Flashcards in Nerves 4 Deck (26):
What channels open when the threshold potential is reached?
- Voltage gated Na channels open
- Sodium moves into the cell and depolarises
How does repolarisation occur?
- Voltage gated potassium channels open and potassium leaves the cell
How do local anaesthetics work?
- Block voltage gated Na channels
- AP's can't be generated
3 properties of action potentials?
- Self propagating
- All or none
- Stimulus intensity shown by frequency of AP's
How do AP's move down the axon?
- Voltage gated channels open in one area
- Causes significant depolarisation in the next part
- Voltage gated Na channels open in this bit and so on
Why does local current not cause the AP to travel back up the cell?
- Voltage gated Na channels have a refractory period where they can't open
What 2 ways are there that allow neurones to transmit AP's ASAP?
- Large axons
How do large axons increase conduction velocity?
- Reduce resistance from the cell membrane (axial resistance)
What is it that limits rate of conduction?
With reference to the refractory period, how do large axons speed up signals?
- Less Na channels required
What is myelin?
Membrane of schwann cells or oligodendrocytes
What nerves do Schwann cells myelinate?
Peripheral nervous system
Where do oligodendrocytes myelinate?
In the CNS
What are the nodes of ranvier?
- Unmyelinated axon in between myelinated axon
- Where voltage gated Na channels are found in the myelinated cell
What does myelination stop?
Leakage of the signal
What is an example of a de myelinating disease?
- Gulliane Barre
What does demyelination cause?
- Local currents decay faster
- Next node won't be depolarised
- Signal won't be sent
How are different nerve fibres classed?
A alpha to A delta
- They are from large to small
What classification is given to the largest nerve fibres?
What are 2 rules of A alpha fibres
- Sensitive to anoxia
- Least susceptible to anaesthetic
What is anoxia?
Lack of oxygen
What are 2 rules of C fibres?
- Least susceptible to anoxia
- Most susceptible to anaesthetic
What fibres are the fastest conductors?
- C fibres
What fibres are the slowest conductors
- A alpha
What 2 functions do A alpha fibres have?