Section 5: Nervous System (Lesson 4: The Meninges and CSF)

CSF circulation

1. CSF is produced by choroid plexus in each ventricle 2. CSF flows from lateral ventricles and 3rd ventricle through the cerebral aqueduct into the 4th ventricle. 3. CSF in 4th flows into subarachnoid space by passing through openings in the roof of the 4th ventricle. These openings are the paired lateral apertures and the single median aperture. CSF also fills the central canal of the spinal cord. 4. As it travels through the subarachnoid space, CSF removes waste products and provides buoyancy for the brain and spinal cord. 5.CSF accumulates w/i the suarachnoid space, it exerts pressure w/i the arachnoid villi. This pressure exceeds the pressure in the venous sinuses. Thus, the arachnoid villi extending into the dural venous sinuses provide a conduit for a one-way flow of excess CSF to be returned into the blood within the dural venous sinuses.

function of blood brain barrier

1. protects cerebrospinal fluid (CSF) from blood-born toxins and drugs 2. allows exchange of gases and nutrients 3. removes wastes

subarachnoid space

Between the pia mater and the arachnoid mater. CSF is circulated here

pia matter

Innermost. Adheres directly to the brain and is made up of capillaries and supporting tissue.

Periosteal Layer

Layer of Dura mater that is attached to the surface of skull.

Substances that Can Cross the BBB

Lipid-soluble substances that diffuse across the BBB: oxygen, carbon dioxide, alcohol, and anesthetics Water-soluble substances that are actively transported across the BBB: glucose Substances that cross the BBB very slowly: creatinine, urea, and ions

dura matter

The outermost layer, the dura mater, is dense and consists of two layers, a periosteal layer, and a meningeal layer.

Substances that Cannot Cross the BBB

antibiotics and proteins

CSF functions

buoyancy, protection, environmental stability

dural sinus

channel through which venous blood flows into jugular vein

Meningeal Layer

folds inwards to form several double thickness sheets known as dural folds, which help to hold the brain in place.

dural folds

meningeal layer of the dura mater that divide the cranial cavity into freely communicating spaces

choroid plexus

produces CSF. present in all 4 ventricles

Meninges

three protective membranes that surround the brain and spinal cord

Arachnoid matter

weblike middle layer of the three meninges. reabsorb the CSF to the blood