10. Neuromuscular Junction Flashcards
What is a neuromuscular junction?
Synapse between a nerve and skeletal muscle fibre
What ion channels are in the nerve terminal?
Voltage gated sodium channels
Voltage gated potassium channels
Voltage gated calcium channels
How are voltage gated calcium channels opened?
Depolarisation
What happens at nerve terminal?
Action potential Opens outage gated calcium channels Calcium entry Increased concentration of calcium inside terminal Release of neurotransmitter
What does increasing the frequency of action potentials do?
It increases the amount of nerve terminal calcium entry
Structure of voltage gated calcium channels
Similar to sodium channels
1 alpha subunit with 4 repeating sections
Pore in middle
Properties of calcium channels
Activate more slowly than voltage gated sodium channels
Calcium channel inactivation is calcium dependent
Increased intracellular [Ca2+], inactivation of calcium channels
Transmitter release
Calcium entry through calcium channels Calcium binds to synaptotagmin Vehicle brought close to membrane Snare complex make fusion pore Transmitter released through this pore
Nicotinic acetylcholine receptor
Ligand gated ion channel
Permeable to cations
Mayasthenia gravis
Autoimmune disease targeting nACh receptors
Weakness (increases with exercise)
Caused by antibodies directed against nAChR on postsynaptic membrane of skeletal muscle
Antibodies lead to loss of functional nAChR
End plate potentials reduced in amplitude
What happens when ACh binds to nAChR on muscle end plate?
Causes receptors to open and flow of cations causes depolarisation called end plate potential
End plate potential depolarises adjacent muscle membrane and activates voltage gated sodium channels, initiate action potential
D-tubocurarine
Blocks nACh receptors competitively
Causes paralysis
Succinylcholine
Depolarising blockers
Cause inactivation of sodium channels adjacent to neuromuscular junction
Muscarinic ACh receptors
Slower response
Coupled to G-proteins which trigger cascade of events in cell
