NMJ Flashcards
Where are cell bodies of motor neurons to skeletal muscle?
Ventral horn of spinal cord
Exit via ventral root
What is the end plate?
Fine terminal branches on the muscle
How do individual axons behave within the end plate?
Swell up into many bulbous presynaptic axon terminals/ terminal boutons
What is contained in the synaptic bouton?
Many mitochondria and small synaptic vesicles
What chemical transmitter is used at the NMJ?
Acetylcholine
How is acetylcholine made in the nerve terminal?
Choline and acetyl-CoA
Using enzyme cholineacetylase
What enzyme is found in the synaptic cleft? Function?
Acetlycholinesterase
Splits of acetyl group to form choline and acetic acid
What is meant by docking?
Involves interactions between proteins on vesicles and presynaptic membrane
Proportion of vesicles attached to presynaptic membranes on bouton
How do docked vesicles behave when action potential arrives?
Fuse with presynaptic membrane and release contents via exocytosis
What triggers release of transmitter?
Entry of calcium ion through voltage gated calcium channels
Where are N and L type calcium channels found?
N type: presynaptic terminals
L type: heart and vascular smooth muscles
How does calcium influx cause acetylcholine release?
Calcium entering twists synatobrevin and syntaxin proteins forcing vesicle membrane to fuse with cell membrane
Creates fusion pore for acetylcholine to pass through
How are empty vesicles returned to presynaptic membrane?
Empty vesicles are bound to protein (clathrin)n which moves them back to cytoplasm
What does released acetylcholine bind to?
Cholinergic receptor on muscle membrane
How many molecules are required to bind to nicotinic ACh receptor for it to open?
2
What can pass through central pore of nicotininc ACh receptor?
Sodium and potassium
What is effect of inward sodium ions to muscle
Depolarisation: End plate potential
What happens in the illness myasthenia gravis
Number of acetylcholine receptors reduced
Endplate potential often not large enough to trigger a muscle action potential
What % of docked vesicles are released with each stimulus
10%
How does botox paralyse muscles
Blocking the doking
How does curare paralyse muscle
Competitive antagonist of nicotininc receptor
How do depolarising blockers work?
Stimulate Ach receptor in same way ACh does
Doesn’t detach
Muscle remains depolarised and unable to carry out more action potentials
How to anticholinesterases work?
Blocks acetylcholinesterase
Makes synapse hyperactive and muscles goes into convulsions then paralysis
