PLEASE PLZ PLZ help me understand how a nerve impulse passes along a non-myelinatedWatch this thread
I understand the whole resting potential- depolarisation-resting potential sequence
What I don't understand is whats written in here : (pic below)
I initially thought, that in a non-myelinated neurone, when a nerve impulse reaches the axon, it causes the depolarisation of the whole axon at once but what I've come to realize is that it actually happens in small parts, with th first little section to get stimulated by the impulse to get depolarised and then that depolarisation moves to a little section next to it and so on .
What I don't understand is how the wave of depolarisation passes along the axon.
In the pic I showed, It says exactly this :
"When stimulated, voltage dependent sodium ion channels open,and sodium ions flow into the axon,depolarising the membrane.
Localised electric currents are generated
in the membrane. Sodium ions move to the
adjacent polarised (resting) region causing
a change in the electrical charge (potential
difference) across this part of the membrane. "
The part in bold is what confused me, as I thought that when the wave of depolarisation reaches section B(this is whatever part of the axon) it causes the Na+ channels to open in that section and the K+ channels to close in that section too so depolarisation occurs there too and the previous sections that the wave passed through, for example Z and A, would be undergoing repolarisation.
What I understood from the paragraph is that the Na+ that entered in the very first part of the axon are diffusing/moving along the axon with the wave of depolarisation and its basically creating the same effect because the potential difference is travelling with the Na+.
I probably confused a few things and I need someone to clarify it to me now please
Here's the same picture in another form
To answer the bit in bold:
You have a voltage gated channel, it opens to allow Na+ in which depolarises the membrane.
The localised electric currents are formed within the membrane.
Sodium ions then travel from positive region (which is more positive since they entered the cell) to the negative (shown in diagram as from left to right)
hence the localised electric current.
Na+ then moves (diagram shows left --> right) which causes transmission of the impulse.
once the impulse has moved down the axon, this is when repolarisation occurs.