BIOL 2457 1st Edition Lecture 30Outline of Last Lecture Spinal Cord and Spinal Nerves Outline of Current LectureThe Brain and cranial nerves Embryology of the brain Brain forms from three swellings at the tip of the developing neural tube Prosencephalon Forms the telencephalon and eventually the cerebrum and diencephalon Mesencephalon Rhombencephalon Forms the metencephalon (cerebellum and pons) and myelencephalon (medulla oblongata)Major regions and landmarks Regions in the adult brain Cerebrum - FOREBRAIN HIGHER Diencephalon Mesencephalon MIDBRAIN LIMBIC Pons Medulla oblongata HINDBRAIN REPTILIAN Cerebellum Brain contains extensive areas of neural cortex Layer of gray matter on the surface of the cerebellum and cerebrumMajor Parts of the Brain Brain stem- continuation of the spinal cord; consists of the medulla oblongata, pons and midbrain. Cerebellum- second largest part of the brain. Diencephalon- gives rise to thalamus, hypothalamus and epithalamus. Cerebrum- largest part of the brain.The cranial meninges Continuous with the three layers of the spinal cord Folds of dura mater help stabilize the position of the brain Falx cerebri Tentorium cerebelli Falx cerebelliProtective Coverings of the Brain Cranium Cranial meninges Dura mater Arachnoid mater Pia materExtensions of the Dura Mater Falx cerebri Separate the two cerebral hemispheres Falx cerebelli Separate the two cerebellar hemispheres Tentorium cerebelli Separate the cerebrum from the cerebellumBrain Blood Flow & the Blood-Brain Barrier Brain receives approximately 20% of the total blood supply. Internal carotid and vertebral arteries carry blood to the brain. Internal jugular veins return blood from the brain. Blood-brain barrier (BBB) protects brain from harmful substances.Cerebrospinal Fluid (CSF) Clear fluid. Circulates through cavities in the brain (ventricles) and the spinal cord (central canal) and also in the subarachnoid space. Absorbs shock and protects the brain and the spinal cord. Helps transport nutrients and wastes from the blood and the nervous tissue.Ventricles CSF-filled cavities within the brain Lateral ventricles: cerebral hemispheres Third ventricle: diencephalon Cerebral aqueduct: midbrain Fourth ventricle: brain stem and the cerebellumFormation & Circulation of CSF in the Ventricles Choroid plexuses- networks of capillaries in the walls of the ventricles. Ventricles are lined by ependymal cells. Plasma is drawn from the choroid plexuses through ependymal cells into the ventricles to produce CSF.Circulation of CSF CSF from the lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space or central canal. CSF is reabsorbed into the blood by arachnoid villi.Medulla Oblongata Connects the brain with the spinal cord Contains relay stations and reflex centers Olivary nuclei Cardiovascular and respiratory rhythmicity centers Reticular formation begins in the medulla oblongata and extends into more superior portions of the brainstemMedulla Oblongata Pyramids Bulges on the anterior aspect of the medulla Formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord. A common site for decussation of ascending and descending tracts.Centers of the Medulla Oblongata Vital centers Cardiovascular center Respiratory center Non-vital centers Centers for vomiting, swallowing, sneezing, coughing and hiccupping. Houses five pairs of cranial nerves, VIII-XII. Portion of the ventricle found here is the fourth
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