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Overview of the diencephalon

Learning objectives

This study unit will help you to:

  1. Locate the diencephalon and its main parts.
  2. Learn about the structure of the diencephalon and its relations to the surrounding structures. 
  3. Understand the functions of each part of the diencephalon.

Introduction

The cerebrum (a.k.a. forebrain) is composed of two parts: the anterior/rostral telencephalon and dorsal diencephalon. The diencephalon is further divided into several distinct parts, namely the:

  • Epithalamus
  • Thalamus
  • Subthalamus
  • Hypothalamus

The thalamus occupies the largest portion of the diencephalon. All the other parts of the diencephalon, take their names based on their relevant position compared to the thalamus. It is an ovoid, paired gray matter structure, found in the center of the cerebrum, just superior to the brainstem. The thalamus has many important functions; in general, it is considered to be the central relay station of the brain that relays limbic, sensory and motor information between the cerebral cortex and the rest of the nervous system.

The epithalamus is the most dorsal part of the diencephalon that participates in the formation of the roof of the third ventricle. It is composed of the pineal gland, habenular nuclei, stria medullaris thalami, and posterior commissure.

The subthalamus lies inferior to the posterior part of the thalamus, posterior and lateral to the hypothalamus. The largest division of the subthalamus is the subthalamic nucleus which plays a fundamental role in the circuitry of the basal ganglia (i.e. movement regulation).

The hypothalamus is the inferiormost part of the diencephalon, located anteroinferior to the thalamus. The hypothalamus can be divided into several regions, each of which is responsible for certain functions. In general, it forms connections with different body systems (endocrine, autonomic and limbic) through which it controls some vital functions of the human body (e.g. homeostasis, energy consumption, hunger, awareness etc.).

Browse atlas

Take a closer look at the diencephalon and surrounding structures in the gallery below.

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Summary

Key facts about the diencephalon
Definition Caudal part of the forebrain that occupies the central region of the brain (around the third ventricle) and connects the telencephalon to the other structures of the nervous system
Main parts Epithalamus
Thalamus
Subthalamus
Hypothalamus
Functions Control of the endocrine system maintaining the homeostasis of the body;
Involved in emotions, behavior and memory (via limbic system);
Relay of the sensory and motor signals from/to the cerebral cortex;
Regulation of circadian rhythms (the sleep-wake cycle)
Key facts about the four main parts of the diencephalon
Epithalamus Location: Distal part of diencephalon
Main parts
: Pineal gland, habenular nuclei, stria medullaris, and posterior commissure
Function
: Regulation of circadian rhythms responsible for regular sleep and wake cycles
Thalamus Location: Superior to brainstem, either side of third ventricle
Main parts
: Anterior and posterior pole
Function
: Relays limbic, sensory and motor information between the cerebral cortex and the rest of the nervous system
Subthalamus Location: Inferior to posterior part of the thalamus; posterior and lateral to hypothalamus
Main parts
: Subthalamic nucleus, nuclei of perizonal fields (of Forel), zona incerta, pregeniculate nucleus
Function
: Movement regulation
Hypothalamus Location: Anteroinferior to thalamus
Main parts
: Periventricular zone, medial zone, lateral zone
Function
: Vital functions of the human body (e.g. homeostasis, energy consumption, hunger, awareness)

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