Holes Human Anatomy and Physiology Twelfth Edition Shier

Hole’s Human Anatomy and Physiology Twelfth Edition Shier w Butler w Lewis Chapter 10 Nervous System I: Basic Structure and Function Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 1

10. 1: Introduction Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites • Cell types in neural tissue: • Neurons • Neuroglial cells (also known as neuroglia, and glial) Cell body Nuclei of neuroglia Axon 2 © Ed Reschke

Divisions of the Nervous System Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Brain • Central Nervous System (CNS) • Brain • Spinal cord Cranial nerves Spinal cord • Peripheral Nervous System (PNS) • Cranial nerves • Spinal nerves 3 (a)

Divisions of Peripheral Nervous System • Sensory Division • Picks up sensory information and delivers it to the CNS • Motor Division • Carries information to muscles and glands • Divisions of the Motor Division: • Somatic – carries information to skeletal muscle • Autonomic – carries information to smooth muscle, cardiac muscle, and glands 4

Divisions Nervous System Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Central Nervous System (brain and spinal cord) Brain Peripheral Nervous System (cranial and spinal nerves) Cranial nerves Sensory division Spinal cord Sensory receptors Spinal nerves Motor division Somatic Nervous System Skeletal muscle Autonomic Nervous System Smooth muscle Cardiac muscle Glands 5 (a) (b)

Functions of Nervous System • Sensory Function (receiving • Integrative Function (deciding information) what to do about information) • Sensory receptors gather • Sensory information used to information create: • Sensations • Information is carried to the • Memory CNS • Motor Function (acting on information) • Decisions are acted upon • Impulses are carried to effectors • Thoughts • Decisions 6

10. 3: Description of Cells of the Nervous System • Neurons vary in size and shape • They may differ in length and size of their axons and dendrites • Neurons share certain features: • Dendrites • A cell body • An axon 7

Neuron Structure Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Chromatophilic substance (Nissl bodies) Dendrites Cell body Nucleus Nucleolus Neurofibrils Axonal hillock Impulse Axon Synaptic knob of axon terminal Nodes of Ranvier Myelin (cut) Axon Nucleus of Schwann cell Portion of a collateral 8

Myelination of Axons • White Matter • Contains myelinated axons • Considered fiber tracts • Gray Matter • Contains unmyelinated structures • Cell bodies, dendrites Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Dendrite Unmyelinated region of axon Myelinated region of axon Node of Ranvier Axon Neuron cell body nucleus (a) Enveloping Schwann cell nucleus Longitudinal groove Unmyelinated axon (c) 9

10. 4: Classification of Neurons and Neuroglia • Neurons vary in function • They can be sensory, motor, or integrative neurons • Neurons vary in size and shape, and in the number of axons and dendrites that they may have • Due to structural differences, neurons can be classified into three (3) major groups: • Bipolar neurons • Unipolar neurons • Multipolar neurons 10

Classification of Neurons: Structural Differences • Multipolar neurons • 99% of neurons • Many processes • Most neurons of CNS • Bipolar neurons • Two processes • Eyes, ears, nose • Unipolar neurons • One process • Ganglia of PNS • Sensory Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites Peripheral process Axon Direction of impulse Central process Axon 11 (a) Multipolar (b) Bipolar (c) Unipolar

Classification of Neurons: Functional Differences • Sensory Neurons • Afferent (approach) • Carry impulse to CNS • Most are unipolar • Some are bipolar • Interneurons • Link neurons in CNS • Aka association neurons • Multipolar Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Central nervous system Peripheral nervous system Cell body Dendrites Sensory receptor Cell body Axon (central process) Axon (peripheral process) Sensory (afferent) neuron Interneurons • Motor Neurons • Efferent (exit) • Carry impulses away from CNS to effectors • Multipolar Motor (efferent) neuron Axon Effector (muscle or gland) Axon terminal 12

Types of Neuroglial Cells in the PNS 1) Schwann Cells • Produce myelin found on peripheral myelinated neurons • Speed up neurotransmission 2) Satellite Cells • Support clusters of neuron cell bodies (ganglia) 13

Types of Neuroglial Cells in the CNS 1) Microglia • CNS • Phagocytic cell 3) Oligodendrocytes • CNS • Myelinating cell 4) Ependyma or ependymal 2) Astrocytes • CNS • Ciliated • Scar tissue • Line central canal of spinal • Mop up excess ions, etc. cord • Induce synapse formation • Line ventricles of brain • Connect neurons to blood • Keep CSF moving vessels 14

Types of Neuroglial Cells Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Fluid-filled cavity of the brain or spinal cord Neuron Ependymal cell Oligodendrocyte Astrocyte Microglial cell Axon Myelin sheath (cut) Capillary Node of Ranvier 15

Regeneration of A Nerve Axon Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal muscle fiber Motor neuron cell body Changes over time Axon Site of injury Schwann cells (a) Distal portion of axon degenerates (b) Proximal end of injured axon regenerates into tube of sheath cells (c) Schwann cells degenerate (d) Schwann cells proliferate (e) Former connection reestablished 16 16

10. 5: The Synapse Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Nerve impulses pass from neuron to neuron at synapses, moving from a pre-synaptic neuron to a post-synaptic neuron. Synaptic cleft Impulse Dendrites Axon of presynaptic neuron Axon of postsynaptic neuron Axon of presynaptic neuron Impulse Cell body of postsynaptic neuron Impulse 17

Synaptic Transmission Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Direction of nerve impulse • Neurotransmitters are released when impulse reaches synaptic knob Axon Ca+2 Synaptic knob Synaptic vesicles Presynaptic neuron Ca+2 Cell body or dendrite of postsynaptic neuron Mitochondrion Ca+2 Synaptic vesicle Vesicle releasing neurotransmitter Axon membrane Neurotransmitter Synaptic cleft Polarized membrane (a) Depolarized membrane 18

Animation: Chemical Synapse Please note that due to differing Please note that duesome to differing operating systems, animations operating systems, some animations is will not appear until the presentation will not in appear until the. Mode presentation viewed Presentation (Slide is viewed in Presentation Mode (Slide Show view). You may see blank slides Show view). You may see blank in the “Normal” or “Slide Sorter”slides views. in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, the latest version of which is available at the Flash Player, which is available at http: //get. adobe. com/flashplayer. 19

10. 6: Cell Membrane Potential • A cell membrane is usually electrically charged, or polarized, so that the inside of the membrane is negatively charged with respect to the outside of the membrane (which is then positively charged). • This is as a result of unequal distribution of ions on the inside and the outside of the membrane. 20

Distribution of Ions • Potassium (K+) ions are the major intracellular positive ions (cations). • Sodium (Na+) ions are the major extracellular positive ions (cations). • This distribution is largely created by the Sodium/Potassium Pump (Na+/K+ pump). • This pump actively transports sodium ions out of the cell and potassium ions into the cell. 21

Resting Potential Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Resting Membrane Potential (RMP): • 70 m. V difference from inside to outside of cell • It is a polarized membrane • Inside of cell is negative relative to the outside of the cell • RMP = -70 m. V • Due to distribution of ions inside vs. outside • Na+/K+ pump restores High Na+ Low Na+ Impermeant anions High K+ Axon Cell body Low K+ Axon terminal (a) + – + – – + – + – + + – – + – 70 m. V (b) + – High Na+ Low K+ + – – Low Na+ Pump K+ High K+ – + – + + – – + – 70 m. V (c) 22 + – – +

Local Potential Changes • Caused by various stimuli: • Temperature changes • Light • Pressure Gatelike mechanism Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Protein Cell membrane (a) Channel closed Fatty acid tail Phosphate head (b) Channel open • Environmental changes affect the membrane potential by opening a gated ion channel • Channels are 1) chemically gated, 2) voltage gated, or 3) mechanically gated 23

Local Potential Changes • If membrane potential becomes more negative, it has hyperpolarized • If membrane potential becomes less negative, it has depolarized • Graded (or proportional) to intensity of stimulation reaching threshold potential • Reaching threshold potential results in a nerve impulse, starting an action potential 24

Local Potential Changes Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Na+ – 62 m. V Neurotransmitter (a) Chemically-gated Na+ channel Presynaptic neuron Voltage-gated Na+ channel Trigger zone Na+ Na+ Na+ – 55 m. V 25 (b)

Action Potentials • At rest, the membrane is polarized (RMP = -70) • Threshold stimulus reached (-55) • Sodium channels open and membrane depolarizes (toward 0) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Na+ Na+ Na+ K+ K+ K+ K+ Na+ Na+ – 0 – 70 Na+ Na+ Na+ Na+ (a) K+ Na+ Na+ K+ Threshold stimulus K+ K+ Na+ K+ K+ K+ – 0 K+ Na+ channels open K+ channels closed K+ Na+ K+ K+ – 70 • Potassium leaves cytoplasm and membrane repolarizes (+30) • Brief period of hyperpolarization (-90) Na+ Na+ Na+ Na+ Region of depolarization (b) K+ K+ Na+ Na+ Na+ K+ K+ K+ Region of repolarization (c) Na+ Na+ K+ channels open Na+ channels closed – 0 – 70 Na+ 26

Action Potentials Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. +40 Membrane potential (millivolts) Action potential +20 0 – 20 Resting potential reestablished – 40 Resting potential – 60 – 80 Hyperpolarization 0 1 2 3 4 5 Milliseconds 6 7 8 27

Action Potentials Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Region of action potential + + + – – – – – + + + + + – – – + + + (a) + – + – + Direction of nerve impulse – – – + + + (b) + – – – – + + – – + (c) + + + + + 28

Animation: Action Potential Propagation in Unmyelinated Neurons Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http: //get. adobe. com/flashplayer. 29

Animation: Action Potential Propagation in Myelinated Neurons Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http: //get. adobe. com/flashplayer. 30

All-or-None Response • If a neuron responds at all, it responds completely • A nerve impulse is conducted whenever a stimulus of threshold intensity or above is applied to an axon • All impulses carried on an axon are the same strength 31

Refractory Period • Absolute Refractory Period • Time when threshold stimulus does not start another action potential • Relative Refractory Period • Time when stronger threshold stimulus can start another action potential 32

Impulse Conduction 33

Animation: The Nerve Impulse Please note that due to differing Please note that duesome to differing operating systems, animations operating systems, some animations is will not appear until the presentation will not in appear until the. Mode presentation viewed Presentation (Slide is viewed in Presentation Mode (Slide Show view). You may see blank slides Show view). You may see blank in the “Normal” or “Slide Sorter”slides views. in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, the latest version of which is available at the Flash Player, which is available at http: //get. adobe. com/flashplayer. 34

10. 7: Synaptic Transmission • This is where released neurotransmitters cross the synaptic cleft and reacts with specific molecules called receptors in the postsynaptic neuron membrane. • Effects of neurotransmitters vary. • Some neurotransmitters may open ion channels and others may close ion channels, making it more likely or less likely for an action potential to occur. 35

Synaptic Potentials • EPSP • Excitatory postsynaptic potential • Graded • Depolarizes membrane of postsynaptic neuron • Action potential of postsynaptic neuron becomes more likely • IPSP • Inhibitory postsynaptic potential • Graded • Hyperpolarizes membrane of postsynaptic neuron • Action potential of postsynaptic neuron becomes less likely 36

Summation of EPSPs and IPSPs Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • EPSPs and IPSPs are added together in a process called summation • More EPSPs lead to greater probability of an action potential • More IPSPs lead to lower probability of an action potential Neuron cell body Nucleus Presynaptic knob Presynaptic axon 37

Neurotransmitters 38

Neurotransmitters 39

10. 8: Impulse Processing • The way the nervous system processes nerve impulses and acts upon them. • Neuronal pools of interneurons • Convergence • Divergence 40

Neuronal Pools • Groups of interneurons that make synaptic connections with each other • Interneurons work together to perform a common function – may be excitatory or inhibitory • Each pool receives input from other neurons • Each pool generates output to other neurons 41

Convergence Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Neuron receives input from several neurons • Incoming impulses represent information from different types of sensory receptors 1 2 • Allows nervous system to collect, process, and respond to information • Makes it possible for a neuron to sum impulses from different sources 3 (a) 42

Divergence • One neuron sends impulses to several neurons via its branched axon Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Can amplify an impulse 4 • Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction or glandular secretion 6 5 43 (b)

Important Points in Chapter 10: Outcomes to be Assessed 10. 1: Introduction ü Describe the general functions of the nervous system. ü Identify the two types of cells that comprise nervous tissue. ü Identify the two major groups of nervous system organs. 10. 2: General Functions of the Nervous System ü List the functions of sensory receptors. ü Describe how the nervous system responds to stimuli. 10. 3: Description of Cells of the Nervous System ü Describe three major parts of a neuron. ü Define neurofibrils and chromatophilic substance. 44

Important Points in Chapter 10: Outcomes to be Assessed ü Describe the relationship among myelin, the neurilemma, and the nodes of Ranvier. ü Distinguish between the sources of white matter and gray matter. 10. 4: Classification of Neurons and Neuroglia ü Identify structural and functional differences among neurons. ü Identify the types of neuroglia in the central nervous system and their functions. ü Describe the Schwann cells of the peripheral nervous system. 10. 5: The Synapse ü Define presynaptic and postsynaptic. ü Explain how information passes from a presynaptic to a postsynaptic neuron. 45

Important Points in Chapter 10: Outcomes to be Assessed 10. 6: Cell Membrane Potential ü Explain how a cell membrane becomes polarized. ü Define resting potential, local potential, and action potential. ü Describe the events leading to the conduction of a nerve impulse. ü Compare nerve impulse conduction in myelinated and unmyelinated neurons. 10. 7: Synaptic Transmission ü Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters. 10. 8: Impulse Processing ü Describe the basic ways in which the nervous system processes information. 46