| Action potential move along neuron as a wave of depolarisation | - When an action potential happens, some of the S ions that enter neuron diffuse sideways
- This causes S ion channels in the next region of neuron to open
- S ions diffuse into that part
- Causing wave of depolarisation to travel along neuron
- The wave moves away from the parts of the membrane in the refractory period coz these parts cant fire an action potential |
| Passage of an action potential along an unmyelinated axon (1) | - At resting potential the conc. of S ion outside axon membrane is higher than inside
- P ion conc. higher inside than outside membrane
- Overall conc. of + ions is greater outside than inside
- Axon membrane is polarised |
| Passage of an action potential along an unmyelinated axon (2) | - As stimulus causes a sudden influx of S ions hence a reversal of charge on axon membrane
- This is the action potential
- Membrane is depolarised |
| Passage of an action potential along an unmyelinated axon (3) | - Localised electrical currents established by influx of S ions cause opening of S voltage-gated channels further along axon
- The resulting influx of S ions in this region causes depolarisation |
| Passage of an action potential along an unmyelinated axon (4) | - Behind new region of depolarisation, S voltage-gated channels close
- P ones open
- P ions leave axon along their electrochemical gradient
- The depolarisation moves along membrane |
| Passage of an action potential along an unmyelinated axon (5) | - The action potential (depolarisation) is spread in the same way further along axon
- Outward movement of P ions has continued to extent that axon mem. behind AP has returned to original charged state (+ outside, - inside)
- It has been repolarised |
| Passage of an action potential along an unmyelinated axon (6) | - Repolarisation of axon allows S ions to be actively transported out
- Returning axon to its resting potential in readiness for new stimulus if it comes |
| Passage of an action potential along an myelinated axon (1) | - In myelinated axons the fatty sheath of myelin around axon acts as an electrial insultor
- Preventing APs from forming
- At intervals of 1-3mm there are breaks in myelin insulation, nodes of Ranvier
- AP can occur at these points |
| Passage of an action potential along an myelinated axon (2) | - Localised circuits arise between adjacent nodes of Ranvier
- APs in effect jump from node to node in a process called saltatory conduction
- So, AP passes along a myelinated neuron faster than unmye. axon of same diameter
- Coz in unmyel. neuron, depolarisation have to take place all the way along axon, so takes time |
