The brain is one of the most complex and intricate structures in the entire human body and continues to puzzle generations of researchers. While the midbrain is only a small part of this complex system, it is nevertheless a small miracle in its own right.
What is the midbrain?
The midbrain is a part of the human brain, and all vertebrates have a midbrain. In medical literature, it is referred to by the ancient Greek term mesencephalon. It is part of the brain stem and thus also part of the developmentally oldest area of the brain. In addition to the brain stem, three other major areas exist in the human brain: the cerebrum, the cerebellum, and the diencephalon.
Anatomy and structure
The midbrain is an area about 1.5 to 2 cm in size, located below the diencephalon and above the so-called bridge (pons). Below the bridge is the medulla oblongata, the medulla oblongata, which extends directly into the spinal cord. Together, these three brain areas form the brainstem. The midbrain itself is also divided into three layers: the cerebral peduncles, the midbrain cap, and the midbrain roof. The two cerebral peduncles form the anterior part of the midbrain. They project into the diencephalon and are separated from each other by a kind of trench, the interpeduncular fossa. They also contain some nerve tracts that run between the brain and the spinal cord, as well as the third cranial nerve. The midbrain cap forms the largest part of the midbrain in terms of area. It contains some important nerve cells for muscle activity, such as the nucleus ruber, the nucleus nervi trochlearis or the nucleus nervi oculomotorii. At the transition from the midbrain cap to the cerebral peduncles is the substantia nigra, the “black matter”. This owes its name to its surface, which is colored black by melanin accumulations. The midbrain roof is the posterior part of the midbrain and is shaped like a thin plate on which there are four elevations. Therefore, this area is also called the “four mound plate”. There are two upper mounds (colliculi superiores) and two lower mounds (colliculi inferiores). At the lower end of the four-mound plate, the IV. Cranial nerve (nervus trochlearis) emerges. Another feature of the midbrain is the aquaeductus mesencephali, a type of water conduit through which cerebrospinal fluid called cerebrospinal fluid passes from the third to the fourth cerebral ventricle.
Function and tasks
The midbrain performs several tasks within the very complex neural system. Among other things, it is responsible for controlling the majority of the eye muscles, such as the opening and closing of the eyes or the contraction of the pupils. Furthermore, it is an important switching center between different nerve pathways in the human body. On the one hand, it transmits information and stimuli from the spinal cord via the diencephalon to the cerebrum and, conversely, stimuli from the cerebrum to the nerve cells in the spinal cord that are responsible for motor activity. This function makes the midbrain an important component of the so-called extrapyramidal motor system, which is responsible for all control processes of human motor function. However, stimuli received by the ears and the eyes also first reach the midbrain, from where they are transmitted to the cerebral cortex and processed there. In addition to this important function for sensory and auditory perception, the midbrain, as part of the limbic system, also plays an elementary role in the perception of pain.
Complaints and diseases
There are a number of diseases and disorders that can occur in connection with dysfunction of the midbrain. Probably one of the best-known diseases in this context is Parkinson’s disease. Often referred to simply as “Parkinson’s disease” in common parlance, it is caused by a progressive decay of nerve cells in the “substantia nigra”. The nerve cells located there use the messenger substance dopamine to transmit stimuli. Due to the progressive lack of dopamine, motor movements can be disturbed, which can lead to malfunctions of the muscles, such as trembling, as well as a general slowing down of movements. Changes in the substantia nigra are also present in attention deficit hyperactivity disorder, or ADHD, and in attention deficit disorder (ADD).This results in partially incorrect transmission and processing of stimuli between the various brain regions for which the midbrain is responsible. In addition, the midbrain can also be affected by a benign or malignant tumor. This can permanently and severely impair its functionality and lead to various symptoms such as disturbances in motor function, breathing, consciousness, concentration or gait. Problems moving the eyes or a dysfunction of the pupils can also be signs of a tumor in the midbrain area. In addition, a number of rare diseases exist that can cause damage to the midbrain. These include, for example, Nothnagel syndrome, in which the four mound region is affected. This can result in problems with eye mobility as well as perceptual disorders and impaired motor skills. In the so-called Benedict syndrome, on the other hand, both nucleus ruber and substantia nigra are damaged. Here, too, the motor function of the eyes as well as the entire musculoskeletal system are permanently affected. The midbrain, like all parts of the human brain, is a very complex structure whose anatomy and functioning have been fairly well researched in the meantime. But many diseases caused by faulty processes in the midbrain are still unfortunately not entirely curable, even if their symptoms can be attenuated and their progression slowed.
