Ventricular system

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Brain: Cerebral ventricles
Gray734.png
Scheme showing relations of the ventricles to the surface of the brain.
Gray735.png
Drawing of a cast of the ventricular cavities, viewed from above.
LatinVentriculi cerebri
NeuroNamesancil-192
MeSHCerebral+Ventricles
 
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Brain: Cerebral ventricles
Gray734.png
Scheme showing relations of the ventricles to the surface of the brain.
Gray735.png
Drawing of a cast of the ventricular cavities, viewed from above.
LatinVentriculi cerebri
NeuroNamesancil-192
MeSHCerebral+Ventricles

The ventricular system is a set of four structures, the ventricles, containing cerebrospinal fluid (CSF) in the brain. It is continuous with the central canal of spinal cord. The ventricle lining consists of an epithelium-like membrane called ependyma. The ventricles are interconnected allowing the passage of cerebrospinal fluid to flow. CSF is produced by the ependymal cells in the choroid plexus, a network of these cells within each of the ventricles.

Components[edit]

The four ventricles

The system comprises four ventricles:

There are several foramina , openings acting as channels, that connect the ventricles. The interventricular foramina (also called the foramina of Monro) connect the lateral ventricles to the third ventricle through which the cerebrospinal fluid can flow.

NameFromTo
interventricular foramina (Monro)lateral ventriclesthird ventricle
cerebral aqueduct (Sylvius)third ventriclefourth ventricle
Median aperture (Magendie)fourth ventriclesubarachnoid space/cisterna magna
right and left Lateral aperture (Luschka)fourth ventriclesubarachnoid space/cistern of great cerebral vein

Ventricles[edit]

3D rendering of ventricles (lateral and anterior views).

The cavities of the hollow human brain are called ventricles.[1] There are four ventricles in human brain: two in cerebrum called lateral ventricles or paracoels, one in diencephalon of forebrain called as diacoel, and one in medulla of hind brain called metacoel.

Flow of cerebrospinal fluid[edit]

The ventricles are filled with cerebrospinal fluid (CSF) which bathes and cushions the brain and spinal cord within their bony confines. CSF is produced by modified ependymal cells of the choroid plexus found in all components of the ventricular system except for the cerebral aqueduct and the posterior and anterior horns of the lateral ventricles. CSF flows from the lateral ventricles via the foramina of Monro into the third ventricle, and then the fourth ventricle via the cerebral aqueduct in the brainstem. From there it can pass into the central canal of the spinal cord or into the cisterns of the subarachnoid space via three small foramina: the central foramen of Magendie and the two lateral foramina of Luschka.

The fluid then flows around the superior sagittal sinus to be reabsorbed via the arachnoid villi into the venous system. CSF within the spinal cord can flow all the way down to the lumbar cistern at the end of the cord around the cauda equina where lumbar punctures are performed.

The cerebral aqueduct between the third and fourth ventricles is very small, as are the foramina, which means that they can be easily blocked, causing high pressure in the lateral ventricles. This is a common cause of hydrocephalus (known colloquially as "water on the brain"), which is an extremely serious condition due to both the damage caused by the pressure as well as nature of whatever caused the block (e.g. a tumour or inflammatory swelling).

Protection of the brain[edit]

The brain and spinal cord are covered by the meninges, (three tough membranes) which protect these organs from rubbing against the bones of the skull and spine. The cerebrospinal fluid (CSF) within the skull and spine is found between the pia mater and the arachnoid mater and provides further cushioning.

The CSF that is produced in the ventricular system has four main purposes: buoyancy, protection, chemical stability, and the provision of nutrients necessary to the brain. The protection purpose comes into play with the meninges: pia mater, and the arachnoid mater. The CSF is there to protect the brain from striking the cranium when the head is jolted. CSF provides buoyancy and support to the brain against gravity. The buoyancy protects the brain since the brain and CSF are similar in density; this makes the brain float in neutral buoyancy, suspended in the CSF. This allows the brain to attain a decent size and weight without resting on the floor of the cranium, which would kill nervous tissue.[2][3]

Role in disease or disorder[edit]

Diseases of the ventricular system include abnormal enlargement (hydrocephalus) and inflammation of the membranes or ventricles, (meningitis or ventriculitis) caused by infection or introduction of blood following trauma or hemorrhage.

The scientific study of CT scans of the ventricles in the late 1970s revolutionized the study of mental disorder. Researchers found that individuals with schizophrenia had (in terms of group averages) enlarged ventricles compared to healthy subjects. This became the first "evidence" that schizophrenia was biological in origin and led to a reinvigoration of the study of such conditions via modern scientific techniques. Whether the enlargement of the ventricles is a cause or a result of schizophrenia has not yet been ascertained, however. Still, this finding was not revolutionary at the time, as enlarged ventricles are found in various other types of organic dementia. In fact, ventricle volumes have been found to be "mainly explained by environmental factors"[4] and to be extremely diverse between individuals, such that the percentage difference in group averages in schizophrenia studies (+16%) has been described as "not a very profound difference in the context of normal variation" (ranging from 25% to 350% of the mean average).[5] Nowadays, magnetic resonance imaging (MRI) has superseded the use of CT in research into the role of ventricular abnormalities in psychiatric illness.

Development[edit]

The structures of the ventricular system are embryologically derived from the centre of the neural tube (the neural canal).

In brainstem[edit]

As the part of the primitive neural tube that will become the brainstem develops, the neural canal expands dorsally and laterally, creating the fourth ventricle, whereas the neural canal that does not expand and remains the same at the level of the midbrain superior to the fourth ventricle forms the cerebral aqueduct. Likewise, the neural canal in the spinal cord that does not change forms the central canal.

Additional images[edit]

See also[edit]

References[edit]

  1. ^ National Institutes of Health (December 13, 2011). "Ventricles of the brain". nih.gov. 
  2. ^ Klein, S.B., & Thorne, B.M. Biological Psychology. Worth Publishers: New York. 2007.
  3. ^ Saladin, Kenneth S. Anatomy & Physiology. The Unit of Form and Function. 5th Edition. McGraw-Hill: New York. 2007
  4. ^ Peper, Jiska S.; Brouwer, RM; Boomsma, DI; Kahn, RS; Hulshoff Pol, HE (2007). "Genetic influences on human brain structure: A review of brain imaging studies in twins". Human Brain Mapping 28 (6): 464–73. doi:10.1002/hbm.20398. PMID 17415783. 
  5. ^ Allen JS, Damasio H, Grabowski TJ (August 2002). "Normal neuroanatomical variation in the human brain: an MRI-volumetric study". American Journal of Physical Anthropology 118 (4): 341–58. doi:10.1002/ajpa.10092. PMID 12124914. 

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