Human Anatomy: Fundamentals of the Nervous System and Nervous Tissue PDF

Human Anatomy Fundamentals of the Nervous System and Nervous Tissue Course: BL3420 Instructor: Benjamin T. Enslow, M.D. Email: [email protected] Phone: (830) 391-4298 Office: Moody 214 Rea...

Human Anatomy Fundamentals of the Nervous System and Nervous Tissue Course: BL3420 Instructor: Benjamin T. Enslow, M.D. Email: [email protected] Phone: (830) 391-4298 Office: Moody 214 Reading: Chapter 12; Sections 12.1-12.4a Slides Adapted From: PowerPoint® Lecture Presentations prepared by Leslie Hendon University of Alabama, Birmingham Molly Selba University of Florida Copyright © 2020 Pearson Education, Inc. All Rights Reserved Learning Objectives 1. List the main functions of the nervous system. 2. Explains the structural and functional divisions of the nervous system. 3. Define neuron, describe its structural components, and relate each structure to its functional role. 4. Describe the structure of a synapse. 5. Classify neurons both structurally and functionally. Need-to-Know Terms Stimuli Axon hillock Satellite cells Sensory input Neurotransmitter Schwann cells Integration Synapse Cerebrospinal fluid Motor output Presynaptic neuron Myelin/Myelin sheath Central nervous system Postsynaptic neuron Nodes of Ranvier Peripheral nervous system Synaptic vesicles Gray matter Somatic sensory (afferent) division Synaptic cleft White matter Visceral sensory (afferent) division Multipolar neuron Nerves Somatic motor (efferent) division Bipolar neuron Endoneurium Visceral motor (efferent) division Unipolar neuron Perineurium Autonomic nervous system Sensory neuron Nerve fascicles Neuron Ganglia Nerve fiber Action potential Central process Epineurium Cell body (soma) Peripheral process Reflex arcs Chromatophilic substance Motor neuron Monosynaptic reflex arc Neurofibrils Interneuron Polysynaptic reflex arc Dendrites Neuroglia Axons Astrocytes Axonal transport Microglia Terminal arborization Ependymal cells Terminal boutons Oligodendrocytes  12.1a Functions of the Nervous System The nervous system has 3 overlapping functions: Monitor changes occurring both outside (Sees refreshing and inside the body glass of water) (“Me want”) These changes are stimuli Gathered information is sensory input Process/interpret sensory input and make decisions about what to do Process is called integration Dictate a response by activating effector (“Gimme that”) organs (muscles and glands) Response is called motor output 12.1b Basic Divisions of the Nervous System Humans have 1 integrated nervous system, but we can think of it in two anatomical parts… Central Nervous System (CNS) Brain and Spinal Cord Occupy the cranium and vertebral canal, respectively Integrating and command center Receives sensory signals, interprets them, and dictates motor responses based on past experiences, reflexes, and current conditions Peripheral Nervous System (PNS) Nerves that extend from the brain and spinal cord Cranial nerves, spinal nerves Communication lines that link all regions of the body to the CNS Ganglia = collections of cell bodies of neurons Central Nervous System Peripheral Nervous System -BRAIN -All other nerves of the body -SPINAL CORD Sensory (afferent) Division Motor (efferent) Division Smooth muscle, Wave hello cardiac muscle, glands Somatic Sensory Visceral Sensory Somatic Motor Visceral Motor Voluntary Involuntary Sensation from Sensation from Skeletal muscle skin, body wall, visceral organs innervation Rest and limbs Digest Man, I really Ouch! Got a gotta pee… Sympathetic Parasympathetic papercut… Fight or Nervous System Nervous System Flight  12.1b Basic Divisions of the Nervous System The nervous system receives sensory Ce ntral nervous system (C NS) Periph eral n ervous system (PNS) Bra in and spinal c ord Cra nial nerves and spina l nerv es inputs and dictates motor outputs Int egrative and control centers Com municat ion lines betw een the CNS and the rest of the body Sensory (affere nt) division Motor (e fferen t) divisi on Sensory (afferent) signals picked up by Somat ic and visce ral sensory nerve fibers Conduc ts im pulses from Motor ne rve fibers Conduc ts im pulses from the CNS to effect ors (muscles and gla nds) sensory receptors in the periphery receptors to the CNS Carried by nerve fibers of P NS to the CNS Somat ic sensory f iber Skin Somat ic ner vou s system Au tonom ic ner vou s system (ANS) Somat ic motor Visceral motor (voluntary) (involunt ary ) Conduc ts im pulses Conduc ts im pulses from the CNS t o from the CNS t o ske let al muscles cardia c m us cle s, sm ooth m us cle s, Visceral sensory fibe r and glands Motor (efferent) signals are carried away from Stoma ch Ske let al muscle the CNS Motor fiber of soma tic nervous sys tem Innervate muscles and glands Sym pathe tic di vision Paraysmpath etic division Mobilizes body syste ms during activity Conserves energy Promotes house- kee ping func tions during re st Sym pa the tic m otor f iber of ANS Heart Structure Function Sensory ( afferent) div ision of PNS Parasy mpathetic m ot or fiber of ANS Bla dder Motor (effe rent) div ision of PNS  12.1b Basic Divisions of the Nervous System Both the sensory inputs and the motor outputs are further divided according to the Ce ntral nervous system (C NS) Bra in and spinal c ord Periph eral n ervous system (PNS) Cra nial nerves and spina l nerv es body regions they serve: Int egrative and control centers Com municat ion lines betw een the CNS and the rest of the body Sensory (affere nt) division Motor (e fferen t) divisi on Somat ic and visce ral sensory Motor ne rve fibers nerve fibers Somatic body region – structures external Conduc ts im pulses from the CNS Conduc ts im pulses from to effect ors (muscles and gla nds) receptors to the CNS to the ventral body cavity (skin, skeletal Somat ic ner vou s Au tonom ic ner vou s Somat ic sensory f iber Skin system system (ANS) muscles, bones) Somat ic motor (voluntary) Conduc ts im pulses Visceral motor (involunt ary ) Conduc ts im pulses from the CNS t o from the CNS t o ske let al muscles cardia c m us cle s, sm ooth m us cle s, Visceral sensory fibe r and glands Stoma ch Ske let al Visceral body region – viscera of the ventral Motor fiber of soma tic nervous sys tem muscle body cavity (heart, lungs, bladder, etc.) Sym pathe tic di vision Mobilizes body syste ms Paraysmpath etic division during activity Conserves energy Promotes house- kee ping func tions during re st Sym pa the tic m otor f iber of ANS Heart Structure Function Sensory ( afferent) div ision of PNS Parasy mpathetic m ot or fiber of ANS Bla dder Motor (effe rent) div ision of PNS  12.1b Basic Divisions of the Nervous System This scheme results in the four main subdivisions of the PNS: Ce ntral nervous system (C NS) Bra in and spinal c ord Periph eral n ervous system (PNS) Cra nial nerves and spina l nerv es Int egrative and control centers Com municat ion lines betw een the CNS and the rest of the body -Somatic sensory Ouch! Got a papercut… Sensory (affere nt) division Somat ic and visce ral sensory Motor (e fferen t) divisi on Motor ne rve fibers nerve fibers Conduc ts im pulses from the CNS Conduc ts im pulses from to effect ors (muscles and gla nds) receptors to the CNS -Visceral sensory Man, I really gotta pee… Somat ic sensory f iber Skin Somat ic ner vou s system Somat ic motor (voluntary) Au tonom ic ner vou s system (ANS) Visceral motor (involunt ary ) Conduc ts im pulses Conduc ts im pulses from the CNS t o from the CNS t o ske let al muscles cardia c m us cle s, sm ooth m us cle s, Visceral sensory fibe r and glands Using your skeletal Stoma ch -Somatic motor muscles to wave hello Motor fiber of soma tic nervous sys tem Ske let al muscle Voluntary nervous system Sym pathe tic di vision Paraysmpath etic Mobilizes body syste ms division during activity Conserves energy -Visceral motor Heat starts pounding during a horror movie Promotes house- kee ping func tions during re st Sym pa the tic m otor f iber of ANS Heart “Autonomic nervous system” Structure Function Sensory ( afferent) Bla dder AKA: Involuntary nervous system div ision of PNS Motor (effe rent) div ision of PNS Parasy mpathetic m ot or fiber of ANS  Somatic Sensory Division of the PNS General somatic senses Receptors spread throughout “outer tube” of body Touch Pain Vibration Pressure Temperature General indicates “widespread” Proprioceptive senses—detect stretch in tendons and muscle Body sense—position and movement of body in space Special somatic senses Hearing Balance Vision  Visceral Sensory Division of the PNS General visceral senses Stretch, pain, temperature, nausea, and hunger Widely felt in digestive and urinary tracts, and reproductive organs Special visceral senses Taste Smell  Somatic Motor Division of the PNS General somatic motor—signals contraction of skeletal muscles Under our voluntary control Often called “voluntary nervous system”  Visceral Motor Division of the PNS Visceral motor Regulates the contraction of smooth and cardiac muscle Controls function of visceral organs Makes up autonomic nervous system Often called “involuntary nervous system”  12.2 Nervous Tissue Cells are densely packed and intertwined Two main cell types Neurons—transmit electrical signals Excitable cells Support cells (neuroglial cells in C NS) Nonexcitable Surround and wrap neurons  12.2a The Neuron Neurons are the basic structural unit of the nervous system- Specialized cells conduct electrical impulses along the plasma membrane Nerve impulse (action potential) Special characteristics of neurons: 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  12.2a The Neuron Cell Body (soma) Size of body varies from 5 to 140 microns Contains usual cellular organelles plus other structures Chromatophilic substance (Nissl bodies) Clusters of rough ER and free ribosome Function to renew abundant membrane of neurons and cytosolic proteins Neurofibrils Bundles of intermediate filaments (part of the cell’s cytoskeleton) Provide the cell with tensile strength.  12.2a The Neuron Dendrites Extensively branching from the cell body Transmit electrical signals toward the cell body Chromatophilic substance—extends only into the basal part of dendrites and to the base of the axon hillock Function as receptive sites for receiving signals from other neurons 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  12.2a The Neuron Axons Neurofilaments, actin microfilaments, and microtubules Provide strength along length of axon Aid in transport of substances to and from the cell body This process is axonal transport Branches along length are infrequent Axon collaterals Multiple branches at end of axon Terminal arborization (telodendria) End in knobs called terminal boutons (axon terminals)  12.2a The Neuron Nerve impulse Generated at the initial segment of the axon (Axon hillock) Conducted along the axon to the terminal boutons Neurotransmitters are released from vesicles at the terminal boutons  12.2a The Neuron; Synapses A synapse is the site at which neurons communicate Most information passed through chemical messengers (neurotransmitters) Some information transmitted electrically through gap junctions Presynaptic neuron Conducts signal toward a synapse Postsynaptic neuron Transmits electrical activity away from a synapse  Structure of an Axodendritic Synapse On the presynaptic side, the terminal bouton Nerve contains synaptic vesicles. impulses Presynaptic axon Membrane-bound sacs filled with neurotransmitters. Microtubule Neurofilament Mitochondria are abundant in the terminal bouton Terminal bouton because the secretion of neurotransmitters requires Mitochondrion a great deal of energy. Vesicle releasing neurotransmitter Synaptic vesicles At the synapse, the plasma membranes of the Synaptic two neurons are separated by a synaptic cleft. cleft When an impulse travels along the axon of the presynaptic neuron, the impulse stimulates the synaptic vesicles to fuse with the Postsynaptic dendrite presynaptic membrane. Enlarged view of the synapse  Structure of an Axodendritic Synapse The fused area then ruptures, causing the Nerve impulses vesicles to release their neurotransmitter Presynaptic axon Microtubule molecules (via exocytosis), which diffuse Neurofilament across the synaptic cleft and bind to the Terminal bouton Mitochondrion postsynaptic membrane. Vesicle releasing neurotransmitter Synaptic vesicles This binding changes the membrane charge Synaptic cleft on the postsynaptic neuron, influencing the membrane’s ability to generate a nerve impulse. Postsynaptic dendrite Enlarged view of the synapse  Very rare neurons; occur in Well over 99% of neurons in some of the special sensory the body belong to the organs where they mostly Usually function as sensory multipolar class. serve as sensory neurons. neurons.  Functional Classification of Neurons Functional classification is according to the direction the nerve impulse travels relative to the C NS Central process Sensory neurons- Transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Ganglia The central process— terminates in the C NS The peripheral process— extends from sensory receptors Peripheral process  Functional Classification of Neurons Functional classification is according to the direction the nerve impulse travels relative to the C NS 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  Neuroglia Six types of neuroglia CNS Neuroglia Four in the CNS -Astrocytes Outnumber neurons 10 to 1 Make up half the mass of the brain -Microglia Can divide throughout life -Ependymal cells Two in the PNS -Oligodendrocytes PNS Neuroglia Functions of neuroglia -Satellite cells Provide supportive functions for neurons -Schwann cells Cover nonsynaptic regions of the neurons  CNS Neuroglia Astrocytes are the most abundant glial cell type Functions include: Regulating neurotransmitter levels by increasing the rate of neurotransmitter uptake in regions of high neuronal activity Signaling increased blood flow through capillaries in active regions of the brain Controlling the ionic environment around neurons Produce molecules necessary for neuronal growth Propagate calcium signals involved with memory  CNS Neuroglia Microglia are the smallest and least abundant glial cell Functions include: Phagocytes—the macrophages of the C NS Engulf invading microorganisms and dead neurons Derive from blood cells called monocytes Migrate to CNS during embryonic and fetal periods  CNS Neuroglia Ependymal cells Line the central cavity of the spinal cord and brain Bear cilia—help circulate the cerebrospinal fluid  CNS Neuroglia Oligodendrocytes—have few branches Wrap their cell processes around axons in C N S Produce myelin sheaths in the C N S  PNS Neuroglia Satellite cells—surround neuron cell bodies within ganglia Schwann cells — surround axons in the PN S Form myelin sheath around axons of the PN S Myelin Sheaths in the PNS 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 In the PNS→ myelin sheaths formed by Schwann cells Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes Myelin sheath gaps (nodes of Ranvier)  Are gaps along axon Speed up nerve transmission          Myelin Sheaths in the CNS Oligodendrocytes form the myelin sheaths in the CNS Have multiple processes Coil around several different axons  12.3a Grey and White Matter of the CNS Gray matter Is gray-colored and surrounds hollow central cavities of the C NS Forms butterfly-shaped region in the spinal cord Dorsal half contains cell bodies of interneurons Ventral half contains cell bodies of motor neurons Is the site where neuron cell bodies are clustered (ganglia) Is where synapses occur  12.3a Grey and White Matter of 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  12.3a Grey and White Matter of the CNS GRAY MATTER Normal brain; frontal T1 MRI WHITE MATTER  12.3b Nerves Nerves—cablelike organs in the PN S Consist of numerous axons wrapped in connective tissue Most nerves contain myelinated and nonmyelinated sensory and motor axons Axon is surrounded by Schwann cells 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  12.4a 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 Monosynaptic Reflex Arc Simplest of all reflexes Just one synapse The fastest of all reflexes Knee-jerk reflex Polysynaptic Reflex Arc: More common type of reflex One or more interneurons are part of the pathway Withdrawal reflexes Interneurons signal the motor neuron to contract muscle involved