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.