ventricular system: Definition and Much More from Answers.com
- ️Wed Jul 01 2015
Definition
A ventricle is an internal cavity of the brain. Within the normal human brain, there is a connecting system of ventricles, commonly referred to as the ventricular system, which is filled with cerebrospinal fluid (CSF). The ventricular system within the brain develops from the cavity of the neural tube in the embryo.
Description
The ventricular system is composed of two lateral ventricles and two midline ventricles, referred to as the third and fourth ventricles. The chambers are connected to allow the flow of cerebrospinal fluid via two interventricular foramen (referred to as the foramen of Monro) and the cerebral aqueduct (referred to as the aqueduct of Sylvius).
The chambers of the ventricular system are lined or covered with ependymal cells and are continuous with the central canal enclosed within the spinal cord. Ependymal cells also line the central canal of the spinal cord.
Basic anatomy
The lateral ventricles
The lateral ventricles are separated by the septum pellucidum and do not communicate directly (i.e., do not allow the flow of cerebrospinal fluid) with each other. Cerebrospinal fluid within the individual lateral ventricles must flow to the third ventricle via the interventricular foramen associated with each lateral ventricle.
Lateral ventricles themselves are descriptively divided into a body with anterior, posterior, and inferior horns.
The third ventricle
The third ventricle is a narrow cavity or cleft located between the two thalami. The third ventricle also contains two saclike recesses called the anterior supraoptic recess and the infundibular recess. The massa intermedia, the neural tissue that connects both halves of the thalamus in some brains, runs through the third ventricle. Posteriorly, the third ventricle communicates with the fourth ventricle via the cerebral aqueduct, a narrow channel that allows the flow of cerebrospinal fluid from the third to the fourth ventricle. There is no choroids plexus within the cerebral aqueduct.
The fourth ventricle
The fourth ventricle is a wide and flattened space located just anterior to the cerebellum and posterior to the upper, or superior, half of the medulla oblongata and the pons. The fourth ventricle also has two lateral saclike pouches that are called the lateral recesses. The fourth ventricle is continuous with the upper (superior) terminal end of the central canal of the spinal cord. The fourth ventricle also connects with the subarachnoid space via three small foramina: the two foramina of Luschka (one in each of the lateral recesses) and the foramen of Magendie.
The subarachnoid space continues as the space between the arachnoid matter and the pia mater (meningal tissues that surround the brain and spinal cord) and is filled with CSF. The subarachnoid space also surrounds cranial and spinal nerves.
CSF flow and blockage of the ventricular system
The normal flow of cerebrospinal fluid—produced from brain surface tissue and the choroids plexuses within the ventricles—is from the two lateral ventricles through their respective interventricular foramina into the third ventricle. Then the CSF flows from the third ventricle through the cerebral aqueduct into the fourth ventricle and from there it can flow into the subarachnoid space where it is reabsorbed into the bloodstream.
Swellings or structures within the ventricular system may be due to congenital defect, trauma, or tumor.
If there is a blockage of the ventricular system the flow of CSF is interrupted. If, for example, there is a blockage within the cerebral aqueduct, the normal flow of fluid formed in the lateral ventricles and the third ventricle is interrupted, and the lateral ventricles and third ventricle begin to swell with cerebrospinal fluid. The swelling or enlargement is termed hydrocephalus. Hydrocephalus can also result from the formation of CSF (as can occur with a tumor in one of the choroid plexuses) that exceeds the amount that can flow through the ventricular system, or from a downstream-diminished capacity to absorb cerebrospinal fluid.
A tumor in one of the interventricular foramen connecting a lateral ventricle to the third ventricle obstructs the flow of cerebrospinal fluid from the same side lateral ventricle and results in an asymmetrical swelling of the blocked lateral ventricle.
Blockage of the flow of CSF through the foramen connecting the fourth ventricle to the subarachnoid space usually produces asymmetrical swelling or dilation of the entire ventricular system. The entire ventricular system can also swell in cases of meningitis in which the flow of cerebrospinal fluid over the outer surface of the brain is obstructed.
Resources
BOOKS
Bear, M., et al. Neuroscience: Exploring the Brain. Baltimore: Williams & Wilkins, 1996.
Goetz, C. G., et al. Textbook of Clinical Neurology. Philadelphia: W.B. Saunders Company, 1999.
WEBSITES
"Development of the Ventricular System." Temple University Department of Neuroanatomy. May 10, 2004 (May 27, 2004). http://courses.temple.edu/neuroanatomy/lab/embryo/ventlate.htm.
Paul Arthur
Wikipedia: ventricular system
| Brain: Cerebral ventricles | |
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| Scheme showing relations of the ventricles to the surface of the brain. | |
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| Drawing of a cast of the ventricular cavities, viewed from above. | |
| NeuroNames | ancil-192 |
| MeSH | Cerebral+Ventricles |
The ventricular system is a set of structures in the brain continuous with the central canal of the spinal cord.
Components
The system comprises four ventricles:
- right and left lateral ventricles
- third ventricle
- fourth ventricle
There are several interconnecting channels leading from these ventricles, though only the first two of the list below are generally considered part of the ventricular system:
| Name | From | To |
| right and left interventricular foramina (Monro) | lateral ventricles | third ventricle |
| cerebral aqueduct (Sylvius) | third ventricle | fourth ventricle |
| Median aperture (Magendie) | fourth ventricle | subarachnoid space/cisterna magna |
| Lateral apertures (Luschka) | fourth ventricle | subarachnoid space/cistern of great cerebral vein |
Each ventricle contains a choroid plexus that produces cerebrospinal fluid (CSF) used to bathe and cushion the brain and spinal cord within their bony confines.
Ventricles
There are four cerebral ventricles: the paired lateral ventricles, and midline the third and fourth ventricles. The two lateral ventricles, located within the cerebrum, are relatively large and C-shaped, roughly wrapping around the dorsal aspects of the basal ganglia. It is in the lateral ventricles of the embryo that the successive generation of neurons gives rise to the 6-layered structure of the neocortex, constructed from the inside out during development. Each lateral ventricle extends into the frontal, temporal and occipital lobes via the frontal (anterior), temporal (inferior), and occipital (posterior) horns, respectively.
The lateral ventricles both communicate via the interventricular foramina with the third ventricle, found centrally within the diencephalon. The third ventricle communicates via the cerebral aqueduct, located within the midbrain, with the fourth ventricle, found within the hindbrain. The three foramina to the subarachnoid space are found here, permitting cerebrospinal fluid produced in the ventricles to surround the brainstem, cerebellum, and cerebral cortex. The fourth ventricle is also continuous with the central canal, allowing CSF to bathe the inside surface of the spinal cord as well.
Flow of cerebrospinal fluid
Cerebrospinal fluid 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 occipital and frontal 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 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--otherwise known as water in the brain--and is an extremely serious condition due to both the damage caused by the pressure as well as nature of whatever caused the block (possibly a tumour or inflammatory swelling).
Protection of the brain
The brain and spinal cord are covered by a series of tough membranes called meninges, which protect these organs from rubbing against the bones of the skull and spine. The cerebrospinal fluid within the skull and spine is found between the pia mater and the arachnoid meninges and provides further cushioning.
Role in disease
Diseases of the ventricular system include abnormal enlargement (hydrocephalus) and inflammation of the CSF spaces (meningitis, ventriculitis) caused by infection or introduction of blood following trauma or hemorrhage.
Interestingly, scientific study of CAT scans of the ventricles in the late 1970s revolutionized the study of mental illness. Researchers found that patients with schizophrenia had enlarged ventricles compared to healthy subjects. This became the first "evidence" that mental illness 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. Nowadays, magnetic resonance imaging (MRI) has superseded the use of CAT in research into the role of ventricular abnormalities in psychiatric illness.
Embryology
The structures of the ventricular system are embryologically derived from the centre of the neural tube (the neural canal).
Additional images
Coronal dissection showing the ventricles of the brain.
External links
References
- Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, McNamara JO, Williams SM, Neuroscience (third edition). Sinauer Associates Inc, July 2004. ISBN 0-87893-725-0
- Edgley S et al, Neuroanatomy from the Department of Anatomy, University of Cambridge.
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