On the figure below, the post-synaptic neuron is innervated by 6 pre-synaptic ax

Question

On the figure below, the post-synaptic neuron is innervated by 6 pre-synaptic axons (labeled A-F) from other neurons. Suppose that V_m = -70 mV, T_o = -50 mV, average velocity of propagation of a potential is 25 nm/msec, and that the potential degrades (returns to V_m) at an average rate of 1 mV/10 nm. Complete the table below. If using the initial potential as the criteria, will the post-synaptic neuron fire an action potential? If using the final potential as the criteria, will the postsynaptic neuron fire an action potential?

Explanation / Answer

Here first the retardation rate of each presynapti neuron is calculated -eg for A, 35/10=3.5 mV ,and then this value is subtracted from the initial potential of A to get final potential 22-3.5=-25.5 mV ,like wise it should be calculated for each presynaptic neuron, to calculate the time take to reach axon hillock by each using 25 nm/msec, eg: for A , 35/25=1.5 msec, likewise it should be calculated for ABCDEF,

Since all the final potential are greater than thresh hold potential (To ) all are EPSP type ,example A=-25.5>-50 hence it is EPSP .

A 35 -22 EPSP 1.4 -25.5 B 45 16 EPSP 1.8 11.5 C 88 19 EPSP 3.5 10.5 D 60 -11 EPSP 2.4 -17 E 40 7 EPSP 1.6 3.0 F 15 13 EPSP 0.6 11.5 Total 22 Total = -6

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