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Unformatted text preview: Chapter 3: Neurological and Genetic Bases of Behavior 3-1 The Neuron Santiago Ramn y Cajal (1852-1934): discovered that the brain consisted of an untold number of separate, distinct cells. Perhaps millions of separate cells. Further, these specialized cells, called neurons appeared to be responsible for sending and receiving information throughout the body. Neurons: specialized cells in the nervous system that send and receive information. 3-1a; Sensory neurons- detect stimuli inside the body (for example, a headache or strained muscle) or in the world (for example, another person's voice). They send this information from sensory receptors to the brain, usually by way of the spinal cord. In the opposite direction, motor neurons send commands from the brain to glands, muscles, and organs, directing them to do, cease, or inhibit something. Finally, the vast majority of neurons are interneurons , which connect other neurons to one another. One of their most important functions is to link the sensory neurons' input signals with the motor neurons' output signals. 3-1b; Neurons have three basic parts; The central part of the neuron is the soma , which is the Latin word for "body." This cell body contains the nucleus, or control center of the neuron, and other components of the cell that preserve and nourish it. Attached to the soma are branchlike extensions known as dendrites (the Greek word for "trees") that receive information from other neurons and bring it to the soma. As previously noted, each neuron may have hundreds or thousands of dendrites. After integrating this information, the soma transmits it to a tubelike extension called an axon (Greek for "axle"), which carries the information from the soma to the other end of the axon in the form of an electrochemical impulse Many axons are covered with a protective coating of white fatty cells known as a myelin sheath , which hastens the transmission of the electrochemical charge. Scientists believe that the myelin sheath developed in humans as our brains evolved and became larger, making it necessary for information to travel faster over longer distances in the nervous system. Part of the reason children cannot learn and respond as fast as adults in many cognitive and motor tasks is that their axons have not yet been fully covered by these neural speed-enhancing fatty cells. At the end of each axon are branches with knoblike tips called terminal buttons , which closely approach, but do not touch, the dendrites of other neurons. The space between the axon's terminal buttons and the dendrites is less than one-millionth of an inch and is known as the synaptic cleft. The entire area composed of the terminal button of one neuron, the synaptic cleft, and the dendrite of another neuron is the synapse , which in Greek means "to clasp." Nerve tissue throughout the body is composed of two kinds of cells: neurons and supporting glial cells ( glial in Greek means "glue"), which supply the...
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- Fall '10