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Chapter 14:The Brain and Cranial NervesNeural TubeThe brain and spinal cord develop from the ectodermal neural tube.-The anterior part of the neural tube expands, along with the associated neural cresttissue. Constrictions in this expanded tube soon appear, creating 3 regions.-The walls of these brain regions develop into nervous tissue, while the hollow interior ofthe tube is transformed into its various ventricles.-The expanded neural crest tissue becomes prominent in head development.-Most of the protective structures of the brain –that is, most of the bones of the skull,associated connective tissues, and meningeal membranes –arise from this expanded neural crestline.Brain DevelopmentThe neural tube forms three primary brain vesicles. The primary brain vesicles give riseto five secondary brain vesicles, which give rise to various adult structures.A. Primary Brain Vesicles:Prosencephalon, Mesencephalon, and Rhombencephalon1. Prosencephalon (Forebrain): Comprises of: (i) The telencephalon (tel- meaning“distant” –encephalon- meaning “brain”) develops into the cerebrum and lateral ventricles. And(ii.) The diencephalon forms the thalamus, hypothalamus, epithalamus, and third ventricle.2. Mesencephalon (Midbrain): gives rise to the midbrain and aqueduct of themidbrain (cerebral aqueduct).3. Rhombencephalon (Hindbrain): (i.) The metencephalon (met meaning “after”)becomes the pons, cerebellum, and upper part of the fourth ventricle. (ii.) The myelencephalon(myel- meaning “marrow”) forms the medulla oblongata and lower part of the fourth ventricle.Major Parts of the BrainThere are 4 major parts of the brain: the brain stem, cerebellum, diencephalon, andcerebrum.Sagittal section of the brain (Medial View)Brain Stem: The portion of the brain immediately superior to the spinal cord, continuous with thespinal cord, made up of the medulla oblongata, pons, and midbrain.Cerebellum: The part of the brain lying posterior to the medulla oblongata and pons; governsbalance and coordinates skill movements.Diencephalon: Superior to the brain stem, which consists of the thalamus, hypothalamus, andepithalamusCerebrum:The two hemispheres of the forebrain (derived from the telenchephalon), making upthe largest part of the brain.Cranial MeningesAlong with the cranium protect the brain.-Are continuous with the spinal meninges, have the same basic structure, and bear thesame names.-The outer dura mater, the middle arachnoid mater, and the inner pia mater.Dura Mater: The outermost layer. The cranial dura mater has 2 layers:(i.) Periosteal Layer (which is external) and;(ii.) Meningeal Layer (which is internal)