Fundamentals of the Nervous System and Nervous Tissue

C H A P T E RElaine N. MariebKatja HoehnPowerPoint ® Lecture Slidesprepared by Vince Austin,Bluegrass Technicaland Community College11P A R T AHumanAnatomy& PhysiologySEVENTH EDITIONFundamentalsof the NervousSystem andNervous TissueCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Nervous System• The master controlling and communicating systemof the body• Functions• Sensory input – monitoring stimuli• Integration – interpretation of sensory input• Motor output – response to stimuliCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Nervous SystemCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.1

Organization of the Nervous System• Central nervous system (CNS)• Brain and spinal cord• Integration and command center• Peripheral nervous system (PNS)• Paired spinal and cranial nerves• Carries messages to and from the spinal cord andbrainCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Peripheral Nervous System (PNS): TwoFunctional Divisions• Sensory (afferent) division• Sensory afferent fibers – carry impulses from skin,skeletal muscles, and joints to the brain• Visceral afferent fibers – transmit impulses fromvisceral organs to the brain• Motor (efferent) division• Transmits impulses from the CNS to effectororgansCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Motor Division: Two Main Parts• Somatic nervous system• Conscious control of skeletal muscles• Autonomic nervous system (ANS)• Regulates smooth muscle, cardiac muscle, andglands• Divisions – sympathetic and parasympatheticCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Histology of Nerve Tissue• The two principal cell types of the nervous systemare:• Neurons – excitable cells that transmit electricalsignals• Supporting cells – cells that surround and wrapneuronsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Supporting Cells: Neuroglia• The supporting cells (neuroglia or glial cells):• Provide a supportive scaffolding for neurons• Segregate and insulate neurons• Guide young neurons to the proper connections• Promote health and growthCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Astrocytes• Most abundant, versatile, and highly branched glialcells• They cling to neurons and their synaptic endings,and cover capillariesCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Astrocytes• Functionally, they:• Support and brace neurons• Anchor neurons to their nutrient supplies• Guide migration of young neurons• Control the chemical environmentCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

AstrocytesCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.3a

Microglia and Ependymal Cells• Microglia – small, ovoid cells with spiny processes• Phagocytes that monitor the health of neurons• Ependymal cells – range in shape from squamousto columnar• They line the central cavities of the brain andspinal columnCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Microglia and Ependymal CellsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.3b, c

Oligodendrocytes, Schwann Cells, andSatellite Cells• Oligodendrocytes – branched cells that wrap CNSnerve fibers• Schwann cells (neurolemmocytes) – surroundfibers of the PNS• Satellite cells surround neuron cell bodies withgangliaCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Oligodendrocytes, Schwann Cells, andSatellite CellsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.3d, e

Neurons (Nerve Cells)• Structural units of the nervous system• Composed of a body, axon, and dendrites• Long-lived, amitotic, and have a high metabolicrate• Their plasma membrane function in:• Electrical signaling• Cell-to-cell signaling during developmentPLAY InterActive Physiology ®:Nervous System I, Anatomy Review, page 4Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons (Nerve Cells)Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.4b

Nerve Cell Body (Perikaryon or Soma)• Contains the nucleus and a nucleolus• Is the major biosynthetic center• Is the focal point for the outgrowth of neuronalprocesses• Has no centrioles (hence its amitotic nature)• Has well-developed Nissl bodies (rough ER)• Contains an axon hillock – cone-shaped area fromwhich axons ariseCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Processes• Armlike extensions from the soma• Called tracts in the CNS and nerves in the PNS• There are two types: axons and dendritesCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Dendrites of Motor Neurons• Short, tapering, and diffusely branched processes• They are the receptive, or input, regions of theneuron• Electrical signals are conveyed as gradedpotentials (not action potentials)Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Axons: Structure• Slender processes of uniform diameter arisingfrom the hillock• Long axons are called nerve fibers• Usually there is only one unbranched axon perneuron• Rare branches, if present, are called axoncollaterals• Axonal terminal – branched terminus of an axonCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Axons: Function• Generate and transmit action potentials• Secrete neurotransmitters from the axonalterminals• Movement along axons occurs in two ways• Anterograde — toward axonal terminal• Retrograde — away from axonal terminalCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Myelin Sheath• Whitish, fatty (protein-lipoid), segmented sheatharound most long axons• It functions to:• Protect the axon• Electrically insulate fibers from one another• Increase the speed of nerve impulse transmissionCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Myelin Sheath and Neurilemma: Formation• Formed by Schwann cells in the PNS• A Schwann cell:• Envelopes an axon in a trough• Encloses the axon with its plasma membrane• Has concentric layers of membrane that make upthe myelin sheath• Neurilemma – remaining nucleus and cytoplasm ofa Schwann cellCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Myelin Sheath and Neurilemma: FormationPLAY InterActive Physiology ®:Nervous System I, Anatomy Review, page 10Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 11.5a–c

Nodes of Ranvier (Neurofibral Nodes)• Gaps in the myelin sheath between adjacentSchwann cells• They are the sites where axon collaterals canemergePLAY InterActive Physiology ®:Nervous System I, Anatomy Review, page 11Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Unmyelinated Axons• A Schwann cell surrounds nerve fibers but coilingdoes not take place• Schwann cells partially enclose 15 or more axonsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Axons of the CNS• Both myelinated and unmyelinated fibers arepresent• Myelin sheaths are formed by oligodendrocytes• Nodes of Ranvier are widely spaced• There is no neurilemmaCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Regions of the Brain and Spinal Cord• White matter – dense collections of myelinatedfibers• Gray matter – mostly soma and unmyelinatedfibersCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Classification• Structural:• Multipolar — three or more processes• Bipolar — two processes (axon and dendrite)• Unipolar — single, short processCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Neuron Classification• Functional:• Sensory (afferent) — transmit impulses toward theCNS• Motor (efferent) — carry impulses away from theCNS• Interneurons (association neurons) — shuttlesignals through CNS pathwaysCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Comparison of Structural Classes of NeuronsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsTable 11.1.1

Comparison of Structural Classes of NeuronsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsTable 11.1.2

Comparison of Structural Classes of NeuronsCopyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsTable 11.1.3

Neurophysiology• Neurons are highly irritable• Action potentials, or nerve impulses, are:• Electrical impulses carried along the length ofaxons• Always the same regardless of stimulus• The underlying functional feature of the nervoussystemCopyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings