(i) Cardiovascular system: chambers of the heart; see BLOOD.
(ii) Brain: The ventricles of the brain are cavities inside the brain that are filled with the CEREBROSPINAL FLUID (CSF). They are lined with the ependyma consisting of a single layer of EPENDYMAL CELLS. The ventricular system is comprised of a pair of the lateral ventricles located in the CEREBRAL HEMISPHERES, the third ventricle located at the midline in the DIENCEPHALON, and the fourth ventricle located between the lower BRAINSTEM and CEREBELLUM. The lateral ventricle is the largest and is composed of the anterior horn, the body, the inferior horn and the posterior horn. The lateral ventricles communicate with the third ventricle through narrow passages called the interventricular FORAMINA OF MONRO. These foramina are used as reference points in radiographic studies. The slit-like third ventricle narrows into the CEREBRAL AQUEDUCT (AQUEDUCT OF SYLVIUS) in the MIDBRAIN, and then opens up as the fourth ventricle, a flat and diamond-shaped ventricle between the lower brainstem and cerebellum. At its widest part, a lateral recess communicates with the CISTERNA MAGNA or CEREBELLOMEDULLARY CISTERN, a large SUBARACHNOID SPACE (space between the ARACHNOID MEMBRANE and PIA MATER [see MENINGES]) posterior to the cerebellum. There is also a small median opening called the FORAMEN OF MAGENDIE.
Caudally, the fourth ventricle is continuous with the CENTRAL CANAL of the SPINAL CORD. The CIRCUMVENTRICULAR ORGANS are present in the third and fourth ventricles. They usually lack the BLOOD-BRAIN BARRIER and have a role in mediating direct actions of blood-borne substances on neurons.
The CSF protects the brain from mechanical shocks, and provides an optimal chemical environment for neuronal signalling. It also has a role in circulating HORMONES and NEUROTRANSMITTERS (see VOLUME TRANSMISSION) and removing waste products and drugs. CSF is formed in the CHOROID PLEXUS on ventricular walls via chemical filtering of the blood across the blood-cerebrospinal fluid barrier. The CSF passes through the ventricles, central canal of the spinal cord, and the surface of the brain and spinal cord and is then absorbed back into the blood through the arachnoid villi located in the superior sagittal sinus, a large superficial vein. Normally, the rate of formation matches the rate of reabsorption of CSR However, an obstruction of the normal drainage, excess formation of CSF, or any space-occupying conditions such as a TUMOUR or haematoma could result in an abnormal increase in the CSF pressure, causing damage to brain tissues and nerves. This condition is called HYDROCEPHALUS. CSF can be sampled in patients by LUMBAR PUNCTURE—insertion of a needle into the central canal of the spinal cord and drawing off of fluid. Chemical analysis of CSF can provide important clues to dysfunction in the state of the brain.
KAZUE SEMBA
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