What is a brain stem

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The Brain stem is the area of ​​the brain covered by the cerebrum below the diencephalon, not including the cerebellum. At the base of the skull, the brain stem passes over the medulla oblongata into the spinal cord. The core areas of the cranial nerves III to XII run through the brain stem. Read everything important about the brain stem: function, structure, the difference to the brain stem as well as important diseases and damage in the area of ​​the brain stem!

What is the brain stem?

The brain stem is the oldest part of the brain in evolutionary terms. Together with the diencephalon, sometimes also with the cerebellum and parts of the endbrain, it is often referred to synonymously as the brain stem. But that is not correct: The brain stem comprises all parts of the brain that developed from the so-called second and third cerebral vesicles during embryonic development. The brain stem, on the other hand, includes all parts of the brain except the cerebrum.

The brain stem consists of the midbrain (mesencephalon), the bridge (pons) and the elongated medulla (medulla oblongata, posterior brain or myelencephalon). The bridge and the cerebellum are also known as the metencephalon (rear brain). Together with the myelencephalon (elongated marrow) it forms the hindbrain (rhombencephalon).


The midbrain (mesencephalon) is the smallest section of the brain. You can read more about this in the midbrain article.

Bridge (brain)

The bridge (pons) in the brain is a strong white bulge at the base of the brain above the medulla oblongata. It is connected to the cerebellum by a cord, the cerebellar stalk.

Medulla oblongata

The elongated medulla (medulla oblongata) forms the transition to the spinal cord. You can read more about this section of the brain in the article Medulla oblongata.

What is the function of the brain stem?

The brain stem forms the interface between the rest of the brain and the spinal cord. It forwards information ascending from the body and descending into the body cross-wise, so the right half of the brain is responsible for the left half of the body and vice versa.

The brain stem is responsible for essential vital functions such as controlling heart rate, blood pressure and breathing. It is also responsible for important reflexes such as the eyelid closing, swallowing and coughing reflexes. Sleep and the various sleep and dream phases are also controlled here.

The pyramidal tract runs inside the bridge - the connection between the motor cortex and the spinal cord, which is important for voluntary motor signals (i.e. voluntary movements). These signals, which come from the cerebral cortex, are passed on to the cerebellum via the pons.

The brain stem is traversed by the reticular formation - a network-like structure made up of nerve cells and their appendages. It is involved in various vegetative functions of the organism, such as controlling attention and the state of wakefulness. The circulation, breathing and vomiting are also controlled here.

Where is the brain stem located?

The brain stem is located in the lower skull area at the base of the skull, covered by the cerebellum and cerebellum. At the bottom, it merges into the spinal cord with a not precisely defined border - this area is called the medulla oblongata (elongated marrow). In this area, the pyramid junction, the nerve pathways coming from the brain cross to the opposite side.

What problems can the brain stem cause?

Damage to the brain stem leads to so-called brain stem syndromes. In most cases, these are characterized by failure of cranial nerves (damage to the cranial nerve nuclei). Depending on the height of the lesion - in the midbrain, pons or elongated marrow - the functions of various nerves fail. With incomplete brainstem lesions, symptoms can appear on the same or opposite side of the body (because of the crossed pathways).

When nerve pathways that lead to cranial nerve nuclei located further down within the brain stem are damaged on both sides, pseudobulbar paralysis occurs. The main symptoms are speech and swallowing disorders, impaired tongue mobility, and hoarseness.

If the cerebrum is damaged on its own, the vital functions are only maintained by the brain stem. In the so-called vegetative state, those affected are awake, but do not gain consciousness and cannot make contact with their surroundings.

A Brain stem- Infarct can affect those areas that are important for consciousness or breathing. In such a case, the lesion is life threatening.

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