Overview
This lecture explains the structure of the brain's ventricular system, the production and flow of cerebrospinal fluid (CSF), and how CSF supports the central nervous system.
Ventricular System Anatomy
- The brain contains four ventricles: two lateral ventricles, a third ventricle, and a fourth ventricle.
- The lateral ventricles are paired, C-shaped chambers located in each cerebral hemisphere below the corpus callosum.
- The interventricular foramen (of Monroe) allows communication between the lateral ventricles and the third ventricle.
- The third ventricle is a narrow, midline space between the left and right diencephalon (includes thalamus and hypothalamus).
- The cerebral aqueduct (aka mesencephalic aqueduct or aqueduct of Silvius) connects the third ventricle to the fourth ventricle and is located in the midbrain.
- The fourth ventricle is between the pons and medulla anteriorly and the cerebellum posteriorly.
Cerebrospinal Fluid (CSF): Production and Flow
- CSF is produced by the choroid plexus in each ventricle by filtering blood plasma.
- CSF flows from lateral ventricles → interventricular foramen → third ventricle → cerebral aqueduct → fourth ventricle.
- CSF exits the fourth ventricle via the median aperture (of Magendie) and lateral apertures (of Luschka) into the subarachnoid space.
- CSF circulates around the brain and spinal cord within the subarachnoid space.
CSF Drainage and Function
- Arachnoid granulations filter CSF from the subarachnoid space into the superior sagittal sinus, returning it to the bloodstream.
- The total adult CSF volume is about 150 mL, replaced every eight hours, with about 500 mL produced daily.
- CSF cushions the brain and spinal cord, providing buoyancy and protecting them from impact with the skull.
- Blockage of the cerebral aqueduct prevents CSF from flowing into the fourth ventricle and subarachnoid space.
Key Terms & Definitions
- Ventricles — Fluid-filled chambers in the brain that produce and circulate CSF.
- Choroid Plexus — Specialized tissue in each ventricle that produces CSF.
- Interventricular Foramen (of Monroe) — Channel connecting each lateral ventricle to the third ventricle.
- Cerebral Aqueduct — Narrow canal connecting the third and fourth ventricles.
- Arachnoid Granulations — Structures that absorb CSF into the venous blood of 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 trace CSF flow.
- Memorize the order of ventricles and the CSF pathway.
- Understand the function and significance of CSF and its drainage.