How is the CNS protected from Injuries?

1. The Meninges Composed of 3 Connective Tissue Membranes 1. Dura Mater – “Tough Mother” outer layer of protection that covers and protects the brain A. Falix Cerbri- extension of the dura mater that separates the two hemispheres of the cerebrum

Meninges Continued B. Tenorium Cerebelli- extension of the dura mater that separates the cerebrum from the cerebellum C. Falx Cerebelli- separates the two hemispheres of the cerebellum

Meninges Cont. 2. Arachnoid Mater- middle layer of the meningies Threadlike layer that looks like spider webs through the entire surface Creates an open space where CSF can circulate

3. Pia Mater Innermost meningeal layer Clings to the surface of the brain and spinal cord Arachnoid villi project up into the arachnoid layer from here and re-absorb CSF to maintain a steady pressure within the meningeal space

CSF Water based cushioning fluid Formed by the choroid plexus of each lateral ventricle (networks of capillaries within the walls of the ventricles) Formed by blood plasma

Circulation of CSF Flows from choroid plexus to the third ventricle More CSF is added at the 3rd ventricle and it moves through the cerebral aqueduct through the midbrain and onto the 4th ventricle Choroid plexus here adds more CSF and it enters the subarachnoid space From here it circulates into the central canal of the spinal cord, through the subarachnoid space around the brain Pressure is 150 mL per vol Spinal tap is used to check it for infection

Blood-Brain Barrier Maintains a constant internal environment for the brain Tight junctions seal together the endothelial cells of the brain capillaries preventing free passage of substances Glucose passes via active transport Creatinine, Urea, and ions cross slowly Proteins and antibiotic drugs do not pass at all This barrier is useless against fat-soluble substances So, Oxygen, Carbon Dioxide, alcohol, and fat-soluble drugs all pass freely