The pineal gland is an endocrine gland located in the posterior aspect of the cranial fossa in the brain. Its importance is in the circadian cycle of sleep and wakefulness. The pineal gland is also known as the epiphysis cerebri. The gland is pine cone-shaped and about 0.8 cm long. In an adult, it weighs about 0.1 g. It is an unpaired gland that resides between the thalamic bodies behind the habenular commissure. It is located near the corpora quadrigemina, which is behind the third ventricle. Cerebrospinal fluid bathes the gland through the pineal recess.
The following are the relations of the pineal gland in the brain on the coronal section:
- Superiorly: Corpus callosum (splenium aspect)
- Inferiorly: Inferior and superior colliculi
- Superolateral: Third ventricle choroid plexus
In a sagittal section, the following is seen:
- Anterosuperior: Thalamus and the habenular commissure
- Anteroinferior: Cerebral aqueduct of Sylvius, posterior commissure, and the cerebral peduncle.
- Posterosuperior: Cerebral vein of Galen
- Inferiorly: Quadrigemineal plate
The epiphysis cerebri is supplied by the adrenergic nerves. The neurons are sensitive to epinephrine. The sympathetic innervation is from the superior cervical ganglion, while the parasympathetic innervation is from the optic and pterygopalatine ganglia. The pineal stalk of the gland also has nerve fibers along with innervation from neurons from the trigeminal ganglion. The neurons from the trigeminal ganglion have nerve fibers that contain the PACAP, which is a neuropeptide.
The blood supply of the pineal gland is derived from the posterior cerebral artery from its choroidal branches. The internal cerebral vein drains the blood from the epiphysis cerebri.
Histologically the gland consists of cells called pinealocytes and supporting cells.