It is anticipated that this review will contribute to the self-learning of the author, as well as extending on insights and understandings of dsyphagia within the literature at this present time.
The trigeminal nerve is the largest of the cranial nerves. It is very important in swallowing due to its afferent control of general sensation to the face, teeth, gum, muscles of mastication and the anterior two thirds of the tongue (Miller, 2006). Its efferent control is of the muscles for mastication. Innervating the tensor velar palatine, the trigeminal is partly responsible for the flattening and tensing of the soft palate. Innervations of the extrinsic laryngeal muscle results in the nerve's support for the upward and anterior movements of larynx.
The facial nerve's main function is its motor portion; although, its afferent portion is involved in taste sensation from the anterior two thirds of the tongue (Miller, 2006). It provides motor innervations to the sublingual and submaxillary salivary glands. More specifically, it is involved in swallowing by regulating the lip sphincter and the buccal muscles, which allows food to be held inside the mouth and also assists in pulling the larynx up and back.
The glossopharyngeal (GPN) is composed of the lingual branch of the GPN (GPN-li) and the GPN-ph. Its sensory portion transits inputs from the posterior third of the tongue, the velum and the pharynx, which includes the tonsils (Miller, 2006). The glossopharygeal nerve gathers sensation from the fauces, the palatine tonsil, upper pharynx, and the back third of the tongue. Sensory fibers carry taste information from the posterior one third of the tongue. Afferent input is received from receptors located in the larynx and these are carried primarily to the superior laryngeal nerve, also known as the cough center of the medulla. The motor portion communicates outputs to the middle pharyngeal constrictor muscle and also innervates the stylopharyngeal muscle, which, together with the palatopharyngeus muscle (X nerve), elevates the palate. The stylopharyngeus muscle dilates the pharynx laterally and contributes to the elevation of pharynx and larynx.
The vagus nerve (X) is the most dominant cranial nerve during the swallowing process. The vagus nerve is the major efferent for the pharyngeal constrictors and is the major afferent for the middle and inferior portions of pharynx (Miller, 2006). It supplies also main efferent innervations to the palatal muscles. Branches of the vagus nerve attach to muscles of the larynx and pharynx. It is also known as the nucleus ambiguous, and it innervates branchial arch muscles of the pharynx and larynx as well as the muscles of the upper esophagus and uvula. Branches also extend to the, glossopalantine, levator veli palatine and the palatoglossus muscles making it primarily responsible for palatal functioning. One of the motor nuclei transmits motor output to the pharyngeal constrictor muscles and in this way can completely control the intrinsic musculature of the larynx. Moreover, taste buds on the root of the tongue and on the epiglottis contribute special visceral afferent fibers to the superior laryngeal branch. General visceral afferent fibers convey sensation from the lower pharynx, larynx, trachea, and esophagus.
Together with the