The brainstem (truncus encephali) is the area of the brain located below the diencephalon. This includes the midbrain, the bridge, and the medulla oblongata.
What is the brainstem?
The brainstem is the section below the diencephalon that includes all the parts of the brain that form from the second and third cerebral vesicles. By definition, it also includes the cerebellum, but this is not counted as part of the truncus encephali for historical reasons.
Anatomy and structure
The brainstem is about the size of a thumb and connects the sections of the central nervous system. The cerebellum connects behind the brainstem, and the diencephalon and cerebrum are located above it. The brainstem includes the midbrain, the medulla oblongata, and the bridge. The midbrain is about two centimeters in size and divides into the tetrapod, the cap, and the two cerebral peduncles. The most important nuclei of this area are the so-called formatio reticularis, the black matter as well as the red nucleus. The bridge consists of the velum medullare, the bridge cap, and the bridge foot. The medulla oblongata has three layers and consists of a hood and an anterior and posterior area, respectively. On the anterior side run the so-called pyramids and the pyramidal tracts, on the side are the olives, on the posterior side is the rhomboid fossa, and in the interior is found the vomiting center. In the brain stem a multitude of neurotransmitters and various chemical substances can be found. In addition, by means of the Berlin blue reaction, a very high content of iron can also be detected, which is stored in the glial cells as well as in the neurons. The enzymes in the brainstem are distributed according to a specific pattern, with a very high activity especially in the nuclei of the cranial nerves.
Function and tasks
The nuclei of the cranial nerves run through the brainstem, as do all the tracts involved in the cerebrum. These include the tracts of the extrapyramidal and pyramidal systems, the cerebellar lateral cord tracts, and the tracts of epicritic and protopathic sensibility. The cranial nerves are mainly located in the area of the rhombencephalon and they are arranged like columns. Thus, the parts of the brain that belong to the brainstem serve to regulate, control, modulate, and coordinate. Thus, the nuclei act as a kind of switching station and control many bodily functions. The brainstem is responsible for controlling heart rate and blood pressure, and it also controls sweating and breathing. In addition, it coordinates waking and sleeping and is also vital for reflexes such as coughing, vomiting or swallowing. The center is formed by the formatio reticularis with the raphe nuclei, and there are also ten cranial nerves in the brainstem that regulate balance, are responsible for controlling the eye and facial muscles, and transmit auditory and gustatory sensations. In addition, muscle movements are also coordinated from the brainstem. The formatio regularis controls mood, motor processes, secretory reflexes during digestion, and oculomotor reflexes. Furthermore, the brainstem is the source of endorphin, norepinephrine, dopamine, and serotonin.
Diseases
One possible disease affecting the truncus encephali is brainstem infarction, which can take different forms. The most severe form is locked-in syndrome, in which affected individuals are almost completely paralyzed and can only make vertical eye movements. Patients are, however, fully conscious and able to take in complex information. Another form is Wallenberg syndrome, in which the spinal cord is not supplied with sufficient blood. This results in movement, swallowing and sensory disturbances. In many cases, brainstem infarction occurs due to hardening of the arteries. How the disease progresses depends on the severity of the brainstem infarction. After a mild infarction, patients can usually lead an independent life again, but in the case of a severe infarction, numerous restrictions must be expected. If affected persons suffer from Benedict’s syndrome, the tissue in the area of the midbrain is damaged. In this case, functional disturbances occur on the contralateral side of the body, the pupil is light-rigid and patients often see double images. A very classic brainstem syndrome is the so-called Weber syndrome. This results from damage to the tissue in the region of the midbrain base.Patients see double vision and ocular motility is limited. The pupil is very wide and paralytic strabismus occurs. Spastic hemiplegia occurs on the opposite side. In Babinski-Nageotte syndrome, the medulla oblongata is damaged. It is an alternating brainstem syndrome in which uncrossed and crossed nerve fibers fail. Affected individuals suffer from neurological deficits that occur on the contralateral side or even on the mild side of the body. Developmental and anatomical disorders of the brainstem include various forms of Chiari malformation as well as Dandy-Walker malformation. Chiari malformation is a malformation characterized by a size mismatch between the metencephalon and the posterior fossa. Symptoms usually appear between the ages of 10 and 40, with affected individuals suffering primarily from neck and occipital pain, visual disturbances, hearing problems, balance disorders, and dizziness. A fetal developmental disorder of the cerebellum results in the Dandy-Walker malformation, in which spasticity and eye movement disorders occur as early as the 1st year of life. Tumors can also occur in the brain stem area, the most common type of tumor being the so-called astrocytoma. A brainstem tumor causes visual and speech disturbances and spastic paresis, and sometimes headaches, nausea, and vomiting occur.
Typical and common brain disorders.
- Dementia
- Creutzfeldt-Jakob disease
- Memory gaps
- Brain hemorrhage
- Meningitis