Involuntary swallow ; Pharyngeal response mechanism ; Pharyngeal swallow response ; Swallowing response. Automatic physiological mechanism that results in breath hold secondary to vocal fold adduction, laryngeal and hyoid anterior and superior movement, velopharyngeal closure, and epiglottal posterior movement to cover the trachea during bolus movement through the hypopharynx and the upper esophageal sphincter.
The swallowing reflex is one phase of the swallow which is under reflexive or involuntary control. This stage of the swallow begins after food which has been masticated has been gathered together in the mouth and formed into a bolus which is passed from the posterior tongue through the faucial arches.
As the bolus begins its descent from the posterior tongue through the hypopharynx to the upper esophageal sphincter, the swallow becomes reflexive. Breathing stops at this time as the epiglottis covers the airway entrance, the vocal folds adduct or close Skip to main content Skip to table of contents.
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Editors: Sam Goldstein, Jack A. Contents Search. Kaken Hospital, Ichikawa, Japan. This article was submitted to Frontiers in Respiratory Physiology, a specialty of Frontiers in Physiology. Received Aug 8; Accepted Dec This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
This article has been cited by other articles in PMC. Abstract Swallowing function, in humans, is very complex. Keywords: swallowing, pulmonary aspiration, upper airway, defensive reflexes, respiration. Introduction Respiration and swallowing utilize a common passageway and the two activities must be coordinated so that mutual compromise does not occur. Neural organization of the swallowing The reflex control system of swallowing consists of afferent, central, and efferent components, and the integrity of the reflex control system seems to contribute to the prevention of pulmonary aspiration.
Afferent pathways The receptive regions for reflex swallowing include many locations in oro-pharyngeal space such as the soft palate, uvula, dorsa surface of the tongue, pharyngeal surface of the epiglottis, faucial pillars, glossoepiglottidinal sinus, dorsal pharyngeal wall, and the pharyngoesophgeal junction Pommerenke, ; Storey, ; Sinclair, ; Mannson and Sandberg, ; Miller, Central integration The NTS is not only an afferent portal but has interneurons that perform a more complex level of swallowing control.
Factors affecting the swallowing reflex Muscle weakness Swallowing causes reflex closure of the glottis, elevation of the larynx, and a transient cessation of respiration. Body position The epiglottis itself is not considered to be essential to effective swallowing function. Open in a separate window. Figure 1. Timing of swallow In order to analyze the timing of swallows, types of swallows were classified into four different types according to swallow-associated airflow pattern.
Changes in respiratory mechanics Changes in respiratory mechanics and an addition of respiratory loads to the respiratory system are frequently observed in several clinical situations. Changes in lung volume In order to see modulation of swallowing reflex by lung volume changes, we studied the effects of changes in lung volume produced by several maneuvers like application of extrathoracic negative pressure Kijima et al.
Clinical implications of the swallowing reflex A variety of etiological insults to any part of the reflex arch consisting of afferent pathways, central integration, and efferent pathways of the swallowing reflex cause impairment of triggering reflex swallowing. Figure 2. Concluding remarks Swallowing reflex serves as a defensive airway reflex.
Conflict of interest statement The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Acknowledgments This paper is dedicated to late Professor John G.
References Broussard K. Central integration of swallow, and airway-protective reflexes. Swallowing dysfunctions associated with radical surgery of the head and neck. Effect of medullary lesions on coordination of deglutition.
Electrophysiological evaluation of pharyngeal phase of swallowing in patients with Parkinson's disease. The role of vagal and glossopharyngeal afferent nerves in respiratory sensation, control of breathing and arterial pressure regulation in conscious man.
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Influence of gravity and body position on normal oropharyngeal swallowing. Coordination of swallowing and phases of respiration during added respiratory loads in awake subjects.
Care Med. Modulation of swallowing reflex by lung volume changes. An anatomical analysis of corticobulbar connections to the pons and lower brain stem in the cat. The frequency of deglutition in man.
Oral Biol. Swallowing disorders following skull base surgery. North Am. Effects of surface anesthesia on deglutition in man. Laryngoscope 84 , — Control of respiratory frequency. Characteristics of the swallowing reflex induced by perieheral and brain stem stimulation. Swallowing as a protective reflex for the upper respiratory tract.
Hypercapnia enhances the development of coughing during continuous infusion of water into the pharynx. Effects of increasing depths of anesthesia on phrenic and hypoglossal nerve activity during the swallowing reflex in cats. Effects of swallowing on the pattern of continuous respiration in human adults.
Nasal constant positive airway pressure inhibits the swallowing reflex. Reflex response and convergence of pharyngoesophageal and peripheral chemoreceptors in the nucleus of the solitary tract. Neuroscience 93 , — Respiratory phase resetting and airflow changes induced by swallowing in humanas. A study of the sensory areas eliciting the swallowing reflex. Swallowing disorders in Parkinson's diseases. Parkinsonism Relat. Effects of withdrawal of phasic lung inflation during normocapnia and hypercapnia on the swallowing reflex in humans.
Origins of the inhibiting effects of nasal CPAP on nonnutritive swallowing in newborn lambs. Effect of nasal continuous or intermittent positive airway pressure on nonnutritive swallowing in the new born lamb. Initiation of reflex swallowing from the naso- and oropharynx. Laryngeal initiation of swallowing. The voluntary oral phase of swallowing leads information to the cortex by the afferent pathways of the nerves V, VII and IX mixed pairs that allow the cortex to activate the motor portions of these mixed nerves in association with the hypoglossal XII - motor pair.
Originating in peripheral receptors, afferent pathways reach the brainstem. From the sensory nuclei of the cranial pair V, through the secondary ventral and dorsal tracts, they reach the thalamus and cortex with tactile also volume and viscosity , thermal and possibly nociceptive sensations. Afferent general sensitivity and special taste pathways led by the cranial nerves VII and IX reach the solitary tract nucleus in the dorsal region of the medulla oblongata.
From this, afferent pathways connect with the base nuclei, including thalamus, and then with the cerebral cortex on the postcentral gyrus of both hemispheres, transferring the received afferent signals to the precentral gyrus, from where efferent pathways go to the brainstem motors nuclei V, VII, IX, XII.
Based on the hemisphere dominance, one can conclude that both afferent general sensitive and special taste , and efferent special motors and general parasympathetic pathways interconnecting both sides of cortex and brainstem arrive and leave as direct and cross paths.
This organization gives to each cerebral hemisphere the total information collected in the oral cavity, enabling effective commands from each hemisphere to reach both sides of the brainstem, integrating the cranial nerves that act in the oral phase 58 After activating the sensorial cortex on both sides from the base nuclei, the peripheral information passes to the motor cortex, where the necessary intensity is modulated and re-transmitted to the base nuclei and brainstem.
In the latter, the efferent pathways of the trigeminal, facial and hypoglossal nerves would produce an oral dynamic that would end by ejecting its contents into the pharynx.
Although one of the hemispheres is dominant, both are fully informed, allowing them to exercise full functions 48 There is evidence that the dysphagia generated by injury to the dominant hemisphere allows increase in the representation of the non-dominant non-injured hemisphere, associated with apparent function recovery 52 There are pathways crossing from one side to the other through the corpus callosum, integrating the hemispheres.
Thus, in healthy individuals, the dominant cortex can exert inhibitory action on the contralateral one by a connection that passes through the corpus callosum. It is also possible to consider the existence of excitatory pathways from the dominant motor cortex to the base nuclei of the contralateral hemisphere. This organization would explain not only the already evidenced function recovery when there is lesion of the dominant hemisphere 52 It is also possible to assume that these excitatory pathways exist in both directions.
Between the brainstem and the cortex, there are also interconnected pathways arriving at, and leaving from, the cerebellum, considered able to modulate muscular contraction intensity and sequence. In this way, cerebellar pathways connect with efferent voluntary cortex-nuclear pathways that will make synapses with the motor nuclei of the cranial nerves V, VII, IX and XII.
From these nuclei, the efferent stimuli follow to the oral effectors, providing them with signaling of adequate contraction intensity and sequence, coordinated by the cortex and modulated by the cerebellum. The bolus volume and viscosity will interfere with the muscular contraction intensity, defined by the cortex according to the oral qualification, to generate the necessary oral ejection.
Nevertheless, the contraction activation sequence of the effectors will be common to all sequences involving the oral phase, suggesting that the neural organization has a predefined sequence.
Taste and temperature do not exert influence on the oral muscular contraction intensity defined by the cortex. This observation means that, within limits of acceptability, chemical-reception, thermo-reception and certainly pain-reception do not interfere with the oral activity, which is governed by the mechanical reception, in particular volume and viscosity, which will affect the amount of motor units to be depolarized for an effective oral phase. The generation of the necessary and adequate muscular contraction intensity will be responsible for the information to be passed and maintained during the reflex phase of swallowing.
The pressure intensity transferred by the oral phase will be the stimulus to be answered to by the neural control of the reflex pharyngeal phase. The esophageal phase, also reflex, should be influenced at least partly by the oral phase 57 One can describe the basic dynamics of the swallowing oral phase as follows: The Dental arcades touch one another by chewing muscle contraction pair V. This dental arcades position allows skin-inserted muscles, in special buccinators and orbicularis oris pair VII , to generate intraoral pressure resistance to prevent pressure escape out of the oral cavity during the bolus transference to the pharynx.
The pressurized and resistant oral cavity will enable ejection of the bolus by the tongue pair XII , which will transfer pressure and bolus to the pharynx.
Still as part of the oral phase actions, the tensor veli palatini muscle pair V will provide resistance to the soft palate, which will be superiorly and posteriorly projected by the levator veli palatini muscle against the first fascicle of the pharynx superior constrictor muscle pterygo-pharyngeus fascicle at the beginning of the pharyngeal phase. The suprahyoid muscles elevate the hyoid and larynx, opening the pharyngeal-esophageal transition because it undoes the tweezers action between the vertebral body and larynx.
The elevation of the hyoid and larynx that acts by undoing of the tweezers action, produced by the apposition of the larynx against the spine is coordinated mainly by the cranial nerves V and VII and also by C1 through the ansa cervicalis. The hyoid elevation starts at the end of the oral phase, and stays active till the end of pharyngeal phase. Contraction of the longitudinal stylopharyngeus muscle IX will reduce the pharyngeal distal resistance. Finally, in the end of oral phase, by possible involvement of the respiratory center on the floor of the fourth ventricle in the brainstem, swallowing apnea preventive apnea takes place.
In sequence, but with an independent mechanism of apnea, beginning the pharyngeal phase, vocal folds adduction will occur. All the oral events remain active during the entire pharyngeal phase by assimilation of the reflex pharyngeal phase coordination 42 Rio de Janeiro: Elsevier; Coordination of respiration and swallowing: functional pattern and relevance of vocal folds closure.
Figure 2. FIGURE 2 Frontal view of schematic diagram over an anatomical specimen representing the neural control of the nutritional oral phase. Black, dotted lines represent the oral afferent pathways that pass through the 1 sensorial ganglion and connect with sensitive nuclei of the solitary tract and nerve V nuclei in the brainstem 2.
From there, they connect with the base nuclei 3 through direct and cross pathways. From the base nuclei 3 , in nutritious swallowing the signals stimulate the postcentral sensorial and precentral motor gyruses 4 , which start the efferent motor pathway. Note 1: Sensory pathways do not exist in the primary cortical voluntary oral phase.
Red, solid lines represent efferent motor pathways from the cortex to the base nuclei 3 and brainstem nuclei 2 where nerves V, VII, IX and XII conduct the stimuli modulated by the cerebellum to the oral effectors.
Note 2: In semiautomatic swallowing and while normality is maintained, motor responses are produced without cortical intervention. From the dominant hemisphere, there is an inhibiting pathway black, dashed line going to the opposite hemisphere and an excitatory pathway red, solid line and also to the base dominant nuclei to the non-dominant side. This type of oral phase reproduces all dynamic events observed in the nutritive oral phase of swallowing, without having any intraoral content to be qualified.
It happens as if the cerebral cortex imagined a bolus with such known features, that the efferent cortical motor area reproduces an oral ejection with the same characteristics and using the same efferent pathways that it would if that imagined bolus could be exposed to oral receptors. Thus, this type of neural control does not have, as an integral part, the afferent signaling coming from the oral receptors to the sensitive cortex. In this way, the sequence from the motor cortex to the oral effectors will be exactly the same 58 This type of neural control is a temporary substitute for the one that occurs during the nutritional swallowing process.
It replaces the voluntary control of the nutritional oral phase when, in a repetitive way, this has its parameters qualified and accepted as usual and within appropriate limits. In such cases, if the attention has been divided with another interest that demands cortical activity, swallowing control can be replaced by a semiautomatic control, which will be processed in subcortical level base nuclei.
Considering the proposed organization for the integration between base nuclei and cortex, we can hold that the base nuclei take control of the oral phase, maintaining its integrative activity, but repressing in their level the information brought from the periphery. Nevertheless, the base nuclei retain the ability to reactivate cortical control at any time, in particular if changes are detected 58 I believe that the dominant hemisphere controls this semiautomatic process from its base nuclei, also through corpus callosum, on the same way of the inhibitory control.
Subsequent gulps oral phase swallowing in subsequent gulps implies liquid intake that, in healthy individuals, demands depolarization of fewer motor units, because the necessary ejection force does not require too much effort.
The control of this oral phase type of swallowing is, at least for the first gulp, similar to the control of nutritional swallowing. Although the material to ingest is liquid, a proper qualification is necessary, since it may have characteristics unexpected or distinct from the appearance.
Taste, temperature and viscosity are assessed during the first gulp and, if accepted, go promptly to semiautomatic coordination, similar to that occurring in the nutritional diet. Like in nutritional swallowing, the resumption of the voluntary cortical control is immediate if desired or if any irregularity is perceived. Spontaneous oral phase is the swallowing that occurs to clarify oral cavity of the saliva produced and released in discrete volumes, but continuously.
These swallowing efforts generate a mechanical sequence similar to the other swallowing types with origin in the oral cavity. However, in some respect it is distinct in its trigger mechanisms. I believe that is possible to assume that this type of swallowing is due to the airways protective mechanism to prevent aspirations and compromising of the respiratory system.
It has been demonstrated that the saliva adsorbed to the mucous membrane is capable of lubricating the laryngeal vestibule and vocal folds without producing discomfort. Also, the resulting volume of accumulated saliva would be compressed between the vestibular folds and epiglottis tubercle during swallowing with the adduced vocal folds, resulting in return of the residual saliva to the pharynx 64 J Voice. It is possible to believe that spontaneous swallowing is a product of this physiological airways permeation.
The spontaneous swallowing that occurs repeatedly, being the individual awake or during sleep and in the absence of conscious control, seems to be the same semiautomatic swallowing observed in the nutritious swallowing sequence, though with a distinct trigger mechanism, probably related to airway protection.
Besides other functions, saliva is important in the chewing bolus preparation and in the lubrication of the mucous membranes to suitable transport. Saliva is produced in continuous volume and physical-chemical characteristics by the salivary glands, with mediation of parasympathetic fibers conducted by the cranial nerves VII facial and IX glossopharyngeal.
Spontaneous swallowing helps in the distribution of saliva over the oral, pharyngeal and even vestibular mucosa, humidifying these membranes and probably helping to maintain fluid the mucus over the laryngeal ventricles.
Inhalation and expiration dry the mucosa by the continuous airflow, and spontaneous swallowing keeps the moisture level of these mucous membranes. Spontaneous swallowing is also important for the control of small volume of liquids adsorbed to the laryngeal vestibule walls, removing any excess over this mucosa. During swallowing, with the adduced vestibule folds, the tubercle of the epiglottis presses against these folds, making the vestibule lumen virtual, expelling to the pharynx any excess existing there 58 The reflex pharyngeal phase takes place without voluntary control or direct cortical command.
This phase starts from the pharyngeal pressure stimulus transferred by the oral phase. In nutritional swallowing, after bolus qualification, in special in relation to volume and viscosity mechanoreceptors , the oral ejection will transfer the qualified information bolus and pressure to the pharynx. From there the perceived stimulus go to the brainstem solitary tract nucleus. In the brainstem, in special in the ambiguous nucleus, a motor reflex response will determine sequential muscle contractions in delay line based on the values qualified and transferred by the oral phase 58 Radiol Bras.
The effect of high- vs low-density barium preparations on the quantitative features of swallowings. Am J Roentgenol. Delay line is the contractile sequential muscular response of the muscles involved in the pharyngeal phase to a single pressure stimulus, which departs from the pharynx to the posterior sensory portion of the brainstem, and which returns to it via a ventral motor pathway, producing the sequential dynamics of the pharynx contractile activity.
Although there is no direct motor cortex influence on the pharyngeal phase, the transferred content can be perceived, for example, for its temperature. This kind of perception means that there is afferent sensitivity, possibly to provide the oral transfer with tolerance limits.
The stimulus that triggers the pharyngeal phase is not the contact produced by the passage of food through the pharynx 67 Pommerenke WT. A study of the sensory areas eliciting the swallowing reflex.
Am J Physiol. Glossopharyngeal evoked potentials in normal subjects following mechanical stimulation of the anterior faucial pillar. In nutritional swallowing, food and pressure are transferred, but in cortical swallowing, only pressure is, and the pharyngeal response is similar to that of nutritious swallowing, indicating that the pressure distending the pharyngeal walls is the element that stimulates the pharyngeal motor activity 58 The pharyngeal distention pressure is identified and transferred to the brainstem through sensitive afferent fibers of the pharyngeal plexus cranial nerves IX, X, XI.
The glossopharyngeal IX nerves in the oropharynx and vagus and accessory X and XI in the laryngopharynx carry to the brainstem dorsal region solitary tract nucleus - sensitive the stimulus based on the pressure value transferred from the oral cavity to the pharynx. A unique stimulus reaches the solitary tract nucleus, and motor reflex response is composed by a sequential action of several muscles in different times, configuring muscular sequential contraction in delay line.
It is reasonable to admit a cerebellum modulation over the pharyngeal reflex responses determined by the brainstem, explaining the sequential muscular contraction in the pharyngeal phase delay line. Among its main functions, the cerebellum coordinates the temporal sequence of the synergic contraction of the different skeletal striated muscles, with the possibility to generate delay of the motor signals by fractions of a second, creating delay in the muscle contraction sequence 1 1. In a didactic way, and not failing to admit the possibility of a delay line control by inhibitory neurotransmitters, we have considered that the sensory-motor connection in the brainstem would be carried out by distinct amounts of synapses between interneurons connecting sensitive and motor nuclei, generating different transfer times between the solitary tract nucleus to the ambiguous one.
Thus, a stimulus perceived by the pharyngeal receptors and transmitted to the solitary tract nucleus as unique would be retransmitted to the ambiguous nucleus, passing by a different and increasing number of interneurons, configuring the delay line observed in the swallowing pharyngeal phase.
Besides the sequence and intensity of muscular contraction determined by the brainstem from pressure reception, the pharyngeal phase incorporates or assimilates, as its functional part, the oral phase developments already in course. The oral phase incorporated elements and the pharyngeal phase will end together. Therefore, the brainstem, during the pharyngeal phase, integrates the sequence of the oral phase with the pharyngeal one. The pharyngeal phase starts by action of the pharyngeal plexus, composed of the glossopharyngeal IX , vagus X and accessory XI nerves, with secondary involvement of the trigeminal V , facial VII , glossopharyngeal IX and the hypoglossal XII , and also some elements of the cervical plexus C1, C2.
The cervical plexus and the hypoglossal nerve on each side form the ansa cervicalis , from which a pathway goes to the geniohyoid muscle, one of the muscles that act in the elevation of the hyoid-laryngeal complex 58 The accessory XI nerve, not always considered among those associated with swallowing, is admitted as having special visceral efferent motor fibers originating from the ambiguous nucleus that would follow associated with the vagus nerve, which would also display this type of fiber 1 1.
Thus, the accessory XI nerve is also responsible for the motor innervation of the musculature of the palate, pharynx, larynx and esophagus, in association with the vagus nerve. The pharyngeal phase shows adjustment, over the tongue on each side, of the palatoglossal muscle, innervated by the motor portion of the pharyngeal plexus X, XI to prevent pressure from returning to the oral cavity.
The tension V and elevation of the palate X, XI against the first fascicle pterygo-pharyngeal of the upper constrictor muscle of the pharynx, innervated by the cranial nerves X and XI, blocks the possible pressure escape from the oropharynx to the rhinopharynx. The superior, middle and inferior constrictor muscles of the pharynx are each one constituted of distinct parts, with individualized insertions.
Each one of these parts is inserted in one side in anterolateral fixed points, and in the other, in the posterior median line of the pharynx pharyngeal raphe. As a consequence of the individualization of their motor units, they can contract in sequential mode. The superior constrictor muscle has four parts pterygopharyngeal, buccopharyngeal, mylopharyngeal and glossopharyngeal , the middle, two parts chondropharyngeal and ceratopharyngeal , and the inferior, two parts thyreopharyngeal and cricopharyngeal.
Between the two fascicles of the cricopharyngeal muscle, there is an anatomically less resistant area due muscular absence 72 Anatomy of the human body. Philadelphia: Lippincott; The four parts of the superior constrictor occupy the entire extension of the oropharynx. Thus, it is necessary that only the first portion of its superior pterygopharyngeal part perform apposition against the palate, isolating and preventing pressure escapes from the oropharynx to the rhinopharynx.
In the same time, the oral pressure can pass to the pharynx without resistance. With closing of the pharyngeal contiguous cavities except for the pharyngeal-esophageal transition, which opens as a result of the elevation of the hyoid and larynx, there is a constrictors muscle contraction generating a pressure sequence in the cranial-caudal direction.
This pressure sequence displaces the transient bolus from the pharynx to the permissive, less resistant esophagus by the opening of the pharyngeal-esophageal transition 42 By definition, peristalsis is a sequential expression produced by a muscle circular layer. In this way this cranial-caudal pressure sequence with distal less resistance without muscle circular layer should not be considered as peristalsis or peristalsis like as is often defined.
The suprahyoid muscles are innervated by the cranial nerves V and VII and by the C1 cervical plexus, connected via ansa cervicalis with the hypoglossal nerve. The mylohyoid branch of mandibular nerve mixed root of trigeminal - V innervates the mylohyoid and the anterior belly of the digastric muscles; the posterior belly of the digastric and the stylohyoid muscles, by the facial nerve VII.
The geniohyoid and thyrohyoid muscles are innervated by ansa cervicalis usually C1 through the hypoglossal XII nerve. The cervical plexus usually C2 through the ansa cervicalis innervate the other infrahyoid muscles. The suprahyoid muscle group is responsible for the forward and upward movement of hyoid and larynx, with modulation by the infrahyoid group.
This action moves the larynx away from the vertebral body and opens the pharyngeal-esophageal transition. Moreover, while moving the larynx away, the suprahyoid group is able to sustain this open condition depending on the bolus volume and viscosity. The opening of the pharyngeal-esophageal transition is also enhanced by the contraction of the longitudinal pharyngeal muscles, the stylopharyngeal ones, innervated by the glossopharyngeal IX nerve, and the palatopharyngeal muscle, innervated by motor fibers from cranial nerves X and XI 42 Still in the oral phase, as a last act, a preventive apnea swallowing apnea ensues, being assimilated by the pharyngeal phase and remaining until its end.
Associated with the airways resistance produced by apnea, there is independent vocal folds adduction X, XI , followed by closure of the vestibular folds with the bolus passage through the already open pharyngeal-esophageal transition. The adduction of the vestibular folds is due to the compression of the pre-epiglottic fatty cushion produced by the elevation of the hyoid and larynx, which compresses this cushion contained in the pre-epiglottic fibrous space. This space has, as its point of least resistance, the lateral aspects of the tapered end of the epiglottis, which corresponds to the projection of the vestibular folds on both sides.
Thus, the compression produced by this fatty cushion on the sides of the epiglottis causes the medial shift of the vestibular folds, which end up in apposition against the epiglottis tubercle. On its turn, the epiglottis, everted by the tongue, moves posteriorly, adjusting its tubercle against the now adduced vestibular folds 59 Figure 3.
FIGURE 3 Neural control representation of the pharyngeal phase over anatomical specimens where 1 - oral cavity, 2 - pharynx, 3 - esophagus, 4 - swallowed bolus, 5 - brainstem, X - pharyngeal receptors, 6 - solitary tract nucleus, 7 - Ambiguous nucleus.
Over 5, lower dotted arrows from six to six - afferent integration, and upper dotted arrows from six to seven - efferent integration. From 6 sensitive nucleus to 7 motor nucleus , multi-dotted arrows are a didactic representation of the growing number of interneurons of the delay line. From 7 ambiguous nucleus to a, b, and c on both sides, dashed arrows represent the efferent stimulus to muscle delay line.
There is pressure transference from 1 to 2 pharyngeal distention , represented by widening of 4. Hollow arrowheads show displacement of the bolus 4 from mouth to esophagus. The pharyngeal and esophageal phases, both reflex, present anatomical and functional relation.
The firsts 10 cm of the esophagus are formed by skeletal striated muscle, like the oral and pharyngeal ones. In the distal extremity of this striated segment, by 2 or 3 cm, a muscular distinction is identified macroscopically in fresh anatomical specimens, which is microscopically defined as a mixture of skeletal striated muscle long and multinucleated fibers and fibers of smooth muscle short and mono-nucleated , where the first ganglion of the myenteric plexus appears 73 Figure 4.
B - histological specimen obtained from A , with 1 first ganglion of the myenteric plexus and mixture of long and multinucleated striated muscle fibers 2 and short and mono-nucleated smooth ones 3.
The high-pressure zone designated as the upper esophageal sphincter is located at the distal pharynx, where a tweezer action closes the pharynx between the larynx cricoid cartilage and the cervical lordosis at the level of the 5th to 6th cervical vertebrae.
Usually this high pressure is considered as due to the maintained contraction of the cricopharyngeal muscle, part of the inferior pharyngeal constrictor. This conception is a severe misunderstanding about the anatomical and functional characteristics of this region. The inferior constrictor of the pharynx is a skeletal striated muscle consisting of two fascicles thyropharyngeal and the cricopharyngeal.
The cricopharyngeal fascicle presents two parts of fibers in its organization, an upper, oblique and a lower, transverse. The upper one inserts on each side of the cricoid cartilage, from where its fibers go from the bottom upwards and from lateral to medial, inserting on the posterior pharyngeal raphe.
The lower or transverse part inserts on each side of the cricoid cartilage, with a transverse direction, intercrossing in the midline, where the raphe cannot be seen. The width of the pharyngeal lumen at the level of the transverse cricopharyngeal part is about 17 mm and there is not muscular ring in this region, which can be described as a muscular half-curvature. This anatomically less resistant area is coincidentally the point of higher-pressure values, certainly due to the tweezer action produced by the vertebral body and the larynx 65 Figure 5.
FIGURE 5 Posterior view of anatomical specimen involving the pharynx, larynx, esophagus and trachea, where 1 - Cricopharyngeal muscle, oblique fascicle, 2 - Cricopharyngeal muscle, transverse fascicle, inserted on the larynx cricoid cartilage, 3 - Kilian zone, the anatomically less resistant zone on the posterior pharyngeal wall where the pharyngeal diverticulum described by Zenker occurs.
This less resistant zone is due to the divergence of the oblique and transverse fascicles of the cricopharyngeal muscle.
The cricopharyngeal muscle has been known as a skeletal striated muscle type that demands expressive consumption of ATP adenosine triphosphate , because it depends on ATP both to contract and to relax.
In order to demonstrate that the cricopharyngeal muscle is not contracted at rest, only to relax when the pharyngeal-esophageal transition opens, as believed by many, we performed manometry of the pharyngeal-esophageal transition. This manometry was carried out with a balloon built with a latex glove finger to measure the positive pressure resistance of the pharyngeal-esophageal transition of 12 fresh corpses, in the first 6 to 12 hours postmortem. The balloon traction shows that positive pressure values remain present on the pharyngeal-esophageal transition in all studied fresh corpses.
A second pressure verification, with insertion of a metallic prosthesis between the vertebral body and the larynx, shows absence of resistance in this region, where the prosthesis eliminates the tweezer mechanism of the larynx against the vertebral body. Based on the positive values observed in the first measure and absent in the second, with the prosthesis insertion, we concluded that resistance on the pharyngeal-esophageal transition is dependent on the tweezer action of the larynx against the vertebral body.
Figure 6. Manometry on a fresh corpse. Scheme highlighting a - pharynx between tweezer formed by vertebral body and larynx that compresses the pharynx at rest, b - elastic and distensible balloon, and c - sphygmomanometer. After verification of basal pressure positive in all 12 cases , cervical dissection for passage of a metallic prosthesis separating the larynx from the spine. Prosthesis installed for re-verification absence of positive pressure in all 12 cases.
In two cricopharyngeal muscles, we also carried out electric stimulation, including analysis of tolerance to calcium pump inhibitors verapamil and polyacrylamide gel electrophoresis with dodecyl sodium sulfate paired with other striated muscles. We obtained these two cricopharyngeal muscles from specimens immediately resected from total laryngectomies, with surgical indication and consent.
These muscles showed the same characteristics of other striated muscles under electric stimulation, including their tolerance to calcium pump inhibitors. The electrophoresis paired with other striated muscles revealed the same protein patterns and molecular weights. These two experiments allow the conclusion that the cricopharyngeal muscle has morphology and function of a striated muscle.
Figures 7 and 8. On top, the polygraph used. The first bar shows constant increase of the contraction force as the stimuli intensity Volts increases.
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