Midbrain – function, structure & symptoms

Midbrain

The midbrain is a section of the brainstem. It is found between the pons and diencephalon.

Definition

The midbrain (mesencephalon) is a part of the human brain , more precisely the brainstem . The mesencephalon is located between the pons (bridge) and the diencephalon ( interbrain ).

The midbrain is one of the most important parts of the extrapyramidal system. It is responsible for the regulation of numerous eye muscles . The mesencephalon transmits stimuli originating from sensory nerves to the cerebrum (telencephalon) via the diencephalon. Switching to motor nerve cells is also possible.

The midbrain is present in all vertebrate species. As part of the brainstem, it is one of the oldest brain sections from an evolutionary point of view.

Anatomy

The midbrain region is approximately 1.5 to 2 centimeters in size. The area of ​​the mescencephalon lies above the pons and below the diencephalon. The medulla oblongata, the extended spinal cord , is located below the bridge . It merges directly into the spinal cord.

The midbrain is divided into three layers. These are the cerebral crus (crura cerebri), the midbrain hood (tegmentum mesencephali) and the midbrain roof (tectum mesencephali). The cerebrum and midbrain hood are located in the anterior portion of the midbrain and are collectively known as the “cerebrum peduncles” (pedunculi cerebri). The water duct of the mesencephalon is found between the tectum and tegmentum. It is called the mesencephalic aquaeductus.

The two cerebral peduncles run in the direction of the diencephalon. Their separation occurs through the interpeduncular fossa. The cerebral peduncles are equipped with several nerve tracts between the spinal cord and the brain. They also contain the third cranial nerve.

The midbrain cap covers the largest area of ​​the midbrain. It contains nerve cells that are important for muscle activity. These include the nucleus nervi trochlearis, the nucleus nervi oculomotorii and the nucleus ruber. The transition between the midbrain cap and cerebral peduncles is marked by the so-called “black substance” (substantia nigra). The name can be traced back to the accumulation of the black pigment melanin on the surface.

The midbrain roof forms the middle section of the mesencephalon and has the shape of a thin plate. There are four elevations on the plateau, to which this section owes the name Vier Hügelplatte. The trochlear nerve, the fourth cranial nerve, exits below the four hillock plate.

Function

The midbrain performs important tasks within the complicated system of neurons. These include, for example, controlling large parts of the eye muscles. These include eye opening and closing as well as pupil contraction .

Furthermore, the midbrain acts as a switching center between the nerve tracts of the organism. For this purpose, stimuli and information from the spinal cord are passed on to the cerebrum via the diencephalon. Conversely, the mesencephalon transmits cerebrum stimuli to the spinal cord nerve cells, which are responsible for motor processes. The midbrain is an important part of the extrapyramidal motor system (EPMS).

Signals picked up by the eyes and ears can also be transmitted to the midbrain. Once there, they are transported to the cerebral cortex, where they are processed. The mesencephalon is also important for the perception of pain because it is part of the limbic system.

Diseases

  • midbrain syndrome
  • Nothnagel Syndrome

In the case of the midbrain, various diseases are in the realm of possibility. This includes acute midbrain syndrome. It is caused by an increase in pressure in the brain. This in turn is caused by edema or bleeding.

The triggering factors are poisoning , an insufficient supply of oxygen due to cardiac arrest or a severe traumatic brain injury . Those affected lose their pain reactions, suffer from stretch cramps in the limbs, sweating , dilated pupils, accelerated heartbeat and hypertension . Eventually they become unconscious.

One of the most well-known diseases of the midbrain is Parkinson’s disease. There is an increasing decay of the nerve cells located in the substantia nigra. These nerve cells depend on the messenger substance dopamine to transmit stimuli. In Parkinson’s disease, however, there is a lack of dopamine, which negatively affects motor movement processes. The result is muscle dysfunction. They become noticeable, among other things, through slowed movements and tremors .

Another possible impairment of the midbrain is ADHD (Attention Deficit Hyperactivity Disorder). Changes in the substantia nigra also occur in this case. As a result, the stimuli that are exchanged between the different sections of the midbrain are sometimes incorrectly transmitted and processed.

Malignant tumors are among the most serious diseases of the mesencephalon. These lead to significant disturbances in breathing, concentration, movement and consciousness.

The so-called Nothnagel syndrome occurs rather rarely. The four-hill region is negatively affected. This becomes noticeable through motor disorders, disturbances of perception or restricted mobility of the eyes.

Dorothy Farrar

Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.

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