Oral and Pharyngeal Reflexes in the Mammalian Nervous System: Their Diverse Range in Complexity and the Pivotal Role of the Tongue

Abstract

ABSTRACT:The oral cavity and pharynx are anatomically separate but functionally integrated regions of the head. The two regions are involved in complex motor responses that include feeding, chewing, swallowing, speech, and respiration. The multiple sensory receptors that innervate these two regions provide the first link in reflexes that control muscles of the entire head, upper gastrointestinal tract, and airway. Most of the reflexes affect the diversity of muscles that compose the tongue, which is vital to all stages of feeding and which continually affects the patency of the airway. Oral-pharyngeal reflexes are evident in the mammalian fetus and continually emerge as the animal or human matures. Some of the first reflexes in the oral region are geared toward nourishment. As the central nervous system matures and the oral and pharyngeal regions develop morphologically, new reflexes develop. Many of these reflexes are protective both of the tissue in the oral cavity, such as the tongue, and of the upper airway in preventing aspiration. While simple reflexes can be evoked in isolation, most reflexes combine with more complex oral and pharyngeal responses such as chewing and vocalization. Oral-pharyngeal reflexes demonstrate a range in complexity. Some sensory stimuli will evoke a series of responses, as is often evident in the infant, and other stimuli will evoke a complex multiple-level recruitment of muscles in a sequence, as in pharyngeal swallowing. Certain sensory inputs evoke an entire motor behavior pattern, such as taste avoidance or facial expression. The oral-pharyngeal reflexes are critical to maintaining life and ultimately serve functions that the oral and pharyngeal regions have in common, such as communication, feeding, and breathing.

Reabilitação em disfagia orofaríngea neurogênica: sabor azedo e temperatura fria

“…Concluem que os achados controversos a outros estudos devem-se, talvez, ao fato de que os estudos encontrados na literatura não diferenciam os mecanismos aferentes dos eferentes na dinâmica da deglutição 10 . Com relação à recepção do sabor a nível periférico, refere-se que o sabor pode desencadear resposta motora da língua e que múltiplas aferên-cias captadas na língua fazem sinapse afetando os motoneurônios do hipoglosso 11 . Já a representação da temperatura na córtex, quando estudada em macacos, foi evidenciada na região orbitofrontal 12 .…”

Taste Disorders in Acute Stroke

“…The impairment of swallowing and taste may be a consequence of the disturbance of such an oropharyngeal reflex. 32 A second point may relate to the idea that the swallowing disorder impairs the self-cleaning of the oral cavity, although not visible to the investigators. This might either impair the contact between tastants and taste receptors or produce desensitization of gustatory receptors.…”

Nerve and Muscle Changes in the Upper Airways of Subjects with Obstructive Sleep Apnea: Structural Basis for the Neurogenic Theory

“…In these UA zones, increase in the density of epithelial afferent nerve endings (based on the expression of substance P and calcitonin gene-related peptide) was also observed which is indicative of nerve lesion [38]. On the other hand, the afferent information from UA muscles is important in regulating the masticatory force and oromotor behaviors, but also in the response of important reflexes related to speech, swallowing, cough, vomit, or normal breathing [10,42]. Patients with OSAS show a significant reduction in the density of nerve fibers in the submucosa as well as morphological abnormalities in mechanosensory corpuscles.…”

“…The structural support of these reflexes consists of sensory receptors connected with sensory nerve fibers, the central synaptic connections that almost always use interneurons, and the efferent pathway composed of the motoneurons, innervating the effector organ. The effector organ in a somatic reflex is the striated muscle innervated by the α-motoneurons [10].…”