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BIOLOGY: myelinated and non-myelinatedneurones question!?!

I don't understand the explanation in the mark scheme??

QUESTION:
There are a number of differences between myelinated and non-myelinated neurones.
One difference is the distribution of voltage-gated sodium ion channels in the membrane.
myelinated neurone
voltage-gated sodium ion channels only occur at
gaps between Schwann cells
each gap is approximately 2 μm long
gaps occur at approximately 1000 μm intervals
non-myelinated neurone
voltage-gated sodium ion channels occur along
the total length of the neurone
Use the information above to explain the difference in the speed of conduction of an action
potential along the length of a myelinated neurone and a non-myelinated neurone.

ANSWER:
in myelinated neurones
1 conduction faster in myelinated neurone
2 depolarisation / action potential , can only occur
where (voltage-gated / Na(+)) channels present ;
3 idea that myelinated neurones have long(er) sections
with no, (voltage-gated / Na(+)) channels present ;
4 ion , movement / transfer ,
can only take place at the gaps / nodes ;
5 longer local circuits / fewer local circuits ;
6 saltatory conduction /
action potential jumps from node to node ;

I don't get point 3. Do the myelin sheaths or the node of Ranvier have the Na+ channels? If there's long(er) sections with no channels present and action potential only occurs when there's channel then how does myelinated neurones transmit action potentials faster.
Original post by princesslife
I don't understand the explanation in the mark scheme??

QUESTION:
There are a number of differences between myelinated and non-myelinated neurones.
One difference is the distribution of voltage-gated sodium ion channels in the membrane.
myelinated neurone
voltage-gated sodium ion channels only occur at
gaps between Schwann cells
each gap is approximately 2 μm long
gaps occur at approximately 1000 μm intervals
non-myelinated neurone
voltage-gated sodium ion channels occur along
the total length of the neurone
Use the information above to explain the difference in the speed of conduction of an action
potential along the length of a myelinated neurone and a non-myelinated neurone.

ANSWER:
in myelinated neurones
1 conduction faster in myelinated neurone
2 depolarisation / action potential , can only occur
where (voltage-gated / Na(+)) channels present ;
3 idea that myelinated neurones have long(er) sections
with no, (voltage-gated / Na(+)) channels present ;
4 ion , movement / transfer ,
can only take place at the gaps / nodes ;
5 longer local circuits / fewer local circuits ;
6 saltatory conduction /
action potential jumps from node to node ;

I don't get point 3. Do the myelin sheaths or the node of Ranvier have the Na+ channels? If there's long(er) sections with no channels present and action potential only occurs when there's channel then how does myelinated neurones transmit action potentials faster.

The Na channels are found at the Nodes of Ranvier - these are the 'gaps' in the myelin sheath. It transmits the AP faster because of 'saltatory conduction' - this is where the AP 'jumps' from one node to the next, rather than travelling continuously down the axon. Thus, transmission of the AP is faster in a myelinated nerve because of this 'jumping' of the AP from node to node.

Does that make sense?
Ooohh ok wow I've got it. Thank you so much!
Original post by princesslife
Ooohh ok wow I've got it. Thank you so much!

Great :smile: And you're welcome.

Just post back if you need help on anything else.

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