Introduction to the Nervous System

Introduction to theNervous SystemAnatomy & PhysiologyNervous Tissue & Homeostasisexcitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue.

together with endocrine system: responsible for maintaining homeostasis

Differences in Nervous & Endocrine Control of HomeostasisNERVOUS ENDOCRINErapid responderaction potentialsslow, prolonged responsereleases hormones Structures of the Nervous Systemtotal mass of 2 kg (~3% of total body mass)SkullSpinal CordSpinal NervesCranial NervesGangliaEnteric PlexusSpecial Senses & other Sensory Receptors

Major Structures of the Nervous System

Functions of the Nervous System3 basic functions:SensoryIntegrativeMotor

Sensory Functionsensory receptors detect internal & external stimulisensory (afferent) neurons carry this sensory information to spinal cord & brain thru cranial & spinal nervesIntegrative Functionintegrate: processnervous system takes information from sensory neurons & processes that information, analyzes it, stores some of it & makes decisions for appropriate responsesserved by interneurons (connect 1 neuron to another neuronPerception: conscious awareness of sensory stimulioccurs in brainMotor Functionserved by motor (efferent) neuronscarry info from brain/spinal cord effectors (muscle or gland) thru cranial or spinal nervesresults in muscles contraction or gland secretingQuick QuizWhat terms are given to neurons that carry input spinal cord & brain?

What terms are given to neurons that carry output out of the brain & spinal cord?Organization of the Nervous System

Histology of the Nervous System2 cell typesNeuronsNeuroglia

Neurons nerve cells that possess electrical excitability:ability to respond to a stimulus & convert it into an action potential

stimulus: any change in environment that is strong enough to initiate an action potentialDirection Action Potential Travels

Action Potentialelectrical signal that propagates along surface of neurolema (membrane)begins & travels due to movement of ions between interstitial fluid & inside of neuron thru specific ion channelsonce begun it travels rapidly @ constant strengthParts of a Neuron

Parts of Neuron: Cell Bodycontains nucleus, cytoplasm, typical organelles,+ Nissl bodies clusters of RERmake materials for: growth of neuronregenerate damaged axons in PNS

Dendrites little treesinput portion of neuronusually, short, tapering, highly branchedtheir cytoplasm contains Nissl bodies, mitochondria

Axon propagates action potentials another neuronmuscle fibergland cell

Parts of an Axonjoins cell body @ cone-shaped elevation: axon hillockpart of axon closest to hillock = initial segmentjct of axon hillock & initial segment where action potential arises so is called the trigger zoneParts of an Axonaxoplasm: cytoplasm of an axonaxolemma: plasma membrane of axonaxon collaterals: side branches along length of axon (most @ 90)axon terminals: axon divides into many fine processes

Synapse site of communication between 2 neurons or between a neuron & effector cellsynaptic end bulbs: tips of some axon terminals swell into bulb-shaped structuressynaptic vesicles: store neurotransmittermany neurons have >1 neurotransmitter, each with different effects on postsynaptic cell

Types of NeuronsFunctional ClassificationStructural ClassificationSensoryInterneuronsMotor use # processes extending from cell bodyMultipolar neuronsBipolar neuronsUnipolar neuronsMultipolar Neuronsseveral dendrites with 1 axonincludes most neurons in brain & spinal cord

Bipolar Neuron1 main dendrite & 1 axonretina, inner ear, olfactory area of brain

Unipolar Neuronare sensory neurons that begin in embryo as bipolarduring development axon & dendrite fuse then divide into 2 branches (both have characteristic structure & function of an axon)1 branch ends with dendrites (out of CNS)2nd branch ends in axon terminal (in CNS)cell bodies of most found in gangliaUnipolar Neuron

Purkinje Cellsfound in cerebellum

Pyramidal Cellsin cerebral cortex of brain

Neuroglia (Glia)~50% vol of CNSgluedo not generate or propagate action potentialsmultiply & divide in mature nervous systemsglioma: brain tumors derived from glial cellsvery malignant, grow rapidlyGlial Cells of the CNSASTROCYTESOLIGODENDROCYTESMICROGLIAEPENDYMAL CELLSAstrocytes star-shapedlargest & most numerous of glial cellsfunctions:physically support neuronsassist in blood-brain-barrier (bbb)in embryo: regulate growth, migration, &interconnections between neuronshelp maintain appropriate chemical environment for propagation of action potentials

Oligodendrocytes few treessmaller & fewer branches than astrocytesFunctions:form & maintain myelin sheath on axons in CNS1 oligo. myelinates many axons

Microglia small cells with slender processes giving off many spine-like projectionsfunction:phagocytesremove cellular debris made during normal developmentremove microbes & damaged nervous tissue

Ependymal Cellssingle layer of cuboidal to columnar cellsciliated & have microvillifunction:line ventricles of brain & central canal of spinal cordproduce, monitor, & assist in circulation of cerebrospinal fluid (CSF)form bbb

Neuroglial Cells of the PNSSchwann cellsSatellite cellsSchwann Cellsfunctions:myelinate axons in PNS1 Schwann cell myelinates 1 axonparticipate in axon regeneration

Satellite Cellsflat cells that surround cell bodies of neurons in PNS gangliafunctions:structural supportregulate exchange of materials between neuronal cell bodies & interstitial fluid

Myelination myelin sheath: made up of multilayered lipid & protein (plasma membrane) coveringfunction:electrically insulates axonincreases speed of nerve impulsesMyelinated & Unmyelinated Axons

Nodes of Ranviergaps in myelin sheath1 Schwann cell wraps axon between nodes of Ranvier

Myelin amount increases from birth to maturity infants responses slower & less coordinated as older child or adult in part because myelination is a work in progress thru infancy

Demyelination loss of myelin sheathsee in disorders:multiple sclerosisTay-Sachsside effect of radiation therapy & chemotherapyGray Matter of the Nervous Systemcontains: neuronal cell bodiesdendritesunmyelinated axonsaxon terminalsneuroglia

White Matter of the Nervous Systemcomposed of:myelinated axons