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Mesencephalon: characteristics, parts and functions

Mesencephalon: characteristics, parts and functions

April 28, 2024

The mesencephalon is one of the most important parts of the brain , in many ways. On the one hand, it is located almost in the center of the brain, occupying a part of its deepest zone, and therefore establishes a direct communication with many of the main structures of the central nervous system.

On the other, it is the area that connects the trunk of the brain to the diencephalon and parts of the cerebral cortex. Without the mesencephalon we could not survive.

Next we will see what are the characteristics of this region of the brain, we will review its main functions and its different anatomical components, and we will see what happens when certain injuries or illnesses alter its functioning.

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What is the mesencephalon?

The mesencephalon is one of the parts of the brainstem . It is located in its upper zone, on the Varolio bridge (or protuberance), and just below the diencephalon, composed mainly of the thalamus and the hypothalamus. It is the part of the brainstem closest to the center of the brain, while the protuberance and spinal bulb are more oriented towards the spinal cord.

In addition, the mesencephalon it is crossed by a narrow channel called aqueduct of Silvio , through which the cerebrospinal fluid flows from the third ventricle to the fourth. This liquid has the function of isolating and protecting various structures of the nervous system.

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Your anatomy

The form of the mesencephalon is that of a trapezoid, with a narrower base than its upper part, and with the aqueduct of Silvio (a small channel through which cerebrospinal fluid circulates) traversing it from top to bottom.

The border between the mesencephalon and the diencephalon is marked by the optical bands (the continuation of the nerve fibers of the optic nerves), while its lower limit, which separates it from the Varolio bridge, is indicated by the pontomesencefálico furrow .

In addition, on its anterior face (close to the face) it is possible to distinguish a vertical slit called interpeduncular fossa , which divides two bodies of nerve fibers that go up to the brain, called cerebral peduncles.

Parts of the mesencephalon

The two fundamental structures that make up the mesencephalon they are the tectum and the tegmentum .


It is located in the dorsal zone of the mesencephalon, oriented towards the nape of the neck, and etymologically means "roof". Its functions are related to automatic reactions to auditory and sound stimuli.

It consists of two pairs of packages, one located on top of the other. These lumps are called colliculi, or quadriguous tubers , and superiors play a role in the vision and orientation of the eyes towards visual stimuli, while those below are involved in involuntary reactions to sounds.


In the ventral area of ​​the mesencephalon is the tegmentum. It contains three main regions, each associated with a color: the substantia nigra, the periaqueductal gray matter and the red nucleus .

The black substance

The substantia nigra is located in the upper zone of the mesencephalon, and is distributed on both sides of this structure, following the division of the cerebral hemispheres. It has many associated functions, especially linked to movements and muscle tone .

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Red core

It is another important element of the motor system. Its function is related to the coordination of movements .

Periaqueductal gray matter

The periaqueductal gray substance, which as its name indicates is located around the aqueduct of Silvio, intervenes in the habituation to pain and in analgesic processes in general.

Mesencephalon functions

The location of the mesencephalon makes the main functions of this structure have to do with the integration between different types of information . On the one hand, it collects nerve impulses linked to motor commands that have to be executed by muscles, and on the other side receives sensory data.

In the same way, the cuadrigéminos tubers located in the téctum are responsible for coordinating this type of information with each other so that they can give rise to sequences of action adjusted to what the senses are registering in real time.

On the other hand, certain regions of the mesencephalon are associated with processes of regulation of consciousness and sleep , to be traversed by the reticular formation.The mesencephalon also intervenes in homeostatic functions oriented to maintain the organism in a good balance, and for that reason, for example, it has a role in the regulation of body temperature.

Thus, the mesencephalon is in charge of carrying out processes of vital importance so that orgganism continues to function, to the point that the activity in this structure of the nervous system is what indicates in a clearer way whether there is brain death or not. .

Diseases and associated injuries

Any lesion that affects the lower areas of the brain can reach the mesencephalon. The consequences of this kind of accidents are almost always very serious, producing coma or death .

The reason is that the mesencephalon is a section of the nervous system whose importance is crucial to coordinate basic physiological functions of the organism, and also serves for several types of nerve impulses reach the higher neuron groups. Like the mesencephalon acts as a link between many areas , the presence of anomalies in this area affects many others.

As regards the diseases that affect these structures of the brain, the most common are Alzheimer's disease and Parkinson's disease. Both are neurological disorders that interfere with the functioning of large areas of the nervous system, mesencephalon included, and can lead to problems of mobility and cognition.

2-Minute Neuroscience: Midbrain (April 2024).

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