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PowerPoint® Lecture Slides prepared by Leslie Hendon, University of Alabama, Birmingham 12 HUMAN ANATOMY fifth edition MARIEB | MALLATT | WILHELM PART 1 Fundamentals of the Nervous System and Nervous Tissue Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System Master control and communication system Has three overlapping functions Sensory receptors monitor changes inside and outside the body Change – a stimulus Gathered information – sensory input Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System Processes and interprets sensory input Makes decisions – integration Dictates a response by activating effector organs Response – motor output Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Integrating and command center Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Peripheral nervous system (PNS) Outside the CNS Consists of nerves extending from brain and spinal cord Cranial nerves Spinal nerves Peripheral nerves link all regions of the body to the CNS Ganglia are clusters of neuronal cell bodies Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.2 Sensory Input and Motor Output Sensory (afferent) signals picked up by sensor receptors Carried by nerve fibers of PNS to the CNS Motor (efferent) signals are carried away from the CNS Innervate muscles and glands Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Input and Motor Output Divided according to region they serve Somatic body region Visceral body region Results in four main subdivisions Somatic sensory Visceral sensory Somatic motor Visceral motor Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Types of Sensory and Motor Information Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.3 Basic Divisions of the Nervous System Somatic sensory General somatic senses – receptors are widely spread Touch Pain Vibration Pressure Temperature (receptors discussed in Chapter 14) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Somatic sensory (continued) Proprioceptive senses – detect stretch in tendons and muscle Body sense – position and movement of body in space Special somatic senses (Chapter 16) Hearing Balance Vision Smell Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Visceral sensory General visceral senses – stretch, pain, temperature, nausea, and hunger Widely felt in digestive and urinary tracts, and reproductive organs Special visceral senses Taste Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Somatic motor General somatic motor – signals contraction of skeletal muscles Under our voluntary control Often called “voluntary nervous system” Branchial motor Typical skeletal muscle derived from somitomeres Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Basic Divisions of the Nervous System Visceral motor Regulates the contraction of smooth and cardiac muscle Makes up autonomic nervous system Controls function of visceral organs Often called “involuntary nervous system” Autonomic nervous system (Chapter 15) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue Cells are densely packed and intertwined Two main cell types Neurons – transmit electrical signals Support cells (neuroglial cells in CNS) Nonexcitable Surround and wrap neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Neuron The human body contains billions of neurons Basic structural unit of the nervous system Specialized cells conduct electrical impulses along the plasma membrane Nerve impulse (action potential) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Neuron Other special characteristics Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose Neurons die after 5 minutes without oxygen Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body Cell body (soma) Perikaryon – around nucleus Size of cell body varies from 5–140µm Contains usual organelles plus other structures Chromatophilic bodies (Nissl bodies) Clusters of rough ER and free ribosomes Stain darkly and renew membranes of the cell Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body Neurofibrils – bundles of intermediate filaments Form a network between chromatophilic bodies Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings The Cell Body Most neuronal cell bodies Located within the CNS Protected by bones of the skull and vertebral column Ganglia – clusters of cell bodies Lie along nerves in the PNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Typical Large Neuron Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.4 Neuron Processes Dendrites Extensively branching from the cell body Transmit electrical signals toward the cell body Chromatophilic bodies – only extend into the basal part of dendrites and to the base of the axon hillock Function as receptive sites for receiving signals from other neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Axons Neuron has only one Impulse generator and conductor Transmits impulses away from the cell body Chromatophilic bodies are absent No protein synthesis in axon Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Axons (continued) Neurofilaments, actin microfilaments, and microtubules Provide strength along length of axon Aid in the transport of substances to and from the cell body Axonal transport Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Axons Branches along length are infrequent Axon collaterals Multiple branches at end of axon Terminal branches (telodendria) End in knobs called axon terminals (also called end bulbs or boutons) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Nerve impulse Generated at the initial segment of the axon Conducted along the axon Releases neurotransmitters at axon terminals Neurotransmitters – excite or inhibit neurons Neuron receives and sends signals Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Synapses Site at which neurons communicate Signals pass across synapse in one direction Presynaptic neuron Conducts signal toward a synapse Postsynaptic neuron Transmits electrical activity away from a synapse PLAY Synapse Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Two Neurons Communicating at a Synapse Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.6 Types of Synapses Axodendritic Between axon terminals of one neuron and dendrites of another Most common type of synapse Axosomatic Axoaxonic, dendrodendritic, and dendrosomatic Between axons and neuronal cell bodies Uncommon types of synapses Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Some Important Types of Synapses Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.7 Synapses Elaborate cell junctions Axodendritic synapses – representative type Synaptic vesicles on presynaptic side Membrane-bound sacs containing neurotransmitters Mitochondria abundant in axon terminals Synaptic cleft Separates the plasma membrane of the two neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Synapses Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.8a, b Signals Carried by Neurons Plasma membranes of neurons conduct electrical signals Resting neuron – membrane is polarized Inner, cytoplasmic side is negatively charged Stimulation of the neuron depolarization Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Signals Carried by Neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.9a, b Signals Carried by Neurons Strong stimulus applied to the axon triggers Nerve impulse/action potential Membrane becomes negative externally Impulse travels the length of the axon Membrane repolarizes itself Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Signals Carried by Neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.9c–d Synaptic Potentials Excitatory synapses Neurotransmitters alter the permeability of the postsynaptic membrane Leads to an inflow of positive ions Depolarizes the postsynaptic membrane Drives the postsynaptic neuron toward impulse generation Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Potentials Inhibitory synapses The external surface of the postsynaptic membrane becomes more positive Reduces the ability of the postsynaptic neuron to generate an action potential Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint® Lecture Slides prepared by Leslie Hendon, University of Alabama, Birmingham 12 HUMAN ANATOMY fifth edition MARIEB | MALLATT | WILHELM PART 2 Fundamentals of the Nervous System and Nervous Tissue Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Neurons Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons Found in some special sensory organs Unipolar (pseudounipolar) – possess one short, single process Start as bipolar neurons during development Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neurons Classified by Structure Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.10a Neurons Classified by Structure Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.10b Neurons Classified by Structure Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.10c Functional Classification of Neurons Functional classification is According to the direction the nerve impulse travels Sensory (afferent) neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons Transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons Motor (efferent) neurons Carry impulses away from the CNS to effector organs Most motor neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Interneurons (association neurons) – most are multipolar Lie between motor and sensory neurons Confined to the CNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neurons Classified by Function Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.11 Supporting Cells Six types of supporting cells Four in the CNS Two in the PNS Provide supportive functions for neurons Cover nonsynaptic regions of the neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuroglial in the CNS Neuroglia Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuroglia in the CNS Astrocytes are the most abundant glial cell type Sense when neurons release glutamate Extract blood sugar from capillaries for energy Take up and release ions in order to control environment around neurons Involved in synapse formation in developing neural tissue Produce molecules necessary for neuronal growth (BDTF) Propagate calcium signals involved with memory Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuroglia in the CNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.12a Neuroglia in the CNS Microglia – smallest and least abundant glial cell Phagocytes – the macrophages of the CNS Engulf invading microorganisms and dead neurons Derive from blood cells called monocytes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.12b Neuroglia in the CNS Ependymal cells Line the central cavity of the spinal cord and brain Bear cilia – help circulate the cerebrospinal fluid Oligodendrocytes – have few branches Wrap their cell processes around axons in CNS Produce myelin sheaths Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuroglia in the CNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.12c, d Neuroglia in the PNS Satellite cells – surround neuron cell bodies within ganglia Schwann cells (neurolemmocytes) – surround axons in the PNS Form myelin sheath around axons of the PNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.13 PowerPoint® Lecture Slides prepared by Leslie Hendon, University of Alabama, Birmingham 12 HUMAN ANATOMY fifth edition MARIEB | MALLATT | WILHELM PART 3 Fundamentals of the Nervous System and Nervous Tissue Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths Segmented structures composed of the lipoprotein myelin Surround thicker axons Form an insulating layer Prevent leakage of electrical current Increase the speed of impulse conduction Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Formed by Schwann cells (neurolemmacytes) Develop during fetal period and in the first year of postnatal life Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes Neurilemma Material external to myelin layers Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the PNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.14a, b Myelin Sheaths in the PNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.14c, d Myelin Sheaths in the PNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.15a Myelin Sheaths in the PNS Nodes of Ranvier – gaps along axon Thick axons are myelinated Thin axons are unmyelinated Conduct impulses more slowly Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths in the CNS Oligodendrocytes form the myelin sheaths in the CNS Have multiple processes Coil around several different axons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.15b Gray and White Matter in the CNS Gray matter Is gray-colored and surrounds hollow central cavities of the CNS Forms H-shaped region in the spinal cord Dorsal half contains cell bodies of interneurons Ventral half contains cell bodies of motor neurons Primarily composed of neuronal cell bodies, dendrites, unmyelinated axons Surrounds white matter of CNS in cerebral cortex and cerebellum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Gray and White Matter in the CNS White matter Lies external to the gray matter of the CNS Composed of myelinated axons Consists of axons passing between specific regions of the CNS Tracts are bundles of axons traveling to similar destinations Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nerves Nerves – cablelike organs in the PNS Consists of numerous axons wrapped in connective tissue Axon is surrounded by Schwann cells You see many nerves in lab Nerves of Brachial Plexus Radial, axillary, median, musculocutaneous, ulnar Nerves of lumbosacral plexus Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nerves Endoneurium – layer of delicate connective tissue surrounding the axon Perineurium – connective tissue wrapping surrounding a nerve fascicle Nerve fascicles – groups of axons bound into bundles Epineurium – whole nerve is surrounded by tough fibrous sheath Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Nerve Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.16a Integration Between the PNS and CNS The CNS and PNS are functionally interrelated Nerves of the PNS Information pathways to and from body periphery Afferent PNS fibers respond to sensory stimuli Efferent PNS fibers transmit motor stimuli from CNS to muscles and glands Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Integration Between the PNS and CNS Nerves of the CNS Composed on interneurons that Process and receive sensory information Direct information to specific CNS regions Initiate appropriate motor responses Transport information from one area of the CNS to another Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Reflex Arcs Reflex arcs – simple chains of neurons Explain reflex behaviors Determine structural plan of the nervous system Responsible for reflexes Rapid, autonomic motor responses Can be visceral or somatic Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Five Essential Components to the Reflex Arc Receptor – site where stimulus acts Sensory neuron – transmits afferent impulses to the CNS Integration center – consists of one or more synapses in the CNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Five Essential Components to the Reflex Arc Motor neuron – conducts efferent impulses from integration center to an effector Effector – muscle or gland cell Responds to efferent impulses Contracting or secreting Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Five Essential Components to the Reflex Arc Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.17 Types of Reflexes Monosynaptic reflex Simplest of all reflexes Just one synapse The fastest of all reflexes Knee-jerk reflex Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Types of Reflexes Polysynaptic reflex More common type of reflex Most have a single interneuron between the sensory and motor neuron Withdrawal reflexes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Types of Reflexes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.18a, b Simplified Design of the Nervous System Three-neuron reflex arcs Basis of the structural plan of the nervous system Similar reflexes are associated with the brain Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Simplified Design of the Nervous System Sensory neurons – located dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal cord Motor neurons – located ventrally Axons exit the ventral aspect of the spinal cord Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Simplified Design of the Nervous System Interneurons – located centrally Synapse with sensory neurons Interneurons are neurons confined to CNS Long chains of interneurons between sensory and motor neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Simplified Design of the Nervous System Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.19 Neuronal Circuits Diverging circuit – one presynaptic neuron synapses with several other neurons (divergence) Converging circuit – many neurons synapse on a single postsynaptic neuron (convergence) Reverberating circuit – circuit that receives feedback via a collateral axon from a neuron in the circuit Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuronal Circuits Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.20 Input Processing – not in notes Serial processing Neurons pass a signal to a specific destination along a single pathway from one to another Parallel processing Input is delivered along many pathways; a single sensory stimulus results in multiple perceptions Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neural Processing Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.21 Disorders of the Nervous System Multiple sclerosis Common cause of neural disability An autoimmune disease Immune system attacks the myelin around axons in the CNS Varies widely in intensity among those affected More women than men are affected When men are affected disease develops quicker and is more devastating Cause is incompletely understood Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue Throughout Life Nervous system develops from the dorsal ectoderm Invaginates to form the neural tube and neural crest Neural tube walls begin as neuroepithelial cells These cells divide and become neuroblasts Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue Throughout Life Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.22 Neuronal Regeneration Neural injuries may cause permanent dysfunction If axons alone are destroyed, cells bodies often survive and the axons may regenerate PNS – macrophages invade and destroy axon distal to the injury Axon filaments grow peripherally from injured site Partial recovery is sometimes possible Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Neuronal Regeneration CNS – neuroglia never form bands to guide regrowing axons and may hinder axon growth with growth-inhibiting chemicals No effective regeneration after injury to the spinal cord and brain Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Regeneration of the Peripheral Nerve Fiber Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.23