channel proteins

Question 3

what is the presynaptic neurone?

Answer 3

action potential (impulse) arrives at the synapse along its neurone

Question 4

what is the postsynaptic neurone?

Answer 4

neurone that receives the neurotransmitter

Question 5

what is the synaptic knob?

Answer 5

swollen end of the presynaptic neurone, with many mitochondria and extensive ER to synthesise neurotransmitters

Question 6

what are the synaptic vesicles?

Answer 6

contain neurotransmitter that fuses with presynaptic membrane and diffuses into synaptic cleft

Question 7

what are neurotransmitters that are sodium ion channel proteins?

Answer 7

specific protein molecules in postsynaptic plasma membrane where the transmitter will bind too

Question 8

what does polarised mean?

Answer 8

more positive charge on outside than inside

Question 9

what does depolarised mean?

Answer 9

more negative charge on outside than inside 1 (Na+ goes into cell)

Question 10

what does repolarisation mean?

Answer 10

more positive goes out, more negative on inside (K+ goes out of cell)

Question 11

what is an excitatory neurotransmitter/what does it do?

Answer 11

• cross synaptic cleft
• cause localised depolarisation of postsynaptic membrane, if this reaches threshold potential then action potential is initiated
• common in CNS and neurotransmitter junctions
• e.g. acetylcholine

Question 12

what is an inhibitory neurotransmitter/what does it do?

Answer 12

• cross synaptic cleft
• cause hyperpolarisation of the postsynaptic membrane
• prevent action potentials being initiated
• e.g. GABA

Question 13

what is an electrical synapse?

Answer 13

• the place where there is a direct physical connection between pre and postsynaptic neurone
• connection takes the form of a channel (gap junction) that allows current int eh form of ions to flow directly from one cell to another
• allows very fast cell signalling

Question 14

what is an example of an electrical synapse?

Answer 14

transmission of the depolarising current from cell to cell, across chambers of the heart, so cells contract in unison

Question 15

what is meant by ‘unidirectional impulses’ as a role of a synapse?

Answer 15

• neurotransmitter receptors are only present in postsynaptic membrane
• allows impulse from one neurone to transmit to a number of neurone

Question 16

what is meant by ‘divergence’ as a role of a synapse?

Answer 16

impulses from a single neurone are passed to more than one neurone

Question 17

what is meant by ‘convergence’ as a role of a synapse?

Answer 17

impulses from morethan one neurone are passed to a single postsynaptic neurone, so stimuli from different receptors produce a single result

Question 18

what is meant by ‘filter out’ as a role of a synapse?

Answer 18

filter out background and low level stimuli, ensuring that only stimulation that is strong enough will be passed on

Question 19

what is summation?

Answer 19

• each stimulus from presynaptic neurone causes same amount of neurotransmitter release into synaptic cleft
• sometimes neurotransmitter from a single impulse isn’t enough to initiate action potential in postsynaptic neurone
• if the amount of neurotransmitter buildup in synaptic cleft, an action potential is initiated

Question 20

what are the 2 types of summation?

Answer 20

• temporal summation
• spatial summation

Question 21

what are 2 types of drugs?

Answer 21

• recreational drugs
• medicinal drugs

Question 22

what are the 2 types of modes of action of drugs on synapses?

Answer 22

1. STIMULATE the NS by creating more action potentials in postsynaptic neurone
2. INHIBIT the NS by reducing amount of action potentials in postsynaptic neurone

Question 23

what is GABA?

Answer 23

• an inhibitory neurotransmitter
• causes hypoerpolarisation of postsynaptic membrane

Question 24

explain GABA receptors and ethanol?

Answer 24

• GABA receptor is a chloride ion channel protein and pore opens when GABA binds to its binding site
• influx of chloride ions into postsynaptic neurone prevents action potentials from being initiated
• ethanol also binds to the GABA receptors and the pore remains open longer, so more Cl- goes into postsynaptic neurone
• this increases inhibitory effects on GABA synapses and cause ethanol induced effects on humans