NMJ Flashcards
what is the function of the NMJ?
responsible for transmission of AP from axon to sarcolemma through non-conductive medium
secretes NTs that bind sarcolemma and create EPP
draw a diagram of the NMJ?
googel
what is the first process underpinning transmission at the NMJ?
loading of ACh into synaptic vessicles by 2ry active transport
H+ pumped into vesicles by H+/ATPase, establishing chemiosmotic gradient for them to flow out again through an antiporter which loads ACh in
how are loaded vesicles moved and where to in the pre-synaptic neuron?
pulled along actin filaments of cytoskeleton by motor protein + positioned at presynaptic membrane
what is the role of Ca2+ in the NMJ?
when AP arrives at endbulb and depol the membrane, v.g. Ca2+ channels open, Ca2+ influxes
faciliattes fusion of vesicle proteins + presyn membrane proteins
which proteins from the vesicle associate with which proteins from the synaptic membrane?
synaptotagmin + synaptobrevin on vesicle assoc with SNAP25 + syntaxin on presyn
SNAP25 coil, forcing proximity
2 membranes can fuse in presence of Ca2+ and cause exocytosis of ACh
what inhibits the process of vesicle fusion with the presyn membrane?
botulinum toxin
what is the structure of the post-syn nicotinic ACh receptor?
2 alpha, beta, gamma, theta
1 molecule of ACh binds to each alpha subunit, causes conform change creating a channel that allows Na+ and K+ to move in and out respectively
why does the post-syn membrane depolarise if K+ is still moving out?
extracellular concentration of Na+ is significantly higher than the intracellular concentration, the influx of Na+ is sufficient to compensate for the loss of positive charge via K+ efflux
how is motor end plate potential ultimately generated?
Na+ influx causes many Mini EPPs which sum to increase membrane pot from -90mV to -60mV, when v.g. Na+ channels open, generating sharp spike in depol, and the motor EPP
what receptors are present on the motor end plate in the G1 tract?
muscarinic
G protein coupled receptors that use second messenger
how can NT release from vesicles be described?
quantal
only whole numbers of vesicles can be released
what happens during hyperpolarisation period?
membrane is responsive to stimulations but requires a much higher input to induce AP
(relative refractory period)
how do motor EPPs generate APs?
the depolarisation voltage spike caused by the depol (from Na+ entering the cell) of the motor end plate triggers an AP, which propagates down post-syn membrane leading to muscle contraction by opening v.g. Ca2+ channels
what is myasthenia gravis?
autoimmune condition characterised by damage to ACh receptors
antibodies bind to receptors + prevent ACh binding, prevent muscle contraction
resp failure: treatment = competitive inhibitors of AChE
