Cerebrospinal Fluid (CSF) Flow and Function

• The ventricular system includes the internal system and external system.
• The internal system consists of two lateral ventricles, interventricular foramina (foramina of Monro), third ventricle, cerebral aqueduct (aqueduct of Sylvius), fourth ventricle, and central canal.
• The external system consists of subarachnoid spaces and cisterns.

Four-filled Ventricles

• Four-filled cavities are located within the brain.
• The four ventricles are two lateral ventricles, third ventricle, and fourth ventricle.
• Ventricles are lined with ependyma and filled with cerebrospinal fluid (CSF).

Communication Between Internal & External Systems

• Communication occurs between the internal and external systems through three foramina in the fourth ventricle.
• These foramina are the Foramen of Magendie and the Foramina of Luschka.
• The Foramen of Magendie has one midline aperture.
• The Foramina of Luschka have two lateral apertures.

Foramina of the Ventricular System

• There are 2 Interventricular foramina/ Foramina of Monro.
• There is 1 Cerebral aqueduct / Aqueduct of Sylvius.
• There is 1 Foramen of Magendie.
• There are 2 Foramina of Luschka.

Lateral Ventricles

• Two large, C-shaped ventricles are located in each cerebral hemisphere.
• Lateral ventricles possess a body and horns with anterior, posterior, and inferior regions.
• Lateral ventricles communicate with the third ventricle via the interventricular (Monro) foramen.

Interventricular (Monro) Foramen

• This is an aperture between the column of the fornix and the anterior end of the thalamus.
• It allows communication between the lateral ventricles and the third ventricle.

Third Ventricle

• A slitlike cleft is positioned between the two thalami.
• It communicates anteriorly with the lateral ventricles through the interventricular foramen (foramen of Monro).
• It communicates posteriorly with the Fourth ventricle through the cerebral aqueduct.

Cerebral Aqueduct

• The cerebral aqueduct is also known as the "Aqueduct of Sylvius".
• It's a narrow, curved channel running from the posterior third ventricle into the fourth ventricle.
• The cerebral aqueduct contains no choroid plexus.

Fourth Ventricle

• The fourth ventricle is a tent-shaped cavity lined with ependyma.
• It is located anterior to the cerebellum and posterior to pons and the superior half of medulla oblongata.
• It possesses two lateral boundaries, a rhomboid-shaped floor, and a roof.

Foramen of Magendie

• This is the median aperture.
• It's an opening in the caudal portion of the roof of the ventricle.
• Most of the outflow of CSF from the fourth ventricle passes through this aperture.

Foramen of Luschka

• It is the lateral aperture.
• It is the opening of the lateral recess into the subarachnoid space near the flocculus of the cerebellum.
• A tuft of choroid plexus is commonly present in the aperture, partly obstructing the flow of CSF from the fourth ventricle to the subarachnoid space.

Subarachnoid Space

• It is the interval between the arachnoid mater and pia mater.
• It receives CSF from the fourth ventricle via the foramina of Magendie and Luschka.
• This space is filled with CSF and contains blood vessels.
• It's traversed by fine trabeculae (CT).
• It ends below at the level of S2-S3 vertebrae.
• Extensions include the perivascular space and subarachnoid cisterns (expansions).

Subarachnoid Cisterns

• Cisterna Magna/Cerebello-Medullary Cistern occupies the interval between the cerebellum and medulla, receiving CSF through the foramen of Magendie.
• Pontine Cistern: Basal cisterns beneath the brainstem and diencephalon.
• Interpeduncular Cistern
• Cistern of the Optic Chiasma
• Cistern of the Lamina Terminalis
• Cistern of Corpus Callosum is a continuation of the cistern of lamina terminalis
• Superior Cistern/Cistern of the Great Cerebral Vein: the subarachnoid space dorsal to the midbrain
• Cisternal Ambiens/Peri-Mesencephalic Cistern is formed by the cistern of the great cerebral vein and the subarachnoid space on the sides of the midbrain.
• Cistern of the Lateral Sulcus corresponds with the lateral fissure.
• Lumbar Cistern extends from the L2 vertebra to the S2 and contains the cauda equina.

Central Canal of the Medulla and Spinal Cord

• This opens superiorly into the fourth ventricle.
• It extends inferiorly through the inferior Medulla and throughout the spinal cord.
• The terminal ventricle is an expansion of the central canal in the conus medullaris.
• Has no choroid plexus

Cerebrospinal Fluid (CSF)

• Clear, colorless fluid.
• Total volume: 150 ml.
• Rate of production: 0.5 ml/min.
• Turnover time: 5 hours.
• Cells: Lymphocytes.
• Biomolecules: Glucose, protein, chloride.
• Location: Subarachnoid, perivascular spaces, central canal of medulla and spinal cord.

Functions of CSF

• Cushions and protects the CNS from trauma.
• Provides mechanical buoyancy and support for the brain.
• Serves as a reservoir and assists in the regulation of the contents of the skull.
• Nourishes the CNS and removes metabolites.
• Serves as a pathway for pineal secretions to reach the pituitary gland.

Formation of CSF

• CSF production is not pressure-regulated.
• Choroid plexuses, located in the lateral, third, and fourth ventricles, are the main producer.
• Ependymal cells line the ventricles.
• Brain substance permeates the perivascular spaces.

Choroid Plexus

• A fringe-like vascular process of pia mater containing capillaries of the choroid arteries is covered by an epithelial layer of ependymal origin.
• It projects into the ventricular cavity.
• Location includes that lateral ventricle (body and inferior horns)
• Also located in the interventricular (Monro) foramen, third ventricle, and fourth ventricle.
• There is no choroid plexus in the anterior and posterior horns, and cerebral aqueduct.

Absorption of CSF

• Occurs when CSF pressure exceeds that of venous pressure in the sinus (arachnoid villi serves as valves).
• Controls CSF pressure. -Arachnoid villi / arachnoid granulations into the venous dural sinuses (especially superior sagittal sinus) are the main site of absorption.
• CSF also is absorbed by the veins in the subarachnoid space.
• CSF also moves through the perineural lymph vessels of cranial and spinal nerves.

CSF Circulation

• Lateral Ventricle → Foramen of Monro / Interventricular Foramen → Third Ventricle → Cerebral Aqueduct → Fourth Ventricle → Foramen of Magendie & Foramina of Luschka → Subarachnoid Space/ Cisterns & Central Canal → Arachnoid Granulations → Dural Venous Sinuses

Facilitation of Slow Flow of CSF

• Pulsations of cerebral and spinal arteries
• Movements of the vertebral column

Mixing of CSF

• Movement of vertebral column.
• Respiration
• Coughing
• Changing body positions.

Test your knowledge of cerebrospinal fluid (CSF) dynamics. Questions cover CSF flow pathways, the roles of ventricles and arachnoid villi, and the functions of CSF in the central nervous system. Learn about CSF pressure and its relation to venous pressure.