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Essentials of Anatomy and Physiology Fifth edition Seeley, Stephens and Tate Chapter 8: Nervous System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 2.1 Functions of the Nervous System Sensory input – gathering information Changes occurring inside and outside the body Changes = stimuli Integration Process and interpret sensory input Determine action needed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.1a Functions of the Nervous System Motor output A response to integrated stimuli Activates muscles or glands (effectors) May be voluntary May be involuntary Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.1b Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves attached to brain and spinal cord Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.2 Functional Classification of the PNS Sensory (afferent) division Nerve fibers that carry information to the central nervous system Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3a Functional Classification of the PNS Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3b Functional Classification of the PNS Motor (efferent) division Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3c Organization of the Nervous System Figure 7.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.4 Nervous Tissue: Support Cells (Neuroglia = “Nerve Glue”) Astrocytes Star-shaped cells Support neurons Form blood-brain barrier Control the chemical environment Figure 7.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.5 Nervous Tissue: Support Cells Microglia “little glue” cells Spider-like phagocytes Dispose of debris Figure 7.3b, c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.6 Nervous Tissue: Support Cells Ependymal cells Line cavities of the brain and spinal cord Circulate cerebrospinal fluid (CSF) Figure 7.3b, c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.6 Nervous Tissue: Support Cells Oligodendrocytes “few branch” cells Produce myelin sheath in the CNS Figure 7.3d Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.7a Nervous Tissue: Support Cells Schwann cells Form myelin sheath in the PNS Figure 7.3e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.7b Nerve Fiber Coverings: Schwann Cells, con’t… Wrap around axons Nodes of Ranvier: gaps in myelin sheath Figure 7.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.12 Nervous Tissue: Neurons Neurons = nerve cells Functional cells of the nervous system Specialized to transmit messages Anatomy Cell body – nucleus and organelles Processes – fibers that extend from the cell body Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.8 Neuron Anatomy Cell body Nissl substance: specialized RER Neurofibrils: cytoskeleton maintains cell shape Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.9a Neuron Anatomy Cell body, con’t. Nucleus Large nucleolus Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.9b Neuron Anatomy Processes Dendrites: conduct impulses toward the cell body Axons: conduct impulses away from the cell body Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Axons and Nerve Impulses Axons end in axon terminals Axonal terminals house vesicles with neurotransmitters Synaptic cleft – gap between adjacent neurons Synapse – junction between nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.11 Neuron Cell Bodies: Location Most are in the CNS Gray matter = cell bodies and unmyelinated fibers Nuclei = clusters of cell bodies within the white matter of the central nervous system Ganglia = collections of cell bodies outside the CNS Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.13 Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from sensory receptors Cutaneous sense organs Proprioceptors: detect stretch or tension Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.14a Functional Classification of Neurons Motor (efferent) neurons Carry impulses from the central nervous system To an effector (muscle or gland) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.14a Functional Classification of Neurons Interneurons (association neurons) Found in neural pathways in the CNS Connect sensory and motor neurons Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.14b Functional Classification of Neurons Figure 7.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.15 Structural Classification of Neurons Multipolar neurons – many extensions from the cell body Most common: these are motor neurons Figure 7.8a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.16a Structural Classification of Neurons Bipolar neurons – one axon and one dendrite Rare: these are sensory neurons (eye, ear) Figure 7.8b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.16b Structural Classification of Neurons Unipolar neurons – short single process leaving the cell body These are Sensory neurons in the PNS Figure 7.8c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.16c Nerve Impulse Transmission Two mechanisms involved Transmission along a neuron An electrical process Transmission between neurons A chemical process Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.17 Functional Properties of Neurons Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized (like a resting muscle fiber) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.17 Transmission of a Nerve Impulse along a Neuron Depolarization – stimulus causes a change in membrane permeability Allows sodium (Na+) to enter the neuron Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.9a–c Slide 7.18 Transmission of a Nerve Impulse along a Neuron The exchange of ions creates an action potential in the neuron “potential to do work” Sound familiar?? Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.9a–c Slide 7.18 The Action Potential Once the action potential (nerve impulse) begins, it spreads along the entire neuron “all-or-none” law: sound familiar?? Potassium ions (K+) leave the neuron after Na+ enters Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.19 The Action Potential Exchange of Na+ and K+ repolarizes the membrane The sodium-potassium pump restores ions to their original location Protein pump in the membrane This action requires ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.19 Nerve Impulse Propagation The impulse continues to move along the neuron Impulses travel faster along myelinated fibers Figure 7.9c–e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.20 Nerve Impulse Propagation Myelinated fibers: ~200 feet/second Unmyelinated fibers: ~10 feet/second Figure 7.9c–e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.20 Transmission of the Nerve Impulse between Neurons Impulses can cross the synapse to another nerve Depolarization activates vesicles in axon terminal Requires Ca++ Neurotransmitter is released Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 Transmission of the Nerve Impulse between Neurons The dendrite of the “next” neuron has receptor sites Neurotransmitter attaches to receptors If enough molecules of NT attach: A new action potential is generated Sound familiar?? Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 How Neurons Communicate at Synapses Figure 7.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.22