Ventricular system

INTRODUCTION:
  • The ventricular system is a set of four interconnected cavities (ventricles) in the brain, where the cerebrospinal fluid (CSF) is produced.
  • Within each ventricle is a region of choroid plexus, a network of ependymal cells involved in the production of CSF.
  • The ventricular system is continuous with the central canal of the spinal cord (from the fourth ventricle) allowing for the flow of CSF to circulate.
  • All of the ventricular system and the central canal of the spinal cord is lined with ependyma, a specialised form of epithelium.
DEVELOPMENT:
  • The structures of the ventricular system are embryologically derived from the neural canal, the centre of the neural tube.
  • The prosencephalon divides into the telencephalon, which forms the cortex of the developed brain, and the diencephalon.
  • The ventricles contained within the telencephalon become the lateral ventricles, and the ventricles within the diencephalon become the third ventricle.
  • The rhombencephalon divides into a metencephalon and myelencephalon.
  • The ventricles contained within the rhombencephalon become the fourth ventricle, and the ventricles contained within the mesencephalon become the aqueduct of Sylvius.
STRUCTURE:
  • The system comprises four ventricles:
  1. lateral ventricles right and left (one for each hemisphere)
  2. third ventricle
  3. fourth ventricle
  • 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.
  • Trigone of lateral ventricle: Junction of the anterior horn and posterior horn of lateral ventricle

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 aperture (Luschka) fourth ventricle subarachnoid space via the cistern of great cerebral vein
Ventricles
  • The four cavities of the human brain are called ventricles
  • 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 lined by Ependymocytes
  • Floor of 4th ventricle (Rhomboid fossa)
  • It is diamond or rhomboidal shaped and is formed by posterior surface of pons (upper triangular part or pontine part) and dorsal surface of medulla (lower triangular part or medullary part) junction of pons and medulla forms intermediate part. Features of 4th ventricle are :?
  1. Median sulcus (a midline groove) divides the floor into two symmetrical halves.
  2. Medial eminence is present an each side of median sulcus. It presents facial colliculus formed by genu (recurving fibers) of facial nerve looping around abducent nucleus.
  3. Facial colliculus lies in pons (i.e. in pontine part of floor).
  4. Hypoglossal triangle overlying hypoglossal nucleus and vagal triangle overlying dorsal nucleus of vagus. Both of these triangle lie in the medulla (medullary part of floor).
  5. Vestibular area overlies vestibular nuclei, partly in pons and partly in medulla.
  6. Sulcus coeruleus, a bluish area due to presence of pigmented neurons containing substantia ferruginea.
  7. Superior and inferior favea.
  • Infundibulum ,Mammillary body & Optic chiasma are seen in floor of 3rd ventricles
  • Lateral ventricle
  • Two lateral ventricles are the cavities of cerebral hemisphere (one in each hemisphere). Each lateral ventricle communicates with third ventricle through interventricular foramen of Monro.
  • It is divisile into four parts :?
1.Central part (body) : It is located in the medial parts of frontal and parietal lobes. It extends from interventricular foramen (of Monro) in front to splenium of corpus callosum behind. It has choroid plexus. It has :- o Roof : Formed by corpus callosum.
  1. Floor : Formed form lateral to medial by caudate nucleus (body), stria terminalis, thalamostriate vein, and lateral part of upper surface of thalamus.
  2. Medial wall (partition between two lateral ventricles) : By septum pellucidum and body of fornix.
2.Anterior horn : It lies in front of interventricular foramen of Monro extending into the frontal lobe. It has no choroid plexus. Its bondries are :-
  1. Anterior : Posterior surface of genu and rostrum of corpus callosum.
  2. Roof : Anterior part of trunk of corpus callosum.
  3. Floor : Head of caudate nucleus and upper surface of rostrum of corpus callosum.
  4. Medial (partition) : Septum pellucidum and column of fornix.
3.Posterior horn : It lies behind splenium of corpus callosum and extends into occipital lobe. It may be variable in size (may be absent). It has no choroid plexus.
  1.  Its boundries are :- Floor and medial wall : Bulb of posterior horn raised by forceps major and calcar avis, an elevation raised by calcarine sulcus (anterior part).
  2. Roof and lateral wall : Tapetum
4.Inferior horn : It is the largest horn and extends into temporal lobe. It has choroid plexus. Its boundries are
  1. Roof and lateral wall : Tapetum, tail of caudate nucleus, stria terminalis and amygdaloid body.
  2. Floor : Collateral eminence (elevation by collateral sulcus) and hippocampus medially.
FUNCTION:
Flow of cerebrospinal fluid
  • The cerebrospinal fluid passes out through arachnoid villi into the venous sinuses of the skull.
  • 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 the fourth ventricle 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 (or granulation villi) into the venous sinuses, after which it passes through the jugular vein and major venous system.
  • Protection of the brain
Exam Question
  • Junction of the anterior horn and posterior horn of lateral ventricle is called as Trigone of lateral ventricle
  • Drainage of CSF from lateral to third ventricle is through Foramen of munro
  • Floor of 4th ventricle is formed by Sulcus limitans,Post. surface of pons & Post. surface of medulla
  • Magendie foramen or the median aperture drains CSF from 4th ventricle to the cisterna magna
  • Fourth ventricle develops from Rhombencephalon
  • Infundibulum ,Mammillary body & Optic chiasma are seen in floor of 3rd ventricles
  • Abducens nuclei, hypoglossal nuclei, vestibular nuclei & Dorsal vagal nuclei are found in floor of fourth ventricles
  • Cerebral aqueduct (Duct of Sylvius) connects III ventricle to IV ventricle.
  • CSF is produced by modified ependymal cells of the choroid plexus
  • Floor of fourth ventricle is formed by rhomboidal fossa.
  • Ventricles of brain are lined by Ependymocytes
  • Anterior horn of lateral ventricle is closed anteriorly by the genu and rostrum of corpus callosum.
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