Posterior one-third and vallate papillae: glossopharyngeal nerve (CN IX), superior laryngeal nerve (branch of vagus nerve CN X)

Basal cells – line the basal lamina of the taste bud. They are short (do not reach the pore) stem cells for the neuroepithelial and basal cells. The palatopharyngeus and tensor veli palatini muscles produce the tension of the soft palate during swallowing. This enables the tongue to press against the soft palate and push the food towards the oropharynx. When it comes to the posterior one-third of the tongue and pharynx, the special visceral afferent fibers from both the superior laryngeal nerve (branch of the vagus nerve (CN X)) and the glossopharyngeal nerve (CN IX) synapse with the inferior ganglion of the vagus nerve and the inferior ganglion of the glossopharyngeal nerve (also known as the petrosal ganglion). From the inferior ganglion, the postganglionic fibers exit and course towards the same spot as the chorda tympani (the nucleus of the solitary tract) after entering the brainstem at the rostral medulla oblongata.The fibers end within the rostral segment of the of anterior (ventral) solitary nucleus. The neurons of this nucleus send fibers that join the ipsilateral central tegmental tract, and then end within parvocellular division of the ventral posteromedial nucleus of the thalamus. The fibers exiting from the thalamus form central thalamic radiations, which pass through the posterior limb of the internal capsule. These fibers end within the primary gustatory cortical areas of the cerebral cortex, found within insulaand frontal operculum. There are two groups of muscles associated with the tongue. One group are muscles that comprise the core of the tongue and are placed within it, and therefore are called the intrinsic muscles. Their main function is altering the shape of the tongue, and they are: the superior longitudinal, inferior longitudinal, transverse and vertical muscles. On the other hand, every organ specialized for a specific sensation, like the tongue is for taste, also has special sensory innervation. The senses of taste and olfaction (smell) are carried by special visceral afferent fibers in cranial nerves. The sense of taste is mediated by the facial (CN VII) and glossopharyngeal (CN IX) nerves. Even though taste receptors and their innervation will be discussed in the following sections of this article, right now, for the sake of the later recap, take the following two sentences for granted:

Robbins JA, Hamilton JW, Lof GL, Kempster G. Oropharyngeal swallowing in normal adults of different ages. Gastroenterology. 1992;103:823–9. Agrawal D, et al. Swallow strength training exercise for elderly: a health maintenance need. Neurogastroenterol Motil. 2018;30(10):e13382.

The taste buds of the soft palate are innervated by the greater petrosal nerve, a branch of the facial nerve (CN VII). The mucous glands of the soft palate are parasympathetically innervated by the postganglionic fibers from the otic ganglion. They reach the soft palate via the lesser petrosal branch of glossopharyngeal nerve.Mechanisms involved in muscular hypertrophy and conditioning with exercise are known to increase in a dose-dependent manner [ 6], making consideration of dose in exercise particularly important. The relationship between resistance exercise dose and muscular hypertrophy have been explored and debated in the limb literature with the goal of optimizing dose prescription to maximize strength-related outcomes [ 5, 6]. Relationships between training intensity and frequency have been well studied, and these findings have contributed to the American College of Sports Medicine (ACSM) Guidelines for Exercise Testing and Prescription (9 th Edition) [ 32]. With increasing intensity of resistance exercise there is a corresponding increase in the synthesis of myofibrillar proteins [ 33]. Similarly, increasing resistance exercise training frequency (number of training sets/week) is related to increasing muscular hypertrophy in a graded, dose-responsive manner [ 34]. Lazarus C, et al. Effects of exercise on swallowing and tongue strength in patients with oral and oropharyngeal cancer treated with primary radiotherapy with or without chemotherapy. Int J Oral Maxillofac Surg. 2014;43:523–30. https://doi.org/10.1016/j.ijom.2013.10.023. Tongue-strengthening exercises can help improve your swallowing. With practice, these exercises may help you increase your tongue strength and mobility. This may improve your ability to swallow, especially when used with other types of swallowing exercises. Crow HC, Ship JA. Tongue strength and endurance in different aged individuals. J Gerontol A Biol Sci Med Sci. 1996;51:M247–50. Press the scraper on your tongue and move it toward the front of your tongue while applying pressure.

Yano J, et al. Effects of anterior tongue strengthening exercises on posterior tongue strength in healthy young adults. Arch Oral Biol. 2019;98:238–42. Neuroepithelial cells – sensory cells that extend from the basal lamina to the taste pore. Their microvilli project into the pore and detect chemical stimuli (taste) from food. They synapse with the facial, glossopharyngeal, or vagus nerve to send taste information to the central nervous systemMann G, Hankey GJ. Initial clinical and demographic predictors of swallowing impairment following acute stroke. Dysphagia. 2001;16:208–15.

Van den Steen L, et al. Tongue-strengthening exercises in healthy older adults: does exercise load matter? A randomized controlled trial. Dysphagia. 2019;34(3):315–24. Park HS, et al. Effect of effortful swallowing training on tongue strength and oropharyngeal swallowing function in stroke patients with dysphagia: a double-blind, randomized controlled trial. Int J Lang Commun Disord. 2019;54(3):479–84. Fungiform papillae are shaped like mushrooms. They can be found all over the dorsal surface of the tongue, but their highest concentration is at the tip and margins of the tongue. Nagao K, Kitaoka N, Kawano F, Komoda J, Ichikawa T. Influence of changes in occlusal vertical dimension on tongue pressure to palate during swallowing. Prosthodont Res Pract. 2002;1:16–23.Kim HD, et al. Tongue-to-palate resistance training improves tongue strength and oropharyngeal swallowing function in subacute stroke survivors with dysphagia. J Oral Rehabil. 2017;44(1):59–64. All studies that meet the inclusion criteria provided extractable data. Means and standard deviations for TSE and control groups were extracted. If the studies assessed the tongue strength at many time points, the baseline and the final post-intervention data were extracted. If intervention groups were divided into different training intensity groups, such as 100% of 1 repetition maximum (RM), 75% of 1 RM, and 50% of 1 RM, data were extracted from the 100% of 1 RM group. On the other hand, the inferior pole of the bud synapses with the corresponding sensory nerve (facial (CN VII), glossopharyngeal (CN IX), or vagus (CN X) that carries information of the chemical stimuli to the central nervous system via the gustatory pathway to be interpreted and perceived as a specific taste sensation. Hagg M, Anniko M. Lip muscle training in stroke patients with dysphagia. Acta Otolaryngol. 2008;128(9):1027–33.