Dr. Rati TandonJ.N.M.C.,AMU,

ALIGARH

THIRD VENTRICLEIT IS CAVITY

WITHIN DIENCEPHALON.

DIENCEPHALON: is a part of brain between the cerebrum and the brainstem.

Pars dorsalis: (a) thalamus, (b) metathalamus: the medial

and lateral geniculate bodies,

and (c) epithalamus: pineal body

(gland),Pars ventralis: (a) subthalamus, and (b) hypothalamus.

It is a midline slit-like cavity situated between the two thalami and the part of hypothalamus.

Communications

It extends from the lamina terminalis anteriorly to the superior end of the cerebral aqueduct of midbrain posteriorly. The cavity of third ventricle is lined by a ciliated columnar epithelium, the ependyma.

BoundariesThe third ventricle

has- Anterior wall, Posterior wall, Roof, Floor, and Two lateral walls.

Anterior wall is formed from above downwards by: – anterior column of fornix, – anterior commissure, and – lamina terminalis.

Posterior wall is formed from above downwards by,

– pineal gland, – posterior

commissure, and – commencement of

cerebral aqueduct.

Roof is formed by the ependyma that stretches across the upper limits of two thalami.

Floor is formed from before backwards by,

– optic chiasma, - infundibulum

(pituitary stalk), – mammillary bodies, – posterior perforated

substance, and – tegmentum of the

midbrain.

Lateral wall is marked by a curved sulcus, the hypotha-lamic sulcus extending from the interventricular foramen to the cerebral aqueduct.

The sulcus divides the lateral wall into:

a larger upper part and smaller lower part. • The larger upper part

formed by the medial surface of anterior two third of the thalamus.

• The smaller lower part of the lateral wall is formed by the hypothalamus.

Recesses of the Ventricle The cavity of third ventricle extends into the

surrounding structures as a pocket-like protrusion called recesses.

These are as follows:1. Infundibular recess. It

is a deep tunnel-shaped recess extending downwards into the infundibulum, i.e. the stalk of the pituitary gland.

2. Optic (or chiasmatic) recess. It is angular recess situated at the junction the anterior wall and the floor of the ventricle just above the optic chiasma.

3. Anterior recess (vulva of ventricle). It is a triangular recess which extends anteriorly in front of interventricular foramen.

4. Suprapineal recess. It is a fairly capacious blind diverticulum which extends posteriorly above the stalk of pineal gland.

5. Pineal recess. It is a small diverticulum, which extends posteriorly between the superior and inferior laminae of the stalk of the pineal gland.

Pineal gland (epiphysis cerebri) midline cone-shaped reddish grey structure

(only 3 mm × 5 mm in size)

between the two superior colliculi below the splenium of corpus callosum.

It has a stalk which divides into two laminae.

The extension of the cavity of third ventricle between the two laminae is termed pineal recess.

The pineal gland is supplied by a nerve called nervus con-arii, which consists of postganglionic sympathetic fibres arising from superior cervical sympathetic ganglion.

Structure

neuroendocrine gland.

Consists: parenchymal cells called pinealocytes, and

neuroglial cells.

secrete a hormone called melatonin.

Functions seat of souldorsal third eye biological clock for physiological and

behavioural control. Regulates sleep wake cycle.secretes a hormone, melatonin. inhibits

secretion of gonadotrophins (GnRH) from hypothalamus.

Clinical Correlation The lesions of the pineal gland are

associated with precocious puberty.

The calcification of the pineal gland is demonstrable radiologically in more than 50% of normal adults. It lies in midline or midsagittal plane of the skull, and is about 5 cm above the external auditory meatus, in lateral view of the X-ray skull.

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