Anatomy and Physiology I The Nervous System Basic

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. 2 a 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 Cell body Axon (central process) Axon (peripheral process) Sensory receptor Sensory (afferent) neuron Interneurons Motor (efferent) neuron Axon Effector (muscle or gland) Axon terminal Copyright © The Mc. Graw-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 600 x Axon © Ed Reschke Copyright © The Mc. Graw-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 Mc. Graw-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. 4 a Medullated or Myelinated Axon Dendrite Unmyelinated region of axon Myelinated region of axon Node of Ranvier Axon Neuron cell body nucleus Schwann cells Neurolemma containing nucleus Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 10. 4 b Schwann Cell Schwann cell nucleus Myelin sheath Axon Myelin Neurofibrils Node of Ranvier Neurilemma 650 x Axon © Biophoto Associates/Photo Researchers, Inc. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 10. 4 c Schwann Cell with non-myelinated Axons Axo n Enveloping Schwann cell nucleus Longitudinal groove Unmyelinated axon Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 10. 5 Schwann cell cytoplasm Myelin sheath Myelinated axon 30, 000 x Unmyelinated axon Copyright © The Mc. Graw-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 Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 10. 9 Neuron cell body Neuroglia SEM 10, 000 x 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 Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fig. 10 Changes over time Axonal Repair Motor neuron cell body Axon Site of injury Skeletal muscle fiber Schwann cells (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 Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.