Flashcards in Nerves 4-5 Deck (26)
What type of channel is responsible for the depolarisation in an action potential?
Sodium voltage gated channels
What is the usual threshold potential of a nerve cell?
What is responsible for repolarisation after an action potential?
K+ voltage gated channels
Why can't an action potential travel back down the same direction of membrane that it just came from?
The channels are in their refractory state
What are the two ways you can increase the speed of action potentials?
Increase the size of the fibre
Why does increasing the size of axons increase the speed of action potentials?
Bigger axons have a lower axial resistance, depolarisation can spread further and so you can spread your sodium channels further apart. It is the opening of sodium channels that is the rate limiting step of self-propagation.
What glial cells are responsible for myelination?
Oligadendrocytes and schwann cells
Where are the sodium channels in an axon that is myelinated?
In the nodes (node of raniver)
What is the effect of myelination on resistance?
Increases resistance - allows current to spread with little decrement
What disease has a lack of myelination in the axons?
What structure is responsible for facilitating the compound action potential?
A bundle of axons (a nerve trunk)
Which fibres are most sensitive to anoxia and least sensitive to local anaesthetics?
Proprioception, touch, pressure
These are the fastest nerve fibres
What fibres are least sensitive to anoxia and most sensitive to local anaesthetics?
Preganglionic autonomic fibres, heat, slow pain
Where is contraction triggered by in the NMJ?
Action potential in the sarcolemma
What ion is responsible for the formation of vesicles and release of acetylcholine in the NMJ?
What are the receptors on the sarcolemma for acetylcholine?
What is the name of the local grade potential produced by activation of ligand gated channels by acetylcholine?
The end plate potential
What is the effect of the end plate potential?
Always depolarises the adjacent membrane to threshold, opening voltage gated channels
What removes acetyl choline?
What is the effect of tetrotoxin?
Blocks Na+ channels and so blocks the action potential
What is the effect of joro spider toxin?
Blocks calcium channels and so stops the release of transmitter
What is the effect of botulinum toxin?
Disrupts the release machinery and so stops the release of transmitter
What is the effect of curare?
Blocks acetylcholine receptors and so prevents the end plate potential
What is the effect of anticholinesterases?
Block ACh breakdown and so increase the transmission at the NMJ
What are the three different types of synapses in the central nervous system?