VENTRICULAR SYSTEM

VENTRICULAR SYSTEM
- The ventricles are four fluid-filled cavities located within the brain
- These are the two lateral ventricles, the third ventricle, and the fourth
ventricle
- The two lateral ventricles communicate through the interventricular
foramina with the third ventricle .
- The third ventricle is connected to the fourth ventricle by the narrow
cerebral aqueduct
- The fourth ventricle, in turn, is continuous with the narrow central canal
of the spinal cord and, through the three foramina in its roof, with the
subarachnoid space.
- The central canal in the spinal cord has a small dilatation at its infe rior
end, referred to as the terminal ventricle
- The ventricles are lined throughout with ependyma and are filled with
cerebrospinal fluid
- They are developmentally derived from the cavity of the neural tube.
The Lateral Ventricles:
- There are two large lateral ventricles, one is present in each cerebral
hemisphere nearer to the base than the top of the brain
- The ventricle is a roughly C-shaped cavity and may be divided into a
body, which occupies the parietal lobe and from which ante rior,
posterior, and inferior horns extend into the frontal, occipital, and
temporal lobes, respectively.
- They are separated from each other by a median vertical partition, the
septum pellucidum, but communicate with the third ventricle and
indirectly with each othe r through the interventricular foramen which
lies in the anterior part of the medial wall of the ventricle
- The foramen is bounded anteriorly by the anterior column of the fornix
and posteriorly by the anterior end of the thalamus
The body (central part):
- Extends from the interventricular foramen posteriorly as far as the
posterior end of the thalamus whe re it becomes continuous with the
posterior and the inferior horns.
- The roof is formed by the undersurface of the corpus callosum
- The floor is formed by the body of the caudate nucleus and the lateral
margin of the thalamus, the superior surface of the thalamus is obscured
in its medial part by the body of the fornix.
- The choroid plexus of the ventricle projects into the body of the ventricle
through the slit-like gap between the body of the fornix and the superior
surface of the thalamus which is known as the choroidal fissure
- Through this fissure, the blood vessels of the plexus invaginate the pia
mater of the tela choroidea and the ependyma of the lateral ventricle.
- The medial wall is formed by the septum pellucidum
The anterior horn:
- Extends forward into the frontal lobe
- It is continuous posteriorly with the body of the ventricle at the
interventricular foramen.
- The roof is formed by the undersurface of the ante rior part of the corpus
callosum, the genu which limits the ante rior horn ante riorly

- The floor is formed by the rounded head of the caudate nucleus medially,
a small portion is formed by the superior surface of the rostrum of the
corpus callosum .
- The medial wall is formed by the septum pellucidum and the anterior
column of the fornix
The posterior horn:
- Extends posteriorly into the occipital lobe
- The roof and lateral wall are formed by the fibers of the tapetum of the
corpus callosum.
- Lateral to the tapetum are the fibers of the optic radiation
- The medial wall of the posterior horn has two elevations:
1- The superior swelling (bulb of posterior horn): is produced by the splenial
fibers of the corpus callosum (forceps major) passing posteriorly into the
occipital lobe.
2- The inferior swelling (calcar avis): is produced by the calcarine sulcus.
The infe rior horn:
- Extends ante riorly into the temporal lobe
- The roof is formed by the inferior surface of the tapetum of the corpus
callosum and by the tail of the caudate nucleus which passes anteriorly to
end in the amygdaloid nucleus.
- Medial to the tail of the caudate nucleus is the stria terminalis, which also
ends ante riorly in the amygdaloid nucleus
- The floor is formed laterally by the collateral eminence, produced by the
collate ral fissure, and medially by the hippocampus
- The anterior end of the hippocampus is expanded and slightly furrowed
to form the pes hippocampus.
- The hippocampus is composed of gray matter; however, the ventricular
surface of the hippocampus is covered by a thin layer of white matter
called the alveus, which is formed from the axons of the cells of the
hippocampus.
- These axons converge on the medial border of the hippocampus to form a
bundle known as the fimbria.
- The fimbria of the hippocampus becomes continuous posteriorly with the
posterior column of the fornix.
Choroid plexus of the lateral ventricle:
- The choroid plexus is, in fact, the irregular lateral edge of the tela
choroidea, which is a two-layered fold of pia mater situated between the
fornix superiorly and the upper surface of the thalamus
- Projects into the ventricle on its medial aspect and is a vascular fringe
composed of pia mater covered with the ependymal lining of the
ventricular cavity
- At the junction of the body of the lateral ventricle and the inferior horn,
the choroid plexus is continued into the infe rior horn and projects
through the choroidal fissure
- The function of the choroid plexus is to produce cerebrospinal fluid
The third ventricle:
- The third ventricle is a median cleft between the two thalami.
- Behind, it communicates with the fourth ventricle through the cerebral
aqueduct, and in front with the late ral ventricles through the
interventricular foramen.
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- Somewhat triangular in shape, with the apex directed backward, it has a
roof, a floor, an ante rior and a posterior boundary and a pair of late ral
walls.
The roof:
- Is formed by a layer of epithelium, which stretches between the upper
edges of the lateral walls of the cavity and is continuous with the epithelial
lining of the ventricle
- It is covered by and adherent to a fold of pia mater, named the tela
choroidea of the third ventricle
- From the under surface of which a pair of vascular fringed processes, one
on each side of the midline, the choroid plexuses of the third ventricle
hang
The floor:
- Slopes downward and forward and is formed mainly by the structures
which constitute the hypothalamus
- From before backward these are: the optic chiasma, the tuber cinereum,
infundibulum, and the corpora mammillaria
- The ventricle is prolonged downward as a funnel-shaped recess, the
recessus infundibuli, into the infundibulum to the apex of which the
hypophysis is attached
The anterior wall:
- Constituted below by the lamina terminalis, a thin layer of gray substance
stretching from the uppe r surface of the optic chiasma to the rostrum of
the corpus callosum; above by the columns of the fornix and the ante rior
commissure
- At the junction of the floor and anterior wall, immediately above the optic
chiasma, the ventricle presents a small angular recess or diverticulum, the
optic recess
- At the junction of the roof and ante rior wall of the ventricle, and situated
between the thalami behind and the columns of the fornix in front, is the
interventricular foramen through which the third communicates with the
lateral ventricles
The posterior wall:
- Formed by the pineal body, the posterior commissure and the cerebral
aqueduct.
- A small recess, the pineal recess, projects into the stalk of the pineal body,
while in front of and above the pineal body is a second recess, the
suprapineal recess
The lateral wall:
- Consists of an upper portion formed by the medial surface of the anterior
two-thirds of the thalamus, and a lowe r consisting of an upward
continuation of the gray substance of the ventricular floor, the 2 are
separated by the hypothalamic sulcus
- The lateral walls are joined to each othe r across the cavity of the ventricle
by a band of gray matter, the massa intermedia or interthalamic adhesion
Cerebral Aqueduct:
- The cerebral aqueduct is a narrow channel about ¾ of an inch (1.8 cm)
long
- It connects the third ventricle with the fourth ventricle
- It is lined with ependyma and is surrounded by a layer of gray matter
called the central gray.
- The direction of flow of cerebrospinal fluid is from the third to the fourth
ventricle.
- There is no choroid plexus in the cerebral aqueduct.
The fourth ventricle:
- Is a tent-shaped cavity filled with CSF
- It is situated anterior to the cerebellum and posterior to the pons and the
superior half of the medulla oblongata
- It is lined with ependyma and is continuous above with the cerebral
aqueduct of the midbrain and below with the central canal of the medulla
oblongata and the spinal cord
- The fourth ventricle possesses lateral boundaries, a roof, and a rhomboidshaped
floor.
Lateral Boundaries:
- Cephalic part: superior cerebellar peduncle
- Caudal part: inferior cerebellar peduncle
The roof (posterior wall):
- The tent-shaped roof projects into the cerebellum
- The superior part is formed by the medial borders of the two superior
cerebellar peduncles and a connecting sheet of white matter called the
superior medullary velum
- The infe rior part of the roof is formed by the inferior medullary velum,
which consists of a thin sheet devoid of nervous tissue and formed by the
ventricular ependyma and its posterior covering of pia mater
- This part of the roof (inferior) is pierced in the midline by a large
aperture, the median aperture or foramen of Magendie
- Lateral recesses extend laterally around the sides of the medulla and open
anteriorly as the lateral openings of the fourth ventricle, or the foramina
of Luschka
- Thus, the cavity of the fourth ventricle communicates with the
subarachnoid space through these three openings
- These important openings provide the only exit which permits the
cerebrospinal fluid to flow from the ventricular system into the
subarachnoid space
- From the subarachnoid space CSF is absorbed continuously in the
arachnoid villi & granulations in the superior sagittal sinus
The floor (rhomboid fossa):
- The diamond-shaped floor is formed by the posterior surface of the pons
and the cranial half of the medulla oblongata
- It is covered by a thin layer of gray substance continuous with that of the
medulla spinalis; superficial to this is a thin lamina of neuroglia which
constitutes the ependyma of the ventricle and supports a layer of ciliated
epithelium
- The floor is divided into symmetrical halves by the median sulcus
- On each side of this sulcus, the re is an elevation, the medial eminence,
which is bounded laterally by another sulcus, the sulcus limitans.
- Lateral to the sulcus limitans, there is the vestibular area beneath which
the vestibular nuclei lie
- The facial colliculus is a slight swelling at the inferior end of the medial
eminence that is produced by the fibers from the motor nucleus of the
facial nerve looping over the abducens nucleus
- At the superior end of the sulcus limitans, there is a bluish-gray area,
produced by a cluster of ne rve cells containing melanin pigment; the
substantia ferruginea
- Strands of nerve fibers, the stria medullaris, de rived from the arcuate
nuclei, eme rge from the median sulcus and pass laterally ove r the medial
eminence and the vestibular area and enter the inferior cerebellar
peduncle to reach the cerebellum
- Infe rior to the stria medullaris, the following features should be
recognized in the floor of the ventricle:
- The most medial is the hypoglossal triangle, which indicates the position
of the unde rlying hypoglossal nucleus
- Lateral to this is the vagal triangle, beneath which lies the dorsal motor
nucleus of the vagus
- The area postrema is a narrow area between the vagal triangle and the
lateral margin of the ventricle, just rostral to the opening into the central
canal
- The infe rior part of the vestibular area also lies lateral to the vagal
triangle
Choroid plexus & tela choroidea:
- The choroid plexus of the fourth ventricle is T shape
- It is suspended from the inferior half of the roof of the ventricle and is
formed from the highly vascular tela choroidea.
- The tela choroidea is a two-layered fold of pia mater that projects
through the roof of the ventricle and is covered by ependyma.
- The blood supply to the plexus is from the posterior infe rior cerebellar
arte ries
Choroid plexus of the
lateral ventricles
Choroid plexus of
the 3rd ventricle
Choroid plexus of the
lateral ventricles
The lateral ventricles The lateral ventricles
The 3rd ventricle
Choroid plexus of
the 4th ventricle
The 4th ventricle
Cisterna
cerbellomedullaris
Other cisterns & SAS
Superior sagittal sinus
Interventricular foramen
Cerebral aqueduct
1 median & 2 lateral apertures of
the 4th ventricle
Arachnoid villi & granulations