Nerves 4 Flashcards
What happens when the membrane potential reaches threshold?
voltage dependent sodium channels open and sodium floods in and depolarises cell
How does depolarisation come about?
by potassium permeability slowly rising (voltage gated potassium channels) allowing potassium to leave the cell
What do local anaesthetics do?
block the voltage gated sodium channels so action potentials cannot be transmitted
Give 3 properties of Action Potentials.
- are all or none
- self propagate
- encode stimulus intensity in their amplitude
How are action potentials maintained?
opening of voltage gated sodium channels causes rush in of sodium which makes that area of the membrane more positive. This causes significant change to depolarise another bit of the cell and cause the next voltage gated sodium channel to open etc until the electrical signal gets to the end axon
Local current can also spread back but does not cause the action potential to go back the way. Why is this?
the channels are in their refactor state and so the AP can only keep sweeping forward
What are the two ways neurones are adapted to transmit APs as quickly as possible?
- larger fibres
- myelination
How are action potentials mediated?
by voltage gated sodium channels
How does having a bigger axon increase conduction velocity?
- bigger axon has lower axial resistance meaning that depolarisation occurring at one channel can spread further
- it is the refractory period of the sodium channels that limits the rate of conduction therefore the fewer sodium channels you require, the faster the electrical signal will be conducted
What is myelin?
folds of membrane from Schwan cell or oligodendrocyte
Where do you find Schwann cells?
in the PNS
Where do you find oligodendrocytes?
in the CNS
What are nodes of Ranvier?
gaps in the myelin sheath on axons where the voltage gated sodium channels are present
What does myelination prevent?
loss of current by leaking out of membrane
Give an example of a de-myelinating disease.
Multiple sclerosis
