In the laboratory, you are studying the neuron shown as a circle in the attached
ID: 3509527 • Letter: I
Question
In the laboratory, you are studying the neuron shown as a circle in the attached figure. This neuron receives twelve identical inhibitory synaptic inputs. When these inhibitory inputs are activated, postsynaptic K+ channels open and the membrane is hyperpolarized. Resting potential is -70 mv, and EK is -80 mV. The results of two experiments are shown in the figure.
In the experiment on the left side of the figure, stimulation of one synaptic input evokes a 1 mV IPSP. Simultaneous stimulation of 2 inputs evokes a 2 mV IPSP, about twice as large. In the experiment on the right side of the figure, simultaneous stimulation of 10 synaptic inputs evokes a 7 mV IPSP, and stimulation of 11 inputs evokes a 7.1 mV IPSP. Briefly explain why these effects do not sum linearly. That is, EXPLAIN WHY stimulating one extra input on the left increases the IPSP by 1 mV, while stimulating one extra input on the right increases the IPSP by only 0.1 mV. Note: the exact sizes of these responses are not important. The numbers are given merely to illustrate the non-linear summation
Stimulate Stimulate 2 inputs Stimulate Stimulate 10 inputs 11 inputs 1 input RP=-70 mV // 1 mV 2 mV 7 mV 7.1 mV EK =-80 mVExplanation / Answer
The above case shows a condition called Fatigue of Synaptic Transmission.
When excitatory synapses are repetitively stimulated at a rapid rate, the number of discharges by the post synaptic neuron is at first very great, but it progressively becomes less in succeeding seconds or milliseconds. This is called Fatigue of Synaptic Transmission.
Fatigue is an extremely important character of synaptic function. When areas of the nervous system become overexcited, fatigue causes them to lose this overexcitability after a while.For example, fatigue is perhaps the most important means by which the brain loses its overexcitability during an epileptic convulsion and finally the convulsions slow down and stop. Thus, fatigue is a protective mechanism against excess neuronal activity.
This is what is observed in the above mentioned lab activity.
In the left side, the neuron was stimulated only twice but on the right side ,after 10 successive stimulations, the neuron shows fatigue. So, the 11th stimulation does not evoke as high a response in it.
This is due to Fatigue of Synaptic Transmission.
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