Neuromuscular Junction Flashcards
what are the five steps of synaptic transmission
5 possible targets of drugs and toxins
synthesis of neurotransmitters
storage of neurotransmitters in vesicles
exocytosis of transmitters
transmitters bind to post-synaptic receptors
transmitters dissociate
why are neurotransmitters stored in vesicles in the pre-synaptic neuron
prevent them from metabolism
package them together
what causes exocytosis of transmitters from pre-synaptic neurons
opening of voltage-gated calcium channel
what do transmitters do when they bind post-synaptic receptors?
cause conformational changes
change the activity of the receptor
what facilitates transmitter dissociation
what happens to them afterwards
enzymes
broken down into components, some recycled
what is an agonist
substances which bind specific receptors and elicit a biological response
agonists:
affinity?
efficacy?
Reversible?
posses affinity and efficacy
always reversible
what is an antagonist
substances which bind specific receptors and do not activate them
antagonists:
affinity?
efficacy?
Reversible?
posses affinity but lack efficacy
not always reversible
which has higher binding affinity, antagonists or agonists?
how can the other still bind first
antagonists tend to have a higher affinity
agonists can bind first if at a higher concentration
what are the two moieties of acetylcholine
acetyl moiety
choline moiety
which subunit of nicotinic receptors does ACh bind
transmitter gated Na+ ion channels
alpha
how can a Na+ ion channel be isolated from a post-synaptic neuron
patch-clamp
how can mepps and epps be measured
microelectrodes
explain mepps
miniature end plate potentials
spontaneous depolarisations
depolarisation caused by a single vesicle
not sufficient to cause an AP
explain epps
end plate potentials
large depolarisation of the endplate of muscle cell
can initiate APs
summation of mepps in response to nerve impulse
muscle contraction
how and why is the size of epps reduced for study
using a high Mg2+, low Ca+ buffer (Mg blocks Ca2+ channels, calcium triggers exocytosis)
prevent the glass microelectrode from breaking
what does quantal mean in relation to transmitter release?
the amplitude of the epp is a multiple of the amplitude of the mepp
smallest epp = mepp
what is quantal content
how is it calculated
number of vesicles per stimulation
QC=mean EPP amplitude / mean MEPP amplitude (mV)
what enzyme synthesises ACh and from what
Choline acetyltransferase (CAT)
from choline and acetyl-CoA
explain the reuptake of choline
Na+ dependant
blocked by hemichlonium 3
effect on mepp, epp and QC if transmitter synthesis is blocked
less Ach per vesicle
-mepp and epps decreased equally
-no change in QC
explain storage of ACh
transported into vesicles
blocked by inhibition of transporter
effect on mepp, epp and QC if ACh storage is blocked
less Ach per vesicle
-mepp and epps decreased equally
-no change in QC
