Basic Information about the Human Voice
Development of Voice
Features of the larynx at birth
At birth, a baby's larynx is 2 cm long and 2 cm wide, about one third the size of an adult's. It is much softer and more flexible than that of an adult. The layers found in adult vocal cords are not yet present. There is no difference in laryngeal characteristics between the sexes at birth.
Contents
Development of the larynx in terms of voice formation
In terms of voice development, the development of the larynx is divided into three parts: Topographic (larynx descends downwards), Morphological (increase in volume and change in shape) and Histological (change in the layers of the vocal cord, especially the lamina propria).
Topographic Development of the Larynx
At birth, the newborn's larynx is positioned higher than at any other time in life relative to the palate and mandible. In infants, the larynx is so high that the epiglottis comes into contact with the soft palate, allowing for simultaneous breathing and feeding. The descent of the larynx begins immediately after birth. Radiographs taken at various ages between one month and fifteen years have shown that the voice tract undergoes the most changes in the first year and during puberty. The ratio between the height of the pharynx and the length of the oral cavity decreases from 1.5 to 1 between birth and ages 6-8, and remains constant thereafter. During the postnatal development period, the relative positions of the vocal folds, the hyoid body, the mandible, and the hard palate do not change significantly. The lower border of the cricoid cartilage is at the level of the third and fourth cervical vertebrae (C3 â C4) at birth. By age five, the larynx descends to the level of C7. Measurements taken between the ages of 15 and 20 show that the larynx is still at the C7 level. Laryngeal descent lengthens the voice tract, lowers the resonance frequency of the voice tract, and creates the perception of a larger body size. This situation has also been shown in studies on chimpanzees and deer. Research indicates that lower male voices are perceived by women as being associated with increased body size. There is a developmental relationship between the descent of the larynx (as the pharyngeal cavity elongates, lower fundamental frequencies gain more resonance) and the drop in average pitch. Laryngeal descent is evolutionarily significant for both swallowing and voice production.
Morphological Development of the Larynx
Morphological changes that begin at birth continue throughout life. At birth, the thyroid cartilage and hyoid bone, which touch each other, move apart along the vertical axis. In infants, the epiglottis is positioned higher and appears swollen. The aryepiglottic folds are thick. The epiglottis is omega-shaped and rests against the root of the tongue. With growth, the epiglottis widens, hardens, and the omega shape flattens. The angle that the thyroid cartilage forms at the front changes to approximately 90 degrees in males during puberty. In females, it remains largely unchanged, around 120 degrees. The increase in the length of the thyroid cartilage is three times greater in boys than in girls. During the first year of life, the entrance to the larynx widens, changing from a T-shape to a rounded-oval shape.
The laryngeal airway is secured by the rigid-round structure of the cricoid cartilage. If the negative pressure inside the voice tract reaches sufficient levels, the newborn's larynx may collapse due to its soft cartilages and loose ligaments. The looseness of the subepithelial connective tissues and their proportionally rich vascularization increase the tendency for fluid accumulation. Therefore, in infants, the incidence of subglottic or supraglottic obstruction due to inflammatory swelling is high. The hyoid begins to ossify at the age of two. Other cartilages begin to harden during puberty, first the hyaline thyroid cartilage, followed by the cricoid cartilage. The hyaline and elastic arytenoid cartilages eventually undergo ossification as well. In males, with the exception of the elastic epiglottis, cuneiform, and corniculate cartilages, all laryngeal cartilages have ossified by the seventh to eighth decades of life. In females, complete ossification of the larynx never occurs.
In infants, half of the vocal folds are cartilaginous and half are membranous, resulting in a wide glottis, whereas in adults, the proportion of membranous parts increases to two-thirds, enhancing the flexibility of the vocal folds. Glottal width and subglottal diameters increase with age.
Histological Development of the Larynx
The most significant histological changes occur in the sensitive structures of the vocal folds, including the thyroarytenoid muscle and mucosa. In children aged one to four, the mucosa is thick, has a uniform structure, and does not show the layering seen in adults. The differentiation of the lamina propria resembles that of adults but becomes prominent during puberty, although histological changes continue throughout life. In older adults, the lamina propria is thick and edematous, with a reduced density of elastin and collagen fibers.
Histological changes in the vocal muscle are also important. In newborns, muscle fibers are thin. In adulthood, they become thicker, but from age 40 onwards, they gradually atrophy. In newborns, there is more type 2 muscle (long sustained contraction) than type 1 (short rapid contraction). As growth occurs, type 1 muscles become more dominant, aiding in greater vocal control and prolonged sound production.
The Vocal Cords
Each person has two vocal cords located in the middle of the neck, just beneath the pharynx and just above the trachea. Throughout the evolutionary development process, the primary function of the vocal cords and, generally, the larynx is to protect the airway and lungs from foreign particles and foods that may enter.
How Do the Vocal Cords Work?
During breathing, the vocal cords are open in a V shape, and they completely come together during swallowing and sound production. Of course, this simple explanation is a very crude description of the excellent functioning mechanism of the vocal cords. Human vocal cords come into contact (vibrate) with each other at an average of 120 times per second in men and 200 times per second in women when speaking.
Fundamental Frequency of the Vocal Cords
Fundamental Frequency in Newborns
The fundamental frequency (F0) of a newborn's vocal cords ranges from 450-520 Hz. This means the vocal cords vibrate this number of times per second when the baby cries.
Fundamental Frequency in Childhood and Pre-Adolescence
During childhood, this number drops to around 300 Hz. F0 decreases to as low as 250 Hz in both girls and boys during pre-adolescence.
Fundamental Frequency During Adolescence
During puberty, due to the effects of androgen hormones, the drop in F0 in boys is very apparent due to changes occurring in the larynx. In boys, the pitch decreases by about an octave during puberty. Although the drop in fundamental frequency is less significant in girls, it reaches adult levels during adolescence. Voice changes during puberty are usually completed within 3-6 months, but can take up to 1 year. Voice changes in girls complete at age 15, while boys experience it between ages 14-15. Although voice changes in girls begin earlier, their completion happens around the same time as boys.
Fundamental Frequency in Adults
In adult males, the vocal cords vibrate approximately 100-140 times during speech, while in women, this range is about 200-240 Hz.
Age-Related Changes in Fundamental Frequency
After puberty, F0 remains relatively stable; however, a decline particularly due to postmenopausal changes can be observed in women after the fifth decade, while a slight increase may begin in men from the seventh decade onwards.
Structure of the Vocal Cords
The vocal cords consist of two separate layers. The upper layer, which comes into contact with each other in both vocal cords, is made up of mucosa, epithelium, and lamina propria. The layer beneath the mucosa is muscle tissue.
Histological Structure of the Vocal Cords
Our knowledge regarding the histological structure of the vocal cords has continuously increased since Hirano revealed the layered structure of the vocal cord's connective tissue, lamina propria, in 1974. The molecular composition of the extracellular matrix of the lamina propria is crucial for understanding the viscoelastic properties of this tissue. This is especially important for the superficial layer of the lamina propria (Reinke's space).
The epithelium and Reinke's cavity form the primary compartment responsible for vibration of the vocal cord. In normal individuals, the jelly-like structure of the Reinke's cavity depends on a balance between loose fibrous elements and interstitial proteins (glycoproteins such as decorin, hyaluronic acid and fibronectin). Increased trauma associated with vocal cord vibration leads to molecular changes in the extracellular matrix in the Reinke's cavity and causes benign vocal cord lesions such as nodules, submucosal fibrotic tissue and vocal cord scars.
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