Expert: John Locke - 4/22/2009

Question
Hi, i am doing a study guide for my Anatomy and Physiology class and could not find answers to these questions in my book. Any help would be greatly appreciated. These questions are over the nervous system.
1.Astrocytes, glial cells, oligodendrocytes, and Schwann cells are all considered what classification of cells?
(I have down neuroglia b/c all of the above except for glial cells are types of glial cells)
2.A neuron's resting membrane potential is established and maintained by what? (I put: unequal distribution of ions in the ECF and cytosol, inablilty of most anions to leave the cell, and electrogenic nature of the Na+/K+ ATPases. The book didnt give a clear answer...)
3.Several neurons in the brain sending impulses to a single motor neuron that terminates at a neuromuscular junction is an example of what type of circuit?
4. Where does integration for reflexes take place?(I put in the brain stem and spinal cord but the book didnt give an answer so I wasnt sure)
5. Define selectivity.(I couldn't find anything on this..I looked in the nervous system chapters and in the index)
6. Where do the axons from the parasympathetic division emerge from? (I couldnt find anyhting on this one either...)
7. What is gestation?(I couldnt find anything on this onerelating to the nervous system..)


Answer
Thanks for using AllExperts.

1. You were right with your initial thought: the listed cells all comprise neuroglia, the supporting cells of the CNS and PNS. "Glial cell" by itself does not refer to a single cell type; it is the entire class of supporting nervous system cells. The list does include glial cells, but that probably means to refer to microglia, which are CNS macrophages.

2. You've already identified the major factors correctly. Three major elements establish the RMP of a neuron: ionic diffusion across the cell membrane with differential permeability, the Na-K ATPase pump, and the inability of most anions to cross the cell membrane. The last factor contributes to the formation of an equilibrium between impermeant anions and permeant cations called the Gibbs-Donnan equilibrium. See here:
http://entochem.tamu.edu/Gibbs-Donnan/index.html

3. I'm not sure what term the question is looking for exactly. I would describe it as an integrating circuit, since the single motor neuron is integrating the various signals it's receiving and converting them into a single impulse when it fires into the NMJ.

4. Integration for reflexes takes place within the gray matter of the spinal cord.

5. There are actually a few definitions of selectivity in reference to the nervous system. Ion channels within the cell membrane display selectivity (often described as a selectivity filter) in that each type of channel can only accommodate a particular ion. Some receptors also display selectivity in the sense that they can bind several different ligands and trigger different signaling pathways depending on which ligand binds. Traditional receptor theory generally holds that a single receptor binds a single type of ligand to activate a single signaling pathway. Receptor selectivity is an alternative.

6. Neurons that comprise the PS nervous system arise from cranial nerves 3, 7, 9, and 10, and the sacral nerves S2, S3, and S4. Cranial nerves 3, 7, and 9 supply structures solely within the head and neck, while cranial nerve 10 (the vagus nerve) supplies some of the head and most of the internal organs. The sacral nerves supply the remainder of the internal organs not covered by the vagus. I'm not sure what the question is asking by where the axons emerge from; if the question wants you to get super specific, these are the bony openings that each of those nerves pass through:

CN 3: superior orbital fissure in the skull
CN 7: internal acoustic meatus in the skull
CN 9 and 10: jugular foramen in the skull
Sacral nerves: sacral foramina 2-4 in the sacrum

7. Gestation is the process of carrying a fetus in utero inside a viviparous (egg-producing) animal. Each embryo that is carried by the female constitutes a single gestation. The term is not synonymous with pregnancy because a single pregnancy can include the development of multiple embryos, which would mean multiple gestations. A woman who gives birth to twins, for instance, would have undergone a single pregnancy but two gestations.

Good luck.