Synaptic transmission 2

Question 1

describe magnesium experiment setup

Answer 1

single neuromuscular junction (neuron + muscle fibre) was isolated
ca2+ in ecf was replaced by Mg2+, which can’t enter cells as easily. therefore, fewer vesicles would be released, allowing us to measure the EPSP of a few vesicles at a time.
axon stimulated, muscle membrane potential recorded.

Question 2

describe magnesium experiment results

Answer 2

• no response
• differing responses
• spontaneous release of vesicles (didn’t require stimulation)

Question 3

how were results of magnesium experiment recorded?

Answer 3

histograms

Question 4

describe miniature end plate potential

Answer 4

potential difference caused by the release of ONE vesicle

Question 5

do each vesicles contain a similar amount of nt, and produce a similar PSP?

Answer 5

yes

Question 6

main mode of conduction in dendrites?

Answer 6

mainly passive.

also active, but not the same as action potentials - don’t depolarise the membrane as much, and are less reliable.

Question 7

describe how passive conduction occurs in dendrites.

Answer 7

current is injected; ions diffuse bidirectionally through open channels
strength of current decays exponentially.

Question 8

what constant is used to quantify passive conduction?

Answer 8

length constant: distance at which depolarisation decays to 1/e of maximumsize

Question 9

factors affecting length consant?

Answer 9

internal resistance: diameter

membrane resistance: density of open channels

Question 10

what mechanism is used to counteract the fact that EPSPS decay along the dendrite?

Answer 10

distal synapses produce larger EPSPs than proximal (closer to axon hillock) synapses

Question 11

Ecl- =

Answer 11

-65mV = resting membrane potential

Question 12

how are chloride channels opened

Answer 12

GABA binds to them

Question 13

two ways in which chlorie channels mediate inhibition?

Answer 13

mathematically summing with EPSPs

shunting inhibition

Question 14

describe shunting inhibition

Answer 14

 Inhibitory (GABA) axo-somatic synapses open chloride channels. This allows charge leakage, preventing EPSP from reaching the cell body

Question 15

ways in which we can modulate the probability of vesicle release (hence strength of EPSP)?

Answer 15

presynaptic modulation
presynaptic faciliation
paired pulse faciliation
autoreceptors
astrocytes

Question 16

describe presynaptic modulation

Answer 16

axo-axonic synapses regulated ca2+ entry into axon terminal (hence modulate vesicle release)
when the synapse is active, it reduces amount of ca2+ going into the cell, reducing number of vesciles released…

Question 17

describe presynaptic facilitation

Answer 17

when the axo-axonic synapse is activated, allows more Ca2+ to enter the cell

Question 18

describe paired pulse faciliation

Answer 18

when second AP arrives, ca2+ might be left over from first AP.
therefore, even more vesicles may be released, so therefore current will increase
depends on temporal summation

Question 19

describe autoreceptors

Answer 19

presynaptic metabotropic receptors which regulate that neuron’s level of nt release

• too much nt in cleft: reduces synthesis and release of nt
• too little: increases nt release
• changes reuptake accordingly

Question 20

describe how astrocytes work

Answer 20

uptake nt’s from synaptic cleft

release substances into synaptic cleft to promote nt release

Question 21

describe temporal summation dependency on time consatn

Answer 21

long time constant: repolarisation slower. so second synaptic current adds onto it, resulting in a high synaptic potential
short time constnat: repolarisation quicker; so second synaptic current doesn’t add onto it, resulting in lower synaptic potential

Question 22

describe spatial summation dependency on length constant

Answer 22

as previous