Cytology and Organization of Cell Types Light and Electron Microscopy Rochelle s cohen and donald w. pfaff CoNTENTS NEURONAL RESPONSE TO A CHANGING ENVIRONMENT MECHANISMS OF NEURONAL FUNCTION CYTOSKELETON DETERMINATION OF NEURONAL FORM NEURONAL SYNAPSES GLIAL CELLS SELECTED READING 1. NEURONAL RESPONSE TO A CHANGING changes in the internal milieu, may have to travel long ENVIRONMENT distances through the bloodstream to reach their tar- Although neurons are cells that conform to funda- gets. This voyage takes time-seconds, hours, oreven dered slow- mental cellular and molecular principles, they are acting agents, although evidence is differentiated from other cells in ways that reflect effects of hormones, such as for the steroid hormones their unique ability to receive, integrate, store, and estrogen and corticosterone. Because hormones are send information Signals received from the internal diluted in the bloodstream, they must be very potent and external environment are processed by neurons, and act at low concentrations to be effective. These resulting in the generation of a response that can be properties are sufficient for endocrine functions neces- communicated to other neurons or tissues. In this sary to keep the organism in a homeostatic state, but way, the organism can successfully adapt to rapidly more immediate challenges require a rapid coupling of changing events, ensuring its survivaL. stimulus and response and a faster rate of communica All organisms possess stimulus-response systems tion among relevant cells. Rapid communication is that permit them to sense environmental fluctuations. achieved exquisitely by the neuron, whose form and In bacteria, for example, intracellular regulatory mole- function are designed to meet such demand cules couple the stimulus to the proper response Mul- The rapidity with which neurons can conduct signals ticellularorganisms must communicate information to (i.e, time is measured in less than I ms) is primarily a other cells, some of which may be local, but others are function of certain basic features common to all neu- positioned some distance away. Communication may rons: polarization of their form, unique associations be accomplished by the release of chemical messengers with their neighboring neurons, and special properties that bind to specific compler itary proteins called of their plasma membranes. Information is conveyed receptors, located on the surface of other cells. For within and between neurons in the form of electrical local communication, diffusion can deliver the mes- and chemical signals, respective\'. functional circuits Neurons are orga senger to the receptive surface. Messengers such as nized into complex networks, or hormones, secreted by endocrine cells in response to which translate these signals into the myriad responses that constitute an organism's behavioral repertoire From: Neuroscience in Medicine, Edited by: P. M. Conn Neural circuits develop in a predictable manner. e Humana Press. Totowa NJ 2008 achieving organizational specificity at functional sites1 Cytology and Organization of Cell Types: Light and Electron Microscopy Rochelle S. Cohen and Donald W. Pfaff CONTENTS NEURONAL RESPONSE TO A CHANGING ENVIRONMENT MECHANISMS OF NEURONAL FUNCTION CYTOSKELETON DETERMINATION OF NEURONAL FORM NEURONAL SYNAPSES GLIAL CELLS SELECTED READING 1. NEURONAL RESPONSE TO A CHANGING ENVIRONMENT Although neurons are cells that conform to funda￾mental cellular and molecular principles, they are differentiated from other cells in ways that reflect their unique ability to receive, integrate, store, and send information. Signals received from the internal and external environment are processed by neurons, resulting in the generation of a response that can be communicated to other neurons or tissues. In this way, the organism can successfully adapt to rapidly changing events, ensuring its survival. All organisms possess stimulus-response systems that permit them to sense environmental fluctuations. In bacteria, for example, intracellular regulatory mole￾cules couple the stimulus to the proper response. Mul￾ticellular organisms must communicate information to other cells, some of which may be local, but others are positioned some distance away. Communication may be accomplished by the release of chemical messengers that bind to specific complementary proteins called receptors, located on the surface of other cells. For local communication, diffusion can deliver the mes￾senger to the receptive surface. Messengers such as hormones, secreted by endocrine cells in response to changes in the internal milieu, may have to travel long distances through the bloodstream to reach their tar￾gets. This voyage takes time—seconds, hours, or even days—and hormones are, in general, considered slow￾acting agents, although evidence is emerging for rapid effects of hormones, such as for the steroid hormones estrogen and corticosterone. Because hormones are diluted in the bloodstream, they must be very potent and act at low concentrations to be effective. These properties are sufficient for endocrine functions neces￾sary to keep the organism in a homeostatic state, but more immediate challenges require a rapid coupling of stimulus and response and a faster rate of communica￾tion among relevant cells. Rapid communication is achieved exquisitely by the neuron, whose form and function are designed to meet such demands. The rapidity with which neurons can conduct signals (i.e., time is measured in less than 1 ms) is primarily a function of certain basic features common to all neu￾rons: polarization of their form, unique associations with their neighboring neurons, and special properties of their plasma membranes. Information is conveyed within and between neurons in the form of electrical and chemical signals, respectively. Neurons are orga￾nized into complex networks, or functional circuits, which translate these signals into the myriad responses that constitute an organism’s behavioral repertoire. Neural circuits develop in a predictable manner, achieving organizational specificity at functional sites From: Neuroscience in Medicine, Edited by: P. M. Conn Humana Press, Totowa, NJ 2008 1