Group 10
Members: Julie, Tim, Thu-Huu
e-Facilitator: Cathy

The_Gag_Reflex.jpg

Learning Outcomes


  • Define what a reflex is, and why they are present in a healthy person
  • Describe the anatomical features involved in the gag reflex
  • Describe the physiological mechanisms which occur that generate the response
  • Anatomy and physiology of swallowing
  • Discuss why the gag reflex is present in a healthy person - and the implications of the absence of a gag reflex
  • List and discuss the strategies which can be implemented by a dental operator to alleviate symptoms in a gagging patient.


I've been searching PubMed and MeSH and have stumbled across some interesting stuff. I will post the relevant info over the next few days! One is: "Palatal and pharyngeal reflexes in health and in motor neuron disease." Also, this site: http://www.csuchico.edu/~pmccaffrey/syllabi/SPPA342/342unit3.html - will be an interesting read I think.
http://www.aafp.org/afp/20000415/2453.html - Evaluation and Treatment of Swallowing Impairments
http://www.dental--health.com/gagreflex_involuntary.html - managing the gag reflex

CONTENTS
1. Reflexes
2. Anatomy/Physiology of Swallowing
3. Gag Reflex (Anatomical Features)
4. Generation of Gag Reflex
5. Why Have a Gag Reflex?
6. Preventing Gag Reflex
7. Abnormalities
References


1. Reflexes

Reflex: Predicted response to a known stimuli
Why do we need reflexes?
Nervous responses occur automatically and rapidly to act as a safety precaution. Assessing reflex responses is a vital utensil in determining the state of the nervous system. An unpredictable ('exaggerated, distorted or absent') reflex response can indicate nervous system disorders (Hoehn & Marieb, 2007)

Two types of reflexes exist :
Autonomic reflexes: responsible for controlling smooth muscles, the heart and glands activity.Other body activities regulated by autonomic reflexes include digestion, waste removal, blood pressure and sweating.
Examples: change in pupil size and saliva secretion

Somatic reflexes: control the skeletal system in attempt to avoid danger. e.g removing hand away from a flame.


Sensory receptors are specialised to respond to changes in the environment ie, stimuli.
Classifying sensory receptors: 1. stimulus type, 2. location and 3. structural complexity
1. a) Mechanoreceptors generate nerve impulses when they, or adjacent tissues, are deformed by mechanical force such as touch, pressure, vibration and stretch.
b) Thermoreceptors are sensitive to temperature changes
c) Photoreceptors such as those of the retina of the eye, respond to light energy
d) Chemoreceptors respond to chemicals in solutions (molecules smelled or tasted, or changes in blood and intenstinal fluid chemistry)
e) Nocireceptors respond to potentially damaging stimuli that result in pain.

2. a) Exteroreceptors are sensitive to stimuli arising outside the body, so most exteroreceptors are near or at the body surface.
b) Interoreceptors also called visceroreceptors, respond to stimuli within the body.
c) Proprioceptors like interoreceptors, respond to internal stimuli; however, their location is much more restricted. Proprioceptors constantly advise the brain of our body movements.

3. a) Simple receptors are modified dendritic endings of sensory neurons. They are found throughout the body and monitor general sensory information.
b) Complex receptors are usually sense organs, localised collections of cells associated with special senses (vision, hearing, equilibrium, smell, and taste).

(Hoehn & Marieb, 2007)

Our survival depends upon sensation (awareness of changes in the environment) and perception (conscious interpretation of those stimuli). Perception determines how the stimulus will be responded to.

reflex_arc.jpg
Figure 1: Neurons involved in generating a reflex response (Hoehn & Marieb, 2007)



2. Anatomy and Physiology of Swallowing

The key purpose of swallowing is to transport food and liquid down through to the stomach from the mouth, in a manner which the airway is protected from potentially dangerous ingress of food and liquid (Miles, Nauntofte & Svensson, 2004).

The movement of food from the mouth to the stomach is by the action of swallowing, or deglutition (Guyton & Hall, 2006). For deglutition to occur, it involves the mouth, pharynx, oesophagus and the secretion of saliva and mucus. There are three stages that occur when swallowing come into play:

Stage 1: The oral preparatory phase, a voluntary stage where the bolus (food that has been chewed and coated with lubricating mucous from salivary glands) is forced back into the oral cavity and is passed into the oropharynx by the movement of the tongue. For swallowing to initiate, the mandible is stabilized by bringing the teeth together, and generally the lips seal (Miles, Nauntofte & Svensson, 2004). The tip of the tongue is then pushed against the hard palate to push the bolus down towards the pharynx aided by the buccinator muscles (Miles, Nauntofte & Svensson, 2004). This is the only stage which can be voluntarily interrupted (Miles, Nauntofte & Svensson, 2004).

Stage 2: The pharyngeal phase (an involuntary stage) is where the bolus stimulates receptors whilst in the oropharynx and sends impulses along the glossopharyngeal and vagus nerves (Tortora & Derrickson, 2006). These nerves then move down to the deglutition centre located in the medulla oblongata and the lower pons of the brain stem (Tortora & Derrickson, 2006). The motor responses of this stimulation causes the soft palate and uvula to move upward to close off the nasopharynx, therefore preventing foods or liquids from entering the nasal cavity. At the same time, the epiglottis closes the opening of the larynx to prevent the bolus from entering the respiratory tract. Entry to the larynx is pulled up towards the pharynx (by the mylohyoid, thyrohyoid and geniohyoid muslces) to a state which the bolus is less likely to enter (Tortora & Derrickson, 2006). The bolus is then passed through the pharynx and heads towards the oesophagus. As the pharyngo-oesophageal sphincter muscle opens, the bolus can enter the oesophagus. Once the bolus passes, as the associated skeletal muscles relax, the epiglottis and entrance to the nasal cavity and trachea are re-opened to resume breathing. The sequence in which associated muscles are activated is crucial in preventing the bolus from entering the airway.

Stage 3: Finally the oesophageal stage, which is an involuntary passage of the bolus being pushed downwards via the action of peristalsis. According to Tortora and Derrickson (2006), Peristalsis is the process in which waves of contractions and relaxations of the circular and longitudinal layers of the muscularis cause the downward movement of the bolus. Superior to the bolus is circular muscle fibres that contract, therefore constricting the oesophageal wall and squeezing the bolus towards the stomach, entering into the opening of the gastro-oesophagus spincter muscle. There is always constant contraction that pushes the food into the stomach.


swallow_1.gif
Figure 2: Steps involved with the action of swallowing (http://www.abe.ufl.edu 2009 )
The latest research on swallowing suggests that the action of the pharyngeal constrictor muscles is not the most critical factor in the movement of food down the pharynx. It seems that the plunger action of the tongue plays a major role in this process (McCaffrey 2008).

In the past, swallowing was classified as a reflex itself. Now most sources agree that swallowing is a pattern-elicited response.

Both sensory and motor information are necessary for the initiation of the swallow response; swallowing is dependent on sensory and motor control or on information from both afferent and efferent systems. Sensory input involved in the initiation in the swallow comes from the trigeminal, facial, and glossopharyngeal nerves. Information about motor movement is received from the muscle spindles in the tongue via the hypoglossal nerve (McCaffrey 2008).
Sensory and motor information from these sources is carried to the swallowing center, which is believed to be located in the medulla. When the swallow response is initiated, this center causes messages to be sent to the glossopharyngeal, the vagus, and the hypoglossal nerves. The glossopharyngeal is considered the major nerve for the swallowing center (McCaffrey 2008).
Six of the cranial nerves provide the innervation for both swallowing and speech (McCaffrey 2008).
1. CN. V The Trigeminal Nerve
2. CN. VII The Facial Nerve
3. CN. IX The Glossopharygeal Nerve
4. CN. X The Vagus Nerve
5. CN. XI The Spinal Accessory Nerve
6. CN. XII The Hypoglossal Nerve


54244-004-892C5169.jpg Figure 3: The 12 Pairs of Cranial Nerves and corresponding innervated tissues (Encyclopedia Britanica, 2007)


3. The Gag Reflex

The Cranial Nerves involved in this reflex is Nerve IX and Nerve X, the Glossopharyngeal Nerve and the Vagus Nerve, respectively (Larner HJ 2002).
Fibres emerge from medulla and leave skull via jugular foramen to run to throat.

glossopharyngeal_nerve_9.jpg
Nerve IX
vagus_nerve_10.jpg
Figure 4: Location of the Glossopharyngeal Nerve (IX) and Vagus Nerve (X) (http://www.clinicalexams.co.uk/cranial-nerves-system.asp)





4. Physiological Mechanisms Which Occur to Generate The Gag Reflex

The gag reflex is completely controlled by the brain stem. Induced by the stimulation of the pharyngeal and the soft palate, once an object such as a finger or debris (often a noxious substance, but not always) comes into contact with the base of the tongue, soft palate, uvular or posterior pharyngeal wall, the pharynx becomes constricted (McCaffrey 2008). This is often referred to as the ‘gag reflex’ and acts in attempt to prevent unwanted materials from entering the pharynx. Other actions followed by the constriction of the pharynx include “lowering of the mandible, forward and downward movement of the tongue, and pharyngeal and velar constriction associated with mild coughing”





5. Why The Gag Reflex is Present In A Healthy Person?

The gag reflex is present in a healthy person to prevent foods or other things from entering the throat in order to prevent choking.

Implications of The Absensce of A Gag Reflex

The gag reflex or ‘pharyngeal reflex’ involves the glossopharyngeal nerve (cranial nerve IX), the absence of gag reflex can be due to many medical conditions, such as damage to the glossopharyngeal nerve, the pneumogastric nerve or vagus nerve (cranial nerve X) or even brain death.

Children who struggle with chewing and swallowing may also experience gagging more easily than others. Children who suffer from delayed motor skills have difficulty chewing and often swallow food before the texture is ready to be swallowed ( Miles T, Nauntofte B & Svensson P, 2004).

A person without a gag reflex has a greater risk of swallowing a potentially harmful substance or choking. Food that has past its use-by date, which can harbour bacteria, mould or exhibit other unpleasant features could be taken down unknowingly. Even small objects (coins, wrappings on foods) can be ingested as the there would be no reflex to shut off the pharynx.




6. Strategies to Alleviate Symptoms In A Gagging Patient

Dental professionals will frequently come into contact with patients who are highly apprehensive and frightened by unknown procedures and may exhibit the gag reflex. As dental procedures such as radiography and alginate impressions come into close proximity with the areas associated with the gag reflex, operators should possess some knowledge on strategies avaliable to reduce symptoms. Generally, simple tactics can be implemented to assist their patient in feeling more comfortable and avoiding the gag reflex from occurring.

During radiography:

  • The operator must ensure that care is taken whilst placing the film in the oral cavity as patients with highly sensitive tissues can precipitate the gag reflex. During film placement, ensure that the patient's tongue is relaxed and positioned well on the floor of the mouth. Before asking the patient to open their mouth, ask them to swallow deeply and avoid mentioning their tongue as this can cause patient to be more conscious about their tongue placement (Langland, Langlais & Preece, 2002).
  • Minimize the number of attempts made to adjust the film, ensure the film packet is placed flat in the mouth. Sliding the film along the palate/tongue can stimulate the gag reflex (Whaites, 2002).
  • Manage time effectively, the longer the film remains within the oral cavity, the chances of the gag reflex occurring increases (White & Pharaoh, 2004).
  • Utilizing a Dentsply/Rinn Snap-A-Ray (film holder for posterior and anterior regions of the mouth) has been discovered to be effective for patients with a hypersensitive gag reflex (Langland, Langlais & Preece, 2002)

Methods of Distraction and Relaxation:

  • Encourage the patient to focus on breathing (rapidly) through their nose. If the patient is experiencing difficulty breathing through their nose, a nasal spray can be utilized to clear the nasal passageways. Alternatively, other methods of distraction include holding their breathe or suspending a foot or arm in the air for the duration (Whaites, 2002).
  • Placing table salt on the patient's tongue (tip and body has been discovered to be successful for some operators).
  • Application of topical gel (via cotton bud) on the palate and back of tongue, this way when something comes into contact with the base of the tongue, soft palate, uvular or posterior pharyngeal wall, it is not detected and as a result the pharynx will not constrict. If possible, have the patient gargle on a suitable local anaesethtic solution or suck on a local anaesthetic lozenge (Whaites, 2002).
  • Provide a calm environment by playing music and discuss the steps to the patient to minimize and clarify their fears.
  • Relax and reassure the patient and increase their confidence in the operator by demonstrating technical competence and confidence in the dental procedure (White & Pharaoh, 2004).
  • Display compassion for the patient (White & Pharaoh, 2004)
  • Ensure the patient is well rested. Arrange appointments earlier in the morning to avoid fatigue which can make the gag reflex more sensitive, especially in children (White & Pharaoh, 2004).
  • Hypnosis if simpler means are ineffective

Sedation:
An excellent way to quell this exaggerated gag reflex is through sedation dentistry (Dental Health Directory 2009). The administration of Oral or I.V. sedation enables patients suffering from this problem to be helped easily and comfortably. Conscious Sedation can control and eliminate the gag reflex response to almost any number of stimuli or conditions that elicit this involuntary behavior (Dental Health Directory 2009). The sedation medications help the patient achieve a state of total relaxation. They can stand hours of dentistry easily and comfortably with little memory of the appointment.

Some of the popular sedation methods used by patients with severe gag reflex responses are (Dental Health Directory 2009):

  • Nitrous Oxide
  • Benzocaine spray can be used to briefly numb the gag reflex areas for simple things like taking x-rays or taking an impression. The back of the throat stays numb long enough for most people to get through these procedures. For severe cases it may not work.
  • Oral sedation with the Benzodiazepine medications like Valium or Halcion can greatly reduce the gag reflex response.
  • I.V. sedation medications such as Versed or Fentanyl are also effective for eliminating the gag reflex.

Although patients will have unique responses to the different types of sedation methods used, the gag reflex can be efficiently controlled. The sedation medications not only eliminate the response but allows the pleasant perception of time passing quickly with little or no memory of treatments performed.

The following link connects to dentalfearcentral.com, where dental practitioners discuss their personal opinions and individual strategies to reduce the gag reflex
http://www.dentalfearcentral.org/gagging_dentist.html


7. Gag Reflex Abnormalities

  • Basilar artery occlusion. Basilar artery occlusion may suddenly diminish or obliterate the gag reflex.
  • Brain stem glioma. Brain stem glioma causes a gradual loss of the gag reflex.
  • Bulbar palsy. Loss of the gag reflex reflects temporary or permanent paralysis of muscles supplied by Cranial Nerves IX and X.
  • Wallenberg's syndrome. Paresis of the palate and an impaired gag reflex usually develop within hours to days of thrombosis.
(American Academy of Family Physicians 2000)





References:

American Academy of Family Physicians 2000, Evaluation of Treatment of Swallowing Impairments, viewed August 20 2008, http://www.aafp.org/afp/20000415/2453.html

Arthur C. Guyton & John E.Hall, 2006, Textbook of medical physiology (11th Edition), Elsevier Saunders, United States.

Dental Health Directory 2009, Involuntary Gag Reflex, Viewed August 20 2008,http://www.dental--health.com/gagreflex_involuntary.html

Encyclopedia Britanica Online, 2007, Cranial Nerve, viewed October 5, 2009
http://www.britannica.com/EBchecked/topic/141797/cranial-nerve

Gerard J Tortora & Bryan Derrickson, 2006, Principles of anatomy and physiology (11th Edition), John Wiley & sons, United States.

Hoehn K, Marieb E.N, 2007, Human Anatomy and Physiology (7th Edition), Pearson Benjamin Cummings, California, USA

Langland O.E, Langlais R.P & Preece J.W, 2002, Principles of Dental Imaging (Second Edition), Lippincott Williams & Wilkins, United States of America

Larner HJ 2002, A Dictionary of Neurological Signs, Kluwer Academic Publishers, Netherlands

McCaffrey P 2008, Anatomy of the Swallow, viewed August 20 2008,
http://www.csuchico.edu/~pmccaffrey/syllabi/SPPA342/342unit3.html

Miles T, Nauntofte B & Svensson P, 2004, Clinical Oral Physiology, Quintessence Publishing Co. Ltd, Copenhagen

Swallowing 2009, Physiology of Swallowing, viewed September 20th, http://www.abe.ufl.edu/~owens/age2062/OnLineBiology/OLBB/www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookDIGEST.html

Syrimis Andreas 2008, Clinical Exams, viewed September 10th, http://www.clinicalexams.co.uk/cranial-nerves-system.asp

Whaites E, 2003, Essentials of Dental Radiograhy (3rd Edition), Churchill Livingstone, USA.

White S & Pharoah J, 2004, Oral Radiology - Principles and Interepretation (5th Edition), Mosby Inc, Missouri.

Wrong Diagnosis 2009, Gag Reflex Abnormalities, viewed September 14th, 2009
http://symptoms.wrongdiagnosis.com/cosymptoms/gag-reflex-abnormalities.htm