Copyright © 2010 Pearson Education, Inc. THE NERVOUS SYSTEM Ch. 7

Copyright © 2010 Pearson Education, Inc. Functions of the Nervous System 1.Sensory input Sensory receptors gather information about internal and external changes 2.Integration Interpretation of sensory input 3.Motor output Activation of effector organs produces a response

Copyright © 2010 Pearson Education, Inc. Figure 7.1 Sensory input Motor output Integration

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. Functional Classification : The Peripheral Nervous System (PNS) Two functional divisions 1.Sensory (afferent) division Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints Visceral afferent fibers—convey impulses from visceral organs 2.Motor (efferent) division Transmits impulses from the CNS to effector organs

Copyright © 2010 Pearson Education, Inc. Motor Division of PNS 1.Somatic (voluntary) nervous system Conscious control of skeletal muscles

Copyright © 2010 Pearson Education, Inc. Motor Division of PNS 2.Autonomic (involuntary) nervous system (ANS) Visceral motor nerve fibers Regulates smooth muscle, cardiac muscle, and glands Two functional subdivisions Sympathetic Parasympathetic

Copyright © 2010 Pearson Education, Inc. Figure 7.2 Central nervous system (CNS) Peripheral nervous system (PNS) Parasympathetic Conserves energy Promotes house- keeping functions during rest Motor (efferent) division Sensory (afferent) division Somatic NS Somatic motor (voluntary) skeletal muscles Sympathetic Mobilizes body systems during activity Autonomic NS Visceral motor (involuntary) cardiac muscles, smooth muscles, and glands Skin Heart Bladder

Copyright © 2010 Pearson Education, Inc. Nervous Tissue: Structure and Function Two principal cell types 1.Neurons—excitable cells that transmit electrical signals

Copyright © 2010 Pearson Education, Inc. 2.Neuroglia (glial cells)—supporting cells: Astrocytes (CNS) Microglia (CNS) Ependymal cells (CNS) Oligodendrocytes (CNS) Satellite cells (PNS) Schwann cells (PNS) Nervous Tissue: Structure and Function

Copyright © 2010 Pearson Education, Inc. Figure 7.3 (a) Astrocytes are the most abundant CNS neuroglia. Capillary Neuron Astrocyte

Copyright © 2010 Pearson Education, Inc. Figure 7.3 (b) Microglial cells are defensive cells in the CNS. Neuron Microglial cell

Copyright © 2010 Pearson Education, Inc. Figure 7.3 Brain or spinal cord tissue Ependymal cells Fluid-filled cavity (c) Ependymal cells line cerebrospinal fluid-filled cavities.

Copyright © 2010 Pearson Education, Inc. Figure 7.3 (d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Nerve fibers Myelin sheath Process of oligodendrocyte

Copyright © 2010 Pearson Education, Inc. Figure 7.3 (e) Satellite cells and Schwann cells (form myelin) surround neurons in the PNS. Schwann cells (forming myelin sheath) Cell body of neuron Satellite cells Nerve fiber

Copyright © 2010 Pearson Education, Inc. Figure 7.5 (a) Myelination of a nerve fiber (axon) Schwann cell cytoplasm Axon Neurilemma Myelin sheath Schwann cell nucleus Schwann cell plasma membrane 1 2 3

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. Figure 7.4 Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleus Nissl bodies Axon (impulse generating and conducting region) Axon hillock Neurilemma Terminal branches Node of Ranvier Impulse direction Schwann cell (one inter- node) Axon terminals (secretory region) (b)

Copyright © 2010 Pearson Education, Inc. 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

Copyright © 2010 Pearson Education, Inc. Myelin Sheaths in the CNS Formed by processes of oligodendrocytes, not the whole cells Nodes of Ranvier are present No neurilemma

Copyright © 2010 Pearson Education, Inc. (d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers. Nerve fibers Myelin sheath Process of oligodendrocyte

Copyright © 2010 Pearson Education, Inc. White Matter and Gray Matter White matter Dense collections of myelinated fibers Gray matter Mostly neuron cell bodies and unmyelinated fibers

Copyright © 2010 Pearson Education, Inc. Structural Classification of Neurons Three types: 1.Multipolar—1 axon and several dendrites Most abundant Motor neurons and interneurons 2.Bipolar—1 axon and 1 dendrite Rare, e.g., retinal neurons

Copyright © 2010 Pearson Education, Inc. Structural Classification of Neurons 3.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

Copyright © 2010 Pearson Education, Inc. Functional Classification of Neurons Three types: 1.Sensory (afferent) Transmit impulses from sensory receptors toward the CNS 2.Motor (efferent) Carry impulses from the CNS to effectors

Copyright © 2010 Pearson Education, Inc. Functional Classification of Neurons 3.Interneurons (association neurons) Shuttle signals through CNS pathways; most are entirely within the CNS