PHONATION FOR SPEECH 1
The aim of this paper is to explorethe phonation process as well as the muscles and other structuresthat help in the production of sound. The theories that explain theadduction and abduction of the vocal folds will also be explored. TheInformation about the anatomy and physiology of the structures thatplay a significant role in the phonation process will form the basisof this paper. This paper has identified four types of muscles thatare central to the phonation process. They include cricothyroidmuscle, posterior cricoarytenoid muscle, lateral cricoarytenoidmuscle, and the interarytenoid muscle. Apart from muscles, the otherimportant structures that help in the process of sound productioninclude the larynx, epiglottis, and the thyroid cartilage.
Phonation is the process that results in the production of sound andspeech. It involves the air from the lungs being forced out throughthe glottis. It is this movement of air that triggers the vibrationof the vocal folds and the ligaments which in turn result in theproduction of voices.
One has to breathe in to create sound. When a person breathes in, thediaphragm drops and this leads to the expansion of the volume of airwithin the lungs. This is followed by the air getting swooped inthrough the mouth or the nose into the larynx, trachea, and bronchiuntil it finally reaches the lungs (University of Iowa, 2016). During breathing, the vocal folds are opened or abducted to allow theair to access the trachea before being directed into the lungs. Theprocess of the production of sound begins in the lungs where an airstream is formed. The vocal folds lie horizontally in the larynx.Additionally, they are connected to the posterior part of thearytenoids cartilages and on the anterior of the thyroid cartilage. When the arytenoids adducts, the vocal folds close. The expulsion ofthe air from the lungs through the glottis results in a decline inthe pressure across the larynx. If the drop in the pressure becomesadequately large, the vocal folds begin to vibrate. The least amountof pressure drop needed to produce sound is referred to as thephonation threshold pressure. For normal human beings, the phonationthreshold pressure is about two-three cm H20. The vibration of thevocal folds aims at modulating the pressure and the movement of airpassing through the larynx. As the vocal folds oscillate, theyalternately trap and release air. This process triggers a vibrationthat emanates from the middle of the vocal folds and it is thisresultant movement that causes sounds. The rapid opening and closingof the vibrating vocal folds disturb the smooth airstream, and thisproduces a glottal tone that is later adjusted within the surfaces ofthe vocal tract(Seikel, et al., 2011).
There are two major theories that explain how the oscillation of thevocal folds occurs. According to the myoelastic theory of speechformation, the vocal cords are made to come together and breathpressure applied to them. They, however, remain closed until such atime when the pressure beneath them is adequate to cause theirseparation. When they are separated, the air is released. Thisreduces the pressure in the larynx, which in turn triggers muscles tobring the vocal folds together. The process repeats itself every timea person speaks. On the other hand, the aerodynamic theory maintainsthat the action of the interaryneoid muscles hold the arytenoidscartilages together as the airstream flows through the glottis. Thisprocess establishes a push-pull effect on the tissues of the vocalfolds which in turn creates self-sustaining vibrations in the glottis(The NationalCenter for Voice and Speech, 2014)
The larynx, which is found in the upper part of the trachea, is themajor structure that causes the airstream emanating from the lungs tovibrate. The larynx also accommodates the vocal folds hence it iscommonly known as the voice box. The laryngeal skeleton is foundbetween the lower part of the trachea and the tongue. It comprises ofnine cartilages connected to the axial skeleton. The axial skeletonis made up of the epiglottis, two arytenoids cartilages, thyroidcartilage, two corniculate cartilages, two cuneiform cartilage andcricoids cartilage (Deirdrem,2016). Numerous muscles are involved in the movement ofthese cartilages. The movements made by the laryngeal skeleton causethe opening and the closing of the glottis. Additionally, thesemovements control the amount of tension in the vocal folds which inturn determines the pitch as well as the volume of the soundproduced.
There are several muscles that are involved in the process ofphonation. The first muscle is the cricothyroid muscle, which isconnected to both the cricoids and thyroid cartilages. Its functionsare to raise the cricoids and lower the thyroid a process thatshortens the cricothyroid space, resulting in the lengthening of thevocal folds. This alters the stiffness of the vocal folds. Theposterior cricoarytenoids muscle runs from the cricoid cartilage andextends laterally to the arytenoids cartilage. The role of thesemuscles is to hold in position the arytenoids facilitating theadduction of the vocal folds (Deirdrem,2016). The lateral cricoarytenoid muscle, on the otherhand, starts at the bottom of the arytenoids and extend to thesurfaces of the cricoid cartilages. These muscles help in the processof phonation by holding the arytenoids in position resulting in theapproximation of the mucous portion of the vocal folds. Some soundssuch as the stop consonants need much intraoral pressure. This meansthat the air pressure in the mouth should be huge and withoutleakage. When the lateral cricoarytenoid becomes rigid, this actioncauses a rotation movement at both arytenoids cartilages which bringthe vocal folds together. The last major muscle is theinterarytenoid muscle that extends horizontally separating the twoarytenoids opening up the vocal folds. The role of these muscles isto help the lateral cricoarytenoid execute its duty of closing theposterior segment of the glottis. The straining of these musclescauses them to shorten which in turn bring closer the two edges ofthe arytenoids cartilage. It is this process that causes the vocalfolds to close(Seikel, et al., 2011).
However, there is a group of muscles located in the anterior part ofthe neck known as laryngeal muscles that are also responsible forsound production. Their role is to trigger the movements of ninevocal cartilages. In turn, each of the nine vocal cartilages performsspecific duties in the process of the production of sound. Thevocalis cartilage causes the vocal cords to increase in thickness.The thyroarytenoid cartilages relax and shorten the vocal folds.Thyroepiglottic cartilage is responsible for depressing theepiglottis. Cricothyroid cartilage stretches and lengthens the vocalcords while the lateral cricoarytenoid cartilages close the glottis.The oblique arytenoids cartilage is responsible for narrowing thelaryngeal inlet. The posterior cricoarytenoid is in charge of theseparation of the vocal folds. Transverse arytenoids close theposterior glottis. Lastly, the aryepiglottic cartilages cause thedepression of the epiglottis. It is also responsible for closing thelarynx during swallowing(Deirdrem, 2016).
Apart from the muscles, there are other structures that are essentialin the phonation process. The epiglottis is one of these structures.It is a leaf-like structure that extends upward from the lower partof the tongue on the entrance to the larynx. It is mainly used toclose the larynx preventing food and other particles from accessingthe trachea. The closing of the larynx involves the pulling down ofthe epiglottis by the thyroepiglottic and aryepiglottic muscles.Apart from the epiglottis, the other structures that play a majorrole in the phonation process is the thyroid cartilage. Out of thenine laryngeal cartilages, the thyroid cartilages are the largest.Their primary purpose is to shield the vocal cords. However, theyalso provide a surface for the muscles and ligaments to attachthemselves to. The thyroid cartilage comprises of two laminae thatjoin anteriorly together and which result in the formation of anextension under the skull that is known as the Adam apple. The otherstructure that plays a crucial role in the process of the productionof sound is the vocal ligaments. They are located beneath the mucouswall of the larynx. On the other hand, the vocalis work to thickenand tensen the vocal cords which in turn causes the variations in thequality and pitch of the sound(Seikel, et al., 2011).
In conclusion, the stages through with sound and voices are producedis called the phonation process. The process begins with aninhalation. During exhalation, the pressure inside the larynx drops.However, it is only when the drop in pressure in the larynx issufficiently large that the vocal folds can start to vibrate. It isthis vibration of the vocal folds that produces sounds. Otherstructures that help the larynx to produce sounds are the fourmuscles. Apart from the larynx, the epiglottis, vocal ligaments andthe vocalis also aid in the process of production of sounds andvoices.
Deirdrem D.(2016). Anatomy 101: Parts of the voice. Accessed on September 24,2016. http://www.lionsvoiceclinic.umn.edu/page2.htm
Seikel, J.A., Drumright, D. G., & King, D. W. (2011). Anatomy& physiology for speech, language, and hearing.Nelson Education.
The NationalCenter for Voice and Speech. (2014). “Modes of vocal foldoscillation. Accessed on September 24, 2016.http://www.ncvs.org/ncvs/tutorials/voiceprod/tutorial/model.html
University of Iowa (2016). “Three parts of speech.” Accessed onSeptember 24, 2016.https://uiowa.edu/voice-academy/three-parts-speech