CHAPTER 45 Nervous system


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CHAPTER 45: THE NERVOUS SYSTEM Neural Organization: -3 types of neurons: 1) Sensory neurons (afferent neurons): carry impulses from sensory receptors to the central nervous system (CNS): which is composed of the brain and spinal chord 2) Motor neurons (efferent neurons): carry impulses from the CNS to effectors – muscles and glands 3) Interneurons (association neurons): present in most invertebrates and all vertebrates, these neurons are located in the brain and spinal cord of vertebrates, where they help provide more complex reflexes and higher associative functions, including learning and memory Peripheral nervous system (PNS): In vertebrates, the sensory and motor neurons Somatic neurons: motor neurons that stimulate skeletal muscles to contract Autonomic motor neurons: regulate the activity of smooth muscles, cardiac muscle, and glands; further broken down into the sympathetic and parasympathetic divisions which act to counterbalance each other. STRUCTURE OF A NEURON: Cell body: an enlarged region containing the nucleus Dendrites: one or more cytoplasmic extensions extending from the cell body Axon: conducts impulses from the cell body; each neuron as a single axon leaving its cell body Supporting cells (neuroganglia): ten times smaller and more numerous than neurons and serve a variety of functions, including supplying the neurons with nutrients, removing wastes from neurons, guiding axon migration, and providing immune functions -2 most important neuroganglia in vertebrates: 1. Schwann cells: produce myelin in the PNS 2. Oligodendrocytes: produce myelin in the CNS Myelin sheats: surround the axons of many neurons; an insulating covering consisting of multiple layers of compacted membrane. The multiple membrane layers facilitate more rapid conduction of impulses.
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-In the CNS, myelinated axons form the white matter , and the unmyelinated dendrites and cell
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This note was uploaded on 04/17/2008 for the course BIOL 001 taught by Professor Noel during the Spring '08 term at Marquette.

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