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J - Nervous System - Central NS.pdf - Anatomy and...

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1Anatomy and PhysiologyThe Central Nervous SystemThe CNS consists of the brain and the spinal cord. It is protected by bony enclosures (the skull and thevertebrae), the membranous meninges, and the watery CSF.The Brain is the largest and most complex part of the nervous system. It is composed of about onehundred billion multipolar neurons and innumerable nerve fibers. The brain contains nerve centersassociated with sensory functions and is responsible for sensations and perceptions. It issues motorcommands to skeletal muscles and carries on higher mental functions, such as memory and reasoning. Italso contains centers that coordinate muscular movements, as well as centers and nerve pathways thatregulate visceral activities. It also provides us with personality.The Brain: has four main regions1) cerebrum, 2) diencephalon, 3) cerebellum, and 4) brain stem.Brain Development:1. a neural tube gives rise to the central nervous system.2. The portion that becomes the brain has three major cavities (vesicles) at one end-forebrain (prosencephalon)-midbrain (mesencephalon)-hindbrain (rhombencephalon)3.Later the forebrain divides into anterior and posterior (telencephalon and diencephalon,respectively).4.The midbrain becomes the mesencephalon5.The hindbrain partially divides into two parts (metencephalon and myelencephalon).6.The resulting 5 cavities persist in the mature brain, along with fluid-filled spaces called ventricles, andthe tubes that connect them.7.The tissue surrounding the spaces differentiates into various structural and functional regions of thebrain.* Anencephalyis a type of birth defect called aneural tube defect (NTD).It occurs on the 28thday ofprenatal development when a sheet of tissue that normally folds to form a neural tube, which developsinto the CNS, remains open at the top. Most fetuses abort spontaneously, but those that are born full-term usually die with 24 hours.A less serious NTD is Spinal bifida, in which an opening occurs fartherdown the neural tube, causing a lesion in the spine and paralysis from that point downward. Sometimesthis can be improved, or corrected with surgery. The cause is not known, but some believe that folic acidis involved. Taking supplements while pregnant decreases the risk of NTD. Most pregnant women take ablood test at the fifteenth week of pregnancy to detect fluid leaking from a NTD.I. The Cerebrum:-develops from theanterior part of the forebrain.-it is thelargest partof the mature brain, consisting of about 83% of total brain mass.-consists oftwo cerebral hemispherescalledright and left, which are mirror images of each other-The hemispheres are connected by bundles of fibers:-corpus callosumconnects the cerebral hemispheres
2-The paired cerebral hemispheres cover and obscure the diencephalon and the top of the brain stem.

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