• Ventricles= expansions of the brain’s central cavity
  • Filled with CSF, lined with ependymal cells
  • Continuous with each other, central canal, and spinal cord
  • 1st/2nd= paired lateral ventricles (lie in cerebral hemispheres) [separated by septum pellucidum– transparent wall]
  • 3rd ventricle lies within diencephalon [connected to each lateral ventricles by interventricular foreamen]
  • In midbrain is central cavity => cerebral aqueduct [connects 3rd/4th ventricle]
  • 4th ventricle lies in the brain steam, dorsal to the pons
  • Three openings in walls of 4th ventricle (2 lateral paired apertures & median aperture) -> these connect to the subarachnoid space and allows CSF to fill both the ventricles and the subarachnoid space
  • Meninges surrounding brain slightly differs from structure around (related to venous drainage of the brain)
  • Dura mater around the brain= two layered (fibrous connective tissue) periosteal layer connects to internal surface of the skull, meningeal layer= covers external covering of the brain/ continuous with dura mater around the spinal cord
  • Two dura layers are fused together, however where they spilt is referred to as dural sinuses (blood filled); collect blood from the brain and send to large jugular veins of the neck (superior sagittal)
  • Over superior part of the brain (arachnoid mater has knoblike projections called arachniod villi; project superiorly and into other dural sinuses as well; acts as valves to allows CSF for pass from subarachnoid space into dural blood sinuses
  • Vascularized pia mater clings tightly to the brain surface -> contains blood vessels
  • The dura mater may extend into the brain and subdivide the brain and limit its movement
  • Falx Cerebri: large, sickles shaped vertical sheet, lies in median plane in longitudinal fissure
  • Falx Cerebelli: continuing inferiorly from the poster part of falx cerebri
  • Tentorium Cerebelli: Resembles tent over cerebellum; almost horizontal sheet in transverse fissure between cerebrum/ cerebellum. Transverse sinus is enclosed by tentorium cerebella

Formation, location, and circulation of CSF. (a) Location and circulatory pattern of cerebrospinal fluid (CSF). Arrows indicate the direction of flow. (b) Each choroid plexus consists of a knot of porous capillaries surrounded by a single layer of ependymal cells joined by tight junctions and bearing long cilia. Fluid leaking from porous capillaries is processed by the ependymal cells to form the CSF in the ventricles.
  • Chroid Plexuses: capillary-rich membranes located in roof of four brain ventricles -> CSF is made here. Layer of ependymal cells covered externally by capillary-rich pia mater (CSF is made in blood plasma and filtered through ependymal cells into the ventricles
  • CSF moves freely through these chambers; enters subarachnoid space via median/ lateral apertures of 4th ventricle
  • Hydrocephalus: “water on the brain”; excessive accumulation of CSF in the ventricles; puts crushing pressure on the brain. Causes tumor or closes off ventricles; usually caused by overactive chroid plexuses
  • Blood Brain Barrier: rich supply of capillaries that provides nervous tissue with nutrients. Oxygen, and other vital molecules. Some blood borne molecules CAN’T CROSS (i.e toxins, urea) -> blood-brain barrier protects neurons of the CNS
  • Made of endothelial cells with  tight junctions, making them almost impermeable (can’t stop lipid molecules)

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