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46 The Voice and Voice Therapy
FIGUR E 210. Extrinsic laryngeal membranes and ligaments.
The Laryngeal Cavity
The laryngeal inlet (aditus laryngis) is the entrance into the larynx (Figure 2–11). It is a triangular
opening, wider in front than in back, that slopes obliquely down and back. Its boundaries are the
epiglottis in the front, the aryepiglottic folds on each side, and the arytenoid cartilages behind.
Its shape is variable, depending on the position of the arytenoid cartilages and the epiglottis. The
laryngeal vestibule is immediately beneath the inlet and contains two protruding sets of mucosal
folds — the ventricular folds (more commonly referred to as the false vocal folds) and the true
vocal folds (more commonly referred to simply as the vocal folds). (We describe these folds later
in this chapter.) The area between the false vocal folds and the true vocal folds is the ventricular
space; within this pocketlike space are sacs that secrete mucus to coat the surface of the vocal folds
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 47
F IGU R E 211. Cross section of the laryngeal cavity.
below. The area between the vocal folds is the rima glottidis; the glottis refers to the vocal folds
and the space in between them. The laryngeal cavity can thus be divided into the supraglottic
(above glottis) space and subglottic (below glottis) space. The subglottis is narrower than the
supraglottis but eventually widens as it joins the tubular trachea. The laryngeal cavity is lined
with a wet mucosa that is continuous with the mucosa of the tongue, pharynx, and trachea. This
mucosa covers the laryngeal cartilages, membranes, ligaments, and muscles and is rich with sensory
48 The Voice and Voice Therapy
receptors and mucous-secreting glands. Irritation or drying of this lining can often contribute to
a hoarse voice quality. In a more serious condition, the epithelial cells constituting this lining can
become malignant, necessitating possible removal of all or part of the larynx.
Laryngeal Joints
The two laryngeal joints are the cricothyroid joint and the cricoarytenoid joint (Figure 2–12).
Both are synovial joints (filled with a lubricating fluid) that achieve movement at the point of
contact of the articulating cartilages. Without these two joints, the vocal folds would not be able to
FI GUR E 21 2. The laryngeal joints.
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 49
approximate (make contact) or change their length. The cricothyroid joint is formed between the
inferior horns of the thyroid cartilage and the posterior cricoid arch. Rotation at this joint results
in the thyroid cartilage tilting downward and also gliding forward and back relative to the cricoid.
This provides the major adjustment for change in pitch. The cricoarytenoid joints are formed
between the superior borders of the cricoid cartilage and the arytenoid cartilages. The movement
at the joint is described primarily as a rocking–gliding motion. The rocking motion at this joint
primarily results in the vocal processes of the arytenoid cartilages swinging downward and inward
(for adduction) or upward and outward (for abduction). The gliding motion primarily results in
changes in vocal fold length. Arthritis or trauma can result in limited or absent motion of the
arytenoid cartilages, resulting in vocal fold immobility (Speyer et al., 2008).
Intrinsic Laryngeal Ligaments and Membranes
Ligaments and membranes connect the laryngeal cartilages to each other. Beneath the mucous
membrane on each side of the larynx is a broad sheet of fibrous tissue containing many elastic
fibers — it is sometimes referred to as the fibroelastic membrane of the larynx. This membrane
(Figure 2–13) has an upper portion, which is called the quadrangular membrane, and a lower
portion, which is called the conus elasticus (also known as the triangular membrane). The dividing
line between these upper and lower membranes is the ventricular space. The paired quadrangular
FI GUR E 213. Conus elasticus and quadrangular membrane.
50 The Voice and Voice Therapy
membrane originates in the lateral margins of the epiglottis and adjacent thyroid cartilage (at a
midpoint between its upper and lower borders) and attaches to the corniculate cartilage and the
lateral surface of the arytenoid. The free superior margins of the quadrangular membranes form
the aryepiglottic folds, which drape an underlying aryepiglottic muscle. The free inferior borders
of the quadrangular membranes form the ventricular ligaments, also known as the false vocal
folds. The conus elasticus connects the cricoid cartilage with the thyroid and arytenoid cartilages
via the medial and lateral cricothyroid ligaments. The free superior borders of the conus elasticus
form the vocal ligaments.
The Intrinsic Laryngeal Muscles
The intrinsic laryngeal muscles connect the laryngeal cartilages to each other. Collectively, the
contraction or relaxation of these muscles results in either the adduction, abduction, tensing, or
relaxing of the vocal folds. These muscles are innervated by various branches of the vagus nerve
(CN X). The following brief descriptions identify each muscle in Figure 2–14; these muscles are
named according to their attachments.
Posterior Cricoarytenoid
This paired muscle is the lone abductor muscle. Its fibers originate from the quadrate lamina of the
cricoid and insert into the posteromedial surface of the muscular process of the arytenoid on that
side (right-sided fibers go to the right muscular process, and so on). Contraction of this muscle
draws the muscular process posteriorly, which pivots the arytenoid cartilage laterally. This results
in abduction of the vocal folds and opening of the glottis. This muscle is particularly active during
more active abduction, such as when needed for a quick or deep inhalation.
Lateral Cricoarytenoid
This paired muscle functions as a direct antagonist to the posterior cricoarytenoid muscle as it
plays its adductor role. Its fibers originate from the arch of the cricoid and insert into the anterolateral surface of the muscular process of the arytenoid on that side. Contraction of this muscle
draws the muscular process anteriorly, which pivots the arytenoid cartilage medially. This results
in adduction of the vocal folds and closing of the membranous glottis. It also results in stiffening
of all layers of the vocal folds (Sataloff, 2005).
Interarytenoid
The only unpaired intrinsic laryngeal muscle, the interarytenoid (IA), is composed of two muscle
bundles, the transverse arytenoid (unpaired) and the oblique arytenoid (paired). Both assist in
adduction and medial compression. Transverse arytenoid fibers originate from the lateral posterior
surface of the arytenoid cartilage on one side and insert into the corresponding surface of the
opposite arytenoid cartilage. Contraction of this muscle bundle draws the body of each arytenoid
cartilage together. Oblique arytenoid fibers originate at the base of one arytenoid cartilage and
attach to the apex of the arytenoid cartilage on the opposite side. Contraction of this muscle
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 51
F IGU R E 2 14. Superior view of the intrinsic laryngeal muscles.
bundle draws the apex of each arytenoid cartilage together, adducting the vocal folds to close the
posterior glottis. The aryepiglottic muscle is composed of oblique IA fibers that have continued
laterally around the apex of the arytenoid and inserted into the epiglottis. Contraction of the
aryepiglottic muscle results in the epiglottis being pulled downward and backward, which results
in the entrance of the larynx being covered.
Thyroarytenoid
This paired muscle forms the bulk of the muscular portion of the vocal folds. Both anatomically
and functionally, this muscle has two compartments: a medial muscle called the thyrovocalis (or
simply, vocalis) and a bulkier lateral portion called the thyromuscularis (or simply, muscularis).
Fibers of the vocalis originate on the inner surface of the thyroid cartilage near the thyroid notch
52 The Voice and Voice Therapy
and insert on the lateral surface of the vocal process of the arytenoid. The vocalis contains a
high proportion of slow-twitch muscle fibers. It is hypothesized that the vocalis is responsible
for controlling the tension of the vocal fold for phonation. Fibers of the muscularis originate on
the thyroid cartilage just lateral to those of the vocalis and insert on the muscular process of the
arytenoid. The muscularis contains a high proportion of fast-twitch muscle fibers and appears
to be specialized to produce fast dynamic movements. It is hypothesized that the muscularis
is responsible for adducting the vocal fold for phonation. Contraction of the vocalis draws the
cricoid and thyroid cartilages farther apart, tensing the vocal folds when balanced by the antagonistic contraction of the cricothyroid muscle. Contraction of the muscularis draws the arytenoid
cartilages forward, relaxing and adducting the vocal folds.
Cricothyroid
This muscle is made up of two components: the pars recta and the pars oblique (pars = part).
Both are vocal fold tensors. The fibers for each component originate from the arch of the cricoid
cartilage and end in two distinctly different insertions. The lower fibers (pars oblique) insert near
the thyroid lamina and the inferior horn of the thyroid cartilage. The upper fibers (pars recta)
insert into the lower surface of the thyroid lamina. When the pars recta contracts, the thyroid
cartilage is tilted downward, and when the pars oblique contracts, the thyroid cartilage is drawn
forward. As a result, the distance between the anterior thyroid cartilage and the arytenoid cartilages
is increased — because the vocal folds are passively strung between the thyroid and arytenoid
cartilages, their length increases, their tension increases, and their mass per unit of length decreases.
This results in faster vibration, which is perceived by the listener as an increase in pitch. The cricothyroid is the only intrinsic laryngeal muscle to receive innervation from the superior laryngeal
nerve (SLN), thus the partial or total inability to change pitch when the SLN is compromised.
The Ventricular (False) Vocal Folds
The ventricular folds (also known as false vocal folds) are two thick, membranous folds, each
enclosing a narrow band of fibrous tissue, the ventricular ligament (see Figure 2–11). The ventricular folds contain numerous mucous glands that help to moisten and lubricate the true vocal folds
beneath them, which is important for laryngeal health and normal voice (Sataloff, 2005). The
ventricular ligament is attached to the thyroid cartilage (immediately below the attachment of
the epiglottis) and to the arytenoid cartilage (a short distance above the vocal process). The lower
border of the ventricular folds is the upper boundary of the laryngeal ventricle. The space between
the ventricular folds is called the rima vestibuli. The ventricular folds should not adduct during
normal phonation; in rare and clinically significant cases, they adduct during phonation, resulting
in what is called ventricular phonation.
The True Vocal Folds
The vocal folds are also two membranous folds, each enclosing a narrow band of elastic tissue,
the vocal ligament. The vocal ligament (see Figures 2–11, 2–14, and 2–15) is attached anteriorly
to the thyroid cartilage (midway between its upper and lower borders) at the anterior commis-
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 53
FI GUR E 215 . The vocal ligaments and thyroarytenoid muscles.
sure, and posteriorly to the vocal process of the arytenoid cartilage. The upper border of the true
vocal folds is the lower boundary of the laryngeal ventricle. The space between the vocal folds is
called the rima glottides (or glottis). Laterally, the vocalis muscle lies parallel with it. The vocalis
is covered by a mucous membrane, which is extremely thin and closely adherent to its surface. In
adult males, the vocal folds are 17 to 20mm long; in adult females, they are 11 to 15 mm long;
and in infants, they are around 3 mm long. The anterior three-fifths of the vocal fold is generally
described as being more membranous, while the posterior two-fifths is described as more cartilaginous, although the ratio of the membranous to cartilaginous portions differs by age and gender.
The midpoint of the membranous part vibrates with the greatest amplitude during phonation; the
cartilaginous part is where the vocal fold attaches to the vocal process of the arytenoid cartilage,
and this part does not participate much in phonation (except at very low pitches). During quiet
breathing, the glottis is somewhat open, with the vocal folds in a paramedian position (that is,
halfway between abduction and adduction). During deep inhalation (forced abduction), the width
may double. During phonation of voiced sounds, the glottis is closed, with the vocal folds in a
median position (adducted). During whispering, the glottis is closed along most of its length but
with a small posterior opening (chink).
The true vocal fold is composed of mucosa and muscle; interwoven throughout are blood
vessels. From top to bottom, the vocal fold has five layers (Figure 2–16), each with a different
cellular makeup and biomechanical properties. The layers are the (a) epithelium; (b) superficial
lamina propria; (c) intermediate lamina propria; (d) deep lamina propria; and (e) vocalis muscle,
which is the medial portion of the thyroarytenoid muscle. The epithelium provides the vocal folds
54 The Voice and Voice Therapy
FIGURE 216. The vocal fold in cross section.
with a shiny white appearance during laryngoscopic exams. Its primary function is to maintain
the vocal folds’ moisture, essential for their health and function. Clinically, its integrity is crucial
for preventing dryness and irritation of the vocal folds.
The superficial lamina propria is composed of elastin fibers, allowing it to be highly stretchable
and to act as a cushion for the vocal folds. This layer’s elasticity is important for the flexibility
and resilience of the vocal folds during speech and singing. Damage or alteration to this layer
can impact voice quality and range. The intermediate lamina propria also contains elastin fibers.
It works in conjunction with the lamina propria above it to provide a balance of flexibility and
strength. Clinically, the health of intermediate lamina propria is essential for maintaining the vocal
folds’ structural integrity and preventing lesions or scarring that could impair voice function. The
deep lamina propria is primarily composed of collagen fibers that restrict excessive stretching. It
CHAPTER 2 Normal Voice: Anatomy and Physiology Throughout the Lifespan 55
plays a supportive role, adding durability to the vocal folds. Clinical issues in this layer can lead
to stiffness and reduced mobility of the vocal folds, affecting voice quality. Beneath the lamina
propria lies the vocal folds’ fifth layer, composed of the thyroarytenoid muscle, which includes the
thyrovocalis and thyromuscularis components. This muscular layer constitutes the majority of the
vocal fold’s mass. Oriented in an anterior-posterior direction, the muscle fibers align accordingly.
This structural arrangement results in a combination of both active and passive elements in the
vocal fold’s anatomy. The thyroarytenoid represents the active component, responsible for vocal
fold movement, while the passive aspects are formed by the lamina propria layers, contributing
strength, cushioning, and flexibility to the vocal folds. Alternative descriptions, such as the coverbody model (Hirano et al., 1983), place these five layers under three headings based on their
biomechanical properties: (a) the compliant cover (epithelium and superficial lamina propria), (b)
a stiffer transitional zone (intermediate and deep layers of the lamina propria), and (c) the least
compliant body (vocalis muscle). Regardless of which description one uses, it is clear that the vocal
fold is not composed of the same tissue from top to bottom; that is, there is a loosely adherent
cover, an underlying vocal ligament providing some stiffness and support, and a further underlying
bulky muscle. The biomechanical properties of the vocal fold have a role in regulating phonation
frequency (F0) and may also play an important role in determining voice quality.
Laryngeal Blood Supply and Lymphatic Drainage
There is a dual blood supply to and from each side of the larynx (Figure 2–17). The two major
arteries supplying the larynx are the inferior and superior laryngeal arteries, branches of the thyroid
artery. The two veins draining the larynx are the inferior and superior laryngeal veins. The inferior
arteries and veins serve the upper larynx, that is, the arytenoid cartilages, the false vocal folds, and
the laryngeal ventricle. The superior arteries and veins serve the lower larynx, that is, the piriform
sinus and the quadrangular membrane. The laryngeal lymphatic vessels drain into the cervical
lymph nodes. Abnormalities in laryngeal blood flow can be observed clinically, most dramatically
in the case of a vocal fold hemorrhage, resulting in immediate and severe dysphonia.
Nervous System Control of the Larynx
Speech production is one of the most complex and rapid motor behaviors, and it involves a precise
coordination of more than 100 laryngeal, velar, orofacial, and respiratory muscles. The paired
vagus nerve (CN X), also known as the wanderer, is a complex and extensive nerve that plays a
crucial role in speech and swallow production. This nerve serves both sensory and motor functions,
sending motor signals to the soft palate, pharynx, and larynx, and picking up sensation from the
entire vocal tract viscera. The sensory branches of the vagus are responsible for informing the
speaker with muscle tension dysphonia that the speaker has the sensation of fullness at the level
of the larynx (globus) after speaking at the bottom of their pitch range. The vagus sends motor
impulses to innervate the muscles of the velum, pharyngeal constrictors, and the larynx that are
so finely tuned that the average speaker is able to produce 14 sounds per second.
Central control of voice production is conducted by two parallel pathways: (a) the limbic
vocal control pathway, which is responsible for the control of innate nonverbal and emotional