Skull and Meninges | Cerebrospinal Fluid and Ventricles
Skull and Meninges
- The brain is very well protected. This protection begins with the scalp, which is mobile and covered with hair which serves as insulation and also mechanical protection.
- Under the scalp is the skull which is composed of dense lamellar bone, At birth, the skull is relatively soft and mobile to allow passage through the birth canal. The fissures in the skull which are present at birth permanently fuse at about two years of age.
- The skull is separated from the dura by the epidural space. This space is only apparent when an injury occurs which allows blood to flow between the skull and the dura, resulting in an epidural hematoma. Epidural hematomas are rapidly expanding hemorrhages of arterial origin and are rapidly fatal if not treated.
- The Dura Mater, or tough mother, is the dense fibrous tissue covering of the brain. The dura extends between the cerebral hemisphere as the falx cerebri. The extension over the cerebellum is known as the tentorium cerebelli (tentorium for short). The inferior extension of the tentorium between the cerebellar hemispheres is called the falx cerebelli. The space between the dura and the arachnoid is known as the subdural space. Bridging veins from the arachnoid empty into the dural sinuses. These veins are especially prone to tears after minor falls in elderly people. These venous tears cause slowly expanding mass lesions known as subdural hematomas. These subdural hematomas may present clinically with confusion and even dementia.
Link to blood supply
- The Arachnoid mater, or spider mother, is a thin connective tissue covering which anchors the arteries and veins to the surface of the brain.
- The arachnoid travels along with the blood vessels as they enter the brain, thus creating the Virchow-Robin spaces. These spaces also may allow access of infectious organisms from the cerebrospinal fluid into the brain itself. Beneath the arachnoid is the subarachnoid space which is filled with cerebrospinal fluid. The cerebrospinal fluid is an additional cushion for the brain.
- The Pia Mater, or soft mother, is a thin delicate membrane, one cell layer thick, placed directly on the surface of the brain. It is a very effective barrrier to infection or hemorrhage.
Cerebrospinal Fluid and Ventricles
Cerebrospinal fluid animation
- Cerebrospinal fluid is the special ultrafiltrate of plasma which bathes and protects the brain. CSF is produced by the choroid plexus which is located in the floor of the lateral ventricles and in the roof of the fourth ventricle. The lateral ventricles are linked to the third ventrcle via the Foramen of Monroe. The Diencephalon surrounds the third ventricle. The third ventricle is connected to the fourth ventricle via the aqueduct of Sylvius in the midbrain. The aqueduct is very narrow and is easily obstructed by tumor or inflammation.
- Obstruction causes hydrocephalus. The fourth Ventricle lies between the cerebellum above and the pons below. The fourth ventricle empty into the subarachnoid space via the Foramina of Luschka , which are lateral and the Foramen of Magendie which is medial. A small amount of CSF flows into the spinal cord via the central canal. The spinal cord is also enveloped in arachnoid, so that CSF covers its surface as well. The spinal cord terminates in the cauda equina which is enclosed by dura. The cauda equina is thus bathed in CSF of the lumbar spine. CSF is commonly removed from the lumbar area when infection is suspected.
- The Arachnoid granulations around the longitudinal fissure reabsorb CSF into the dural sinuses. Link to blood supply
last update Jan 21, 2002