Neuromuscular Junction Flashcards
What is the main neurotransmitter in the NMJ?
Acetylcholine
What neurones release ACh?
Lower/alpha/somatic motor neurones
Why does the NMJ fold?
To increase surface area
What is transmitter release dependent on?
Calcium
What does ACh binding to nicotinic receptor do?
Triggers end plate potential in muscle cell
What breaks ACh down?
Acetylcholinesterase
What are the products of the breaking down of ACh?
Acetyl CoA and choline
What must neurotransmitters do at first to be released?
Must fuse with presynaptic cell membrane
Must dock at active zones of the presynaptic membrane
Then primed to fuse with the presynaptic membrane
What coordinates the Docking/Priming/Fusion?
SNARE proteins
What does SNARE stand for?
Soluble n-etylmaleimide sensitive factor attachment protein receptor
Name the v snare proteins.
Synaptobrevin
Synaptotagmin
Name the t snare proteins.
Syntaxin
SNAP 25
What is transmitter release directly related to?
Pre-synaptic uptake of Ca++ by the neurone
What does Ca++ bind to?
Synaptotagmin
What does the Ca++ step allow?
Fusion of the vesicle to the presynaptic membrane and exocytosis
What can be retrieved from the postsynaptic membrane and recycled?
Synaptic vesicles
How do the SNARE proteins function?
Action potential has arrived at the nerve terminal
T snares form a complex
Synaptobrevin begins to join with syntaxin and SNAP 25 complex and 3 snares wind round each other bringing the vesicle and the nerve terminal closer together
Ca++ binding to synaptotagmin causing fusion of vesicle and release of ACh into synaptic cleft
ATP required disassemble SNARE porteins
Vesicle recycled
What do the small amounts of ACh cause in a resting neurone?
Tiny depolarisations - minature end plate potential
What causes End plate potentials?
Release of ACh from many different vesicles - quantal release of neurotransmitter
What are the two theories for vesicle recycling?
Kiss and run
Fusion and collapse
How does ACh release lead to a muscle action potential?
Binding of ACh to nicotinic receptors allows simultaneous flow of Na+ and K+ through the receptor (acts as ion channel - ligand gated ion channels)
Movement of ions lead to generation of EPP
What increases the amplitude of the end plate potential?
More ACh
What will lead to an action potential in the muscle?
Summation of end plate potentials
What disease decreases the number of functioning ACh receptors?
Myasthenia Gravis
Name an anticholinesterase.
Neostigmine
When is AChE sinisterly used and how does it work?
Nerve gases lead to ACh not being degraded prolonging muscle stimulation
What does a decreased release of ACh lead to?
Impaired synaptic transmission - botulism
What causes decreased interaction between ACh and ACh receptors?
Curare
