Speech Components

As noted previously, production of speech requires input from respiratory, phonatory, and articulatory sys­tems. An airstream is generated by the lungs, passes through the vocal cords, and is then shaped by the articulators to form speech sounds.

Respiration

The respiratory system is composed of the upper and the lower airways. The upper airway consists of the nose, mouth, pharynx, and larynx, and the lower airway consists of the tracheobronchial tree and the lungs (2).

Upper Airway. The upper airway has many functions. The mucous membranes covering much of the upper airway structures are softer, looser, and more fragile in infants and young children than in older children and adults, and more susceptible to edema and injury from trauma.

Nose.

Mouth. The lips, mandible, maxilla, cheeks, teeth, tongue, and palate are the most important compo­nents of the oral cavity with regard to manipulation of airflow for respiration and speech production. The infant tongue takes up a larger area in the mouth and rests more anteriorly in the oral cavity than that of the adult. There are numerous congenital cranio­facial anomalies, often associated with syndromes, that have an adverse impact on airflow. Some anom­alies, such as cleft palate, prevent sufficient valving of the airstream, resulting in inaccurate production of speech sounds. Other anomalies, such as glossop- tosis (oropharyngeal or hypopharyngeal obstruction during feeding caused by tongue retraction, and common in Pierre Robin Sequence), can result in blockage of the airstream and subsequent respira­tory distress.

Pharynx. The pharynx, a muscular tube shared by the respiratory and digestive tracts, is sometimes referred to as the aerodigestive tract, and serves vital functions for both respiration and swallowing. It is divided into three portions: the nasopharynx, oro­pharynx, and the hypopharynx. The pharynx in an infant is gently curved, and as the child grows and develops, the angle increases to approximately 90 degrees.

The nasopharynx is the portion of the pharynx directly behind the nasal cavity, extending from the roof of the nasal cavity to the roof of the mouth. In addition to conducting air, the nasopharynx acts as a resonator for voice. The Eustachian tubes from the middle ear open into the nasopharynx.

The oropharynx is that portion of the pharynx directly behind the oral cavity, extending from the roof of the mouth (pharyngeal aspect of the soft palate) down to the base of the tongue, at the level of the tip of the epiglottis. Movement of the pharyngeal walls in this portion, together with elevation of the soft palate and the posterior portion of the tongue, are crucial for velopharyngeal closure. Inadequate closure, or velopha­ryngeal incompetence, can result in disordered speech production.

The hypopharynx extends from the base of the tongue at the level of the hyoid bone and tip of epiglottis down to the entrance of the larynx and esophagus.

Lower Airway

The lower airway consists of the tracheobronchial tree and the lungs. The tracheobronchial tree consists of a system of connecting tubes that conduct airflow in and out of the lungs and allow for gas exchange.

Trachea. The trachea is situated anterior to the esoph­agus, beginning at the cricoid cartilage and extend­ing inferiorly to the carina, where it bifurcates into the right and left main-stem bronchi. It is composed of C-shaped cartilage rings joined by connective tis­sue. These cartilage rings assist in keeping the tra­chea open during breathing. As noted previously, the mucous membranes of the trachea are softer, looser, and more fragile than those of the adult and more sus­ceptible to damage, increasing the risk of obstruction from edema or inflammation.

Lungs. The lungs are situated in the thoracic cavity, enclosed by the rib cage and diaphragm, the major muscle of ventilation, which separates the thoracic cavity from the abdominal cavity. The diaphragm in an infant is flatter than that of an adult, resulting in less efficient functioning for respiration. The air pas­sages in infants and small children are much smaller, increasing their susceptibility to obstruction. The respiratory bronchioles, alveolar ducts, and alveoli grow in number until about 8 years of age, after which they continue to grow in size. Impairments in lung function can occur as a result of birth-related condi­tions such as bronchopulmonary dysplasia and dia­phragmatic hernia, or due to acquired disorders such as spinal cord injury. These impairments often require tracheostomy and/or mechanical ventilation, which in turn have an impact on speech production.