Question

1. Name the three phases of an action potential. Describe for each the underlying molecular basis and the ion involved. Why is the term voltage-gated channel applied to Na+ channels involved in the generation of an action potential?

2. Explain why the strength of an action potential doesn’t decrease as it travels down an axon.

3. Neurons, particularly those in the brain, receive multiple excitatory and inhibitory signals. What is the name of the extension of the neuron at which such signals are received? How does the neuron integrate these signals to determine whether or not to generate an action potential?

Answer 1

1.

The action potential consists mainly of three phases, namely:

a. Depolarization : This phase is also known as the rising phase. Here the positively loaded sodium ions, immediately move via accessible voltage congregated sodium pathways into the neuron.

b. Repolarization : This phase is also known as the falling phase. This is induced by delayed concluding of sodium pathways and opening of voltage congregated potassium pathways.

c. Hyperpolarization : This is a phase where certain potassium pathways stay exposed and sodium pathways gets reformed.

In the condition where voltage congregated sodium pathways are open, they create a small aperture in the the cytoplasm which permits the sodium ions to move inside the cell wile depolarizing the cell and creating the upstroke within the action potential.

2.

When the action potential travels down as axon, the covering layer of the axon performs depolarization and repolarization. There are certain breaks known as the Nodes of Ranvier within the myelin, which accomodate sodium and potassium pathways, permitting the action potential to migrate promptly dropping within the axon by vaulting from node to node.