Metathalamus

Metathalamus

Question 1. Write a short note on the metathalamus.
Answer.

The metathalamus consists of medial and lateral geniculate bodies, which are rounded elevations on the inferior aspect of the pulvinar.

Lateral geniculate body: The lateral geniculate body (LGB) is a small ovoid swelling that projects downwards and laterally from the pulvinar of the thalamus.

• It is visible at the terminal end of each optic tract. It is the thalamic visual nucleus. It receives fibres from the optic tract and gives fibres (optic radiation) to the visual cortex of the occipital lobe (areas 17, 18 and 19). It is the last relay station on the visual pathway.
• Structurally, the LGB consists of six laminae, numbered 1–6 from the ventral to the dorsal side. Laminae 1, 4 and 6 receive fibres from the contralateral retina and laminae 2, 3, and 5 from the ipsilateral retina.

Lateral geniculate body

Medial geniculate body: The medial geniculate body is a small oval swelling on the inferior surface of the pulvinar and is more prominent than the LGB. It is the thalamic auditory nucleus.

It receives the fibres from the lateral lemniscus through the inferior colliculus and inferior brachium and gives fibres (auditory radiation) to the auditory cortex in the temporal lobe (areas 41 and 42). It is the last relay station on the auditory pathway.

Question 2. Write a short note on the pineal gland.
Answer.

The pineal gland is a small cone-shaped body (only 3 × 5 mm in size) projecting downwards in the midline from the posterior wall of the 3rd ventricle. It is located in the groove between the superior colliculi below the splenium of the corpus callosum.

Its stalk divides into two laminae – ventral and dorsal. The ventral lamina is continuous with the posterior commissure, while the dorsal lamina is continuous with the habenular commissure.

Pineal Gland Functions

• Produces melatonin – a hormone that inhibits the secretion of gonadotrophins (Gnrh) from the hypothalamus. Melatonin probably holds back the development of reproductive organs till a suitable age (i.e. puberty). In other words, melatonin is believed to regulate the onset of the puberty.
• Acts as a biological clock and is responsible for circadian rhythm.
• Regulates the secretion of all other endocrine glands.

Medial geniculate body

Pineal Gland Applied Anatomy

• Tumours of the pineal gland cause precocious puberty.
• Calcification of the pineal gland: The calcareous concretions appear in the pineal gland after 17 years of age and form aggregations called brain sand or corpora arenacea.

The calcification of the pineal gland is seen as a radiopaque shadow in 50% of individuals in the midline and provides a useful landmark to detect any shift of the brain due to a tumour, etc.

Geniculate body anatomy