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)

10.2: General Functions of the Nervous System The three general functions of the nervous system: Receiving stimuli = sensory function Deciding about stimuli = integrative function Reacting to stimuli = motor function

Functions of Nervous System Sensory Function Sensory receptors gather information Information is carried to the CNS Motor Function Decisions are acted upon Impulses are carried to effectors Integrative Function Sensory information used to create: Sensations Memory Thoughts Decisions

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)

10.2 Clinical Application Multiple Sclerosis

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

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)

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 20

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.

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.

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 +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 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.

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.

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

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.

Factors Affecting Impulse Conduction 10.3 Clinical Application Factors Affecting Impulse Conduction

10.7: Synaptic Transmission This is where released neurotransmitters cross the synaptic cleft and react 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.

Neurotransmitters

Neurotransmitters

Neuropeptides Neurons in the brain or spinal cord synthesize neuropeptides. These neuropeptides act as neurotransmitters. Examples include: Enkephalins Beta endorphin Substance P