Overview
This lecture covers the anatomy and function of the brain's ventricular system, the production and flow of cerebrospinal fluid (CSF), and its role in protecting the central nervous system.
Ventricular System Anatomy
- The brain has four ventricles: two lateral ventricles, a third ventricle, and a fourth ventricle.
- The two lateral ventricles are C-shaped, one in each cerebral hemisphere, and are the largest ventricles.
- The lateral ventricles sit below the corpus callosum and connect to the third ventricle via the interventricular foramen (foramen of Monroe).
- The third ventricle is a midline cavity between the left and right diencephalon (includes thalamus, hypothalamus, epithalamus).
- The cerebral aqueduct (also called mesencephalic aqueduct or aqueduct of Silvius) connects the third and fourth ventricles and passes through the midbrain.
- The fourth ventricle is located between the pons/medulla (anteriorly) and the cerebellum (posteriorly), and connects to the subarachnoid space via apertures.
Cerebrospinal Fluid (CSF): Production and Flow
- CSF is produced by the choroid plexus within all four ventricles.
- CSF flows from the lateral ventricles → interventricular foramen → third ventricle → cerebral aqueduct → fourth ventricle.
- From the fourth ventricle, CSF enters the subarachnoid space via the median aperture (of Magendie) and paired lateral apertures (of Luschka).
- CSF circulates around the brain and spinal cord in the subarachnoid space.
- The subarachnoid space also surrounds the spinal cord, providing cushioning.
CSF Reabsorption and Function
- CSF is reabsorbed into the bloodstream through arachnoid granulations into the superior sagittal sinus (a dural venous sinus).
- The total adult CSF volume is about 150 mL; about 500 mL is produced daily, with complete turnover every ~8 hours.
- CSF provides buoyancy, reducing the effective weight of the brain by ~97-98%, and cushions the brain and spinal cord.
Key Terms & Definitions
- Ventricle — Cavity in the brain filled with cerebrospinal fluid.
- Cerebrospinal Fluid (CSF) — Clear fluid produced in the ventricles that surrounds and protects the brain and spinal cord.
- Choroid Plexus — Network of cells that produces CSF within each ventricle.
- Interventricular Foramen (Foramen of Monroe) — Passage between each lateral ventricle and the third ventricle.
- Cerebral Aqueduct — Narrow channel connecting the third and fourth ventricles.
- Arachnoid Granulations — Structures allowing CSF to drain into the superior sagittal sinus.
- Subarachnoid Space — Area between the arachnoid mater and pia mater filled with CSF.
Action Items / Next Steps
- Review diagrams of the ventricular system and CSF flow pathways.
- Memorize the sequence of CSF flow and key anatomical structures involved.
- Prepare for exam questions on CSF function and the consequences of flow blockage.