Development of vocal folds from infancy to Puberty
The
larynx and all parts of the vocal tract are changing throughout life and the
voice reflects these changes. Some vocal features are the result of gross
alterations such as the size of the vocal folds and the dimensions of the vocal
tract structure, but there are the result of more subtle changes, such as the
changing histology of the vocal folds and the timing of the neuronal impulses
that initiate and regulate phonation.
The
structure and the controlling mechanism of the phonation are in a process of maturation
for the first 20 years of life. From embryological stage to old age, maturation
and subsequent decline of the anatomy, physiology and histology of the vocal
tract and its related systems results in acoustic changes in the voice.
Throughout the lifespan the voice is affected by a number of internal and
external factors which are tabulated as follows.
Factors affecting the
voice from infancy to senescence
·
Growth, eg: bones, muscles, cartilages.
·
Hormones, especially androgens and
oestrogens
·
Health: good, poor
·
Use: occupation and leisure activities
·
Lifestyle, eg: busy, relaxed, smoking,
excessive alcohol, gastric reflux
·
Environment, eg: quite, pleasant, noisy,
dusty, excessively dry atmosphere
·
Psychological status: eg: happiness,
serenity, depression, anxiety, stress
·
Cultural factors: eg: vocally loud social/
family group
·
Degenerative changes, eg: bones, muscles,
cartilages, nervous system, and respiratory system.
PRENATAL DEVELOPMENT
·
The respiratory primordium
begins at about the fourth week of gestation with the formation of the
laryngotracheal groove, which extends lengthwise in the floor of the gut just
caudal to the pharyngeal pouches.
·
This groove deepens into the
laryngotracheal diverticulum, whose ventral endoderm will become the larynx and
trachea, while the more caudal endoderm will give rise to the bronchi and
lungs. Lateral furrows develop on either side of the laryngotracheal groove or
diverticulum, at the level of the junction between the groove and the future
esophagus.
·
These furrows gradually deepen
and extend cephalad, elongating this structure to form the primitive
laryngotracheal tube. The lateral furrows join, splitting off first the lung
bud and then the trachea.
·
The upper end of this tube advances
slightly cephalad until it lies between the fourth branchial arches, and this region will form the primitive
laryngeal aditus.
·
A tracheoesophageal septum
develops caudally too cranially and separates the respiratory system from the
esophagus.
·
It is at the end of the fourth
week of gestation that the single lung bud appears at the caudal end of the
laryngotracheal tube. This bud soon divides into right and left bronchial buds,
and these grow caudally and laterally into the pericardioperitoneal cavities.
The primitive lung buds then subdivide into secondary and tertiary bronchi.
Throughout fetal development, the surrounding pulmogenic mesoderm continues to
develop into the lung parenchyma.
·
The larynx develops on the
proximal end of the laryngotracheal groove between the fifth and sixth
gestational weeks, as three swellings appear at the laryngeal aditus. The
anterior swelling, which is the future epiglottis, may be a derivative of the
hypobranchial eminence from the fourth arch, although its actual origin and
relationships to the branchial arches remain unclear. It should be noted that
in contrast to the first, second, and third arches, little is clearly known
about the precise development of the caudal
arches, the fourth through sixth arches. The two lateral masses give
rise to the future arytenoids, from the fourth or fifth-sixth arches. These two
lateral swellings migrate cranially and medially to oppose each other and,
together with the epiglottic swelling, surround a T-shaped laryngeal aditus.
·
The laryngeal lumen becomes
occluded at eight weeks of gestation due to epithelial proliferation. If normal
recanalization does not occur during the tenth gestational week, a laryngeal
web results. The formation of the vocal (true) and vestibular (false) folds
(cords) is related to the condensation of mesenchyme and the outpouching of the
laryngeal sinus or ventricle.
·
The two vocal folds separate
during the third gestational month and failure of this recanalization process
results in congenital atresia of the larynx.
·
The laryngeal cartilages
develop from the branchial arches, with the more cranial cartilages possibly
arising from the fourth arch and the more caudal ones from the sixth (with the
caveat that the epiglottis may not be arch derived, as mentioned above) . The
thyroid cartilage develops from the fourth arch as two lateral plates that fuse
in the midline. This process is almost completed by the ninth gestational week.
The cricoid cartilage appears to begin as two cartilaginous centers of the
sixth arch. First, the centers grow and unite in the ventral midline; then, by
the seventh gestational week, they fuse dorsally. The rostral advancement of
the tracheoesophageal septum results in the fusion of the dorsal cricoid
lamina. Failure of advancement of this septum results in a fistula. At first,
the cricoid lumen is slit-like in shape, but eventually the ventral and lateral
walls of the cricoid cartilage condense and there is progressive enlargement of
the lumen. Failure of this condensation process results in congenital
subglottic stenosis.
·
The arytenoid cartilages
develop from the arytenoids swellings, most likely derivatives of the sixth
arch but possibly arising from the fourth arch. They are initially fused to the
cricoid cartilage, but they eventually separate from it and form the
cricoarytenoid joints. The origins of the corniculate and cuneiform cartilages
remain unclear. The intrinsic laryngeal muscles develop from the mesoderm of
the fourth through sixth arches. The tracheal tube elongates, and the future
carina or point of bifurcation descends caudally eight somite segments. The
right bronchus descends more directly than the left bronchus, a relationship
that is maintained in the adult. The smooth muscle fibers and the cartilaginous
tracheal rings differentiate from the surrounding mesenchyme at the end of the
seventh week. The minor salivary glands develop as ingrowths from the
epithelium after four months of gestation.
1.
INFANCY
Ø Upper
respiratory tract
Laryngeal position
The configuration of the infant
aerodigestive region is radically different from adult aerodigestive region. At
birth, the larynx is high in the vocal tract with the lower border of the
cricoids cartilage at the level of cervical vertebrae 3 and 4 (C3-C4) (Maddern,
Campbell and Stool, 1991). The tip of the epiglottis is parallel with the upper
portion of the body of C1 and in some cases it is in contact with the soft
palate. This arrangement allows the infant to breathe and swallow almost
simultaneously, as in some other mammals. The root of the tongue is in the oral
cavity but during the first 4 years of life, the larynx and the root of the
tongue descend into pharynx (most of the descent occurs in infancy). The vocal
tract above larynx is also primitive in development and restricted in resonance
variability. The narrowest point of the airway in the neonate is the subglottis
within the cricoids ring, whereas in the adult the narrowest point is the
glottis itself (Tucker, 1987). It is estimated that, in about 50% of infants,
the epiglottis is omega or U-shaped. At this early stage of life, the hyoid
bone and the thyroid cartilage are closely approximated, but they gradually
separate as the larynx descends in the vocal tract throughout childhood.
Vocal fold
length
There is some difference of opinion
concerning the exact length of the vocal folds at birth, but the most notable feature is the minute size of the
laryngeal sphincter. Negus (1949) reported that the folds are 3 mm long at 14
days, 5.5 mm at 1 year; 7.5 mm at 5 years, 8.0 mm at 6 years 6
months, and 9.5 mm at 15 years .Hirano, Kurita and Nakashima (1983), in the
examination of 88 Japanese
infants, calculated that the length of vocal folds i the newborn varied from
2.5 mm to 3.0 mm. Von Leden (1961) and Hollien (1980) reported that the length of the vocal folds increases about
80% from birth to 12 months of age. Variance in size and eight of infants
determines laryngeal size. More
than 50% of the glottis opening in the infant is
cartilaginous, in contrast to two-thirds of the glottis being bordered by soft
tissue in the adult (Tucker, 1987)
|
Age
|
Vocal fold length
|
authors
|
||
|
Neonate
|
|
2.5-3.0
|
|
Hirano, Kurita and Nakashima (1983)
|
|
14 days
|
|
3
|
|
Negus(1949)
|
|
1year
|
|
5.5
|
|
Negus(1949)
|
|
5 years
|
|
7.5
|
|
Negus(1949)
|
|
6 years 6 months
|
|
8
|
|
Negus (1949)
|
|
9 years
|
|
9
|
|
Mueller (1997)
|
|
Puberty
|
|
12-15
|
|
Mueller (1997)
|
|
Women
|
|
12-17
|
|
Mueller (1997)
|
|
|
|
17-23
|
|
Mueller (1997)
|
Vocal fold histology
The fibres of the vocalis muscle are
incomplete at birth and develop alongside the thyroarytenoid muscle, which
increases considerably in size from the ninth postnatal month. The mucosal
cover of the vocal folds is very thick in relation to
its length and there is no vocal ligament observable in early infancy. This
develops between 1 and 4 years. The intermediate and deep layers of the lamina
propria are not differentiated into collagenous and elastic fibres. The thick
loose layer of the lamina propria is prone to develop acute oedema which is the
cause of croup. Although the airway becomes constricted, total obstruction does
not occur because the membranous length is almost the equivalent of the
cartilaginous length of the fold (Hirano, 1981; Hirano, Kurita and Nakashima,
1983; Kahane, 1986). Hirano, Kurita and Nakashima (1983) provide an excellent
set of histological pictures illustrating the differences in structure of the
vocal folds at birth, in the child and in the adult.
Ø Lower
respiratory tract
Structure
Before
birth,
the lungs are yellowish and solid, tucked away in the back c e chest. Immediately
the child is delivered, 'the tissues of the lung expand like the petals of a
flower and the color changes to rose red (Thomson, 1976). This is because of
the inrush of blood and air into the expanding lung tissues. From the dramatic
moment of the birth cry, the infant is launched into automatic life-supporting
respiration. The glottis is sphincteric and widens and narrows reflexly in
concert with inspiration and expiration (Terracol, Guerrier and Camps, 1956).
The pharynx is hypersensitive which ensures instant spasmodic closure of the
glottis at the slightest excitation from saliva or milk.
This is
followed by immediate, expulsion by coughing and spluttering
accompanied by poorly coordinate inspiratory and expiratory action which, however, proves effective. The diaphragm is the chief muscle involved in respiration in infancy. The ribs are
relatively perpendicular to the spine and do not contribute to thoracic
movement until the child is able to sit and assume upright posture. The act of crying necessitates changes in respiratory
patterns and provides essential preliminary exercise for phonic respiration.
Function
During the first year, control over
vegetative respiration gradually develops. The infant
acquires the ability to change from quiet breathing to the changed rhythm and volume necessary in
vocalization, in babbling and eventually in speech. Study of respiratory
movements can be registered by magnetometry, which tracks the anteroposterior
diameter of the rib cage and abdominal wall. Impedance pneumography measures
the circumference of the same structures. Such measurements are non-intrusive
but accurate, and have revealed that breathing in infants is extremely
variable. At 1 month, breaths may be taken at a rate of 87/min and irregularity
is not uncommon (Perkins and Kent, 1986).
The rate decreases gradually to 61 breaths at 6 months and 42 at 12 months (Langlois, Wilder and
Baken-1975; Langlois, Baken and Wilder, 1980).
As the infant grows and the laryngeal airway increases in size, the
airflow increases and airway resistance
decreases (Netsell et al., 1994).
Phonation
Infant
cries
The voice is used to signal
distress and discomfort and to emit cries for help. The first cry at birth is
probably the most dramatic use of voice that an
individual will ever make. It signals that the infant is alive and respiration
has commenced. The primitive nature of the baby's vocal apparatus means that
comparison with a musical instrument at this stage is invalid. The sounds
emitted encompass a considerable range of frequencies and an amazing volume of
sound considering the tiny size of the instrument (Murry, 1980; Raes
and Dehaen, 1998). The vocal tract of the newborn is incapable of producing the
full range of speech sounds, although the formants of vowels /a/ and /a/
are apparent in sound spectrographic analysis (Ringel and Kluppel, 1964; Stark,
1978) The formants produced inevitably reflect the characteristics of a vocal
tract that, at birth, resembles
that non-human primate more than that of human adult (Lieberman, 1967). The larynx is elevated in the vocal tract during crying.
An early study was carried out by Fairbanks (1942) on his son from the age of 1 to 9 months. He recorded the fundamental frequency
of hunger wails. At 1 month, the mean fundamental frequency was 373 Hz and subsequently increased to a mean of 814 Hz at 5 months, and then stabilized, to a
decreased mean of 640 Hz at 9 months. He attributed the regular and rapid
rise in frequency up to 5 months to increased neuromuscular development and
not to increasing length of the vocal folds.
A study, by Sheppard and Lane (1968), of a male and
female for the first 141 days of life showed that the
fundamental frequency for the male baby's cry was 443 Hz with a range of
404-481 Hz. The mean for the female baby was 414 Hz with a range of 384-481 Hz.
Ostwald (1963) emphasized that the fundamental frequency of a newborn infant's
cry may fluctuate from 400 Hz to 600 Hz. Other studies have shown that a pitch
range from 300 Hz to 800 Hz is possible. The cries of pain and hunger of the
average neonate are produced within a frequency range rising to
500 Hz (Maddern, Campbell and
Stool,1991). This accounts for the heartrending and ear-splitting potential of
the infant cry. The amplitude of these wails appears not to have engaged the
interest of most researchers in the field. Langlois, Baken and Wilder (1980)
comment on the fact that scant attention has been paid to the infant's
development of respiratory control despite its relevance to the understanding
of speech development.
It is generally believed that a mother is able to identify the cause of her baby's crying, whether hunger
or pain, by its acoustic quality. However, it has been found that mothers could
not identify cry samples correctly according to the cause of the cry. In a review of studies of perceptual identification of cry types, Hollien
(1980) concluded that cries actually contain insufficient perceptual information
to identify the reason for crying. The cry attracts the mother's attention and
is subsequently categorized by environmental clues. Increases in amplitude and
duration of wails provide information regarding the degree of distress.
However, a mother can identify the voice of her own infant
crying. Valanne et al. (1967) examined the ability of mothers to identify the
hunger cry of their own newborn infants during the lying-in period. They found
that mothers were successful in identifying their own babies from an audiotape
recording that included various other infants. Formby (1967) and Murry (1980) reported similar findings. The baby's cry has individual and personal characteristics, as one would expect from the fact that they have different physiognomies.
Vegetative sounds
Infants produce a range
of non-crying sounds described as
'vegetative'. These include coughs, burps, hiccups, lip smacking and sucking, spitting, etc., accompanied by ingressive
as well as ingressive breathing.
The study of vegetative sounds is naturally less
interesting than that of infant
cries. The gradual emergence of 'comfort sounds', as Lewis (1936)
described them, as distinct from discomfort cries, is the first step in
the acquisition of speech.
Vocal play and babbling are an
important transitional stage of development leading
into the prosodic features of speech.
Prelinguistic tonal
development
Lewis (1936), in his classic study of infant speech, distinguished
both discomfort and comfort sounds. He stressed the pleasure evinced by the
baby in making and experimenting with musical vowel-like sounds, and also the
pleasure shared by the mother and her response in encouraging these first
elements of vocal communication. At 6 weeks an advanced baby's response to a strange face
and voice is negative, but mother's face and voice evoke when she is out of sight. The first smile appears a
couple of weeks later and coos, gurgles and little shrieks are produced,
especially when the baby is spoken to and caressed (Weisberg, 1963; Stark, 1979; Illingworth, 1980).
Mother and responsive
childminders reinforce social reactions, especially by talking to the baby, all
of which is crucial for normal emotional and speech development. The child
therefore needs to be caressed and talked to when handled.
The comfort sounds increase
steadily. A healthy sign is the variability and pitch range of the musical glides
that are emitted. This indicates the maturation of the vocal folds and improved
muscular coordination. Expiration is matched to phonation and control of breath
groups subserves vocal expression (Lieberman, 1967). Throughout the developmental sequence cortical and neuromuscular
maturation keep pace.
Upward glides appeared in these
babies first, then rising and falling glides which increased in quantity and
range progressively, covering approximately an octave at 6-7 months. The influence of heard speech, described by Piaget (1952) as
'contagion', is obviously strong in this development and is present as early
as 1 month of age. The great versatility in vocal behavior is confirmed by
Murry, Hoit Dalgaad and Gracco (1983) in their study of one child's hunger,
discomfort and non-distress cries from 2 to 12 weeks of age. They clearly
distinguished seven melody types in each of the three categories of
vocalization. The rapid shifts and wide frequency range reflected increasing
respiratory and phonatory control, exhibiting early communication behavior.
CHILDHOOD
Ø Upper respiratory tract
From 4 years until puberty, the
dimensions of the entire vocal tract are increasing in conjunction with
improving neuromuscular coordination. The larynx of the 2-year-old child is at
the level of the mid-portion of C5, and it continues to descend relatively
rapidly until it is at the level of C 6 at the age of 5 years. It does not
reach its adult position with the lower border of the cricoid cartilage at the
level of the C6-C7 vertebral disc until the individual is aged 15 years
(Maddern, Campbell and Stool, 1991).
Ø Lower respiratory tract
Throughout childhood, there are
developmental changes in the respiratory system and breathing for speech
differs significantly from adults' speech breathing patterns. Four-year-old children,
for example, exert far more expiratory effort in speech breathing than adults,
and 7 year olds use relatively higher
lung volumes to initiate vocal fold vibration than older children and adults
(Netsell et al., 1994). Before puberty, lung function is
almost identical in boys and girls of equal size. Boys' chests, however, grow
in lateral and longitudinal dimensions more than those of girls. It is interesting
to note that a low level of activity in childhood affects the size of the
lungs. Cotes (1979) found that children living in high blocks of flats, where
the opportunity for exercise was limited, had 7% less vital capacity than
physically active children. This is a factor that must not be overlooked in
measurements of airflow and phonation time in children.
Phonation
The fundamental frequency
continues to decrease with age as the larynx enlarges and the vocal folds
increase in mass (Robb and Saxman, 1985). By 5 years, the child's speaking voice settles at a median pitch in the region of middle C, or maybe two or three semitones higher. The child's singing range varies
very little between "boys and girls at the age of 7 years (Tarneaud, 1961). At 8 years, the lower range is only slightly extended and
by 9 years the range extends a little further in both directions from B2 to D4.
ADOLESCENCE
Ø Upper respiratory tract
Laryngeal
skeleton changes
At the onset of puberty and
during the period from 10 to 14 years, there is a dramatic period of general
growth associated with increased secretion of androgens in the male and
oestrogens in female. As the hormonal changes take place, male and female secondary
sexual characteristics emerge. The mutational period may be complete at 14
years in boys, but in girls it continues on average until 15 years. The
dimensions of the vocal tract reflect this period of growth and differences
between males and females. Laryngeal dimensions in the male are generally
larger and the thyroid cartilage changes its configuration. Until puberty, the
angle of the thyroid cartilage is 120° in both males and females. During
pubertal change in the male, the thyroid cartilage enlarges significantly and
the angle, decreases to 90°, giving rise to the marked thyroid prominence known
as the Adam's apple.
Vocal
fold length
The
increased size of the laryngeal skeleton is reflected in the length of the
vocal folds. In girls, the mean length of the vocal folds is 15mm before
puberty and this may increase to 17 mm in a contralto. During the mutational
period, a boy’s vocal folds double in length and may increase to a maximum of
23 mm in the bass voice. The normal minimum vocal fold length for the male is
17 mm, so it can be seen that a tenor and a contralto may have much the same
pitch range, but it is the larger resonators of the larynx, pharynx and the
chest that distinguish the male from the female voice.
Vocal fold histology
The
layer structure of the lamina propria of the vocal fold continues mature in
adolescence and it is not until 16
years
that it resembles the structure of the adult vocal fold. Before this, the
layers are less well defined. The change in the inner structure of the vocal
fold mucosa is a significant factor in voice mutation, besides the increase in
length of the vocal folds.
Ø Lower
respiratory tract
The
young adult has approximately four times the lung volume of the 5 year old. Vital capacity is at its peak
during the late teens and early 20s, after
which it gradually
deteriorates with reduced diaphragmatic action. Breathing rate rest is between 10 and 22
breaths/min
(Perkins and Kent, 1986).
Laryngeal cartilage enlarges,
laryngeal muscles enlarge, V.F lengthen, epiglottis
enlarges,
flattens, elevates, neck elongates, larynx descends,
thorax enlarges, resonators enlarge.
Post-puberty
18
years
137 Hz 210
Hz
Phonation
Speaking fundamental
frequency
As
the vocal folds double in length in the male, the voice drops an octave whereas
girl’s voices mature gradually as a result of the enlargement of the larynx,
consistent with general body growth. Voice mutation and voice pitch are
associated with the growth of the larynx and lengthening of the vocal folds. It
is possible, however that the dramatically lowered speaking fundamental
frequency in the male does not result entirely
from the lengthening of the vocal folds, but also reflect changes in their mass
and the developing differentiation of the histological layers
(Harries et al., 1998). McGlone and Hollien (1963) found that a girl's
vocal pitch is at its highest at 7-8 years, drops 2.4 semitones between 11 and
15 years, and remains at much the same level throughout life. Michel, Hollien
and Moore (1966) recorded the speaking fundamental pitch of 15-, 16- and
17-year-old girls and found that this was 207 Hz. This indicates that
fundamental frequency is established at 15 years in girls when pubertal
mutation is over, although body growth continues up to 20 years of age and
beyond.
Vocal
shifts and breaks
Weiss
(1950) defined 'break of voice' as a sudden and involuntary change in the pitch
and quality. 'Voice break' should therefore be properly confined to the
characteristic fluctuations in pitch and quality in adolescence during the
period of voice mutation. The voice may rise or fall an octave, rising to
falsetto or falling to the bass notes. The voice 'breaks' analyzed in the work
of American workers described below refer either to the
mutational period of voice break in adolescence or to
'shifts' in pitch during childhood. These shifts consist of abrupt and
uncontrolled rises and falls in vocal pitch resulting from poor coordination of the
laryngeal musculature, associated with general bodily growth. In pre pubertal
boys, these shifts do not have the masculine quality that is so conspicuous and
bizarre a feature of the real break of voice in adolescence. The
young boy's resonator system naturally cannot produce the necessary resonance
characteristics of the adult male voice.
Vocal shifts appear to be a normal physiological
feature of juvenile laryngeal function. These shifts may also be aggravated by vocal
strain imposed by vocal abuse in children who shout and scream at
football matches and in the playground. Vocal shifts
and subharmonic breaks were recorded in infants by Wasz-Hockert et al.
(1968). Fairbanks, Wiley and Lassman (1949) studied
the voice breaks in voices of 7- and
8-year-old boys and girls. They concluded that the pitch changes recorded
occurred as frequently in girls as in boys and were not sex linked or confined
to adolescence.
Luchsinger (1962) stated
that the real voice 'break' or 'stormy' mutation occurring in male adolescence
is not the general rule and is encountered in only a minority of boys as a
result of vocal or psychogenic strain. Weiss (1950) suggested that the sudden
drop or rise in the voice, changing momentarily from the childish treble to the
adult male voice or vice versa, is so conspicuous that it has accordingly been
considered the main characteristic of the pubertal voice change, whereas it is
actually uncharacteristic.
Singing in adolescence
In his book The Voice of the Boy (1919), Dawson
attributed pitch breaks to collapse of
the voice caused by misuse and
vocal strain. None of his pupils suffered from 'breaking' of the speaking or
singing voice. The boys' voices just slid down the scale. He evaluated the pitch of their singing voices at frequent
intervals and shifted them after 12.5
years from soprano to alto, and
gradually to tenor or baritone by 15 years as their voices dropped with growth of the
larynx. He attributed failure to sing well to vocal abuse in
early childhood and advocated early framing in breathing technique. Most
experts stress the dangers for both boys and girls of singing in the mutation
period and will not permit serious voice training to begin until 17 years with
girls and 18-19 years with boys. Weiss pointed out that very few
choirboys, possibly a mere 2%,
ever turn into good adult singers
and this he attributed to the irreparable damage that had occurred in adolescence. Some singing teachers
and choirmasters have little knowledge of the anatomy and physiology of the
vocal tract, do not instruct their pupils in the fundamentals of good voice
production and fail to appreciate the dangers of the pubertal period.
The
mutational period of the singing voice lasts much longer than that of the
speaking voice and this also is not often understood and recognized. Growth in
height may continue long after the voice has 'broken', and during this time the
voice is vulnerable and cannot achieve its adult potential on account of
physiological immaturity.
In a gist:
|
Structure
|
Infant
|
Adult
|
|
Position of larynx
|
Higher C2-C3(helps infant to suck and
breath simultaneously)
|
Lower, C6-C7
|
|
Vocal tract shape
|
Short and funnel shaped
|
Long and tubular
|
|
Epiglottis
|
Omega
|
Broader
|
|
Thyroid angle
|
Boys:110
Girls:120
|
Males:90
Females:120
|
|
Vocal fold length
|
6-8mm
|
Males:17-23mm
Females:12-17mm
|
|
Vocal fold mucosal
|
Undifferentiated layers & immature
vocal ligament
|
Complex layered
|
|
Laryngeal structure form
|
Soft and cartilaginous
|
Hyoid bone ossifies by 2 years, thyroid
and cricoid ossify by 20-23 years, arytenoids ossify by late 30s
|
|
Thyroid cartilage
|
Broad & short
|
Becomes elongated and assumes proper
shape
|
|
Mean fundamental frequency
|
440Hz
|
Males:120hz
Females:220Hz
|
|
Connection of thyroid cartilage to hyoid
bone
|
Present
|
Absent
|
|
Length of membranous portion of the
vocal folds
|
Same as the cartilaginous portion
|
Membranous portion is 2/3 of the
cartilaginous portion
|
Summary
The cartilages of the infant larynx are much softer and more
pliable than the adult. The thyroid laminae form of a semicircle, which during Growth
becomes more and more angulated, until it approaches 90 degree in mature male
and 120 degree in the female.
• Vocal
fold: 3mm
• 1st
year : 5.5mm
• 5th
year:7.5mm
• 6th
year: 8mm
• 15th
year: 9.5 mm
Rate of growth Of vocal fold
• Growth
rate of vocal fold/antero-posterior growth of the laryngeal cartilages
• At
infancy=1 to 2.3
• At
1st year= 1 to 1.5
• Pubertal
age???
• Male=
10mm
• Female=4mm
With increasing age ossification and calcification of the
laryngeal cartilages begin to occur.
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