Diencephalon
Diencephalon
Also known as: interbrain, between-brain
The central core of the forebrain surrounding the third ventricle, made up of the thalamus, hypothalamus, epithalamus and subthalamus; it relays almost all information to the cortex and links the nervous and endocrine systems.
Overview
The diencephalon lies between the cerebral hemispheres and the midbrain and is almost completely hidden by the hemispheres. Its two halves form the lateral walls of the third ventricle, and the hypothalamic sulcus in each wall separates the thalamus above from the hypothalamus below. Laterally it is bounded by the posterior limb of the internal capsule. It has four parts:
• Thalamus (≈80% of the diencephalon): the gateway relay to the cortex.
• Hypothalamus: the floor and lower walls of the third ventricle (optic chiasm, tuber cinereum with the infundibulum and pituitary stalk, mammillary bodies). It controls the autonomic nervous system and the pituitary.
• Epithalamus: the pineal gland (melatonin), the habenular nuclei (reward-prediction error, aversion) and the posterior commissure.
• Subthalamus: the subthalamic nucleus of the basal-nuclei circuitry and the zona incerta.
The retina and optic nerve are outgrowths of the diencephalon, which is why the optic nerve is really a CNS tract.
- Location
Deep midline forebrain around the third ventricle, between the cerebral hemispheres and the midbrain.
Parts & subdivisions
- Paired relay and integrative nuclei for sensation, motor loops, limbic circuits and arousal.
- Homeostasis, autonomic and endocrine control (owned by the endocrine system in this atlas).
- Pineal gland, habenula, stria medullaris, posterior commissure.
- Subthalamic nucleus and zona incerta; part of the motor circuitry of the basal nuclei.
- Midline cavity whose walls are formed by the diencephalon.
Anatomy
- Arterial supply
Perforating branches of the posterior cerebral and posterior communicating arteries (thalamoperforating, thalamogeniculate), the anterior choroidal artery and branches from the circle of Willis.
- Development
From the caudal part of the prosencephalon. The optic vesicles evaginate to form the retina, and the infundibulum grows down to form the posterior pituitary.
Function
- Relay and gating of sensory, motor and limbic information to the cortex
- Regulation of autonomic function, body temperature, appetite, thirst and sexual behaviour
- Control of the pituitary gland
- Circadian and seasonal rhythm (suprachiasmatic nucleus, pineal melatonin)
- Arousal and sleep regulation
Clinical significance
Parinaud (dorsal midbrain) syndrome
A pineal tumour (germinoma) compresses the posterior commissure and pretectum. The result is paralysis of upward gaze, light–near dissociation of the pupils, convergence–retraction nystagmus and lid retraction (Collier sign), often with obstructive hydrocephalus from aqueductal compression.
Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.