Synaptic Transmission

Question 1

types of synapses

Answer 1

• electrical synapses (gap junctions)
• chemical synapses

Question 2

benefit of electrical synapses

Answer 2

faster –> favours synchrony

Question 3

benefit of chemical synapses

Answer 3

• diversity of neurotransmitters
• receptors can lead to excitation OR inhibition

Question 4

structure of gap junctions

Answer 4

comsits of two connexons (type of ion channel, one in each membrane)

Question 5

quantal hypothesis

Answer 5

• neurotransmitter released in quanta (parcels)
• binds to receptors on end plate
• stimulates MEPPs (miniature end plate potentials)
• EPP amplitude corresponds to the sum of MEPPs

Question 6

evidence for quantal hypothesis and what was the conclusion?

Answer 6

in low [Ca2+] solution, the EPPs had smaller amplitudes

in high [Ca2+] solution, the EPPs had higher amplitudes

both amplitudes reflect no. of quanta

conc: Ca2+ are responsible for the exocytosis of vesicles

Question 7

blurt voltage clamp

Question 8

blurt Na+ and K+ voltage-gated channels

Question 9

structure of end plate

Answer 9

junctional folds (increase SA) containing lots of nAChR

Question 10

what are nAChR? what are they permeable to?

Answer 10

• nicotinic acetylcholine receptors
• ligand-gated ion channels
• permeable to Na+ and K+

Question 11

what is the resting membrane potential of an end plate?

Answer 11

≈ -100mV

Question 12

what is the threshold for an end plate?

Answer 12

≈ -65mV (strongest driving force for Na+)

Question 13

blurt patch clamp

Question 14

blurt synapse vs neuromuscular junction comparison

Question 15

how do EPPs compare to voltage changes at most synapses? why?

Answer 15

• EPPs > voltage changes at most synapses
• motor neurons have more ACh vesicles
• junctional folds contain more AChRs
• more ligand-gated ion channels open

Question 16

how are synapses energy efficient?

Answer 16

only important synaptic signals evoke APs

Question 17

how are APs only evoked from important synaptic signals?

Answer 17

• EPSPs are received by dendrites so decay on their way to the soma (cell body) and axon (many signals needed to generate AP)
• CNS neurons have inhibitory synapses which generate IPSPs which counteract EPSPs so only a strong stimulus will evoke a response

Question 18

two types of neurotransmitter receptors

Answer 18

• ionotropic (LGIC)
• metabotropic (G-protein coupled receptors)

Question 19

two types of ionotropic receptors

Answer 19

• excitatory
• inhibitory

Question 20

three types of excitatory ionotropic neurotransmitter receptors

Answer 20

• AMPA
• NMDA
• Kainate

(ligand-gated Na+ channels)

Question 21

what binds to excitatory ionotropic neurotransmitter receptors?

Answer 21

glutamate (amino acid)

Question 22

what binds to inhibitory ionotropic neurotransmitter receptors?

Answer 22

• GABA (brain)
• glycine (spinal cord)

both are amino acids

Question 23

what ion channels are inhibitory receptors bound to?

Answer 23

Cl- channels –> cause a slight hyperpolarisation

Question 24

what binds to metabotropic neurotransmitter receptors and what effect do they have?

Answer 24

• glutamate
• GABA

inhibitory effects

Question 25

how does the effect of glutamate differ between ionotropic and metabotropic receptors?

Answer 25

- excitatory when bound to ionotropic receptors - inhibitory when bound to metabotropic receptors

Question 26

how do metabotropic receptors work?

Answer 26

- neurotransmitter binds to metabotropic receptor - G protein is bound to GDP (inactive trimer of α, β, γ subunits) - GDP on α subunit of G protein is replaced with GTP - G protein activated and α subunit dissociates from G protein - α subunit OR β, γ complex can either bind directly to an ion channel to open it OR bind to an effector protein to cause an enzyme cascade

Question 27

blurt knee-jerk reflex