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    Copyright (c) The McGrawCopyright (c) The McGraw--HillHillCompanies, Inc. Permission requiredCompanies, Inc. Permission required

    for reproduction or display.for reproduction or display. 11

    Chapter FourteenChapter Fourteen

    The Spinal Cord andThe Spinal Cord andSpinal NervesSpinal Nerves

    Lecture OutlineLecture Outline

    22

    The Spinal CordThe Spinal Cord -- FunctionsFunctions

    The spinal cord serves threeThe spinal cord serves three

    principal functions:principal functions:

    1.1. ConductionConduction

    2.2. LocomotionLocomotion

    3.3. ReflexesReflexes

    The Spinal CordThe Spinal Cord -- FunctionsFunctions

    Conduction.Conduction.

    The spinal cord contains bundles of nerveThe spinal cord contains bundles of nerve

    fibers that conduct information up and downfibers that conduct information up and down

    the body, connecting different levels of thethe body, connecting different levels of the

    trunk with each other and with the braintrunk with each other and with the brain

    It enables sensory information to reach theIt enables sensory information to reach the

    brain, motor commands to reach thebrain, motor commands to reach the

    effectors, and input received at one level ofeffectors, and input received at one level ofthe cord to affect output from another levelthe cord to affect output from another level

    44

    The Spinal CordThe Spinal Cord -- FunctionsFunctions

    Locomotion.Locomotion.

    Walking involves repetitive, coordinated contractionsWalking involves repetitive, coordinated contractionsof several muscle groups in the limbsof several muscle groups in the limbs

    Motor neurons in the brainMotor neurons in the brain initiateinitiate walking, but thewalking, but thesimple repetitive muscle contractions that put onesimple repetitive muscle contractions that put onefoot in front of another, over and over, arefoot in front of another, over and over, arecoordinated by groups of neurons calledcoordinated by groups of neurons called centralcentralpattern generatorspattern generators in the cord.in the cord.

    These neuronal circuits produce the sequence of outputsThese neuronal circuits produce the sequence of outputs

    to the extensor and flexor muscles that cause alternatingto the extensor and flexor muscles that cause alternatingmovements of the legsmovements of the legs

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    55

    The Spinal CordThe Spinal Cord -- FunctionsFunctions

    Reflexes.Reflexes.

    Reflexes are involuntary stereotypedReflexes are involuntary stereotyped

    responses to stimuliresponses to stimuli

    They involve the brain, spinal cord, andThey involve the brain, spinal cord, and

    peripheral nervesperipheral nerves

    66

    Surface AnatomySurface Anatomy

    TheThe spinal cordspinal cord beginsbegins

    at the foramenat the foramen

    magnum of the skullmagnum of the skull

    and passes through theand passes through the

    vertebral canal as farvertebral canal as far

    as the inferior marginas the inferior margin

    of the first lumbarof the first lumbar

    vertebra (L1) or slightlyvertebra (L1) or slightly

    beyond.beyond.

    FIGURE 14.1

    77

    Surface AnatomySurface Anatomy

    In adults, it averages about 1.8 cm thick and 45 cmIn adults, it averages about 1.8 cm thick and 45 cmlonglong

    It occupies only the upper twoIt occupies only the upper two--thirds of thethirds of thevertebral canalvertebral canal

    The cord gives rise to 31 pairs of spinal nervesThe cord gives rise to 31 pairs of spinal nerves

    The first pair of nerves pass between the skull andThe first pair of nerves pass between the skull andvertebra C1, and the rest pass through thevertebra C1, and the rest pass through theintervertebral foramina.intervertebral foramina.

    The part supplied by each pair of spinal nerves isThe part supplied by each pair of spinal nerves iscalled acalled a segment.segment.

    88

    Surface AnatomySurface Anatomy

    The cord is divided intoThe cord is divided intocervicalcervical,, thoracicthoracic,, lumbarlumbar,,

    andand sacral regionssacral regions, named, namedfor the levels of thefor the levels of the

    vertebral column throughvertebral column through

    which the spinal nerveswhich the spinal nerves

    emergeemerge

    A bundle of nerve rootsA bundle of nerve roots

    called thecalled the cauda equinacauda equinaoccupies the canal from L2occupies the canal from L2

    to S5to S5

    FIGURE 14.1

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    99

    Meninges of the Spinal CordMeninges of the Spinal Cord TheThe dura materdura mater forms a toughforms a tough collagenouscollagenous

    membrane sleeve called themembrane sleeve called the dural sheathdural sheath around thearound thespinal cordspinal cord

    The space between the sheath and vertebral bone,The space between the sheath and vertebral bone,called thecalled the epidural spaceepidural space, is occupied by blood vessels,, is occupied by blood vessels,adipose tissue, and loose connective tissueadipose tissue, and loose connective tissue

    TheThe arachnoidarachnoid matermater consists of a simpleconsists of a simple squamoussquamousepithelium, theepithelium, the arachnoidarachnoidmembranemembrane,, adhering toadhering tothe inside of thethe inside of the duradura, and a loose mesh of, and a loose mesh ofcollagenouscollagenous and elastic fibers spanning the gapand elastic fibers spanning the gapbetween thebetween the arachnoidarachnoid membrane and themembrane and the piapiamatermater

    TheThe piapia matermater is a delicate, translucent membraneis a delicate, translucent membranethat closely follows the contours of the spinal cord.that closely follows the contours of the spinal cord.

    Anatomy of the Spinal CordAnatomy of the Spinal Cord

    The spinal cord isThe spinal cord is

    made up of regionsmade up of regions

    of gray & whiteof gray & white

    matter, and servesmatter, and serves

    as anas aninformationinformation

    highwayhighway..

    The spinal cord canThe spinal cord can

    range from 40range from 40--45 cm45 cm

    in length for anin length for an

    adult.adult.

    1111

    Cross Sectional AnatomyCross Sectional Anatomy

    The spinal cord, like the brain, consists of twoThe spinal cord, like the brain, consists of two

    kinds of nervous tissue called gray and whitekinds of nervous tissue called gray and white

    matter.matter.1.1. Gray MatterGray Matter: consists of neuronal cell bodies, dendrites,: consists of neuronal cell bodies, dendrites,

    unmyelinatedunmyelinated axons, axon terminals,axons, axon terminals, neuroglianeuroglia, and blood, and blood

    vessels.vessels.

    2.2. White MatterWhite Matter: consists of: consists ofmyelinatedmyelinated &&unmyelinatedunmyelinated nervenerve

    axons, and blood vessels.axons, and blood vessels.

    Gray MatterGray Matter

    Gray matterGray matter has a relatively dull colorhas a relatively dull color

    because it contains little myelinbecause it contains little myelin

    It contains the somas, dendrites, andIt contains the somas, dendrites, and

    proximal parts of the axons of neurons.proximal parts of the axons of neurons.

    It is the site of synaptic contact betweenIt is the site of synaptic contact between

    neurons, and therefore the site of all informationneurons, and therefore the site of all information

    processing in the central nervous systemprocessing in the central nervous system

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    White MatterWhite Matter

    White matterWhite matter contains an abundance of myelinatedcontains an abundance of myelinated

    axons, which give it a bright, pearly whiteaxons, which give it a bright, pearly white

    appearanceappearance

    It is composed of bundles of axons, calledIt is composed of bundles of axons, called tractstracts,,

    that carry signals from one part of the CNS tothat carry signals from one part of the CNS to

    another.another.

    Gray & White MatterGray & White Matter

    Internal Anatomy of the Spinal CordInternal Anatomy of the Spinal Cord

    1616

    Gray MatterGray Matter

    The central gray matter consists of twoThe central gray matter consists of two dorsaldorsal

    ((posteriorposterior)) hornshorns, and two thicker, and two thicker ventralventral

    ((anterioranterior)) hornshorns..

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    Gray MatterGray Matter

    In the thoracic and lumbar regions, an additionalIn the thoracic and lumbar regions, an additional

    lateral hornlateral horn is visible on each side of the gray matteris visible on each side of the gray matter

    It contains neurons of the sympathetic nervousIt contains neurons of the sympathetic nervous

    system, which send their axons out of the cord by waysystem, which send their axons out of the cord by way

    of the ventral root along with the somatic efferentof the ventral root along with the somatic efferent

    fibersfibers 1818

    Spinal Nerve RootsSpinal Nerve Roots

    As a spinal nerve approaches the cord, it branches into aAs a spinal nerve approaches the cord, it branches into adorsal rootdorsal rootandand ventral rootventral root

    The dorsal root carries sensory nerve fibers, which enter theThe dorsal root carries sensory nerve fibers, which enter the

    dorsal horn of the cord.dorsal horn of the cord.

    The ventral horns contain the large somas of the somaticThe ventral horns contain the large somas of the somatic

    motor neurons, which send their axons out to the body.moto