The nerve impulses always travel in one direction from dendrites to axon terminals. What prevents an action potential from travelling backward?

Select one:

a. Hyperpolarization of the neuron makes the membrane more positive and prevents another action potential.

b. After repolarization, the reversal of ions prevents another action potential as there would not be enough sodium ions outside the cell to rush in.

c. After repolarization, the refractory period occurs, where the sodium ions are found outside the cell.

d. The refractory period prevents another action potential by lowering the threshold potential. My answer is B but not sure if its correct or not. 

 

When a single photon from a source of light hits the retina in the eye, it triggers a signal that travels along the optic nerve to the occipital lobe of the brain. 

The interaction of a photon with the photoreceptors in the retina first causes the movement of sodium ions into a sensory neuron. What happens after the movement of sodium ions?

Select one:

a. Sodium ions move out of a sensory neuron.

b. Potassium ions move into an interneuron.

c. Potassium ions move out of a sensory neuron.

d. Sodium ions move into an interneuron. 

my answer is c but not sure if its correct or not 

 

 

 

 

 

A neuron was isolated from structure number 3 in the diagram above. 

When comparing the velocity of action potentials, structure numbered 3 is much slower than that of structure numbered 4. 

Which of the following explains why this is?

Select one:

a. Structure number 3 has a larger diameter than structure number 4.

b. Structure number 4 does not have myelin sheaths.

c. Structure number 3 does not have myelin sheaths.

d. Structure number 4 has a larger diameter than structure number 2. I put C for this but again not sure if my answer is correct.