Question

Question 5 1 pts Myelination occurs quickly in humans during infancy, leading, e.g., to a child's fast motor development (crawling, walking -- those toddlers can move!) as the speed of voltage pulses through their neurons increases with myelination of those nerve fibers. However there are a number of neurodegenerative diseases, such as multiple sclerosis and Guillain- Barre syndrome (which they mention when you get your flu shot), in which demyelination (loss of the myelin sheath insulating the nerves) occurs. The effective reduction of the membrane then leads to degradation or complete loss of nerve signals. If the capacitance of a membrane increases because of an effectively thinner membrane (degradation of the myelin sheath), but the resistances of the axon and its membrane do no change appreciably due to other effects, how would degradation of myel in affect the speed of a pulse? The speed of a pulse would decrease. The speed of a pulse would increase. The speed of a pulse would remain the same.

Answer 1

We can formulate a simple formula to get a general idea of how current ( or in other words speed of pulse) decreases or increases with increase or decrease in capacitance.

We make a simple circuit with Battery V, Resistance R and capacitance C

let i be the current at any time t and q be the charge on the capacitor

V - ir -

o = =--41

+4=V

= =v-

da dt CV- TC

do 1 CV-gro

-In(CV – 9) = +0

at t=0 q=0

+c= -In (CV)

therefore the equation becomes

-In(CV – 9) = 6 - In (CV)

= (In(CV — q) – In (CV)) =

$\Rightarrow \left (ln\frac{(CV-q)}{CV} \right )=-\frac{t}{rC}$

(CV – 9) - e no

q=CV - CVec

to get current we differentiate both sides by t

şi-CVe

i=-ee

V/r = I, which is the current when there is no capacitance

i=le

So, we can see as the capacitance increases current decrease. So, velocity of pulses will also decrease.

So, ans is option A)

if any doubt feel free to comment