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D-Anatomy and Physiology Chapter 10 Lecture PowerPoint Nervous System I 10.1: Introduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites • Cell types in neural tissue: • Neurons • Neuroglial cells (also known as neuroglia, glia, and glial) Cell body Nuclei of neuroglia Axon 2 © 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 3 (a) Divisions Nervous System Copyright © The McGraw-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 4 (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 5 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 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 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) Axon Nucleus of Schwann cell 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 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) 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 • 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 11 (a) Multipolar (b) Bipolar (c) Unipolar Classification of Neurons: Functional Differences • Sensory Neurons • Afferent • Carry impulse to CNS • Most are unipolar • Some are bipolar • Interneurons • Link neurons • Aka association neurons or internuncial neurons • Multipolar • Located in CNS Copyright © The McGraw-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 • Multipolar • Carry impulses away from CNS • Carry impulses to effectors Motor (efferent) neuron Axon Effector (muscle or gland) Axon 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 • Phagocytic cell 3) Oligodendrocytes • Myelinating cell 2) Astrocytes • Scar tissue • Mop up excess ions, etc. • aid in metabolism of certain substances • form blood-brain barrier 4) Ependyma or ependymal • Ciliated • Line central canal of spinal cord • Line ventricles of brain • help regulate composition of CSF 14 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 15 Regeneration of A Nerve Axon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal muscle fiber Motor neuron cell body 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 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 Impulse Cell body of postsynaptic neuron Impulse 17 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 • As nerve impulse reaches the synaptic knob, Ca2+ channels open & allow Ca2+ to move into the synaptic knob • this stimulates the synaptic vesicles to fuse with the membrane allowing exocytosis of the neurotransmitter 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 Depolarized membrane (a) 18 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. 19 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. • also due to the presence of ion-selective channels 20 Resting Potential • Resting Membrane Potential (RMP): • It is a polarized membrane • Inside of cell is negative relative to the outside of the cell • Due to distribution of ions inside vs. outside • Na+/K+ pump restores • 70 mV difference from inside to outside of cell • RMP = -70 mV Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High Na+ Low Na+ Impermeant anions High K+ Axon Cell body Low K+ Axon terminal (a) + – + – + – + – – + + – + – + – – + – + – + – + – + + – – + – + –70 mV (b) + – High Na+ Na+ Low K+ + + – – Low Na+ Pump K+ High K+ + – – + + – + – + – – + – + – + – + + – – + + – – + –70 mV (c) 25 21 + – – + Local Potential Changes • Caused by various stimuli: • Temperature changes • Light • Pressure Gatelike mechanism Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Cell membrane Fatty acid tail (a) Channel closed Phosphate head • Environmental changes affect the membrane potential by opening a gated ion channel (b) Channel open • Channels are 1) chemically gated, 2) voltage gated, or 3) mechanically gated 22 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, meaning the greater the stimulation, the greater the depolarization • if the depolarization is great enough, reach threshold potential • Reaching threshold potential results in a nerve impulse, starting an action potential 23 Local Potential Changes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na+ Na+ –62 mV Neurotransmitter (a) Chemically-gated Na+ channel Presynaptic neuron Voltage-gated Na+ channel Trigger zone Na+ Na+ Na+ Na+ Na+ –55 mV 24 (b) Action Potentials • At rest, the membrane is Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na+ polarized (RMP = -70) • Threshold stimulus Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ reached (-55) Na+ Na+ Na+ Na+ –0 –70 Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ (a) • Sodium channels open and membrane depolarizes (toward 0) K+ Na+ Na+ K+ Na+ K+ K+ K+ K+ K+ –0 K+ Na+ channels open K+ channels closed Threshold stimulus K+ K+ Na+ K+ Na+ K+ Na+ K+ K+ K+ K+ –70 • Potassium leaves Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Region of depolarization (b) cytoplasm and membrane repolarizes (+30) K+ • Brief period of hyperpolarization (-90) Na+ K+ K+ K+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+ Na+ Na+ Na+ K+ K+ K+ K+ K+ –0 –70 K+ K+ Region of repolarization (c) K+ channels open Na+ channels closed K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ 25 Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. +40 Action potential Membrane potential (millivolts) +20 0 –20 Resting potential reestablished –40 Resting potential –60 –80 Hyperpolarization 0 1 2 3 4 Milliseconds 5 6 7 8 26 Action Potentials Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Region of action potential + + + + + + + + + + + – – – – – – – – – + + – – – – – – – – – + + + + + + + + + + + + + – – – – – – + – – – – – – + + + + + + + + (a) + – + – + – + Direction of nerve impulse – – – + + + + + + + + + + + + (b) + – – – – – – – + + – – – – – – – – – + + – – + (c) + + + + + + + + + 27 Animation: The Nerve Impulse Please note that due to differing Please note that duesome to differing operating systems, animations will operating animations not appearsystems, until the some presentation is will not appear until the presentation is Show viewed in Presentation Mode (Slide viewed in Presentation Mode (Slide Show view). You may see blank slides in the view). Youor may see Sorter” blank slides inAll the “Normal” “Slide views. “Normal” orwill “Slide Sorter” Allin animations appear afterviews. viewing animations appear viewing Presentationwill Mode andafter playing each in Presentation Mode and playing animation. Most animations willeach require 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. http://get.adobe.com/flashplayer. 28 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. 29 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. 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 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. 34 Animation: Chemical Synapse Please note that due to differing Please note that duesome to differing operating systems, animations will operating animations not appearsystems, until the some presentation is will not appear until the presentation is Show viewed in Presentation Mode (Slide viewed in Presentation Mode (Slide Show view). You may see blank slides in the view). Youor may see Sorter” blank slides inAll the “Normal” “Slide views. “Normal” orwill “Slide Sorter” Allin animations appear afterviews. viewing animations appear viewing Presentationwill Mode andafter playing each in Presentation Mode and playing animation. Most animations willeach require 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. http://get.adobe.com/flashplayer. 35 Neurotransmitter Release 36 Fate of Neurotransmitters • Enzyme degradation • Reuptake Synaptic Potentials • EPSP • Excitatory postsynaptic potential • Graded • Depolarizes membrane of postsynaptic neuron by opening Na+ channels • Action potential of postsynaptic neuron becomes more likely • IPSP • Inhibitory postsynaptic potential • Graded • Hyperpolarizes membrane of postsynaptic neuron by opening K+ channels • Action potential of postsynaptic neuron becomes less likely 38 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 Neuron cell body Nucleus Presynaptic knob Presynaptic axon 38 39 Neurotransmitters 40 Neuropeptides • Neurons in the brain or spinal cord synthesize neuropeptides. • These neuropeptides act as neurotransmitters or neuromodulators. •Alter the neuron’s response to the neurotransmitter or block neurotransmitter’s release • Examples include: • Enkephalins • Beta endorphin • Substance P 41 10.8: Impulse Processing • Way the nervous system processes nerve impulses and acts upon them • Neuronal Pools • Convergence • Divergence 42 Neuronal Pools • Groups of interneurons that make synaptic connections with each other • Interneurons work together to perform a common function • Each pool receives input from other neurons • Each pool generates output to other neurons • May be excitatory or inhibitory effect • If excitatory but not to threshold, makes the neuron more responsive to further stimulation – called facilitation 43 Convergence 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 1 • Allows nervous system to collect, process, and respond to information 2 • Makes it possible for a neuron to sum impulses from different sources 3 (a) 45 44 Divergence • One neuron sends impulses to several neurons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Can amplify an impulse • Impulse from a single neuron in CNS may be amplified to activate enough motor units needed for muscle contraction 4 6 5 46 45 (b)