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Anatomy and Physiology I The Nervous System Basic Structure and Function Instructor: Mary Holman Three Basic Functions of the Nervous System Sensory Function Sensory or afferent neurons Integrative Function Interneurons Motor Function Motor or efferent neurons Fig. 10.2a CNS Central Nervous System vs PNS Peripheral Nervous System Brain Cranial nerves (12 pairs) Spinal cord Spinal nerves (31 pairs) Divisions of the Nervous System Central Nervous System CNS Brain Spinal Cord Peripheral Nervous System PNS Cranial Nerves Spinal Nerves Ganglia Sensory Receptors Divisions of the PNS Somatic Nervous System Sensory neurons Motor neurons to skeletal muscle only Autonomic Nervous System Autonomic sensory neurons - visceral Motor neuron impulses to smooth & cardiac muscle, glands and adipose tissue Sympathetic vs. Parasympathetic Motor Divisions Enteric Nervous System Enteric complexes of the gut Fig. 10.7 Central nervous system Peripheral nervous system Cell body Dendrites Sensory receptor Cell body Axon (central process) Axon (peripheral process) Sensory (afferent) neuron Interneurons Motor (efferent) neuron Axon Effector (muscle or gland) Axon Axon terminal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cells of Neural Tissue • Neurons The electrically excitable nerve cells responsible for the functions of the nervous system • Neuroglia (glia, neuroglia, glial) Support, nourish, & protect neurons Fig. 10.1 The Neuron Dendrites Cell body Nuclei of neuroglia 600x Axon © Ed Reschke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.3 Neuron with Myelinated Axon Chromatophilic substance (Nissl bodies) Dendrites Cell body Nucleus Nucleolus Neurofibrils Axonal hillock Synaptic knob of axon terminal Impulse Axon Nodes of Ranvier Myelin (cut) Axon Schwann cell Nucleus of Schwann cell Portion of a collateral Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.6 Dendrites Peripheral process Direction of impulse Axon Central process Axon (a) Multipolar Axon (b) Bipolar (eyes,nose,ears) (c) Unipolar Neuroglia of the PNS • Schwann Cells Produce myelin sheath • Satellite Cells Support neuronal clusters in ganglia Fig. 10.4a Medullated or Myelinated Axon Dendrite Unmyelinated region of axon Myelinated region of axon Node of Ranvier Axon Neuron Neuron cell body nucleus Schwann cells Neurolemma containing nucleus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.4b Schwann Cell Schwann cell nucleus Myelin sheath Axon Myelin Neurofibrils Node of Ranvier Neurilemma 650x Axon © Biophoto Associates/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.4c Schwann Cell with non-myelinated Axons Enveloping Schwann cell Schwann cell nucleus Longitudinal groove Unmyelinated axon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.5 Schwann cell cytoplasm Myelin sheath Myelinated axon 30,000x Unmyelinated axon Copyright © The McGraw-Hill Companies, Inc. Permission © Dennis Emery required for reproduction or display. Neuroglia of the CNS • Astrocytes major support cells provide nutrients, monitor metabolism etc • Oligodendrocytes myelinate axons in CNS • Microglia phagocytic • Ependymal line ventricles & central canal produce cerebrospinal fluid (CSF) Fig. 10.8 Neuroglia of CNS Fluid-filled cavity of the brain or spinal cord Neuron Ependymal cell Oligodendrocyte Astrocyte Microglial cell Axon Myelin sheath (cut) Capillary Node of Ranvier Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.9 Neuron cell body Neuroglia SEM 10,000x Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R.G. Kessel and R.H. Kardon. ©1979 W.H. Freeman and Company Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 10.10 Changes over time Axonal Repair Motor neuron cell body Site of injury Skeletal muscle fiber Schwann cells Axon (a) Distal portion of axon degenerates (b) Proximal end of injured axon regenerates into tube of Schwann cells (c) Schwann cell tube extends distal to injury (d) Schwann cells Form new myelin sheath (e) Former connection reestablished Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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