Lecture 14 Flashcards
(17 cards)
What ion channels are found at nerve terminal but not along whole axon?
Voltage gated calcium channels
How is amount of calcium release determined at nerve terminal?
More action potentials= more calcium release
Calcium channels?
Diverse, different calcium channel types found in different tissues
Activate and inactivate slower than sodium channels
Increasing intracellular calcium closes calcium channels
What is the synapse between nerve and muscle called?
Neuromuscular junction
How is skeletal muscle depolarised?
Acetylcholine released into neuromuscular junction. Binds to nicotinic acetylcholine receptor. This ligand gated ion channel is permeable to cations so sodium moves in and potassium moves out to cause depolarisation
What factor affects the amplitude of the muscle AP
Extracellular calcium levels. If they are lowered then less neurotransmitter release. Same pre synaptic action potential can have differen muscle AP’s depending on calcium levels and neurotransmitter release.
How is muscle action potential generated?
ACh binds and is later degraded by ACh esterase. Causes depolarisation adjacent to end plate as sodium channels activated. Action potential propagates in both directions. Excitation contraction coupling
How does curare hunting poison work?
Prevents transmission between nerve and muscle
What are the two types of block used for nACh receptors?
Competitive and depolarising
What is the use of nACh blockers?
Can be used in surgery as neuromuscular blockers
Give an example of a competitive blocker of the nACh receptor
D-tubocurarine. Prevents depolarisation and so muscle AP. Can be overcome by increasing ACh concentration
Depolarising blocker drug use?
Succinylcholine. Continually activates nACh receptors and this leads to sodium channel inactivation
Whats important to note in surgery when using neuromuscular blockers?
Ensure both anaesthetic and neuromuscular blockers are working. Can have patient awake but unable to move
What is myasthenia gravis?
Autoimmune disease targeting nACh receptors and leads to loss of their function. End plate potentials fail to reach threshold so impaired muscle function.
What test is used to diagnose myasthenia gravis?
Endrophonium test, endrophonium chloride acts as anti cholinesterase
What is organophosphate poisoning?
Caused through insecticides and nerve agents. Acetylcholineterase inhibitors form stable covalent bond. Recovery can take weeks as new enzymes required.
Muscarinic vs nicotinic
Muscarinic parasympathetic at the point of contact with target tissue. Muscarinic G protein coupled instead of ion channel.
