Ventricular system

Source: Wikipedia, the free encyclopedia.
Ventricular system
Interventricular foramina (Monro)
Yellow - Third ventricle
Red - Cerebral aqueduct (Sylvius)
Purple - fourth ventricle
Green - continuous with the central canal
(Parts between median aperture and subarachnoid space are not shown)
Details
Identifiers
Latinventriculi cerebri
MeSHD002552
NeuroNames2497
FMA242787
Anatomical terms of neuroanatomy]

In neuroanatomy, the ventricular system is a set of four interconnected cavities known as cerebral ventricles in the brain.[1][2] Within each ventricle is a region of choroid plexus which produces the circulating cerebrospinal fluid (CSF). The ventricular system is continuous with the central canal of the spinal cord from the fourth ventricle,[3] allowing for the flow of CSF to circulate.[3][4]

All of the ventricular system and the central canal of the spinal cord are lined with ependyma, a specialised form of epithelium connected by tight junctions that make up the blood–cerebrospinal fluid barrier.[2]

Structure

Size and location of the ventricular system in the human head.

The system comprises four ventricles:[5]

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.

Name From To
interventricular foramina
(Monro)
lateral ventricles third ventricle
Cerebral aqueduct (Sylvius) third ventricle fourth ventricle
Median aperture (Magendie) fourth ventricle
subarachnoid space via the cisterna magna
Right and left lateral apertures (Luschka) fourth ventricle subarachnoid space via the
cistern of great cerebral vein

Ventricles

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

The four cavities of the human brain are called ventricles.[6] The two largest are the lateral ventricles in the cerebrum, the third ventricle is in the diencephalon of the forebrain between the right and left thalamus, and the fourth ventricle is located at the back of the pons and upper half of the medulla oblongata of the hindbrain. The ventricles are concerned with the production and circulation of cerebrospinal fluid.[7]

Development

The structures of the ventricular system are

neural canal, the centre of the neural tube.[citation needed
]

As the part of the primitive neural tube that will develop into the brainstem, 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. The fourth ventricle narrows at the obex (in the caudal medulla), to become the central canal of the spinal cord.[citation needed]

In more detail, around the third week of development, the embryo is a three-layered disc. The embryo is covered on the dorsal surface by a layer of cells called ectoderm. In the middle of the dorsal surface of the embryo is a linear structure called the notochord. As the ectoderm proliferates, the notochord is dragged into the middle of the developing embryo.[8]

As the

neural stem cells of the developing brain, principally radial glial cells, line the developing ventricular system in a transient zone called the ventricular zone.[9]

Separating the anterior horns of the lateral ventricles is the

septal nuclei, fornix, corpus callosum and other midline structures. Lack of such limbic development interrupts this posterior-to-anterior fusion, resulting in the continuation of the CSP into adulthood.[10]

Function

Flow of cerebrospinal fluid

MRI showing flow of CSF
venous sinuses
of the skull.
A schematic illustration of the venous sinuses surrounding the brain.

The ventricles are filled with

interventricular foramina into the third ventricle, and then the fourth ventricle via the cerebral aqueduct in the midbrain. From the fourth ventricle it can pass into the central canal of the spinal cord or into the subarachnoid cisterns via three small foramina: the central median aperture and the two lateral apertures
. According to the traditional understanding of cerebrospinal fluid (CSF) physiology, the majority of CSF is produced by the choroid plexus, circulates through the ventricles, the cisterns, and the subarachnoid space to be absorbed into the blood by the arachnoid villi.[citation needed]

The fluid then flows around 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.

Protection of the brain

The brain and spinal cord are covered by the

subarachnoid space between the pia mater and the arachnoid mater.[citation needed
]

The CSF that is produced in the ventricular system is also necessary for chemical stability, and the provision of nutrients needed by the brain. The CSF helps to protect the brain from jolts and knocks to the head and also provides buoyancy and support to the brain against gravity. (Since the brain and CSF are similar in density, the brain floats in neutral buoyancy, suspended in the CSF.) This allows the brain to grow in size and weight without resting on the floor of the cranium, which would destroy nervous tissue.[11][12]

Clinical significance

The narrowness of the cerebral aqueduct and foramina means that they can become blocked, for example, by blood following a hemorrhagic stroke. As cerebrospinal fluid is continually produced by the choroid plexus within the ventricles, a blockage of outflow leads to increasingly high pressure in the

basal cisterns, thereby bypassing any obstruction. A surgical procedure to make an entry hole to access any of the ventricles is called a ventriculostomy. This is done to drain accumulated cerebrospinal fluid either through a temporary catheter or a permanent shunt.[citation needed
]

Other diseases of the ventricular system include inflammation of the membranes (

subarachnoid haemorrhage
).

During

choroid plexus cysts
can form.

The

(MRI) has superseded the use of CT in research in the role of detecting ventricular abnormalities in psychiatric illness.

Whether the enlarged ventricles is a cause or a result of schizophrenia has not yet been established. Enlarged ventricles are also found in organic dementia and have been explained largely in terms of environmental factors.[13] They have also been found 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).[14]

The

dementia pugilistica.[18]

Additional media

  • Transverse dissection showing the ventricles of the brain.
    Transverse dissection showing the ventricles of the brain.
  • 3D Model of ventricular system
    3D Model of ventricular system
  • Scheme showing relations of the ventricles to the surface of the brain.
    Scheme showing relations of the ventricles to the surface of the brain.
  • Drawing of a cast of the ventricular cavities, viewed from above.
    Drawing of a cast of the ventricular cavities, viewed from above.
  • View of ventricles and choroid plexus
    View of ventricles and choroid plexus
  • Lateral ventricles along with subcortical structures, in glass brain
    Lateral ventricles along with subcortical structures, in glass brain
  • Brain Ventricles Anatomy

See also

References

  1. . The ventricular system is an elaboration of the lumen of cephalic portions of the neural tube, and its development parallels that of the brain.
  2. ^ . The ventricles contain the choroid plexus, which produces CSF, and serve as conduits for CSF flow in the CNS. Ventricular walls are lined with ependymal cells, which are connected by tight junctions and constitute a CSF-brain barrier.
  3. ^ . The ventricular system arises from the hollow space within the developing neural tube and gives rise to cisterns within the CNS, from the brain to the spinal cord.
  4. . Cerebrospinal fluid flows in bulk from sites of production to sites of absorption. Fluid formed in the lateral ventricles flows through the paired interventricular foramina (foramen of Monro) into the third ventricle, then through the mesencephalic aqueduct (aqueduct of Sylvius) into the fourth ventricle. The majority of CSF exits from the fourth ventricle into the subarachnoid space; a small amount may enter the central canal of the spinal cord.
  5. .
  6. ^ National Institutes of Health (December 13, 2011). "Ventricles of the brain". nih.gov.
  7. ^ International school of medicine and applied sciences kisumu library
  8. ^ .
  9. .
  10. ^ .
  11. ^ Klein, S.B., & Thorne, B.M. Biological Psychology. Worth Publishers: New York. 2007.
  12. ^ Saladin, Kenneth S. Anatomy & Physiology. The Unit of Form and Function. 5th Edition. McGraw-Hill: New York. 2007
  13. PMID 17415783
    .
  14. .
  15. .
  16. .
  17. .
  18. .