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:
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.
Main articles: meningitis,
hydrocephalus,
cerebral hemorrhage,
subarachnoid 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
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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