swallowing disorders in infants, children, and adults

SWALLOWING DISORDERS IN INFANTS, CHILDREN, AND ADULTS

NEUROPHYSIOLOGY OF SWALLOWING

Normal Aerodigestive Tract Anatomy

Anatomical Orientation

The evolution of human anatomy has produced a system in which the structures of speech, swallowing, and respiration are shared.

The major systems involved in the aerodigestive tract include:a. The Oral Systemb. The Pharyngeal Systemc. The Laryngeal Systemd. The Esophageal Systeme. The Respiratory System

The Oral System

The cheeks, hard and soft palates, lips, and tongue form the oral cavity, which aid in mechanical digestion.

The vestibule is the space between the cheeks and lips and teeth and gums.

The oral cavity proper extends from the vestibule to the fauces.

The oral system is composed of both rigid and flexible tissues.

Rigid elements include the teeth, mandible and maxilla, temporo-mandibular joint (TMJ), and hard palate.

The Oral System

In addition, the oral system contains multiple major and minor glands, other soft tissues including mucosa, and an elaborate array of vascular and nervous tissue.

These components function to serve both nutritive and nonnutritive oral functions.

All of these component parts must operate in harmony for function to be optimal.

Maxillae and Mandible

Whereas the maxilla is the stable member of the jaws, the mandible is the moveable part.

The maxilla is fused to the skull and to move the maxilla one must move the entire head.

Portions of the maxilla form the hard palate, and provide for a physical separation of the oral from the nasal cavities.

The hard palate also serves as a surface against which the tongue pushes to propel the bolus into the pharynx in preparation for swallowing.


On the other hand, the mandible attaches to the skull via the temporomandibular articulation and a sling of muscles.

TMJ articulation is a complicated hinge and glide articulation.

Mandibular movements involve the entire mandible and the points of the movement are the TMJs.

As one side of the mandible moves, the opposite side must move accordingly.


Mandibular movements, dictated and limited by the TMJs, the muscular sling, and the occlusion of the teeth, may be classified as masticatory and nonmasticatory.

The masticatory movements are the ones necessary for the manipulation and chewing of foods, whereas the nonmasticatory movements entail all other normal and abnormal movements used in speech and oral-facial habits.

Teeth

Humans have two sets of dentition: an initial deciduous, or primary set, which is unerupted yet well developed at birth; and a secondary or permanent set, which are developing in the dental arch at the time of birth and while the deciduous teeth emerge.

Clinical eruption of the primary teeth begins before the age of 12 months and continues until approximately 24 months.

Teeth

Shedding of the primary arch begins around age 6-7 years and continues until the age of 11 or 12 years, when the full complement of permanent teeth has erupted.

The adult dental arch as 4 types of teeth, each type differs in appearance and reflects their divergent functions: o the incisors (4 central and 4 lateral);o the canines (4);o the bicuspids (8); and o the molars (12).

Teeth

The diet of primitive humans necessitated a greater reliance on incisors and canines for cutting and tearing foodstuffs prior to ingestion.

In the modern diet of highly processed foods, incisors and canines retain their utility for turkey legs, carrot sticks, lengths of thread, cookies, tortilla chips, etc.

The human diet also requires significant amounts of grinding.

The bicuspids and first molars perform the main portion of heavy grinding, and loss of these teeth severely impairs chewing ability.

Muscles of Mastication

As a group, the muscles of mastication are responsible for the actions of the mandible in chewing.

They are all innervated by the Vth trigeminal cranial nerve.

Temporalis Muscle

The temporalis muscle is a large fan-shaped muscle originating from the temporal fossa of the skull.

It inserts in the ramus and coronoid (anterior) process of the mandible.

Its muscle fibers are long and parallel and assist in elevating the mandible and in maintaining the mandible in place during inactivity.

Masseter Muscle

The masseter muscle stretches in a rectangular plate from the zygomatic arch to the outer surface of the mandible ramus.

It elevates the mandible for crushing and grinding movements of chewing and provides stable closure during the swallowing pattern.

Internal Pterygoid Muscle

The internal (medial) pterygoid muscle is a rectangular-shaped muscle found deep to the masseter muscle.

It originates in the pterygoid fossa of the sphenoid bone and inserts in the ramus.

It is a weaker counterpart to the masseter and helps elevate the mandible in unity with the masseter and the temporalis muscles.

External Pterygoid Muscle

The external (lateral) pterygoid muscle is a short, thick, pyramidal-shaped muscle running on a horizontal plane along the upper part of the mandible.

It originates in the pterygoid fossa of the sphenoid bone and inserts in the condyloid (posterior)process.

External Pterygoid Muscle

Because the mandible is only hinged at the condyloid process, when this muscle contracts, it releases the hinge and the coronoid process is swung forward and downward in an opening movement.

It is also responsible for side-to-side grinding action in rotary chewing by alternating contraction and relaxation on each side of the mandible.

The Tongue

The tongue is an extremely complex structure composed of intrinsic and extrinsic musculature.

It is connected to the hyoid bone, soft palate, pharynx, and epiglottis, but its anterior, lateral, and superior borders are not connected.

The Tongue

The tongue is composed almost entirely of muscle fibers going in all directions.

The muscles are all paired with the exception of one.

The tongue has extensive vascular and neural supply to allow it to perform very precise movements patterns necessary for the production of intelligible speech and for bolus preparation and transport.

The Tongue

The oral tongue includes the tip, blade, front, center, and back, ending at the circumvallate papillae.

The papillae add texture, increase the surface area, and assist with taste perception and the preparing of foods for digestion.

The Tongue

The oral tongue is active during speech and during the oral stage of swallow.

It is under voluntary neural control.

The pharyngeal tongue, or tongue base begins at the circumvallate papillae and extends to the hyoid bone.

The Tongue

The hyoid bone forms the foundation of the tongue, the body of which sits on the hyoid.

The hyoid bone is embedded in the base of the tongue and articulates with no other bone.

The Tongue

The pharyngeal tongue is active during the pharyngeal stage of swallow.

It provides anchoring during hyoid elevation and upper esophageal sphincter opening.

It is under involuntary neural control.

The Soft Palate

The soft palate, or velum, has dual sphincter functions in both speech production and swallowing.

At rest, when it is fully relaxed and resting on the tongue base, it acts to divide the oral and pharyngeal cavities.

The Soft Palate

This state is found during the production of nasal sounds, and during the oral phase of swallowing.

It can also be pulled down and forward against the back of the tongue by the palatoglossus muscle of the anterior faucial arch.

The Soft Palate

For non-nasal sound production and during the pharyngeal phase of swallowing, the soft palate elevates and divides the nasopharynx from the oropharynx.

Elevation and retraction for velopharyngeal closure is achieved by a combination of muscles.

The Soft Palate

The muscle involved in velopharyngeal closure include the palatopharyngeal muscles of the posterior faucial arch, the levator veli palatini muscles, and the fibers of the superior pharyngeal constrictor muscles.

Oral Mucosa

Lining the inside of the mouth, and continuous with the lining of the pharyngeal spaces, is the oral mucosa.

This mucosa is similar in function to the skin that covers the outer body in that it is the first line of defense against infections of the mouth.

Oral Mucosa

The oral mucosa is made of three distinctly different types of cells, giving specific function to different areas within the mouth.

The more keratinized tissues with heavy underlying connective tissue firmly attach to bone.

Oral Mucosa

They provide protection to some areas of the gingiva and mucosa of the hard palate.

Mucosa that is less keratinized and lacks the underlying thick connective tissue covers the other areas of the gingival of the gums, cheeks, and floor of the mouth.

Oral Mucosa

Very specialized mucosa covers the dorsum of the tongue.

Here taste receptors are abundant and are composed of many different specialized cells types.

Taste receptors are also located throughout other soft tissues of the mouth.

Vestibule

The vestibule is bounded externally by the cheeks and lips and internally by the gums and teeth.

Soft tissue pockets are created by the normal juxtaposition of structures in the oral cavity.

In patients with swallowing disorders, food or liquid collects frequently in these natural cavities and may remain after the swallow.

Vestibule

The soft tissue pockets of the vestibule are the lateral sulci, between the alveolus and the cheek, and the anterior sulci, between the alveolus and the lip musculature, both superiorly and inferiorly.

Vestibule

The cheeks, muscular structures covered on the outside by skin and lined by non-keratinized stratified squamous epithelium, form the lateral walls of the oral cavity.

The anterior portions of the cheek terminate in the superior and inferior lips.

Vestibule

The lips are fleshy folds surrounding the orifice of the mouth.

They are covered on the outside by skin and on the inside by a mucous membrane.

Vestibule

The transition zone where the two kinds of covering tissue meet is called vermilion.

The vermilion of the lips is nonkeratinized, and the color of the blood in the underlying blood vessels is visible through its transparent surface layer.

Vestibule

The inner surface of each lip is attached to its corresponding bone by a midline fold of mucous membrane called the labial frenulum.

Vestibule

The orbicularis oris muscle and connective tissue lie between the external covering and the internal mucosal lining.

During chewing, the cheeks and lips help keep food between the upper and lower teeth.

They also assist in speech.

Anterior Floor of the Mouth

The hyoid bone is suspended in the soft tissue by muscles of the floor of the mouth which originate postero-laterally from the region of the temporal bone.

These include the posterior belly of the digastric muscle and the stylohyoid muscles.


Other muscles in the floor of the mouth are important for deglutition.

They elevate the hyoid bone and provide tongue stabilization.

These include the mylohyoid, geniohyoid, and anterior belly of the digastric muscle.


They all attach to the body of the mandible anteriorly, and the body of the hyoid bone posteriorly.

The pliability of the floor of the mouth region and the attachments of the tongue musculature to the anterior mandible allow for tongue mobility in the anterior and posterior directions.

Major and Minor Glands

The mucous membranes lining the mouth contains many small glands, in the tongue, lips, cheeks, and the roof of the mouth, that secrete small amounts of saliva.

However, the major portion of saliva is secreted by the salivary glands, accessory structures that lie outside the mouth and pour their contents into ducts that empty into the oral cavity.


Saliva is essential for the maintenance and protection of the oral mucosa, teeth, and epithelium of the intestinal tract.

It protects the hard and soft tissues through antibacterial, antifungal, antiviral, hydration, buffering, and remineralization processes.

It has lubricating functions that facilitate speech, eating, and swallowing.

It also greatly assists taste perception by its cleansing action of taste buds.


The three major salivary glands are the parotid glands, the submandibular glands, and the sublingual glands.

The parotid glands are located inferior and anterior to the ears between the skin and the masseter muscle.


Each gland secretes into the oral cavity vestibule via a duct, called the parotid (Stensen's) duct, that pierces the buccinator muscle of the cheek to open into the vestibule opposite the second molar tooth.


The submandibular glands are found beneath the base of the tongue in the posterior part of the floor of the mouth.

The submandibular (Wharton’s) ducts run just under the mucosa on either side of the midline of the mouth floor and enter the oral cavity on either side of the lingual frenulum.


The sublingual glands are anterior to the submandibular glands.

Their ducts, the lesser sublingual (Rivinus's) ducts, open into the floor of the mouth in the oral cavity proper.


Chemically, saliva is 99.5% water and 0.5% solutes.

Among the solutes are salts--chlorides, bicarbonates, and phosphates of sodium and potassium.

Some dissolved gases and various organic substances including urea and uric acid, serum albumin and globulin, mucin, the bacteriolytic enzyme lysozyme, and the digestive enzyme salivary amylase are also present.


Each saliva-producing gland supplies different proportions of ingredients to saliva.

The parotids contain cells that secrete a watery serous liquid containing the enzyme salivary amylase, which works on starches and is vital in moistening the food to facilitate chewing and swallowing


The submandibular glands contain cells similar to those found in the parotids and some mucous cells.

Therefore, they secrete a fluid that is thickened with mucous, but still contains quite a bit of enzyme.

The sublingual glands contain mostly mucous cells so they secrete a much thicker fluid that contributes only a small amount of the enzyme to the saliva.


The water in saliva provides a medium for dissolving foods so they can be tasted, and for initiating digestive reactions.

The chlorides in the saliva activate the salivary amylase.

The small glands on the circumvallate papillae of the tongue secrete a lingual lipase, which briefly mixes with food, and will later help with beginning fat digestion.


The bicarbonates and phosphates buffer chemicals that enter the mouth and keep the saliva at a slightly acidic pH of 6.35 to 6.85.

Urea and uric acid are found in saliva because the saliva-producing glands help the body to get rid of wastes.

Mucin is a protein that forms mucous when dissolved in water.

Mucus lubricates the food so it can be easily moved about in the mouth, formed into a ball, and swallowed.


The mouth carries pathogenic bacteria, that, if uncontrolled, can harm oral tissues and cause dental caries

The constant flow of saliva helps to wash away the bacteria and food particles on which they feed

The enzyme lysozyme destroys bacteria, protecting the mucous membrane from infection and the teeth from decay.

Swallowed saliva is also natural neutralizer of stomach acid.


Food stimulates the salivary glands to secrete heavily.

When food is taken in the mouth, chemicals in the food stimulate receptors in taste buds on the tongue.

Impulses are conveyed from the receptors to two salivary nuclei in the brainstem called the superior and inferior salivatory nuclei.

The salivary nuclei are located at the juncture of the pons and medulla.

They send signals to the salivary glands via the parasympathetic nervous system.


Normal salivary secretion ranges from 1.0 to 1.5 liters per day.

Moderate amounts of saliva are continuously secreted in response to parasympathetic stimulation to keep the mucous membranes moist and to lubricate the movements of the tongue and lips during speech.

This saliva is then swallowed and reabsorbed to prevent fluid loss.

Salivation also occurs in response to swallowing irritating foods or during nausea.

Reflexes originating in the stomach and upper small intestine stimulate salivation.


This mechanism presumably helps to dilute or neutralize the irritating substance.

Saliva continues to be secreted heavily some time after food is swallowed.

This continued flow washes out the mouth and dilutes and buffers the chemical remnants of irritating substances.

Dehydration causes the salivary glands to cease secreting saliva to conserve water, which, if chronic, can lead to a bacterial imbalance in the oral cavity.

swallowing disorders in infants, children, and adults

Documents