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