If you increase the stimulus intensity past the threshhold level for a neuron, the response intensity ___?

Question

[a] increases dramaticly

[b] increases proportionately

[c] ceases

[d] remains constant

Answer 1

Remains constant.  Action potentials are all or nothing and they do not exceed the all.

Answer 2

mom said [D] but she was not 100% sure ;)

Answer 3

This depends on the neuron in question.  For example, if you were recording a neuron in the primary auditory cortex, you would find that each neuron had a characteristic frequency at which it responded with the lowest sound intensity going into the ear.  If you raise the sound intensity, the neuron in the cortex responds by raising the frequency of its firing.  That is, for a neuron in primary auditory cortex, answer b is the best, but not entirely correct answer.  The reason that it is not completely correct is that the increase in firing is not necessarily proportional to the increase in intensity.  Whether it increases dramatically, as in answer a, is unclear because the term dramatically is not defined here.

In other neural systems, the firing rate might decrease because of lateral inhibition.  This happens in the eye of the moth where high light intensity causes some neurons in the eye to slow down their responses because their neighboring cells are responding more quickly but are inhibiting their neighbors.  Moths are flying towards the darkest locations which they perceive to be next to the brightest sources of light.

In summary, there is no answer that will apply to all neurons.

However,