Biology, Eighth Edition (Raven)

Chapter 43: The Animal Body and Principles of Regulation

Action Potential Propagation in Myelinated Neurons

What is the function of myelinated neurons? The myelin sheath around most vertebrate axons provides a layer of insulation that prevents the loss of the electrical signal from an action potential. Myelin is lipid rich substance that does not conduct electricity well. Because of the insulation provided by the myelin, action potentials can travel much more rapidly down myelinated axons than down unmyelinated axons. Myelin also isolates axons from one another in the white matter of the brain preventing the short-circuiting of nerve signals in the central nervous system.

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

1.		Upon arriving at the node of a myelinated neuron, the excitatory postsynaptic potential (EPSP)...
			A)	causes potassium channels to open and potassium to flow out of the neuron.
			B)	causes sodium channels to open and sodium to flow into the neuron.
			C)	causes the neurons inner cell membrane potential to peak.
			D)	causes the neurons inner cell membrane to become more positively charged.
			E)	causes the neurons outer cell membrane to become more positively charged.
2.		As a result...
			A)	the neurons inner cell membrane potential increases.
			B)	sodium ions diffuse through the neuron’s intracellular fluid of the internode.
			C)	repolarization of the neurons inner cell membrane occurs.
			D)	the sodium channels open and sodium ions pour into the intracellular fluid.
			E)	the potassium channels open and potassium ions pour into the extracellular fluid.
3.		Which results in...
			A)	the neuron’s inner cell membrane returning to resting membrane potential.
			B)	the EPSP causing the next node to become more positive.
			C)	the neuron’s outer cell membrane returning to resting membrane potential.
			D)	sodium ions diffusing through the intracellular fluid of the internode to the next node.
			E)	repolarization of the neurons inner cell membrane.
4.		The inflow of sodium ions into the intracellular fluid causes depolarization of the neuron’s inner cell membrane.
			A)	True
			B)	False
5.		During the transmission of an action potential along the neurilemma of a myelinated neuron, as one node is repolarizing, the next node is depolarizing.
			A)	True
			B)	False