Biology, Eighth Edition (Raven)

Chapter 44: The Nervous System

The Nerve Impulse

What is the source of the electrical impulse in a neuron? The source of the impulse in a neuron is a rapid change in the polarity of the cell membrane in a restricted area. The direction of the electrical gradient is rapidly reversed and then returns to normal. The change in charge stimulates the process to happen in adjacent parts of the cell and the change in polarity travels down the neuron. The change in polarity does not go backward – the area immediately ‘behind’ the action potential is still returning to the resting state and is not stimulated to form another action potential.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	Which of the following statements about the resting membrane potential is TRUE?

		A)	the exterior of the cell has a net negative charge and the interior has a net positive charge
		B)	the exterior of the cell has a net negative charge and the interior is neutral
		C)	the exterior of the cell has a net positive charge and the interior has a net negative charge
		D)	the exterior of the cell has a net positive charge and the interior is neutral
		E)	the exterior of the cell is neutral and the interior has a net negative charge

2.	During depolarization, which of the following statements about voltage-gated ion channels is TRUE

		A)	K⁺ gates open before Na⁺ gates
		B)	Na⁺ gates open before K⁺ gates
		C)	Na⁺ and K⁺ gates open at the same time
		D)	Na⁺ gates open while K⁺ gates remain closed
		E)	K⁺ gates open while Na⁺ gates remain closed

3.	Depolarization occurs because

		A)	more K⁺ diffuse into the cell than Na⁺ diffuse out of
		B)	more K⁺ diffuse out of the cell than Na⁺ diffuse into it
		C)	more Na⁺ diffuse into the cell than K⁺ diffuse out of it
		D)	more Na⁺ diffuse out of the cell than K⁺ diffuse into it
		E)	both Na⁺ and K⁺ diffuse into the cell

4.	The sodium-potassium pump is involved in establishing the resting membrane potential.

		A)	True
		B)	False

5.	The nerve impulse is an electrical current that travels along dendrites or axons.

		A)	True
		B)	False