The pharyngeal plexus is located in the pharynx and is a plexus of nerves containing predominantly fibers from the ninth and tenth cranial nerves. It controls muscles of the pharynx and palate as well as glands in the pharyngeal mucosa, which it also innervates sensitively. Swallowing disorders (dysphagia) and sensory disturbances may be due to damage to the pharyngeal plexus.
What is the pharyngeal plexus?
The pharyngeal plexus is located in the pharynx, where it forms a network of nerve fibers that include motor, autonomic, and sensory pathways. They control the pharyngeal constrictor (pharyngeal constrictor muscle), the pharyngeal elevator (pharyngeal levator muscle, without stylopharyngeal muscle), and glands and sensory nerves in the pharyngeal mucosa. The pharyngeal levator and elevator together form the pharyngeal musculature. The pharyngeal plexus lies on the pharyngeus medius constrictor muscle, which is related to the ontogenetic development of the nervous plexus. While the muscles are still developing, they pull their nerves along with them and change the position of the individual nerve fibers – a neural plexus is formed, which contains parts from different pathways. Medicine roughly divides neural plexuses into two groups based on their functions. A vegetative plexus predominantly innervates the smooth muscles of organs, blood and lymph vessels, and glands. In contrast, both the control of striated skeletal muscles and the transmission of sensory information are among the tasks of a somatic plexus.
Anatomy and structure
The pharyngeal plexus is located in the pharynx on the constrictor pharyngeus medius muscle. The fibers of the plexus derive largely from the ninth cranial nerve (glossopharyngeal nerve) and from the tenth cranial nerve (vagus nerve). The glossopharyngeal nerve divides its course into several branches, from which the rami pharyngei run to the pharyngeal plexus. The vagus nerve also has a pharyngeal branch that leads to the plexus. The two cranial nerves arise from different nuclei of the central nervous system. Each of them contributes motor parts to the pharyngeal plexus. Other pathways include vegetative fibers of the glossopharyngeal nerve, which influence the pharyngeal glands, and sensory fibers of the vagus nerve, which lead afferently to the brain. Neurons from the glossopharyngeal and vagus nerves make up the bulk of the pharyngeal plexus. In addition, the plexus contains fibers from the superior laryngeal nerve and the superior cervical ganglion.
Function and Tasks
With the help of motor fibers, the pharyngeal plexus controls the superior pharyngeal constrictor (superior constrictor pharyngis muscle), the middle pharyngeal constrictor (medius constrictor pharyngis muscle), and the inferior pharyngeal constrictor (inferior constrictor pharyngis muscle). The superior constrictor pharyngis muscle is located in the upper part of the pharynx. During swallowing, its function is to close the nasopharynx (pars nasalis pharyngis or epipharynx) so that no fluid or food enters the access to the nose. Of the three pharyngeal constrictors, the constrictor pharyngis medius muscle lies in the middle. When it contracts, it narrows the pharynx (pars oralis pharyngis or mesopharynx), which is located at the junction of the pharynx and oral cavity. In this way, the constrictor pharyngis medius muscle transports food or fluid dorsally – the constrictor pharyngis inferior muscle performs the same function in the lower pharynx. The pharyngeal elevators also rely on the pharyngeal plexus. They include three muscles, but only the palatopharyngeus and salpingopharyngeus muscles receive their commands from the pharyngeal plexus. In the swallowing process, their role is to lift the pharynx. Via the torus tubarius, they can also contribute to pressure equalization in the middle ear. The pharyngeal plexus controls these muscles with the help of its motor parts. Efferent fibers also control the glands in the pharyngeal mucosa. They produce a secretion that keeps the sensitive skin moist and improves the sliding down of food. The nerves involved belong to the autonomic nervous system and are not subject to voluntary human control. In addition, sensitive fibers of the pharyngeal plexus end in the pharyngeal mucosa. They pick up stimuli and transmit them as electrical impulses to the nerve plexus and higher processing areas.The sensitive nerve fibers carry information about temperature, pressure and touch stimuli, and pain.
Diseases
Swallowing and sensitivity disorders in the pharynx can occur when the pharyngeal plexus becomes damaged. In the case of such a sensitivity disorder, the sensitive nerve endings in the pharyngeal mucosa are able to detect stimuli, but a damaged pharyngeal plexus can no longer (fully) process them. Swallowing disorders are also referred to as dysphagias in medicine. In connection with the pharyngeal plexus, both motor and sensory disturbances can cause complaints during swallowing. In practice, both symptom areas often occur together because the fibers in the pharyngeal plexus are intermingled. Sensory disorders of the pharynx may interfere with the swallowing reflex: Normally, irritation of the pharynx, tongue, and palatal arches automatically triggers the swallowing reflex. However, if the swallowing centers, located primarily in the brainstem, no longer receive appropriate signals, the motor response may fail to occur or occur too late. Food and fluid can thus more easily enter the nasopharynx or pass into the respiratory tract. Aspiration of foreign bodies carries the risk of mechanical tissue damage and infection. If the motor fibers of the pharyngeal plexus are damaged, the pharyngeal cords and pharyngeal elevators no longer receive nerve signals to contract. In this case, dysphagia is also the result. The sense of taste need not be affected by these complaints. Numerous causes can be considered for pharyngeal plexus lesions, including neuromuscular disease, accidental surgical or radiation damage, inflammation, and central nervous system disease.