Question

A mutation causes the incorporation of fewer voltage-gated sodium channels into the membrane of a neuron.

a) What effect will this mutation have on synaptic potentials if this neuron receives excitatory input?

b) What effect will this mutation have in the axon hillock area?

Answer 1

a) Synaptic potential will not change because for an impulse to be transmitted through the synapse action potential remains constant. Once the potential is more than the threshold an impulse is fired. Although the lesser number of Voltage-gated sodium ion channels will slow down the transmission of impulse through the neurons. The reason for this is lesser number of ion channels will result in slower polarization and depolarization across the membrane which in turn results in more time to generate the required potential to fire the same impulse.  

Action Potential Before Mutation +40m V After Mutation Polarization Depolarization Voltage Threshold -55mV Resting period -70mV Stimulus Refractory period Time(m/s)

The above graph clearly represents how the mutation will affect the potential. The mutation doesn't affect the potential in any way because a required potential has to be generated to fire a neuron and this potential is known as action potential. But the time taken for generating this amount of potential will drastically increase depending on how less the ion channels are.

b) The Axon hillock area is the region where all the generated potential is kept till the action potential is generated. Once the potential reaches action potential, Axon hillock fires the impulse further to the synapse of the next neuron after which again polarization and depolarization will occur across the membrane till the impulse is collected by the next axon hillock to be fired.

In case of this mutation nothing much will change in the axon hillock area. Although the time taken to fire an impulse will increase since polarization and depolarization across the membranes will now take much longer. Hence, the collection of potential in the axon hillock area will take longer as well.