Chapter 12

Chapter 12 - Chapter 12, NERVOUS TISSUE Overview of the...

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Chapter 12, NERVOUS TISSUE Overview of the Nervous System A. Fundamental Types and Properties of Neurons 1. There are three general classes of neurons, which correspond to the three major aspects of nervous system function. a. Sensory (afferent) neurons are specialized to detect changes in their environment called stimuli. b. Interneurons (association neurons) lie within the central nervous system where they receive signals from other neurons and carry out the integrative function of the nervous system. c. Motor (efferent) neurons send signals to muscle and gland cells that carry out the body’s responses to stimuli. 2. Nerve cells exhibit excitability, conductivity and secretion of neurotransmitters and other chemical messengers. B. Subdivisions of the Nervous System 1. The two major subdivisions of the nervous system are the central nervous system or CNS and the peripheral nervous system or PNS. a. The CNS consists of the brain and the spinal cord, and is composed of two types of nervous tissue – gray matter and white matter. b. The PNS consists of the nerves leading to and from the CNS. 2. The motor component of the nervous system is divided into the somatic nervous system, which innervates skeletal muscle and the autonomic nervous system, which innervates cardiac and smooth muscle to control body function. II. Cells of the Nervous System A. Structure of a Neuron 1. The control center of the neuron is its soma or perikaryon (cell body). It contains the nucleus, nucleolus, Nissle bodies (rough ER) many other organelles and supportive neurofibrils. 2. Mature neurons lack centrioles and do not undergo mitosis part adolescence. 3. Major cytoplasmic inclusions are glycogen granules, lipid droplets, melanin and lipofusion. 4. Dendrites, cellular extensions from the cell body, have receptors for neurotransmitters and receive signals from other neurons.
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5. On one side of the soma is the axon hillock, which gives rise to the axon. Axons vary greatly in length and end in a synaptic end bulb through which neurotransmitters are passed to the next neuron. 6. Neurons are classified structurally according to the number of processes extending from the soma: multipolar, bipolar, unipolar and anaxonic. a. Neurons with one axon and several dendrites are multipolar (the most common type). b. Neurons with one axon and one dendrite are bipolar. c. Unipolar neurons have only a single process leading away from the soma. d. Anaxonic neurons have multiple dendrites, but no axon. B. Axonal Transport 1. Axonal transport is the two-way transport of materials along an axon that may be fast o slow. Movement away from the soma is anterograde transport and employs a motor protein called kinesin. 2. Movement toward the soma is retrograde transport and employs a motor
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This note was uploaded on 04/17/2008 for the course BIOL 211 taught by Professor Wilson during the Fall '07 term at Winona.

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Chapter 12 - Chapter 12, NERVOUS TISSUE Overview of the...

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