Excitatory and inhibitory postsynaptic potentials. Spatial and temporal summation of postsynaptic potentials

Question 1

EPSP definition

Answer 1

depolarising changes in membrane potential = more likely to be excited enough to reach threshold = more likely to result in AP

Question 2

EPSP mechanism

Answer 2

1 - INITIATION OF ACTION POTENTIAL

action potential travels along its axon to reach pre-synaptic membrane

2 - DEPOLARISATION

voltage-gated calcium ion channels open
calcium enters due from extracellular environment + due to electrochemical gradient

3 - CALCIUM-SENSING PROTEINS

influx of Ca2+ is detected by calcium-sensing proteins such as synaptotagmin

these are part of vesicular membrane

synaptotagmin binds to Ca2+ = conformational changes

4 - SYNAPTIC VESICLE DOCKING

synaptic vesicles are docked onto pre-synaptic termina

with the help of SNARE proteins
- syntaxin
- SNAP25
- synatobrevin

5 - NEUROTRANSMITTER RELEASE

vesicle membrane + pre-synaptic membrane fuse = pore opening for neurotransmitter to exit via exocytosis
travels to post-synaptic membrane receptors via diffusion into synaptic cleft

6 - POST SYNAPTIC MEMBRANE RESPONSE

neurotransmitter inside = glutamate

• NDMA = influx of ca2+ of na+ and depolarisation needed to subside their magnesium block
• AMPA = influx of na+

7 - TERMINATION
neurotransmitter outcomes
1 - reuptaken into pre-synaptic terminal by transport proteins
2 - diffused away from cleft
3 - enzyme degradation

Question 3

IPSP definition

Answer 3

hyperpolarising changes = influx of negative ions into the cell
= cell less excited
less likely to produce AP

Question 4

IPSP mechanism

Answer 4

GABA_A
- ligand gated ion channel that binds to neurotransmitter = conformational changes
influx of cl- ions inside post-synaptic membrane

GABA_B
- g-coupled protein channels that bind to neurotransmitter = intracellular cascade event pathway
influx of k+ inside post-synaptic membrane

Question 5

spatial summation - definition

Answer 5

different pre-synaptic neurones combine different IPSP + EPSP land on different post-synaptic neurones

Question 6

spatial summation - characterisitics

Answer 6

• can occur at the same time
• generate local post-synaptic potential

Question 7

spatial summation - examples

Answer 7

combined EPSPs
- different pre-synaptic neurones release different excitatory neurotransmitters on different post-synaptic neurones = cumulative depolarisation

combined IPSP
- different pre-synaptic neurones releade different inhibitory neurotransmitters on different post-synaptic neurones = cumulative hyperpolarisation

mixed EPSP-IPSP
- mixed excitatory + inhibitory neurotransmitter released, strongest one dominates

Question 8

temporal summation - definition

Answer 8

single pre-synaptic neurone releases many AP at once

Question 9

temporal summation - characteristics

Answer 9

successive APs on post-synaptic potential that overlap + combine

Question 10

temporal summation - examples

Answer 10

successive EPSP
- many excitatory neurotransmitters released at the same time to reach same post-synaptic neurone, they overlap in process, increasing chances of reaching threshold

successive IPSP
- many inhibitory neurotransmitters released at the same time to reach same post-synaptic neurone, they overlap in process, decreasing chances of reaching threshold

mixed EPSP-IPSP
- many excitatory + inhibitory neurotransmitters released at the same time to reach same post-synaptic neurone, the one they gets there first dominates