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56 The Voice and Voice Therapy
F I GU R E 2 17. Laryngeal arterial circulation.
vocalizations, and (b) the laryngeal motor cortical pathway, which regulates the fine motor control
of voluntary voice production, such as speech and song, as well as voluntary production of innate
vocalizations (Simonyan & Horwitz, 2011). The ability to control various laryngeal behaviors
voluntarily is most prominent in humans, whereas other species, including nonhuman primates,
have limited ability to produce their vocalizations voluntarily. The laryngeal motor cortex, located
within the motor homunculus in the primary motor cortex, executes voluntary laryngeal control
through the multiple pathways both directly and indirectly descending to the brainstem laryngeal
motor neurons in the medulla.
The vagus nerve originates in the nucleus ambiguus of the medulla (Figure 2–18). As it
descends, it splits into the pharyngeal branch, which innervates the soft palate and upper pharyngeal constrictors. It then courses inferiorly and splits off into the superior laryngeal and recurrent
laryngeal branches, the latter of which is so named because it doubles back on itself before
ascending to innervate the larynx. Both the right and left recurrent laryngeal nerves innervate all
of the intrinsic muscles of the larynx except for the cricothyroid. This is innervated by the SLN.
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 57
FIGU R E 218 . The vagus nerve.
58 The Voice and Voice Therapy
The extrinsic muscles are primarily innervated from the ansa cervicalis. Innervation of the soft
palate, pharynx, and larynx is explored further in Chapter 5.
Lifespan Changes in the Larynx and Voice
The larynx undergoes significant changes throughout the human lifespan, evolving from birth,
through adolescence and adulthood, and into the older adult years. These transformations, observable in both the external and internal structures of the larynx, play a critical role in the variations
heard in the voice over time. Understanding these changes is fundamental for voice clinicians to
effectively manage voice disorders in patients across different age groups. (The interested reader is
referred to Chodzko-Zajko [1997] for a review of normal aging and human physiology.)
Contrary to common perception, the pediatric larynx is not merely a smaller version of the
adult larynx. Key differences include the position of the larynx in the neck, the size and shape of
the laryngeal cartilages, and the structure of the vocal folds. In children, the larynx is positioned
higher in the neck and descends to its adult position after puberty. This descent is accompanied
by a lengthening and widening of the pharynx, influencing voice resonance changes. The laryngeal
framework in children is softer, making it less prone to blunt trauma but more susceptible to
collapse and airway compromise. The pediatric hyoid bone is positioned lower and may overlap
the thyroid cartilage. Notably, the Adam’s apple, or thyroid prominence, is absent in children and
emerges during puberty. The angle of the thyroid laminae in newborns is around 120°, similar to
adult females but wider than in adult males. The cricothyroid space in children is narrow and less
palpable. Pediatric vocal folds are significantly shorter, growing rapidly during puberty to reach
adult lengths of approximately 17 to 21 mm in males and 11 to 15 mm in females. Newborns lack
a vocal ligament, which develops between ages 1 and 4 years. The vocal fold mucosa in newborns
is thinner, with the lamina propria evolving from a single layer to a fully differentiated covering
by the end of puberty.
As individuals enter their 60s and beyond, physiological systems undergo structural changes,
impacting the muscular movements’ accuracy, speed, range, endurance, coordination, stability,
and strength. These changes, along with alterations in the nervous, respiratory, and supralaryngeal
systems, contribute to the modifications observed in the older voice. (The interested reader is
referred to Zraick and colleagues [2006] for an extensive review of speech and voice changes in
older adult speakers.)
Age-related laryngeal changes include hardening of the laryngeal cartilages, atrophy and
degeneration of intrinsic laryngeal muscles, deterioration of the cricoarytenoid joint, degeneration
of glands in the laryngeal mucosa, and changes in the lamina propria and conus elasticus. Additionally, there is a decrease in laryngeal blood flow. These changes often lead to presbyphonia, an
age-related voice disorder characterized by perceptible alterations in pitch, pitch range, loudness,
and voice quality in older speakers. Presbyphonia, as detailed in Chapter 8, presents unique challenges in voice therapy and requires specialized approaches for effective management.
Understanding the developmental and aging processes of the larynx is crucial for the voice
clinician. This knowledge allows for a more tailored approach in diagnosing and treating voice
disorders, taking into account the physiological and anatomical variations that occur from infancy
to older age. This comprehensive view ensures that the clinician can provide the most effective
care for their patients, regardless of age.
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 59
Voice Production
In this section, we go into further detail about the muscular and aerodynamic adjustments essential
for initiating and sustaining phonation. This section provides a comprehensive understanding
of these processes, crucial for students in speech-language pathology to grasp both normal and
abnormal voice production.
To commence phonation, sufficient respiratory drive is imperative. The minimum phonation
threshold pressure (PTP), estimated at 2 to 3 cm H
O, is necessary to initiate voice production.
2
Beyond this, a series of neurologically controlled adjustments take place, involving both laryngeal
and respiratory mechanisms. These adjustments modulate the larynx’s resistance to subglottal
air pressure, the stiffness of the vocal folds, and the configuration of the glottis. The combined
effect of these changes influences key aspects of the voice such as pitch, loudness, and register, as
highlighted by Hixon, Weismer, and Hoit (2018).
For the vocal folds to vibrate, they must first be correctly positioned within the larynx.
This positioning is achieved through active muscular forces that draw the vocal folds toward the
midline, allowing them to be set into motion by the exhaled air. Once the vibration of the vocal
folds begins, their movement becomes largely passive. This means that the vocal folds are no
longer actively pulled apart or drawn together by muscular forces. Instead, sustained vibration is
maintained by the interplay of aerodynamic forces with the biomechanical properties of the vocal
folds. Each cycle of vibration involves a consistent movement of the vocal folds toward and away
from the midline. These rapid and repetitive movements serve to valve the airstream, producing
puffs of air that excite the pharyngeal, oral, and nasal cavities, resulting in the production of sound
(Hixon et al., 2018).
In the following sections, we present an overview of voice registers and discuss the mechanisms for modifying vocal pitch, loudness, and quality. This information forms the foundation
for understanding the complex processes involved in voice production. It is our hope that this
knowledge will equip voice clinicians with the necessary tools to analyze and approach both typical
and atypical voice conditions effectively.
One Cycle of Vocal Fold Vibration
Figure 2–19 illustrates one cycle of vocal fold vibration: (1) The vocal folds adduct (come to
midline) by contraction of certain intrinsic laryngeal muscles; when fully approximated, there is an
increase in subglottal air pressure relative to supraglottal air pressure. (2) The increased subglottal
air pressure causes the vocal folds to separate first on their inferior border and then (3)their
superior border, eventually abducting completely (but not necessarily widely). (4) A puff of air
is released as the vocal folds abduct (separate completely). (5 and 6) The decreased air pressure,
coupled with the elastic recoil of the vocal folds, causes them to move back toward midline.
(6–8) The vocal folds approximate first on their inferior border and then their superior border in
a zipper-like manner, eventually adducting (but not necessarily tightly or forcefully). Thus, the
vocal folds have completed one cycle of vibration (closed–open–closed) due to both myoelastic
and aerodynamic forces, not simply repetitive muscle contraction.
This cycle of vibration will repeat as long as sufficient subglottal air pressure (on the order of 3
to 5 cm H
O at minimum) can build up to blow the vocal folds apart again (see Sidebar 2–14). This
2
60 The Voice and Voice Therapy
cycle is repeated approximately 125 times per second (Hz) in the habitual phonation of an adult
male, approximately 225 Hz in an adult female, and approximately 265 Hz for a prepubertal child.
SIDEBAR 214. To appreciate the role of air pressure, do the following: Hum an
/i/ and while holding the tone, occlude the nostrils with your thumb and forefinger.
Note that the sound stops. Why? Because the cross glottal pressure drop is eliminated.
You cannot have phonation without the airflow, which is created by the transglottal
pressure stop.
Cover-Body Theory
The cover-body theory, as proposed by Hirano and colleagues (1983), offers an insightful perspective on vocal fold vibration. This theory meticulously dissects the complex structure of the vocal
F IGU RE 219. Schematic coronal section through
the vocal folds, demonstrating mucosal wave
propagation.
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 61
folds into three distinct vibratory divisions based on their biomechanical characteristics. These
divisions include (a) the compliant cover, composed of the outermost layers that are relatively
pliable; (b) the transitional zone, which is somewhat stiffer; and (c) the body, the least compliant
part of the vocal fold, providing essential mass and stiffness.
In this model, the body of the vocal fold is the foundation or the core structure, contributing
mass and rigidity. This solidity forms the base on which the more pliable cover can oscillate, or
in more descriptive terms, “undulate.” This dynamic is particularly evident during a laryngostroboscopic examination, where the motion of the cover can be observed as the mucosal wave, a key
indicator of healthy vocal fold function (Hirano & Bless, 1993).
Stemple and colleagues (2018) expand on this concept by describing three specific vibratory
patterns observed in wave phonation. These include horizontal vibration, moving from the medial to
the lateral edges of the vocal folds; longitudinal vibration, extending from the anterior to the posterior
aspects; and vertical vibration, traveling from the inferior to the superior part of the vocal folds. Each of
these vibratory patterns contributes to the overall movement and effectiveness of vocal fold vibration during phonation.
In a typical scenario of normal vocal fold vibration, the extent of movement is quite remarkable. The horizontal excursion of the vocal folds, for example, is estimated to range from 1 to
2 mm, while the longitudinal excursion can span from 3 to 5 mm. This intricate interplay of
movements across multiple planes underscores the complexity and efficiency of the vocal fold
mechanism.
Understanding the cover-body theory is crucial. It provides a fundamental framework for
analyzing vocal fold function and is essential for diagnosing and treating various voice disorders.
Recognizing the nuances of vocal fold vibration as well as the specific roles and behaviors of its
different layers is vital in developing a comprehensive approach to voice therapy.
Laryngeal Adjustments for Speech
The larynx is capable of making remarkably fast and accurate phonatory adjustments during
speech. To illustrate, examine the following two written phrases: “He went to seven zoos” and
“Iwore seven shoes.” When saying these phrases aloud, one can appreciate that each phrase consists
of a combination of voiced and voiceless phonemes (sounds), in different sequences. For these
phrases to sound right when spoken aloud, the larynx must adjust to the phonetic demands placed
on it. That is, the laryngeal musculature must adjust so that the voice turns on when it should,
stays on when it should, and turns off when it should. On top of that, the voice that is produced
must be acceptable in terms of pitch, loudness, and quality.
Moore and von Leden (1958) described three types of vocal onset (or attack) (see Sidebar2–15):
breathy, glottal, and simultaneous. Breathy vocal attack involves releasing significant airflow
before adducting the vocal folds. This occurs frequently during running speech, because we keep
air flowing throughout the production of long strings of words (Seikel et al., 2025). Glottal
attack is characterized by adduction of the vocal folds prior to the airflow (much like a cough).
Adduction of the vocal folds occurs during the prephonatory adjustment (Seikel et al., 2025).
Simultaneous vocal attack involves coordinating adduction and onset of respiration so that
they occur simultaneously. The vocal folds reach the critical degree of adduction at the same
time that the respiratory flow is adequate to support phonation (Seikel et al., 2025). These three
types of attack are all normal. Problems arise, however, when a particular type of attack (typically,
62 The Voice and Voice Therapy
glottal or breathy) is misused. For example, hard glottal attack is a misuse of normal glottal attack.
This abnormal laryngeal adjustment is often associated with the “drill sergeant” voice — a voice
where the onset of each word is greatly punctuated in terms of attack and loudness. In another
example, breathy vocal attack is often associated with the Marilyn Monroe voice — a voice that
is light and airy throughout an utterance, regardless of linguistic content. Simultaneous attack is
considered the most optimal means of initiating phonation, because it places less stress and strain
on the vocal folds. In Chapter 7, we present voice facilitating approaches to reduce breathy or
hard glottal attack.
SIDEBAR 215. To illustrate each of these, look again at the two phrases and do
this: place your right index finger on your Adam’s apple and your left index finger just
in front of (but not touching) your lips. Now, say the first word of each phrase (he
versus I ), paying close attention to the sensations on each finger during each utterance.
When saying he, you should feel exhaled air on your left finger prior to feeling vibration
of the vocal folds on your right finger. This is an example of breathy vocal attack; that
is, air begins to flow before the vocal folds adduct. When saying I, you should feel the
opposite sensation; that is, exhaled air on your left finger is felt after vibration of the
vocal folds is felt on your right finger. This is an example of glottal attack; that is, air
begins to flow after the vocal folds are firmly adducted (much like in a cough). A third
type of attack, called simultaneous vocal attack, can be appreciated by examining the
word zoos in the first sentence. During production of the /z/ phoneme in the initial
word position, you should feel exhaled airflow and vocal fold vibration at the same time.
Looking again at the word zoos in the first sentence, one can also appreciate two additional
laryngeal adjustments: sustained phonation and termination of phonation. Once phonation
begins, the vocal folds must be actively held in a position within the airstream that allows their
continued vibration. Placing your two index fingers in position again, you should feel ongoing
airflow and vocal fold vibration throughout the utterance. Compare this to production of the word
vice, where vocal fold vibration ceases just prior to production of the final /s/ phoneme. As with
voice onset, we terminate phonation continuously during running speech to accommodate voiced
and voiceless speech sounds. To help you appreciate this phenomenon, analyze the following
phrase, “When sunlight strikes raindrops in the air.” Count the number of times vibration begins
and then ceases and identify the sounds on which these events occur.
Voice Registers
Consider for a moment whether your voice quality changes as you speak or sing at various pitch
levels within your overall pitch range. Chances are it does. The voice quality near the bottom of
your pitch range is likely very different from that near your habitual speaking pitch, and both are
likely very different from the voice quality near the top of your pitch range. You probably also
perceived a consistent voice quality within each of these three broad areas of your range but not
across them. That is, there may have been an abrupt change in voice quality as you moved through
your range (particularly if you are an untrained singer). The concept of vocal register addresses the
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 63
vocal phenomena we just considered. To best understand vocal registers, it is helpful to first define
the mode of vibration of the vocal folds during sustained phonation. Mode of vibration refers
to the pattern of activity that the vocal folds undergo during a cycle of vibration (Laver, 1994).
Vocal register refers to differences in the mode of vibration of the vocal folds. There are a number
of vocal registers, the most commonly used of which are modal, glottal fry, and falsetto, with
other registers such as whispering, breathy, and pressed also available (Laver, 1980). The modal
register, often referred to as the “normal” or “chest” voice, is one of the primary vocal registers
utilized in everyday speech and singing. In this register, the vocal folds vibrate in their entire
length and mass, producing a range of pitches that are typically used in normal, conversational
speech. This register is distinguished by a comfortable pitch and loudness level, with a clear,
natural tone quality. Conditions such as vocal fold nodules, polyps, or muscle tension dysphonia
can be linked to inefficient or excessive use of this register. The glottal fry register, also known as
the pulse register, represents the lowest range of vocal pitches and is characterized by a distinct,
creaky, popping sound. It occurs at the lower limits of the vocal pitch range and is marked by a
loose, slack vibration of the vocal folds. In glottal fry, the vocal folds vibrate at a much slower rate
compared to the modal register. The vibration involves only a portion of the vocal folds, with the
arytenoid cartilages being drawn together tightly, causing the vocal folds to compress and release
in a periodic, slow “popping” manner. This results in a series of low-frequency, irregular vibrations
that produce the characteristic “creaky” sound. Excessive or prolonged use of this register can lead
to vocal fatigue and strain. The falsetto register represents the highest range of pitches a person can
produce. It is characterized by a light, airy, and flute-like quality. This register is markedly different
from the modal voice in terms of pitch and tonal quality. In falsetto, the vocal folds lengthen and
thin out significantly, allowing only their edges to vibrate. Unlike the full-bodied vibration seen
in the modal register, the falsetto involves a much more limited contact area, resulting in higher
frequency vibrations. This reduced contact area minimizes the mass of the vibrating portion of the
vocal folds, enabling the production of higher pitches. Misuse or overuse of the falsetto register
can lead to vocal pathologies, such as vocal nodules or polyps. In therapy, voice clinicians often
focus on helping patients find a balance between registers and use their voice efficiently across the
entire vocal range. Teachers of voice strive to blend the various registers so that the difference in
quality of the voice becomes almost imperceptible as the singer transitions from one register to the
next. Some singers seem to have only one register; no matter how they change their pitch, their
voice always seems to have the same quality, with no discernible break toward the upper part of
the pitch range. This is no small accomplishment and requires considerable voice training. It is a
highly regarded attribute in the professional singing voice.
How We Change Vocal Pitch
Vocal pitch, an essential attribute of voice perception, is directly correlated with the frequency or
rate of vocal fold vibration. When the fundamental frequency of the vocal folds changes, this is
perceived as a change in pitch by the listener. The rate of vocal fold vibration is primarily influenced by three bio mechanical factors: the length of the vocal folds, their tension, and their mass
per unit length. Additionally, changes in subglottal pressure accompany frequency adjustments,
playing a role in achieving the desired vibration rate. All these elements interact intricately to
modulate the target frequency of the vocal folds.
64 The Voice and Voice Therapy
A key aspect in this modulation is the lengthening of the vocal folds. When the vocal folds are
elongated, similar to the stretching of a rubber band, their tension increases, and their mass per
unit length decreases. This process results in faster vibration of the vocal folds. The cricothyroid
muscle is the primary intrinsic laryngeal muscle involved in this lengthening and consequent
pitch change. Its contraction increases the distance between the anterior thyroid cartilage and
the arytenoid cartilage. Another muscle, the thyrovocalis, also contributes to pitch alteration. Its
contraction pulls the cricoid and thyroid cartilages farther apart, increasing tension in the vocal
folds, particularly when counterbalanced by the antagonistic action of the cricothyroid muscle.
Conversely, when the vocal folds become shorter, less tense, and thicker, their rate of vibration
slows down, leading to a lower pitch perception. The thyromuscularis muscle plays a pivotal role in
this process. Its contraction brings the arytenoid cartilages forward, which relaxes and adducts the
vocal folds, thus lowering the pitch. At the higher end of the natural pitch range, an increase in the
elasticity of the vocal folds leads to greater glottal resistance. This necessitates a rise in subglottal air
pressure to produce higher frequency phonations (see Video 2–3). The tension of the vocal folds,
which increases with higher pitch, requires more air pressure for vibration initiation. As outlined
by van den Berg (1958), to increase pitch, an average person must slightly elevate subglottal
air pressure. However, this increase in pressure tends to separate the vocal folds, necessitating
a continuous increase in their tension (longitudinal tension) to maintain their approximated
position. While the length, mass, and tension of the vocal folds are the primary determinants
of vocal frequency, frequency increases are generally accompanied by rising subglottal pressures,
enhanced medial compression of the vocal folds, and increased rates of glottal airflow.
How We Change Vocal Loudness
Vocal loudness is a perceptual attribute that is correlated with the intensity of the sound wave
generated during phonation. As intensity changes, the listener perceives a change in loudness. The
intensity of the voice, which significantly influences our perception of loudness, is governed by three
primary biomechanical factors. First, subglottal pressure, as explained by Hixon and Abbs (1980),
plays a pivotal role. This pressure, generated by the respiratory pump and contingent on the volume
Video 2–3. In this video, we observe a
patient who presents with strained, strangled
vocal quality and monopitch and monoloudness associated with spastic dysarthria due
to a series of small ischemic strokes. Note
how the voice facilitating approach of pitch
inflection increases the inflection of target
words. Grand Rounds: What is happening at
the laryngeal level to produce words that are
longer, louder, and elevated in pitch?
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 65
of air in the lungs, increases with prolonged closure of the vocal folds during phonation, thereby
enhancing vocal intensity. Second, medial compression of the vocal folds also determines intensity.
When the vocal folds are brought together more forcefully, they offer greater resistance to subglottal
pressure, resulting in a more powerful release of air on opening and thus increased loudness. Last,
the dynamics of vocal fold closure, including the duration, speed, and completeness of closure,
directly affect sound intensity. Faster and more complete closure of the vocal folds contribute to a
heightened intensity, leading to a louder voice. (see Sidebars 2–16 and 2–17). In addition to the
biomechanical factors, supraglottal adjustments play a role in modulating vocal loudness. These
adjustments involve the articulators above the vocal folds, including the pharynx, oral cavity, and
nasal passages. Alterations in the shape and configuration of these structures can amplify or dampen
the sound produced by the vocal folds, thereby influencing the perceived loudness. For example,
individuals with Parkinson’s disease often present with reduced vocal loudness (hypophonia) because
of reduced range of motion of mouth opening. Instructing these patients to open their mouth wider
for speech results in a louder voice because the voiced energy now has a greater space to exit.
SIDEBAR 216. Place your fingertips on your rib cage and feel what happens as you
count aloud from 1 to 10 at a normal and constant loudness level. Repeat this exercise,
steadily increasing loudness as you say the numbers 6 to 10. What you likely felt was
an expansion of your rib cage.
SIDEBAR 217. Think of the sound of a hairdryer and how much louder the air
is coming out of the nozzle when the dryer is set to a higher fan speed compared to a
lower fan speed.
How We Change Vocal Quality
Voice quality, as outlined by Behrman (2007), is a complex perceptual attribute that extends
beyond the basic parameters of pitch and loudness. It is this aspect of voice that imparts uniqueness,
allowing us to distinguish one voice from another even when pitch and loudness are comparable.
According to Pershall and Boone (1987), alterations in voice quality are primarily influenced by
two factors: the characteristics of the glottal source and the resonant features of the vocal tract.
These elements interact to shape the distinct sound of an individual’s voice.
The glottal source, or the sound generated by the vibration of the vocal folds, plays a critical
role in determining voice quality. Variations in the tension, mass, and closure of the vocal folds
can significantly affect the timbre and texture of the voice. For instance, a breathy voice quality
may result from incomplete closure of the vocal folds, while a harsh or strained quality might arise
from excessive tension.
In addition to the glottal source, the resonant characteristics of the vocal tract, including the
throat, mouth, and nasal passages, contribute to the overall voice quality. The shape and size of
these resonant spaces can amplify or dampen certain frequencies, thereby coloring the sound of
the voice. Alterations in articulation, such as changes in tongue and lip position, also play a role
in modifying these resonant characteristics, further influencing voice quality.