Cranial Cavity, Venous Sinuses and Brain - LO4
4. What is cerebrospinal fluid (CSF)? What is CSF’s functions, and where is it located? Describe the ventricular system.
CSF is formed in the brain from arterial blood supplying the choroid plexuses of the ventricles, and drains via arachnoid granulations projecting into the superior sagittal sinus.
Parts of the ventricular system:
The cerebral hemispheres are hollow, each containing a lateral ventricle. The ventricles contain secretory tissue, choroid plexuses, which convert arterial blood into cerebrospinal fluid (CSF). The lateral ventricles communicate with the midline third ventricle by way of the interventricular foramen. A thin membrane with an attached choroid plexus roofs the third ventricle. In the midbrain, the narrow cerebral aqueduct connects the third and fourth ventricles.
The fourth ventricle lies between the pons, cerebellum, and the medulla. It communicates with the cerebral aqueduct, the central canal of the spinal cord, and the subarachnoid space. The roof of the fourth ventricle also has a choroid plexus. The roof of the fourth ventricle is perforated by a small median aperture and two lateral apertures that allow cerebrospinal fluid to exit the ventricular system and bathe the brain and spinal cord.
The flow of CSF from production to reabsorption:
CSF is secreted (produced) by the choroidal epithelial cells of the choroid plexuses in the lateral, third, and fourth ventricles.
CSF leaves the lateral ventricles through the interventricular foramen and enters the third ventricle. CSF then passes through the cerebral aqueduct into the fourth ventricle. CSF leaves this ventricle through its median and lateral apertures and enters the subarachnoid space, which is continuous around the spinal cord and brain. The arachnoid forms borders of cisterns (spaces around the brain), filled with CSF.
Reabsorption of CSF (reabsorption into the venous system) - the main site of CSF absorption (reabsorption) into the venous system is through arachnoid granulations. The subarachnoid space containing CSF extends into the arachnoid granulations, which in turn project upward through the dura into the superior sagittal sinus and lateral projections from it called lateral lacunae.