Diencephalon

Question 1

What are the subdivisions of diencephalon?

Answer 1

The hypothalamic sulcus divides the Diencephalon into a dorsal part (pars dorsalis) and a ventral part (pars ventralis)

• Pars dorsalis- Thalamus, Epithalamus, Metathalamus
• Pars Ventralis- Hypothalamus, subthalamus

Question 2

Location of Thalamus.

Answer 2

The thalamus is an egg shaped mass of grey matter located immediately lateral to the 3rd ventricle.

Question 3

Presenting parts if Thalamus?

Answer 3

Anterior pole 
Posterior pole 
Superior surface
Inferior surface 
Medical surface 
Lateral surface

Question 4

Relations of Thalamus?

Answer 4

• Anterior pole is forms Posterior wall of Foramen of Monro.
• Posterior Pole (pulvinar) is separated from the geniculate bodies by the brachium of superior colliculus.
• Lateral surface related to internal capsule.
• Medial surface forms lat. wall of 3rd ventricle & connected to the opposite Thalamus by Interthalamic adhesion (mass of grey matter)
• Superior surface - The Lateral part forms floor of central part of lateral ventricle and the medial part is separated from the lat ventricle by the fornix & Tela choroidea.
• Inferior surface- Hypothalamus , ventral Thalamus and tegmentum of midbrain.

Question 5

Name the white matter of Thalamus.

Answer 5

Stratum zonale- layer of white matter covering superior surface

External Medullary lamina- covers lateral surface

Internal Medullary lamina - Y shaped band which divides the grey matter into three groups of nuclei — Anterior, Medial, Lateral

Question 6

Nuclei of Thalamus.

Answer 6

Anterior Group

Lateral group
•Ventral - Ventral Posterior , Ventral Lateral , Ventral Anterior
•Lateral - Lateral Dorsal, Lateral Posterior

Medial group
Largest among these is the Medial Dorsal nucleus

Question 7

Boundaries of Hypothalamus?

Answer 7

• Anterior- Lamina terminalis
• Posterior - Subthalamus and Tegmentum of midbrain
• Superior - Hypothalamic Sulcus
• Inferior - Structures forming floor of 3rd ventricle: Optic chiasma, Tuber cinereum, mammillary bodies
• Lateral- Internal capsule in the ventral part and the Subthalamus in Posterior part.

Question 8

Subdivisions of Hypothalamus?

Answer 8

The column of fornix divides it parasaggitally into medial and lateral zones.

Anteroposteriorly it can be divided into following zones

1) Preoptic
2) Supraoptic
3) Tuberal
4) Mammillary

Question 9

Components of Epithalamus?

Answer 9

1. Habenular nuclei
2. Pineal body
3. Habenular commissure
4. Posterior commissure

Question 10

Location of pineal body?

Answer 10

Between the two superior colliculi, below the splenium of corpus callosum.

Question 11

Function of pineal body?

Answer 11

1. Endocrine gland which influences other glands like pituitary, thyroid , adrenal cortex and medulla and gonads.
2. Melatonin is a hormone which is influenced by exposure of an animal to light.
3. Melatonin affects pigmentation in many animals.
4. Melatonin is said to influence the sleep wake cycle, mood etc.

Question 12

Afferents to the Hypothalamus.

Answer 12

1. Fornix - hippocampus to mammillary body
2. Stria Terminalis - amygdaloid body to preoptic and anterior nuclei
3. Mammillary Peduncles- from Reticular formation of brain stem and spinal cord
4. Medial Forebrain Bundle - from autonomic and limbic cortex of frontal lobe
5. Thalamohypothalamic
6. Subthalamohypothalamic
7. Pallidohypothalamic
8. Direct physical and chemical receptors

Question 13

Efferent connections of hypothalamus?

Answer 13

1) Mammillothalamic tract - Mammillary bodies to anterior nucleus of Thalamus
2) Descending fibres to brainstem and autonomic neurons in the Lateral horn of spinal cord
3) Parasympathetic nuclei of Occulomotor, Facial, Glossopharyngeal and Vagus nerves in brainstem.
4) To preganglionic sympathetic neurons in Lateral horn of T1-L2 spinal segments. And to preganglionic parasympathetic neurons in Lateral horns of S2-S4 segments.