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Vandan Desai BIOL 251—Anatomy & Physiology I 1 Chapter 11—Action Potentials I.Functions and Divisions of the Nervous System (pp. 386–387; Figs. 11.1–11.2) A. The central nervous system consists of the brain and spinal cord, and is the integrating and command center of the nervous system (p. 386; Figs. 11.1–11.2). B. The peripheral nervous system is outside the central nervous system (pp. 386–387; Fig. 11.2). 1. The sensory, or afferent, division of the peripheral nervous system carries impulses toward the central nervous system from sensory receptors located throughout the body. 2. The motor, or efferent, division of the peripheral nervous system carries impulses from the central nervous system to effector organs, which are muscles and glands. a. The somatic nervous system consists of somatic nerve fibers that conduct impulses from the CNS to skeletal muscles, and allow conscious control of motor activities. b. The autonomic nervous system is an involuntary system consisting of visceral motor nerve fibers that regulate the activity of smooth muscle, cardiac muscle, and glands. II. Histology of Nervous Tissue (pp. 388–395; Figs. 11.3–11.5; Table 11.1) A. Neuroglia, or glial cells, are closely associated with neurons, providing a protective and supportive network (pp. 388–389; Fig. 11.3). 1. Astrocytes are glial cells of the CNS that regulate the chemical environment around neurons and exchange between neurons and capillaries. 2. Microglia are glial cells of the CNS that monitor health and perform defense functions for neurons. 3. Ependymal cells are glial cells of the CNS that line the central cavities of the brain and spinal cord and help circulate cerebrospinal fluid. 4. Oligodendrocytes are glial cells of the CNS that wrap around neuron fibers, forming myelin sheaths. 5. Satellite cells are glial cells of the PNS whose function is largely unknown. They are found surrounding neuron cell bodies within ganglia. 6. Schwann cells, or neurolemmocytes, are glial cells of the PNS that surround nerve fibers, forming the myelin sheath. B. Neurons are specialized cells that conduct messages in the form of electrical impulses throughout the body (pp. 389–395; Figs. 11.4–11.5; Table 11.1). 1. Neurons function optimally for a lifetime, are mostly amitotic, and have an exceptionally high metabolic rate requiring oxygen and glucose. a. The neuron cell body, also called the perikaryon or soma, is the major biosynthetic center containing the usual organelles except for centrioles. b. Dendrites are cell processes that are the receptive regions of the cell.
Vandan Desai BIOL 251—Anatomy & Physiology I 2 c. Each neuron has a single axon that generates and conducts nerve impulses away from the cell body to the axon terminals.