Biology 235 The Brain and Cranial NervesUnit 14Neural tubeThe brain and spinal cord develop from the ectodermal neural tube .- The anterior part of the neural tube expands, along with the associated neural crest tissue.Constrictions in this expanded tube soon appear, creating three regions-The walls of these brain regions develop into nervous tissue, while the hollow interior of thetube 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, associatedconnective tissues, and meningeal membranes—arise from this expanded neural crest tissue.Brain developementThe neural tube forms three primary brain vesicles. The primary brain vesicles give rise to fivesecondary brain vesicles, which give rise to various adult structures> primary brain vesicles: prosencephalon, mesencephalon, and rhombencephalon1. prosencephalon (forebrain)>The telencephalon (tel′-en-SEF-a-lon; tel- = distant; -encephalon = brain) develops into thecerebrum and lateral ventricles.>The diencephalon (dī′-en-SEF-a-lon) forms the thalamus, hypothalamus, epithalamus, and thirdventricle.2. Midbrain>The mesencephalon (mes′-en-SEF-a-lon (mes- = middle)), or midbrain, gives rise to themidbrain and aqueduct of the midbrain (cerebral aqueduct).3. rhombencephalon (hindbrain)>The metencephalon (met′-en-SEF-a-lon; met- = after) becomes the pons, cerebellum, and upperpart of the fourth ventricle.>The myelencephalon (mī-el-en-SEF-a-lon; myel- = marrow) forms the medulla oblongata andlower part of the fourth ventricle.Major Parts of the Brainfour major parts: brain stem, cerebellum, diencephalon, and cerebrumSagittal section of the brain (Medial View)
Brain stemThe portion of the brain immediately superior to the spinal cord, continuous with the spinal cord,made up of the medulla oblongata, pons, and midbrain.CerebellumThe part of the brain lying posterior to the medulla oblongata and pons; governs balance andcoordinates skilled movements.DiencephalonSuperior to the brain stem, which consists of the thalamus, hypothalamus, and epithalamusCerebrumThe two hemispheres of the forebrain (derived from the telencephalon), making up the largestpart of the brain.cranial meningesalong with the cranium protect the brain- are continuous with the spinal meninges, have the same basic structure, and bear the samenames- the outer dura mater (DOO-ra MĀ-ter), the middle arachnoid mater (a-RAK-noyd), and theinner pia materdura mater (outermost layer)- cranial dura mater has two layers- The two dural layers are called the periosteal layer (which is external) and the meningeal layer(which is internal).- The dural layers around the brain are fused together except where they separate to enclose thedural venous sinuses- Blood vessels that enter brain tissue pass along Three extensions of the dura mater separateparts of the brain:(1) The falx cerebri separates the two hemispheres (sides) of the cerebrum.