The Anatomy And Physiology Of The Aging Larynx

ANATOMY OF THE LARYNX

            The larynx commonly called as the voice box has basically four anatomic component. The voice box is a tube-shaped structure “comprised of a complex system of muscles, cartilage and connective tissue.” (M. Dance) It vitally functions as an “airway to the lungs” in order for human beings to vocalize. Suspended from the hyoid bone, the larynx is made up of cartilages which directly work with the muscles attached to it in order for the voice box to function.

SKELETAL COMPONENTS OF THE LARYNX

            The cartilages of the Larynx- The cartilages of the larynx are grouped into two: the paired and unpaired cartilages each composed of three significant cartilages. The shield-shaped Thyroid cartilage is the largest of the unpaired cartilages, commonly referred to as the “Adam’s Apple” and is prominent in males. The cricoid cartilage, also known as the “signet ring” is a complete laryngeal cartilage connected to the thyroid cartilage through its inferior horn. The leaf-shaped unpaired cartilage is called the epiglottis which inverts to function as a guide for food and liquid movement down to the esophagus. The epiglottis also functions as shield for the vocal cords and the airway during swallowing.

            The Arytenoid cartilages are pyramid-shaped paired cartilages which serve as a point of attachment for the vocal cords. It allows the vocal cords to open and close for respiration and vocal functions. Arytenoids are located on top of the cricoids lamina where it slides at a medial and lateral manners and rotates at the cricoarytenoid joints at an anterior and posterior movements. The cuneiform and the corniculate are small cartilages which are said to have no vital and clear-cut functions.

THE LARYNGEAL MUSCLES

            The muscles of the larynx are grouped into two: the intrinsic and the extrinsic muscles. The intrinsic muscles are the ones attached within the larynx. These paired muscles function in the opening and closing of the vocal cords. The interarytenoid, lateral cricoarytenoid, cricothyroid and the true vocal cord called thyroarytenoid are intrinsic laryngeal muscles that work together to adduct or close the vocal cords. The posterior cricoarytenoid muscle is the one responsible for the opening (adduct) of the vocal cords.

            On the other hand, the eight laryngeal muscles attached to sites both inside and outside of the larynx are called extrinsic muscles. The suprahyoid group of extrinsic muscles includes the stylohyoid, mylohyoid, geniohyoid and digastric muscles which all function to raise the larynx. The infrahyoid muscles on the other hand work together to lower the hyoid bone to the larynx. This group includes the sternothyroid, sternohyoid, thryrohyoid and omohyoid muscles located below the hyoid bone.

THE FUNCTIONS OF THE LARYNX

            The larynx has three basic functions: deglutition (swallowing), respiration (breathing) and phonation (voice production). Voice production begins with the production of airflow through respiration or breathing. In order to produce sound, the adductor muscles must be activated which provide resistance to the exhaled air from the lungs. (University of Pittsburgh Voice Center) The exhaled air bursts through the closed vocal cords then rushes resulting to the dropping of pressure between the cords. The action of the vocal cords being blown apart and then sucked back together is called “vibration” which produces sound known as the voice. This vibration is repeated thousands of times in a second in order to produce sound. The sound produced is shaped my muscular changes in the pharynx and the oral cavity resulting to what we call “speech”. (W. Norman, 1999)

CHANGES IN THE LARYNX RELATIVE TO AGE

            The larynx also undergoes a maturation process. This process begins at the early age throughout the life of the person. The changes in the larynx are more evident in the puberty stage. These changes affect two main aspects of laryngeal functions: functions relative to the laryngeal muscles and those relative to the tissues of the voice box.

            As have been mentioned, the vocal cords are moved by the muscles. These muscles can either tighten or loose the vocal cords. “The tighter the cord is, the higher the voice.” (D.L. Schlomer) The muscles undergo a changing process called, Atrophy, where the vocal fold muscles loses bulk. As the person age, the cords get elastic which cause a change in the voice. The framework cartilages of the larynx gradually turn to bone, a process called ossification, and “the cartilages responsible for vocal cord movement become less mobile.”(A. Gout) Over time, the cartilages of the vocal cords calcify and become more rigid. The joints that allow the three-dimensional movement of the vocal folds get stiffer. (H. Von Leden, 1994) The vocal folds get slightly bowed. This change in the vocal folds prevents the vocal folds to close tightly resulting to a breathy voice.

            The superficial lamina propia also becomes thinner, stiffer and less pliable as the person gets old. (L.Sulica) These flexible tissues are the ones responsible for the vocal cord vibration. With the changes in the vocal cord muscles, the changes in these tissues result to a high-pitched voice, reedy and rough voice which is considered to be evidences of aging. The loss of projection and resonance are also results of these changes.

            The mucous and saliva secretions also decrease with age. Since the vibration of the vocal folds requires moisture on the vocal fold surface, the reduction of the saliva in the larynx directly affects the voice production, that is, it reduces smooth vibration. In women, changes in laryngeal structures begin just after their menopausal periods. In men, the changes generally begin at the age of sixty.

CHANGES IN THE LARYNX RELATIVE TO THE NERVOUS SYSTEM

            Voice production is a result of the coordination of the nerves and the muscles of the larynx. The voice production therefore changes as people due to the decrease in the speed of nerve transmission. With age, the coordination of the muscular movements also reduces. These changes affect the control of pitch and voice range. Along with the age-related neurological disorders as Parkinson’s disease, diseases of the larynx also occur. These voice disorders may include voice tremor and neuromuscular paresis or paralysis.

CHANGES IN THE VOCAL FOLDS

            The vocal folds normally stretch in a straight line between its attachments to cartilage, both in the front and back of the larynx. As the person gets old, the margin of the vocal folds appeared to be that of a scallop or concave shape. This is caused by the atrophy of the vocal fold muscles and the thinning of the superficial lamina propia. The vocal folds also become thinner and less plump and the cartilages become starkly outlined. In the thinned vocal folds, abnormal masses develop, which look like a cyst or a polyp, causing the vocal process to stand out. Because of the vocal folds got thinner, its edges are prevented from closing completely during the voicing process. This result to a gap between the vocal folds shaped like a spindle.

MEN AND THEIR AGING LARYNX

            If women undergo menopausal periods, men on the other hand experience the so-called “Andropause”. The androgen secretion by the testicles decreases during this period which typically begins at the age of 70. The androgens have direct effect on the voice of males which act on the bony tissues and on the brain. Androgens increase blood flow, improve oxygenation and muscle performance. Thus, the lack of androgens directly affects the shape of the vocal cords and the tonicity of the resonators.

WOMEN AND THEIR AGING LARYNX

            “As the menopausal woman advances in age, her new hormonal balance can no longer sustain the tonicity and strength of the vocal cords.”(M. Benninger) During the perimenopause period of a woman, the activity of the ovary slows down and consequently reduces the level of progesterone and estrogen levels. The reduction of estrogens enables the sex hormones receptors to receive more androgens. This event causes the vocal cord mucous membrane to thicken and will then exhibit a lack of tonicity and a deficiency in its contour. Thus, the voice becomes more masculine as it becomes deeper.

The reduction of estrogen and progesterone levels directly affects women’s nervous system and is directly connected to the female’s larynx. The vagus nerve controls and the neurological motor and sensation functions of the larynx, which is improved by the estroprogesterones. During a woman’s menopausal period, the estrogen secretion radically drops and progesterone secretion completely stops. This results to a slower nervous conduction from the brain to the larynx. The vocal responses then slows down and “bring rapid changes in frequencies when singing.” (C. Schwimmer, 1995)

The voice box plays a vital role in the human life. Without the larynx, it is impossible for human beings to speak aside from the vital functions of deglutition and respiration. Like all parts of the human body, the larynx also undergoes changes brought about by aging. Although the changes in the larynx brought about by aging is inevitable, experts always recommend that people have to understand at least the basics of the larynx, how it functions and how to take care of it. Like any other part of the human body, the larynx can also be overused and misused so it is important and required that human beings learn to take care of it. It is also vital for people to distinguish the normal changes in the larynx and the voice from that of the changes brought about by diseases.

REFERENCES

Abitbol, J. et. Al (1999) Sex Hormones and the Female Voice. 13:424-446

Benninger, Michael S. (2006). Voice. Dysphonia and the Aging Voice. American Academy of Otolaryngology.

Hopkins, JR Lee (1996). What the Doctor May Not Tell You About Menopause. Warner Books

Kansaku, K.A., Yamura, S. and S. Kitazawa (2000). Sex Differences in Lateralization Revealed in the Posterior Languages Areas. 10:866-872

Schwimmer, C. (1995). Diagnosis and Care of Vocal Disorders. Tokyo: Igaku-Shoin Publishers. Pp. 105-121.

Schlomer, Darby Lee. What is Happening to my Voice? Retrieved on April 03, 2007 from http://www.angelfire.com/folk/therapy/vocal.html

Sulica, Lucian. Aging Voice. Retrieved on April 03, 2007 from http://www.voicemedicine.com/aging.htm

Von Leden, H. and DM Alessi (1994). The Aging Voice. Thieme Medical Publishers, Inc. New York. Pp. 105-121

Wesley, Norman (1999). Larynx. Retrieved on March 29, 2007 from http://mywebpages.comcast.net/wnor/lesson11.htm

Anatomy of the Larynx. University of Pittsburgh Voice Center. Retrieved on March 29, 2007 from http://biology.about.com/gi/dynamic/offsite.htm?zi=1/XJ/Ya&sdn=biology&cdn=education&tm=601&gps=44_10_1020_53&f=20&tt=14&bt=1&bts=http%3A//www.pitt.edu/%7Ecrosen/voice/anatomy2.html

The Anatomy and Physiology of the Voice. Retrieved on March 29, 2007 from http://www.gbmc.org/voice/anatomyphysiologyofthelarynx.cfm