CH 12-2 The Brain and Cranial Nerves.doc - CH 14 THE BRAIN...

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CH 14THE BRAIN AND CRANIAL NERVESI.IntroductionA.Thebrainis the center for registering sensations, correlating them with one another and with storedinformation, making decisions and taking action.1.It is also the center for intellect, emotions, behavior and memory.2.It also directs our behavior towards others.B.In this chapter we will consider the principal parts of the brain, how the brain is protected andnourished, and how it is related to the spinal cord and to the 12 pairs of cranial nerves.II.Overview of Brain Organization and Blood SupplyA.The principal parts of the brain are thebrain stem, diencephalon, cerebrumandcerebellum.B.Protective Covering of the Brain1.The brain is protected by thecranial bones(Fig 7.2) and thecranial meninges(Fig 14.2).2.The cranial meninges are continuous with the spinal meninges and are nameddura mater,arachnoidandpia mater.3.Three extensions of the dura mater separate parts of the brain: thefalx cerebri, falx cerebelliandthetentorium cerebelli.C.Blood Flow and the Blood-Brain Barrier1.Blood flows to the brain mainly via blood vessels that branch from the cerebral arterial circle(circle of Willis) at the base of the brain (Fig 21.20); the veins that return blood from the head tothe heart are seen in Figure 21.24.2.Although the brain comprises only about 2% of the total body weight, it utilizes about 20% of theoxygen used by the entire body.The brain is one of the most metabolically active organs of thebody and the amount of oxygen it uses varies with the degree of mental activity.3.Any interruption of the oxygen supply to the brain can result in weakening, permanent damage ordeath of brain cells.Interruption of the mother’s blood supply to a child during childbirth before itcan breathe may result in paralysis, mental retardation, epilepsy or death.4.Because carbohydrate storage in the brain is limited, the supply of glucose to the brain must becontinuous.Glucose deficiency may produce mental confusion, dizziness, convulsions andunconsciousness.5.Ablood-brain barrier (BBB)protects brain cells from harmful substances and pathogens byserving as a selective barrier to prevent passage of many substances from the blood to the brain.6.An injury to the brain due to trauma, inflammation, or toxins causes a breakdown of the BBB,permitting the passage of normally restricted substances into brain tissue.The BBB may alsoprevent entry of drugs that could be used as therapy for brain cancer or other CNS disorders, soresearch is exploring ways to transport drugs past the BBB.III.Cerebrospinal Fluid Production and Circulation in Ventricles

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