Question

Explain why a larger diameter axon can tolerate a larger fenestration node separation and still conduct impulses efficiently (incorporate into your answer what you have learned about R_m, Ri, and capacitance):

Answer 1

Larger diameter axon

Conduction velocity in myelinated axons is proportional to the axon diameter, and the general rule of thumb is that for axons with an outside diameter greater than 11 μm, the speed of conduction, in meters per second, is about six times the axon diameter, in micrometers

Larger diameter axon have a higher conduction velocity, which means they are able to send signals faster. This is because there is less resistance facing the ion flow.

The larger the diameter of the axon, the less likely the incoming ions will run into something that could bounce them back.

learned about Rm, Ri, and capacitance........

Passive spread of the depolarizing current is the rate limiting step on an action potential

- if ri is high - current spread is not as far, speed of the action potential is slower

- if rm is high - internal current spread is farther, speed is faster

- the velocity of the action potential depends on the rate at which the membrane capacitance ahead of the action potential can be charged

- this depends on cm and ri

- if cm is high - the longer and more charge it takes to charge the capacitor and the slower the action potential

the action potential causes a local depolarization that will passively spread to adjacent regions

- the neighbouring regions will become depolarized to threshold which will then trigger an action potential in this region and so on down the length of the axon...

Capitance..

The ability to accept and pile up charge without changing voltage. The capacitance of a certain membrane is the number of ions that have to move through the membrane (pile up on the capacitor plates) to get a voltage change to occur. High capacitance means lots of charges moved per volt change.

How does capacitance affect the action potential.

Capacitance affects the velocity [rate] of the action potential. Decrease the capacitance, and increase the velocity of the action potential.