A neuron that engages in spatial summation acquires a mutation that causes dendrite overgrowth and promiscuous synapsing. What is the likely outcome?

Question

A.  abnormally low frequency of action potentials
B.  summation will not occur
C.  abnormally high frequency of action potentials
D.  action potentials with stronger depolarization


Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content/Choose Answer
· What do you already know about summation? What other information is related to the question?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  abnormally high frequency of action potentials

Clarify Question
· What is the key concept addressed by the question?
        o The effects of dendrite overgrowth on spatial summation.
· What type of thinking is required?
        o The question is asking you to evaluate the effects of dendrite overgrowth on spatial summation and action potential production.

Gather Content/Choose Answer
· What do you already know about summation? What other information is related to the question?
        o To solve this problem, you’ll need to understand spatial summation. Often, the excitatory post-synaptic potential (EPSP) coming from one dendrite is not great enough to reach threshold, and thus elicit an action potential in the post-synaptic neuron. But as the post-synaptic neuron usually has many dendrites synapsing with it, the potential of the neuron is determined by the summation of all the excitatory (EPSP) and inhibitory (IPSP) inputs from these multiple synapses. If a neuron produces more dendrites, it will increase the chance of more EPSPs from separate dendrites, thus improving the probability that an action potential will “fire” and increasing the rate of firing.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o If you figured out the correct answer, good job! If not, where did you go wrong? Did you think that more dendrites and more summation would lead to action potentials with greater amplitudes? Remember that action potentials are “all-or-none” responses that increase in frequency, not amplitude, in response to excitatory stimuli. Answer (b) stated that summation would not occur, but increasing the number of synapses increases the probability of summation instead of decreasing it.