Explain what would happen if depolarization of the trigger zone led to a negative feedback loop instead of a positive one.

Harry has a kidney condition that causes changes in his body's electrolyte levels (concentration of ions in the extracellular fluid). As a result, he is exhibiting tachycardia, an abnormally fast heart rate. Which ion is involved, and how does a change in its concentration cause Harry's symptoms?

In the CNS, a neuron typically receives information from other neurons at its:

(a) Axon

(b) Nissl bodies

(c) Dendrites

(d) Nucleus

Casey is taking a new medication that blocks potassium channels. What stage of an action potential would be MOST affected by this drug? 

What happens when the neuron reaches threshold (-55 mV)?