Objectives•Define CNS•Explain how the nervous system is protected•Describe the meninges•Describe CSF•Describe ventricles of the brain•Describe the brain
Objective 1: Define CNS•It is formed by the brain and the spinal cord•It forms the control centre of all activities inthe body.
Objective 2: Explain Protection ofthe CNSThe brain is protected by:•Cranial bones•The spinal cord protected by the vertebralcolumnBoth brain and spinal cord are protected by:•Meninges•Cerebrospinal fluid
Objective 3: Describe theMeninges•Three connective tissue membranes lieexternal to the CNS–dura mater–arachnoid mater–pia mater•Functions of the meninges–Cover and protect the CNS–Contain cerebrospinal fluid (CSF)–Form partitions within the skull
Dura Mater•Leathery, strong meninx composed of twofibrous connective tissue layers•The two layers separate in certain areas andform dural sinuses.•It forms the outer layer of the meninges andinner periosteum of cranial bones.
•Three dural septa extend inward and limitexcessive movement of the brain–Falx cerebri – fold that dips into the longitudinalfissure between the two hemispheres–Falx cerebelli – separates the 2 hemispheres of thecerebellum–Tentorium cerebelli – horizontal dural fold extendsinto the transverse fissure ie separates thecerebrum from the cerebellum.
Dura MaterFigure 12.24
Arachnoid Mater•The middle layer, which forms a loose braincovering•It is separated from the dura mater by thesubdural space which contains lubricatingserousfluid.•Beneath the arachnoid is a wide subarachnoidspace filled with CSF and large blood vessels•Arachnoid villi protrude superiorly and permitCSF to be absorbed into venous blood
Arachnoid MaterFigure 12.23a
Pia Mater•The innermost layer composed of delicateconnective tissue that clings tightly to the brain
Objective 4: DescribeCerebrospinal Fluid (CSF)•Watery solution similar in composition to bloodplasma produced by choroid plexus in eachventricle.
Functions•Forms a liquid cushion that gives buoyancy tothe CNS organs•Prevents the brain from crushing under itsown weight•Protects the CNS from blows and othertrauma•Nourishes the brain and carries chemicalsignals throughout it
Composition of CSF•Water•Mineral salts•Proteins eg albumin,globulin•Glucose•Urea•Few leukocytes
Objective 5: Describe Ventricles ofthe Brain•These are hollow chambers with CSF and linedwith ependymal cells•The ventricles are:–The paired C-shaped lateral ventricles i.e. the rightand the left ventricles.–The third ventricle found in the diencephalon–The fourth ventricle found in the hindbrain dorsalto the pons
Lateral ventricles•They are located within each hemisphere andare separated by a thin membrane calledseptum pellucidum.