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

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

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

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

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

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

Neuron Structure Chromatophilic substance (Nissl bodies) Dendrites Copyright © The McGraw-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) Nucleus of Schwann cell Axon Schwann cell Portion of a collateral

Myelination of Axons White Matter Contains myelinated axons Considered fiber tracts Gray Matter Contains unmyelinated structures Cell bodies, dendrites Copyright © The McGraw-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 Neuron nucleus (a) Enveloping Schwann cell Schwann cell nucleus Longitudinal groove Unmyelinated axon (c)

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

Classification of Neurons: Structural Differences Multipolar neurons 99% of neurons Many processes Most neurons of CNS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites Peripheral process Bipolar neurons Two processes Eyes, ears, nose Axon Direction of impulse Unipolar neurons One process Ganglia of PNS Sensory Central process Axon Axon (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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central nervous system Peripheral nervous system Cell body Dendrites Sensory receptor Interneurons Link neurons in CNS Aka association neurons Multipolar Cell body Axon (central process) Axon (peripheral process) Sensory (afferent) neuron Interneurons Motor (efferent) neuron Motor Neurons Efferent (exit) Carry impulses away from CNS to effectors Multipolar Axon Effector (muscle or gland) Axon Axon terminal

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)

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

Types of Neuroglial Cells Copyright © The McGraw-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

Regeneration of A Nerve Axon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor neuron cell body Skeletal muscle fiber Changes over time Site of injury Schwann cells Axon (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

10.5: The Synapse Copyright © The McGraw-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 Cell body of postsynaptic neuron Impulse Impulse

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

Animation: Chemical Synapse 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. 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.

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.

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.

Resting Potential Resting Membrane Potential (RMP): Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Resting Membrane Potential (RMP): 70 mV 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 mV Due to distribution of ions inside vs. outside Na+/K+ pump restores High Na+ Low Na+ Impermeant anions High K+ Low K+ Cell body Axon Axon terminal + + + + – – – (a) – + + – + + + – – – – – – – – – + + – + – – – + + + + + + –70 mV (b) + + + + – – – High Na+ – Low Na+ Na+ + + – – + + Pump – – – – – K+ High K+ – + – – Low K+ – + + + + + + – + –70 mV 22 (c)

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

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

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

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

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

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

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.

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.

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

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

Impulse Conduction

Animation: The Nerve Impulse 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. 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.

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.

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

Summation of EPSPs and IPSPs Copyright © The McGraw-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

Neurotransmitters

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

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

Convergence Neuron receives input from several neurons Copyright © The McGraw-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 Allows nervous system to collect, process, and respond to information Makes it possible for a neuron to sum impulses from different sources 2 1 3 42 (a)

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

Important Points in Chapter 10: Outcomes to be Assessed 10.1: Introduction Describe the general functions of the nervous system. Identify the two types of cells that comprise nervous tissue. Identify the two major groups of nervous system organs. 10.2: General Functions of the Nervous System List the functions of sensory receptors. Describe how the nervous system responds to stimuli. 10.3: Description of Cells of the Nervous System Describe the three major parts of a neuron. Define neurofibrils and chromatophilic substance.

Important Points in Chapter 10: Outcomes to be Assessed Describe the relationship among myelin, the neurilemma, and the nodes of Ranvier. Distinguish between the sources of white matter and gray matter. 10.4: Classification of Neurons and Neuroglia Identify structural and functional differences among neurons. Identify the types of neuroglia in the central nervous system and their functions. Describe the Schwann cells of the peripheral nervous system. 10.5: The Synapse Define presynaptic and postsynaptic. Explain how information passes from a presynaptic to a postsynaptic neuron.

Important Points in Chapter 10: Outcomes to be Assessed 10.6: Cell Membrane Potential Explain how a cell membrane becomes polarized. Define resting potential, local potential, and action potential. Describe the events leading to the conduction of a nerve impulse. Compare nerve impulse conduction in myelinated and unmyelinated neurons. 10.7: Synaptic Transmission Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters. 10.8: Impulse Processing Describe the basic ways in which the nervous system processes information.