Consider a “typical” motor neuron with a resting membrane potential of -70mV and
ID: 300096 • Letter: C
Question
Consider a “typical” motor neuron with a resting membrane potential of -70mV and a
threshold potential of -55mV. This neuron receives two signals, X and Y, at the same
time. Signal X arrives at the far end of a dendrite, and causes ten neurotransmittergated
K+ channels to open. Signal Y arrives at the cell body and causes three
neurotransmitter-gated Na+ channels to open.
a) How will signal X affect the membrane potential at its reception site? Explain.
b) How will signal Y affect the membrane potential at its reception site? Explain.
c) Both of these signals arrive at the axon hillock at exactly the same time. Will the neuron fire
an action potential? Yes, no, or maybe? Explain your answer.
Explanation / Answer
During the activation of the membrane in depolarisation phase, a slight increase in the resting membrane potential is due to passive distribution of ions, that leads to increase in k+ and Cl- influx.this causes the opening of 10 K+ channels leads to development of resting membrane potential in the given situation. When depolarisation exceeds 7 mV, Na+ channel activation occurrs through M gates.i.e . Sodium channel open at higher potential than the potassium channels. Potassium channels require less stimulation than sodium channels. The opening of 3 Na+ channels leads to depolarisation potential. If both of these signals arrive at the axon hillock at the same time, their excitatory post synaptic potentials get summated to critical level that produce spike discharge from the motor neuron, this is called as summation of potentials. The excitation of either alone dose not produce a spike potential and activity in on synaptic knob is said to facilitate activity in another to approach firing level. Hence more action potential get generated .