Mesencephalon: features, parts and functions

The midbrain 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 part of its deepest area, and therefore establishes direct communication with many major structures of the central nervous system.

On the other hand, it is the zone which joins the brainstem to the brain and parts of the cerebral cortex. Without the midbrain, we could not survive.

Next, we’ll look at the characteristics of this region of the brain, review its main functions and different anatomical components, and see what happens when certain injuries or illnesses interfere with its functioning.

    What is the midbrain?

    The midbrain is one part of the brainstem. It is located in its upper part, on the bridge of Varolio (or protuberance), and just below the diencephalon, consisting 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 medulla oblongata are more oriented towards the spinal cord.

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

      His anatomy

      The midbrain is shaped like a trapezoid, with a base narrower than its upper part, and with the Silvio aqueduct (a small channel through which cerebrospinal fluid circulates) running through from top to bottom.

      The limit between the mesencephalon and the diencephalon is marked by the optic ribbons (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 pontomesencephalic sulcus.

      In addition, on its anterior surface (near the face) we can distinguish a vertical fissure called an interpeduncular fossa, Which divides two bodies of nerve fibers that run up to the brain, called cerebral peduncles.

      Parts of the midbrain

      The two fundamental structures that make up the midbrain these are the tectum and the tegmentum.


      It is located in the dorsal area of ​​the midbrain, facing the nape of the neck, and etymologically means “roof”. Its functions are related to automatic reactions to auditory and auditory stimuli.

      It consists of two pairs of packages, one on top of the other. These packages are called collicles or quadrijumeaux tubercles., And the upper ones play a role in seeing and directing the eyes to visual stimuli, while the lower ones are involved in involuntary reactions to sounds.


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

      The black substance

      The substantia nigra is located in the upper part of the midbrain, and is distributed on either side of this structure, following the division of the cerebral hemispheres. It has many associated functions, particularly related to movement and muscle tone.

        red core

        This is another important part of the motor system. His function it is linked to the coordination of movements.

        Periaqueductal gray matter

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

        Functions of the midbrain

        The location of the midbrain means that 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 related to motor commands that must be executed by the muscles, and on the other hand it receives sensory data.

        Likewise, the quadrigeminal tubercles located in the Tectum are responsible for coordinating this type of information among themselves so that they can give rise to sequences of actions adjusted to what the senses register in real time.

        In contrast, some regions of the midbrain are associated with regulatory process of consciousness and sleep, Being crossed by the reticular formation. The midbrain is also involved in homeostatic functions aimed at keeping the body in good balance and therefore plays, for example, a role in the regulation of body temperature.

        Thus, the midbrain is responsible for carrying out processes of vital importance for the body to continue functioning, to the point that the activity in this structure of the nervous system is what more clearly indicates whether there is brain death or no.

        Associated diseases and injuries

        Any injury that affects lower areas of the brain can reach the midbrain. The consequences of this type of accident are almost always very serious, producing coma or death.

        The reason is that the midbrain is a section of the nervous system that is critically important to coordinate the basic physiological functions of the body and also serves various types of nerve impulses to reach higher neural groups. Like the midbrain it acts as a connecting link between many domains, The presence of anomalies in this area affects many others.

        When it comes to diseases that affect these brain structures, 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, including the midbrain, and can lead to mobility and cognition problems.

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