Supporting neural signals
In this section, we’ll see how neurons support neural signals by using the sodium–potassium pump to maintain the ion gradients that underlie membrane potentials, and by using myelination to speed up the spread of action potentials along axons.
1) We'll start with the sodium-potassium pump. Watch this video and read the associated article:
Article: Know Your Brain - Sodium-Potassium Pump
2) Now, watch this video about myelin:
3) Next, watch this video about multiple sclerosis, the most common disease that affects myelination:
4) Finally, answer these questions to test your understanding:
1. The sodium-potassium pump is a protein pump whose main function is to transport sodium ions out of the cell and potassium ions into the cell. Each cycle of the pump moves ____ sodium ions out of the cell and ____ potassium ions into the cell.
- A. 1, 3
- B. 2, 3
- C. 3, 2
- D. 3, 1
Show Answer
Correct answer: C
Each cycle of the pump moves 3 sodium ions out of the cell and 2 potassium ions into the cell. The actions of the pump help to ensure that sodium ions are more concentrated outside the cell and potassium ions are more concentrated inside the cell.
2. Which of the following supplies the energy needed for the sodium-potassium pump to function?
- A. sodium moving down its concentration gradient
- B. breakdown of ATP
- C. changes in membrane potential
- D. osmosis of water across the cell membrane
Show Answer
Correct answer: B
The sodium-potassium pump is a large membrane-associated enzyme that uses the energy of adenosine triphosphate, or ATP, to transport sodium and potassium ions across the cell membrane.
3. Each section of myelination on an axon is called a/an:
- A. node of Ranvier
- B. neurofibril
- C. axon hillock
- D. internode
Show Answer
Correct answer: D
Sections of myelin on an axon are called internodes. The gaps between internodes are called nodes of Ranvier.
4. What makes the nodes of Ranvier important to the propagation of action potentials?
- A. They store and release neurotransmitters
- B. They prevent the action potential from traveling backward along the axon
- C. They insulate the axon to increase conduction velocity
- D. They are densely populated with voltage-gated sodium channels
Show Answer
Correct answer: D
Nodes of Ranvier contain high concentrations of voltage-gated sodium channels, which allow action potentials to be regenerated at each node. This enables saltatory conduction, where the signal “jumps” from node to node, greatly increasing conduction speed along myelinated axons.
5. These glial cells are responsible for myelinating neurons in the central nervous system:
- A. Schwann cells
- B. microglia
- C. astrocytes
- D. oligodendrocytes
Show Answer
Correct answer: D
Myelin is an insulating material that covers the axons of most neurons in the nervous system. Oligodendrocytes are the cells responsible for myelinating central nervous system neurons, while Schwann cells myelinate neurons in the peripheral nervous system.
6. Multiple sclerosis, an immune-mediated disease that targets myelin, primarily affects the:
- A. central nervous system
- B. peripheral nervous system
- C. autonomic nervous system
- D. enteric nervous system
Show Answer
Correct answer: A
Multiple sclerosis is a central nervous system disorder that is characterized by damage to myelin, the insulatory material that surrounds the axons of neurons. This damage is linked to disruptions in healthy neuronal function, which are thought to lead to the symptoms of the disease.
