Anatomy & Organs

Nucleus tractus solitarii – structure, function & diseases

Nucleus tractus solitarii

The nucleus tractus solitarii is the neuronal taste nucleus in humans and is located in the rhomboid pit in the brainstem . Its nerve fibers connect the brain to the taste buds of the tongue , as well as to the vagus nerve . Damage to the nucleus tractus solitarii – for example due to masses, traumatic damage or circulatory disorders – can cause taste disorders.

What is the nucleus tractus solitarii?

The nucleus tractus solitarii (NTS) or nucleus solitarius is a neural processing center in the brain. The nucleus connects nerve fibers from the tongue and in this way contributes to gustatory perception.

Only at a higher level of processing does this become the conscious perception of a certain taste; this step takes place in the cortex, to which the signals from the taste nucleus ultimately also reach. The nucleus tractus solitarii is one of the cranial nerve nuclei because it forms a node where cranial nerves end or begin. It belongs to the group of general and special viscerosensitive nuclei; unlike other central anatomical brain structures, it carries both types of fibers.

Anatomy & Structure

The nucleus tractus solitarii lies in the medulla oblongata , which connects the spinal cord to other parts of the central nervous system . The spinal cord and medulla oblongata are not sharply demarcated, but rather flow into one another. Within the elongated medulla, the solitary tract nucleus begins at the rhombic fossa, which forms the floor of the fourth cerebral ventricle.From there, the NTS extends to the pyramidal junction (decussatio motoria or decussatio pyramidum), where nerve pathways originating from the motor cortex cross. Three different nerves run through the Nucleus tractus solitarii : the Nervus glossopharyngeus (9th cranial nerve), the facial nerve or Nervus facialis (7th cranial nerve) and the Nervus vagus (10th cranial nerve or Nervus X). According to these areas, physiology also divides the nucleus tractus solitarii into three broad regions, which are often only called caudal, medial and rostral NTS according to their location. The only exception to this is the rostral part, which is also known as the nucleus gustatorius, nucleus ovalis or pars gustatoria.

Function & Tasks

The nucleus tractus solitarii plays an important role in the processing of gustatory information. The sense of taste is one of the chemical senses: receptors on the tongue react to substances that come into contact with them. The sensory cells then generate an electrical impulse that moves along the nerve fiber as an action potential. These signals travel to the brain via various nerves, where all three converge in the nucleus tractus solitarii. The task of the glossopharyngeal nerve is to collect information from the back of the tongue. So that it can pick up all nerve signals, it divides into three main branches and several smaller branches.

The nucleus tractus solitarii also receives information from the anterior region of the tongue via the facial nerve . The sensitive fibers in the nerve are responsible for this task. However, the functions of the facial nerve are much more extensive and also play a role in hearing, temperature, pain and pressure perception in the face. The facial nerve also connects the lacrimal gland and salivary gland to the central nervous system.

The vagus nerve is also not limited to innervating the taste buds. Instead, it combines various viscerosensitive, somatosensitive and visceromotor signals from large areas of the body. The vagus nerve covers areas of the head, neck, abdomen and chest and forms numerous branches that become increasingly fine. The Nucleus tractus solitarii is not the only cranial nerve nucleus that is relevant for the Nervus vagus; its fibers also lead to the spinal nucleus of the trigeminal nerve, the dorsal nucleus of the vagi nerve, and the nucleus ambiguus.

Diseases

The nucleus tractus solitarii can contribute to the development of various taste disorders . In principle, however, the causes of such perceptual disturbances are possible anywhere in gustatory processing.Damage to the nucleus tractus solitarii can be based, for example, on circulatory disorders ( stroke , increased intracranial pressure, etc.), masses caused by tumors , craniocerebral trauma , congenital malformations and neurodegenerative diseases. If the lesion is not directly on the solitary tract nucleus, but on all, some or one of the nerves, the nucleus receives no, incomplete or incorrect information and, accordingly, operates on the basis of erroneous signals; however, the NTS itself can be undamaged.

Which taste disorder manifests itself and whether other symptoms occur depends on the affected brain areas in each individual case. If, for example, damage to the facial nerve is the cause of the taste disturbance, paralysis of the face often also manifests itself.

Medicine distinguishes between quantitative and qualitative taste disorders. Persons suffering from total ageusia can no longer perceive taste; a special form occurs in the context of the post-traumatic anosmia-ageusia syndrome, which also affects the sense of smell and goes back to a traumatic brain injury. Hypogeusia limits gustatory perception but does not completely eliminate it.

Partial hypogeusia occurs when sufferers can still perceive certain tastes with normal intensity; this is the case, for example, when only certain sections of the nerve fibers are damaged, but the information processing is otherwise correct. In contrast, people with hypergeusia suffer from a pathological increase in taste.

A qualitative taste disorder is phantogeusia, which is characterized by gustatory perceptions for which there is no actual stimulus. On the other hand, an exchange of flavors occurs in parageusia. Qualitative taste disorders do not have to be permanent, but can also occur temporarily.

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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.