13- Synaptic physio lab

Question 1

visually observed transition from indiv muscle twitches to tetanus as the ____

Answer 1

frequency of stim to motor nerve is incr

Question 2

events that cause transition from muscle twitch to tetanus with incr freq of motor n. stim

Answer 2

1) single AP causes NT release
2) post syn membrane depol
3) Ca2+ release from SR
4) @ high freq, muscle cell can’t remove all Ca so builds up
5) so can’t relax btwn contractions and muscle stays contracted

Question 3

describe quantum hypothesis

Experimental observations underlying Quantum hypothesis of transmitter secretion

Answer 3

each secretion of NT occurs in integral # of multimolec packets (quanta)

small 1 mV depol at random intervals
stim of nerve –> large synch release of quanta

EPP proportional to # quanta release or summation of MEPP

Question 4

Difference btwn MEPP and EPP

Answer 4

MEPP = small depol (~ 1 mV amplitude) from spont release of vesicle

EPP = caused by nerve stim with synch release of many vesicles (if large enough, can depol postsyn cell –> twitch)

Question 5

Describe effects of bathing prep with curare

Answer 5

no MEPPs or evoked potentials even with high freq stim

Question 6

Describe effects of bathing prep with elev Mg/low Ca

mimics the effect ____

Answer 6

MEPPs seen but evoked potentials can’t be seen until high freq stim (to cause facilitation)

Question 7

Describe mechanism by which curare produces effects

Answer 7

blocks postsyn transmission by bind to nAChR so no MEPP or EPP

Question 8

Describe mechanism by which high Mg/low Ca produces effects

mimics the effect of ____

Answer 8

pre-synaptic block since not enough Ca to allow NT release

Ca influx into cell is req’d for exocytosis
MEPP visible as not regul by Ca2+ release

mimics the effect of botulism

Question 9

Effect of neostigmine on synaptic transmission

Answer 9

Neostigmine = AChE inhibitor so ACh prolonged in cleft

potentiates effects of ACh on incr in neurotransmission and incr muscle twitch

but neostigmine also similar strxr to ACh so overdose can cause to bind ACh receptor and antagonize
–> facilitation then depression @ high freq

Question 10

Understand synaptic facilitation

Answer 10

of quanta secreted from terminal is larger b/c residual calcium allows exocytosis of more vesicles since can’t clear calcium fast enough

Question 11

Understand synaptic facilitation in low Ca/high Mg solution

Answer 11

presynaptic block that prevents neurons from releasing NT (not enough Ca to cause exocytosis)

but high freq stim will cause Ca level to be high enough to release enough vesicles for twitch

Question 12

Understand synaptic depression

Answer 12

depletion of releasable synaptic vesicles

repeated stim can’t replenish vesicles fast enough to keep pace so decr # of secreted quanta

Question 13

Understand synaptic depression in curare solution

Answer 13

curare blocks nAChR

so muscle cells won’t respond to single or high freq stim because ACh can’t bind

Question 14

Causes of myasthenia syndrome

Answer 14

Ab to pre-synaptic Ca channel

prevent influx of calcium

vesicles cannot fuse with membrane and NT cant be released

Question 15

Symptoms of myasthenia syndrome

Answer 15

weak but get stronger with activity due to facilitation

continuous AP with activity incr Ca2+ in axon since not all Ca pumped out

Question 16

Causes of myasthenia gravis

Answer 16

Ab to ACh receptors at NMJ

post-synaptic block

MEPP amplitude will be small (proportional to # of blocked receptors)

more vesicles necessary to depol muscle cell but with repeat stim, get depression

Question 17

Symptoms of myasthenia gravis

Answer 17

since postsynaptic cell now requires more vesicles to achieve contraction, vesicles depleted rapidly when person exerting

–> weakness

Question 18

high Mg low Ca

mimics the effect of ___

Answer 18

botulism