Central Nervous SystemProtection to the BrainSlide 3MeningesSlide 5Slide 6The Dura MaterSlide 8Slide 9Slide 10Slide 11Slide 12Slide 13The Arachnoid MaterSlide 15Slide 16The Pia MaterSlide 18Cerebrospinal Fluid (CSF)Cerebrospinal Fluid CSFSlide 21Slide 22Choroid PlexusSlide 24Slide 25Slide 26The Choroid PlexusCSF CirculationBlood-Brain BarrierSlide 30Slide 31Slide 32Slide 33Slide 34Slide 35The Spinal CordSlide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48The SpinalCordSlide 50Gray Matter of the Spinal CordGray Matter and Spinal RootsSlide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64White Matter and Spinal CordSlide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Sensory and Motor PathwaysSlide 74Ascending (Sensory) PathwaysNeuron PathwaysAscending (Sensory) TractsSlide 78Slide 79Slide 80Slide 81Slide 82Slide 83Descending (Motor) TractsSlide 85Slide 86Slide 87Slide 88Slide 89Slide 90Slide 91Spinal Cord TraumaDevelopmental Aspects of CNSEmbryonic DevelopmentSlide 95Slide 96Slide 97Slide 98Slide 99Slide 100Slide 101Slide 102Central Nervous SystemPart IIChapter 13Protection to the BrainNervous tissue is soft and delicate, and the irreplaceable neurons can be injured or destroyed by even slight pressureThe brain is protected from injury by…–The skull–Surrounding membranes called meninges–A watery cushion of cerebrospinal fluid–The blood-brain barrierProtection to the BrainThe skull is a self-bracing arrangement of bones that encapsulates the brainIt was presented in Chapter 7 and thus will receive only passing reference in this sectionMeningesThe meninges are three connective tissue membranes that lie just external to the brain and spinal cordMeningesThe meningeal membranes –Cover and protect the CNS structures–Protect blood vessels and enclose venous sinuses–Contain cerebrospinal fluid–Form partitions within the skullMeningesFrom external to internal, the meningeal layers are–Dura mater–Arachnoid–Pia materThe Dura MaterThe leathery dura mater is by far the strongest of the meningesWhere it surrounds the brain it is a double layer membraneThe Dura MaterThe periosteal layer is the superficial and lines the inner surface (periostium) of the skullThe deeper meningeal layer forms the true external covering of the brainThe Dura MaterThe brain’s dural layers are fused together except in certain areas where they enclose the blood filled dural sinusesThe dural sinuses collect venous blood and direct it into the internal jugular veins of the neckThe Dura MaterIn several places the meningeal dura mater extends inward to form flat septa (partitions) that limit movement of the brain within the skullThe Dura MaterThe falx cerebri dips into the longitudinal fissureIt attaches to the crista galli of the ethmoid boneThe Dura MaterThe falx cerebelli forms a midline partition that runs along the vermis of the cerebellumThe Dura MaterThe tentorium cerebelli extends into the transverse fissure between the cerebral hemispheres and the cerebellumThe Arachnoid MaterThe middle membrane forms a loose brain covering over the surface of the cerebrumIt is separated from the dura mater by a narrow serous cavity, the subdural spaceBeneath the arachnoid membrane is the wide subarachnoid spaceThe Arachnoid MaterThe subarachnoid space is filled with cerebrospinal fluid and contains the largest blood vessels serving the brainSince the arachnoid is fine and elastic, these blood vessels are rather poorly protectedThe Arachnoid MaterArachnoid villi protrude through the overlying dura mater and into the dural sinuses overlying the superior aspect of the brainCerebrospinal fluid is absorbed into the venous blood sinuses through these valvelike villiThe Pia MaterThe pia mater is a delicate connective tissue that is richly invested with tiny blood vesselsIt is the only membrane that clings tightly to the brain, following its every convolutionThe Pia MaterMeningitis is an inflammation of the meningeal layers that is caused by either a bacterial or viral infection that can spread to the underlying nerve tissueBrain inflammation is called encephalitisCerebrospinal Fluid (CSF)CSF is a watery “ broth”found in and around the brain and spinal cordIt forms a liquid cushion that gives buoyancy to the CNS organsWith the brain floating, CSF reduces brain weight by 97% and thus prevents the brain from crushing under its own weightCSF also protects the brain and spinal cord from traumaCerebrospinal Fluid CSFCSF also helps to nourish the brainIt also helps to remove wastes produced by neuronsFinally, it carries chemical signals between different parts of the CNSAlthough it performs many functions there is 100-160 ml of fluid (about a half cup) present in the body at any one timeCerebrospinal Fluid (CSF)CSF is a similar in composition to blood plasma, from which it arisesIt contains less protein and more sodium and chloride ionsCerebrospinal Fluid (CSF)The figure at the right depicts the sites of CSF production and its circulationMost CSF is made in the choroid plexuses which are membranes on the roofs of the four brain ventriclesChoroid PlexusChoroid plexus hang from the roof of each ventricleThe plexuses are clusters of thin walled capillaries enclosed by a layer of ependymal cellsChoroid PlexusThe capillaries of the choroid plexus are fairly permeable and fluid filters continuously from the bloodstream into the ventriclesChoroid PlexusThe choroid plexus cells are joined by tight junctions and have ion pumps that allow them to modify this filtrate by actively transporting only certain ions across their membranes into the CSF poolChoroid PlexusAfter entering the ventricles, the CSF moves freely through these chambersSome CSF enters the central canal of the spinal cord, but most enters the subarachnoid space through the lateral and median apertures in the walls of the fourth ventricleIn the subarachnoid space, the CSF bathes the outer surface of the brain and cordThe Choroid PlexusCerebrospinal fluid arises from the blood and returns to it at a rate of about 500 ml a dayThe choroid plexus also helps to cleanse the CSF by removing waste products and other unnecessary solutesCSF CirculationThe motion of the CSF is aided by the long microvilli of the ependymal cells