Synonyms in the broadest sense
Diencephalon
Introduction
The diencephalon as a part of the brain is located between the end brain (cerebrum) and the brain stem. Its components are:
- Thalamus
- Epithalamus (epi = on it)
- Subthalamus (sub = below) with Globus pallidus (pallidum)
- Hypothalamus (hypo = below, less)
Thalamus
The ovoid paired thalamus is the largest and together with the hypothalamus the most important of these structures in the diencephalon and is located in the center of the brain. It delimits the III ventricle; above it runs the caudatus nucleus, below it is the hypo- and subthalamus and the midbrain. Above the III ventricle is the epithalamus. The thalamus in turn is composed of several nuclei and medullary lamellae. At its rear pole is the pineal gland (epiphysis, glandula pinealis) as part of the epithalamus.
Subthalamus
The subthalamus contains among other things the globus pallidus, which belongs to the diencephalon in terms of developmental history.
Hypothalamus
In the brain, the hypothalamus forms the base of the diencephalon under the floor of the III ventricle. In front of it is the optic chiasma (chiasma opticum), behind it is the pituitary gland stem with the transition to the pituitary gland (hypophysis). The hypothalamus is divided into different areas, which contain typical nuclei with vegetative functions.
The bean-shaped pituitary gland is divided into the neuro- and adenohypophysis, with the neurohypophysis being the rear part and the adenohypophysis the front part of the pituitary gland. Only the neurohypophysis belongs to the diencephalon, the adenohypophysis does not belong to the brain, since it develops from the so-called Rathke’s pocket, which is part of the ectoderm, one of three cotyledons in embryonic development. The above-mentioned structures – with the exception of the pituitary gland, which is created once – are also found twice in total (left and right) in the brain (diencephalon).
Function
The thalamus, as the largest part of the diencephalon, fulfills a variety of functions in the brain. It is where all information for the cerebral cortex is switched. On the one hand, it is involved in the limbic system, in processes of well-being and mood, in visual, hearing and olfactory processes, and on the other hand in motor processes.
The thalamus is also referred to as the “gateway to consciousness”, as it transmits sensory information to the cerebral cortex and in this way makes us conscious. The epithalamus (interbrain) is connected to the limbic system, the olfactory system, nuclei of the secretion processes of the mouth and vegetative centers of the brain stem. The pineal gland, which is part of the epithalamus, is a gland that produces and releases the hormone melatonin.
It also influences the sympathetic nervous system and the control of the day-night rhythm. The subthalamus (diencephalon) as part of the brain includes the motor system in its function, as well as the globus pallidus, which is part of the basal ganglia loop as the motor center. The hypothalamus has an impact on a wide range of bodily processes.
These include regeneration, performance, the daily rhythm, the female cycle, food and water intake including the feeling of satiety. In addition, the hypothalamus regulates sweating, organ activity and tremors and produces various hormones: Endogenous opiates, antidiuretic hormone (ADH), oxytocin and control hormones with effect on the adenohypophysis (liberine, statine). It is possible to influence these different processes via connections of the hypothalamus to the limbic system, brain stem and pituitary gland.
