Tutorial 1: Structure of the Neuron

Intro | Axon | Axon Hillock | Dendrites | Myelin Sheath | Nodes of Ranvier | Soma | Synapse | Terminal Buttons

Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test

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A neuron is the functioning unit of the nervous system; specialized to receive, integrate, and transmit information. The flow of information moves in the following direction: dendrite to soma to axon to terminal buttons to synapse. Although there are many types of neurons among the estimated ten billion in the human brain, each typically shares the characteristics shown in Figure 1.

Advanced

Neurons are distinguished and categorized according to general function; there are receptor or sensory neurons, motor neurons and interneurons. Sensory or afferent (carrying toward the brain) neurons are specialized to be sensitive to a particular physical stimulation such as light (vision), sound (audition), chemical (olfaction), or pressure (touch). Motor or efferent (carrying away from the brain) neurons receive impulses from other neurons and transmit this information to muscles or glands. Interneurons or intrinsic neurons form the largest group in the nervous system. They form connections between themselves and sensory neurons before transmission of control to motor neurons. Neurons also vary according to shape. For example, some have more elaborate dendritic branching while others differ in the placement of the cell body relative to other portions of the neuron.

In addition to neurons, the nervous system is populated with another category of cells, glial cells. Glial cells are approximately 10 times more plentiful than neurons. But since they are approximately one-tenth the size, they take up equal space. Glia is a Greek term meaning glue. Researchers originally believed that glial cells served as the putty that held the neurons together. Recent research indicates that these cells provide very important contributions.

Oligodendrocytes and Schwann cells form the myelin sheaths that insulate axons in the central and peripheral nervous systems, respectively. The tiny microglia and the star-shaped astrocytes remove waste materials that are created primarily when neurons die. Both glial types release chemicals in the vacinity of dying neurons (for e.g., following a stroke) and promote the growth of dendrites and axons of healthy neurons in the same area, perhaps stimulating recovery of function. Nitric oxide speeds up the dying process when released close to weakened neurons. Radial glial cells (a type of astrocyte) guide the migration of neurons and the path of sprouting and growing dendrites and axons during embryonic development of the nervous system. Astrocytes also exchange K+ and other chemicals with neurons and act as an intermediary by transporting substances between neurons and the bloodstream.

Suggestions for further study

SUGGESTED READINGS:

Baker, P.F. (1966, March). The nerve axon. Scientific American, 214(3) , 74-82.

Berridge, M.J. (1985, October). The molecular basis of communication within the cell. Scientific American, 253(4), 142-152.

Fischbach, G.D. (1992, September). Mind and brain. Scientific American, 267(4), 48-57.

Glausiusz, J. (1996, August). Brain, heal thyself. Discover, 17(8), 28-29.
About stimulating new neuronal growth in old brains.

Goldberger, A.L. Rigney, D.R., West, B.J. (1990, February). Chaos and fractals in human physiology, Scientific American, 262(2), 42-49.

Goldman, C.SS., Bastiani, M.J. (1984, December). How embryonic nerve cells recognize one another. Scientific American, 251(6), 58-66.

Halloway, M. (1992, January). Under construction. Temporary scaffolding guides nerves in the developing brain. Scientific American, 266(1), 25-26.

Halloway, M. (1992, December). Unlikely messengers. How do nerve cells communicate?. Scientific American, 267(6), 52, 56.

Horgan, J. (1995, August). It's all in the timing. Neurons may be more punctual than had been supposed. Scientific American, 273(2), 16-18.

Hubel, D.H. (1979, September). The brain. Scientific American, 241(3), 44-53.

Kalil, R.E. (1989, December). Synapse formation in the developing brain. Scientific American, 261(6), 76-79, 82-85.

Kandel, E.R. (1979, September). Small systems of neurons. Scientific American, 241(3), 66-76.

Lusted, H.S. & Knapp, R.B. (1996, October). Controlling computers with neural signals. Scientific American, 82-87.

Morell, P., Norton, W.T. (1980, May). Myelin, Scientific American, 242(5), 88-90, 92, 96.

Nauta, W.J., Feirtag, M. (1979, September). The organization of the brain. Scientific American, 241(3), 88-111.

Patterson, P.H., Potter, D.D., Furshpan, E.J. (1978, July), The chemical differentiation of nerve cells, Scientific American, 239(1), 50-59.

Radetsky, P. (1991, April). The brainiest cells alive. Discover, 12(4), 83-90.
About culturing neurons.

Rennie, J. (1990, January). Nervous excitement. Scientific American, 262(1), 21.

Schwartz, J.H. (1980, April). The transport of substances in nerve cells. Scientific American, 242(4), 152-71.

Selkoe, D.J. (1992, September). Aging brain, aging mind, Scientific American, 267(3), 134-142.

Shepherd, G.M. (1978, February). Microcircuits in the nervous system, Scientific American, 238(2), 93-103.

Snyder, S.H., Bredt, D.S. (1992, May), Biological roles of nitric oxide, Scientific American, 266(5), 68-71, 74-77.

Stent, G.S. (1972, September). Cellular communication. Scientific American, 227(3), 43-51.

Stevens, C.F. (1979, September). The neuron. Scientific American, 241(3), 54-65.

Streit, W.J. & Kincaid-Colton, C.A. (1995, November).The brain's immune system. Scientific American, 54-61.
About the brain's supportive astrocytes.

Tank, D.W., Hopfield, J.J. (1987, December). Collective computation in neuronlike circuits, Scientific American, 257(6), 104-114.

Taubes , G. (1998, May). Ontogeny recapitulated, Discover, 19(5), 66-72.
About the regeneration of neurons.

Wessels, N.K. (1971, October). How living cells change shape, Scientific American, 255(4), 77-82.

RELATED LINKS:

http://www.sfn.org/briefings/neurotrophic.html
(Neurotropic Factors)
Society for Neuroscience -- Brain Briefings, 1994.
Neuronal growth.

http://www.sfn.org/briefings/axon.html
(Axon Guidance)
Society for Neuroscience -- Brain Briefings, 1995.
Mechanisms of brain development and regeneration.

http://www.cogsci.soton.ac.uk/bbs/Archive/bbs.sinden.html
(Neural transplantation and recovery of cognitive function)
Sinden, J.D., Hodges, H., & Gray, J.A. (1995). Behavioral and Brain Sciences 18 (1): 10-35.