Tegmental Structure, Function & Diseases
Tegmentum
The tegmentum is a portion of the brainstem that includes the midbrain , pons , and medulla. It contains numerous core areas (nuclei) and nerve tracts, some of which exercise motor, some sensory or sensitive functions. Non-specific lesions on the tegmentum can occur, for example, in the context of a stroke , a neurodegenerative disease or as a result of mechanical injuries.
What is the tegmentum?
The word “tegmentum” comes from Latin and literally means “hood”. The tegmentum owes its name to the fact that it forms a cohesive layer that looks like it has been put on. The anatomical structure is made up of three parts spanning the midbrain, pons and medulla.
All three areas belong to the brainstem, also known as the truncus cerebri or truncus encephali. In the embryo , this brain area develops from the second and third cerebral sacs, although the cerebellum is excluded from the brainstem. The tegmentum connects to the inner liquor space, which the four cerebral ventricles form together with the spinal cord canal (canalis centralis).
Anatomy & Structure
When the tegmentum is mentioned in general, the mesencephalic tegmentum or the midbrain hood is often meant; in the narrower sense, however, the mesencephalic tegmentum is only one of three parts of the tegmentum.The other two areas form the tegmentum myelencephali (post-brain hood) and the tegmentum pontis (pontine hood). The myelencephalic tegmentum belongs to the extended medulla ( medulla oblongata ), while the pontine tegmentum represents part of the bridge (pons).
The mesencephalic tegmentum in the midbrain is followed by the cerebral crus (crura cerebri) and the mesencephalic aqueduct, on the other side of which the mesencephalic tectum lies opposite the mesencephalic tegmentum. In the pons and in the extended medulla, the tegmentum lies in the rear area of the structures. All three parts of the tegmentum house different core areas and nerve pathways. Because of the layer of insulation that surrounds nerve fibers, neurologists refer to them as white matter , while the core areas are made up of aggregations of nerve cell bodies known as gray matter .
Function & Tasks
The fifth cranial nerve (triple nerve, trigeminal nerve) has its origin in the tegmentum. Its motor fibers originate from the motor nucleus trigemini, while the sensory fibers arise from the spinal nucleus trigemini in the medulla dilatation, the nucleus principalis nerv trigemini in the pons, or the nucleus mesencephalic nucleus trigemini in the midbrain.
Like the trigeminal nerve, the medial loop (lemniscus medialis) runs through the entire brainstem. The core areas of the medial loop are in the medulla, but its course is through the pons and midbrain to the thalamus .
In the tegmentum pontis lies the nucleus caeruleus or locus caeruleus . It belongs to the reticular formation , which is a network of nuclei and other neurons . His task includes attention and orientation control, for which he is not the only one responsible. The sixth cranial nerve (Nervus abducens) controls certain eye movements, while the seventh cranial nerve (Facial nerve, Nervus facialis ) leads in addition to motor, sensory, sensitive and parasympathetic nerve fibers. The motor fibers of the facial nerve participate in the control of facial expressions , hearing, speech, jaw opening, and swallowing. The nuclei of the eighth cranial nerve ( auditory nerve , vestibulocochlear nerve) are also located in the tegmentum pontis.
The mesencephalic tegmentum contains, among other things, the substantia nigra , which belongs to the extrapyramidal motor system and is therefore involved in the control of movement. The red nucleus is also part of this system. In addition, the mesencephalic tegmentum is home to the nucleus nervi oculomotorii and the nucleus accessory nervi oculomotorii; both are responsible for eye movements. The nucleus nervi trochlearis is the motor nucleus of the fourth cranial nerve (nervus trochlearis), which is involved in controlling eye movements. In addition, numerous other fibers pass through the mesencephalic tegmentum.
Diseases
The nuclei of the abducens nerve in the pontine tegment can be damaged in a skull base fracture , resulting in double vision and impaired eye movement.The trochlear nerve is also a possible cause of disorders affecting eye movements: Typically, if the trochlear nerve is damaged , the eye rotates medially upwards. Facial nerve lesions may be due to tumors , hemorrhages , Lyme disease , a petrous bone fracture or a stroke and often result in facial paralysis . The trigeminal nerve can also be responsible for paralysis; Damage to it also allows sensory disturbances in the face.
Functional restrictions of the nerves and their core areas can come about in different ways. A possible cause that can affect any area of the tegmentum is stroke. In this case, the occlusion of a blood vessel that supplies the brain leads to undersupply and corresponding failures in the affected brain areas. This damage can be permanent if the undersupply leads to the death of the nerve cells , which is the case with prolonged circulatory disorders . In order to limit the damage, rapid action is therefore required in the event of a stroke.
Another example of a disease affecting the tegmentum is Parkinson’s disease. It is based on the loss of nerve cells in the substantia nigra and manifests itself in the form of muscle rigidity ( rigor ), muscle tremors ( tremor ), slowing of movements (bradykinesia) and postural or postural instability. Furthermore, other neurodegenerative diseases such as Alzheimer’s dementia or multiple sclerosis can affect the gray and white matter of the tegmentum.
Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.