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The nervous system

Ch. 7. The nervous system. Functions of the Nervous System. Sensory input Sensory receptors gather information about internal and external changes Integration Interpretation of sensory input Motor output Activation of effector organs produces a response. Sensory input. Integration.

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The nervous system

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  1. Ch. 7 The nervous system

  2. Functions of the Nervous System • Sensory input • Sensory receptors gather information about internal and external changes • Integration • Interpretation of sensory input • Motor output • Activation of effector organs produces a response

  3. Sensory input Integration Motor output Figure 7.1

  4. Structural Classification of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Integration and command center • Peripheral nervous system (PNS) • Paired spinal and cranial nerves carry messages to and from the CNS

  5. Functional Classification : The Peripheral Nervous System (PNS) • Two functional divisions • Sensory (afferent) division • Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints • Visceral afferent fibers—convey impulses from visceral organs • Motor (efferent) division • Transmits impulses from the CNS to effector organs

  6. Motor Division of PNS • Somatic (voluntary) nervous system • Conscious control of skeletal muscles

  7. Motor Division of PNS • Autonomic (involuntary) nervous system (ANS) • Visceral motor nerve fibers • Regulates smooth muscle, cardiac muscle, and glands • Two functional subdivisions • Sympathetic • Parasympathetic

  8. Peripheral nervous system (PNS) Central nervous system (CNS) Sensory (afferent) division Motor (efferent) division Somatic NS Autonomic NS Somatic motor (voluntary) Visceral motor (involuntary) Skin cardiac muscles, smooth muscles, and glands skeletal muscles Sympathetic Parasympathetic Conserves energy Mobilizes body systems during activity Promotes house- keeping functions during rest Heart Bladder Figure 7.2

  9. Nervous Tissue: Structure and Function • Two principal cell types • Neurons—excitable cells that transmit electrical signals

  10. Nervous Tissue: Structure and Function • Neuroglia (glial cells)—supporting cells: • Astrocytes (CNS) • Microglia (CNS) • Ependymal cells (CNS) • Oligodendrocytes (CNS) • Satellite cells (PNS) • Schwann cells (PNS)

  11. Capillary Neuron Astrocyte (a) Astrocytes are the most abundantCNS neuroglia. Figure 7.3

  12. Neuron Microglial cell (b) Microglial cells are defensive cells inthe CNS. Figure 7.3

  13. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinalfluid-filled cavities. Figure 7.3

  14. Myelin sheath Process of oligodendrocyte Nerve fibers (d) Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers. Figure 7.3

  15. Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells(form myelin) surround neurons in the PNS. Figure 7.3

  16. Schwann cell plasma membrane 1 Schwann cell cytoplasm Axon Schwann cell nucleus 2 Neurilemma 3 Myelin sheath (a) Myelination of a nervefiber (axon) Figure 7.5

  17. Cell Body • Network of neurofibrils help maintain cell shape • Axon hillock—cone-shaped area from which axon arises • Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS

  18. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Axon (impulse generating and conducting region) Impulse direction Nucleus Node of Ranvier Nissl bodies Axon terminals (secretory region) Axon hillock Schwann cell (one inter- node) Neurilemma (b) Terminal branches Figure 7.4

  19. Processes • Dendrites • Receptive (input) region of a neuron • Convey electrical signals toward cell body • Axons • Generate & transmits nerve impulses away from cell body • One axon/cell arising from axon hillock • Long axons=nerve fibers • Bundles of processes are called: • Tracts in the CNS • Nerves in the PNS

  20. Myelin Sheaths in the CNS • Formed by processes of oligodendrocytes, not the whole cells • Nodes of Ranvier are present • No neurilemma

  21. Myelin sheath Process of oligodendrocyte Nerve fibers (d) Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers.

  22. White Matter and Gray Matter • White matter • Dense collections of myelinated fibers • Gray matter • Mostly neuron cell bodies and unmyelinated fibers

  23. Structural Classification of Neurons • Three types: • Multipolar—1 axon and several dendrites • Most abundant • Motor neurons and interneurons • Bipolar—1 axon and 1 dendrite • Rare, e.g., retinal neurons

  24. Structural Classification of Neurons • Unipolar—single, short process that has two branches: • Peripheral process—more distal branch, often associated with a sensory receptor • Central process—branch entering the CNS

  25. Functional Classification of Neurons • Three types: • Sensory (afferent) • Transmit impulses from sensory receptors toward the CNS • Motor (efferent) • Carry impulses from the CNS to effectors

  26. Functional Classification of Neurons • Interneurons (association neurons) • Shuttle signals through CNS pathways; most are entirely within the CNS

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