At a CNS synapse the mean postsynaptic current amplitude is

At a CNS synapse, the mean postsynaptic current amplitude is 100 +/- 10 pA (mean +/- S.D., 100 stimuli delivered). This is measured at resting potential (-80 mV) under voltage-clamp coniditons. The Na+ and K+ equilibrium potentials are +40 and -90 mV respectively.

a. What range of EPPs (mean +/- SD) would you expect if the postsynaptic cell has input resistance of 1 megaohm (assume it is isopotential)? Assume that the (post) synaptic current is conducted exclusively by Na+.

b. What range of EPPs would you expect if the postsynaptic cell has an input resistance of 1 gigaohm. Assume that the (post) synaptic current is carried exclusively by K+.

c. What conclusion can you draw as to the probability of release, p, for the above synapse? What is the likely range of p?

Solution

A) AT INPUT RESISTENCE OF 1 MEGAOHMS THE EPP IS ASSUMED TO BE APPROXIMATELY 4* 10⁴ mV. THIS CAUSE THE POLARIZATION OF NERVE.

B) AT INPUT RESISTENCE OF 1 GIGAOHMS THE EPP IS ASSUMED TO BE APPROXIMATELY 9*107 mV. THIS WILL CAUSE DEPOLARIZATION OF THE NERVE.

C) IT CAN BE CONCLUDED THAT IF RELEASE PROBABILITY IS LESS THAN 0.4 THEN THE SIGNAL FORWADED BY THE POSTSYNAPTC CELL FOR THE RELEASE OF HORMONE WILL BE LESS.THE RANGE CAN BE FROM 0.4 TO 0.8