Larynx

The larynx, also commonly called the voice box, is a cylindrical space located in the neck at the level of the C3–C6 vertebrae. The larynx is continuous superiorly with the oropharynx and inferiorly with the trachea. This structure is made up of 9 cartilages that are connected by membranes, ligaments, and muscles and that house the vocal cords. The major structures forming the framework of the larynx are the thyroid cartilage, cricoid cartilage, and epiglottis. The larynx serves to produce sound (phonation), conducts air to the trachea, and prevents large molecules from reaching the lungs.

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Development and Gross Anatomy

Development

  • The laryngeal cartilages develop from the 4th and 6th pairs of the pharyngeal arches.
  • The cricothyroid muscle originates from the 4th pharyngeal arch.
  • The rest of the intrinsic muscles of the larynx originate from the 6th pharyngeal arch.

Gross anatomy

The larynx is a framework composed mainly of cartilages held together by muscles and ligaments, both of which are divided into intrinsic and extrinsic forms.

Table: Gross anatomy
CartilageUnpaired
  • Epiglottis
  • Cricoid
  • Thyroid
Paired
  • Arytenoid
  • Corniculate
  • Cuneiform
LigamentsExtrinsic
  • Thyrohyoid membrane
  • Hyoepiglottic ligament
Intrinsic
  • Cricothyroid ligament (also called cricovocal or cricothyroid membrane)
  • Vocal ligaments
  • Quadrangular membrane
  • Vestibular ligaments
  • Aryepiglottic membrane
MusclesExtrinsic
  • Suprahyoid group: stylohyoid, digastric, mylohyoid, and geniohyoid
  • Infrahyoid group: sternohyoid, omohyoid, sternothyroid, and thyrohyoid
Intrinsic
  • Cricothyroid
  • Thyroarytenoid
  • Posterior cricoarytenoid
  • Lateral cricoarytenoid
  • Transverse arytenoid
  • Oblique arytenoid
  • Vocalis
Anterior and right lateral views of the larynx

Anterior (top) and right lateral (bottom) views of the larynx, displaying its anatomical landmarks

Image: “Larynx” by OpenStax. License: CC BY 4.0

Joints of the larynx: 

  • Cricothyroid: allows forward and down tilting movement of the thyroid cartilage between the inferior horns of the thyroid cartilage and the cricoid cartilage 
  • Cricoarytenoid: allows abduction and adduction of the vocal ligaments by means of the cricoid and arytenoid cartilages

Regions of the larynx:

  • Supraglottis: also called the vestibule, extends from the entrance of the larynx to the vestibular folds
  • Glottis: extends from the vestibular folds to the vocal folds
  • Subglottis: extends from the vocal folds to the lower margin of the cricoid cartilage (beginning of the trachea)
Components and regions of the larynx

Components and regions of the larynx

Image by Lecturio.

Cartilages

Unpaired cartilages

  • Epiglottis:
    • Elastic cartilage
    • Leaf-shaped body
    • Entirely covered by mucosa
    • Projects superiorly and posteriorly into the pharynx and functions to close the larynx during swallowing to prevent food from entering the airway
    • Attaches to the hyoid bone superiorly via the hyoepiglottic ligament 
    • Attaches to the thyroid cartilage via the midline thyroepiglottic ligament 
  • Cricoid:
    • Hyaline cartilage
    • Ring-shaped body, making it the only complete ring of cartilage in the larynx
    • Attaches to the thyroid cartilage via the cricothyroid ligament
    • Attaches to the 1st tracheal ring via the cricotracheal ligament
  • Thyroid:
    • The largest of the laryngeal cartilages
    • Hyaline cartilage
    • V-shaped body, with an anterior connection point and no posterior components
    • The anterior connection forms the laryngeal prominence, also known as the Adam’s apple.
    • The posterior aspects of the thyroid’s 2 lateral laminae project upward and downward, creating the superior (bigger) and inferior horns.
    • Attaches to the hyoid bone superiorly via the thyrohyoid membrane and median and lateral thyrohyoid ligaments
    • Attaches to the cricoid cartilage inferiorly via the cricothyroid ligament

Paired cartilages

  • Arytenoid:
    • Hyaline cartilage
    • Pyramid-shaped bodies:
      • Superior apex
      • Anterior vocal process (site of attachment of the vocalis muscle)
      • Lateral muscular process
    • Located superiorly to the posterior portion of the cricoid cartilage, between the lateral laminae of the thyroid cartilage
    • Attaches to the corniculate cartilages at their superior apexes
  • Corniculate:
    • Elastic cartilage
    • Cone-shaped bodies
    • Located superiorly, posteriorly, and medially to the arytenoids and serves to prolong them
    • Enclosed within the aryepiglottic folds of mucosa
  • Cuneiform:
    • Elastic cartilage
    • Club-shaped bodies
    • Located superiorly and anteriorly to the corniculate cartilages
    • Enclosed within the aryepiglottic folds of mucosa

Ligaments and Membranes

The ligaments and membranes of the larynx are responsible for connecting the cartilages and forming 1 single fibrocartilaginous structure. The membranes also fold over and enclose certain cartilages and membranes to comprise the moving and functional parts of the larynx (e.g., vocal cords).

Extrinsic

Thyrohyoid membrane:

  • Wide, fibrous sheet of tissue
  • Connects the hyoid bone to the thyroid cartilage
  • Pierced by the internal laryngeal artery and the internal laryngeal nerve
  • Thickened areas comprise the single median thyrohyoid ligament and the two thinner and smaller thyrohyoid ligaments.

Hyoepiglottic ligament:

  • Thin, elastic tissue
  • Connects the anterior surface of the epiglottis to the upper border of the hyoid bone
  • Protects the supraglottic larynx
Lateral view of the larynx, featuring the membranes and cartilages

Lateral view of the larynx, featuring the membranes and cartilages

Image by Lecturio.

Intrinsic

Cricothyroid ligament:

  • Also called the cricovocal or cricothyroid membrane
  • Connects the lower border of the thyroid cartilage to the upper border of the cricoid cartilage
  • Composed of the median and lateral cricothyroid ligaments:
    • Median: a thickened area at the anterior midline between the cartilages
    • Lateral: also known as the conus elasticus (elastic cone); thinner than the median ligament and extend from the superior border of the cricoid to the inferior border of the vocal ligaments, with which they are continuous
  • An incision is made through this structure during a cricothyrotomy to establish an emergency patent airway.

Vocal ligaments:

  • The free borders of the conus elasticus (lateral cricothyroid ligaments)
  • Extend from the vocal processes of the arytenoid cartilages to the angle of the thyroid cartilage

Quadrangular membrane:

  • Thin, extends between the lateral borders of the epiglottis and the anterolateral margins of the arytenoid cartilages
  • Vestibular ligament:
    • The thick free lower edge of the quadrangular membrane
    • Enclosed in a fold of mucosa to form the vestibular folds (false vocal cords) that extend from the thyroid cartilage to the arytenoid cartilages
  • Aryepiglottic membrane:
    • The free upper edge of the quadrangular membrane
    • Enclosed in a fold of mucosa to form the aryepiglottic folds
    • Reinforced in its posterior portion by the corniculate and cuneiform cartilages, seen as small nodules within the fold
The ligaments and membranes of the larynx

The ligaments and membranes of the larynx

Image by Lecturio.

Muscles

Extrinsic laryngeal muscles

Suprahyoid group:

The suprahyoid laryngeal muscles are characterized by their location above the hyoid bone and function of elevating the hyoid bone and larynx during swallowing and phonation.

Table: Suprahyoid group
MuscleOriginInsertionInnervation
StylohyoidStyloid process of the temporal boneBody of the hyoid boneFacial nerve
DigastricAnterior belly: digastric fossa of the mandibleAnterior and posterior bellies: intermediate tendonAnterior belly: mylohyoid nerve, branch of the mandibular nerve
Posterior belly: mastoid notch of the temporal bonePosterior belly: facial nerve
MylohyoidMylohyoid line of mandibleBody of the hyoid bone and median rapheMylohyoid nerve, branch of the mandibular nerve
GeniohyoidMental spine of the inner surface of the mandibleBody of the hyoid boneC1–C2 of the cervical plexus and the hypoglossal nerve
The suprahyoid group of the extrinsic laryngeal muscles

The suprahyoid group of the extrinsic laryngeal muscles:
The geniohyoid muscle is not shown.

Image by BioDigital, edited by Lecturio

Infrahyoid group:

The infrahyoid laryngeal muscles are characterized by their location below the hyoid bone and by their function of depressing the hyoid bone and larynx during swallowing and phonation.

Table: Infrahyoid group
MuscleOriginInsertionInnervation
SternohyoidDorsal surface of the manubrium and the sternoclavicular jointBody of the hyoid boneC1–C3 of the cervical plexus
Omohyoid
  • Superior border of the scapula
  • Central tendon: deep cervical fascia (clavicle, 1st rib)
Body of the hyoid bone (connected to the carotid sheath)
SternothyroidDorsal surface of the manubriumOblique line of the thyroid cartilage
Thyrohyoid (continuation of sternothyroid)Oblique line of the thyroid cartilageBody and greater horns of the hyoid boneHypoglossal nerve (cranial nerve XII), via the anterior rami of C1
Anterior and lateral views of the infrahyoid group of the extrinsic laryngeal muscles

Anterior and lateral views of the infrahyoid group of the extrinsic laryngeal muscles

Image by BioDigital, edited by Lecturio

Intrinsic laryngeal muscles

The intrinsic laryngeal muscles serve to produce phonation by modifying the length and tension of the vocal cords and the size of the rima glottidis (the opening between the vocal cords).

Table: Intrinsic laryngeal muscles
MuscleOriginInsertionInnervation
CricothyroidAnterolateral portion of the cricoid
  • Oblique portion: inferior horn of the thyroid cartilage
  • Straight portion: inferior margin of the thyroid cartilage
External laryngeal nerve, branch of the superior laryngeal nerve
ThyroarytenoidAngle of the thyroid cartilage and cricothyroid ligamentAnterolateral surface of the arytenoidsInferior laryngeal nerve, branch of the recurrent laryngeal nerve
Posterior cricoarytenoidPosterior surface of the cricoidMuscular process of the arytenoids
Lateral cricoarytenoidArch of the cricoid
Transverse arytenoidLateral border and muscular process of the arytenoidsLateral border and muscular process of the opposite arytenoid
Oblique arytenoidMuscular process of the arytenoidsApex of the opposite arytenoid (with a prolongation to the aryepiglottic folds)Recurrent laryngeal nerve
VocalisLateral portions of the vocal processes of the arytenoidsAnterior portion of the ipsilateral vocal ligament
  • Recurrent laryngeal nerve
  • External laryngeal nerve

Neurovasculature

Blood supply

  • Superior laryngeal artery:
    • Branch of the superior thyroid artery
    • Originates near the upper margin of the thyroid cartilage
    • Accompanies the internal branch of the superior laryngeal nerve
    • Supplies the internal surface of the larynx
  • Cricothyroid artery:
    • Branch of the superior thyroid artery 
    • Supplies the cricothyroid muscle
  • Inferior laryngeal artery:
    • Branch of the inferior thyroid artery
    • Accompanies the inferior laryngeal nerve
    • Supplies the mucous membranes and muscles in the inferior portion of the larynx

Venous drainage

  • Superior laryngeal vein:
    • Joins the superior thyroid vein
    • Drains into the inferior vena cava
  • Inferior laryngeal vein:
    • Joins the inferior thyroid vein
    • Drains into the brachiocephalic vein
Larynx blood supply and innervation

Larynx blood supply and innervation

Image by Lecturio.

Innervation

The innervation of the larynx is supplied by 2 branches of the vagus nerve: the superior and inferior laryngeal nerves.

Superior laryngeal nerve:

  • Originates from the inferior vagal ganglion
  • Divides into 2 branches:
    • Internal laryngeal nerve:
      • Sensory and autonomic
      • Larger of the 2 branches
      • Supplies sensory fibers to the mucous membranes in the laryngeal vestibule and middle laryngeal cavity and to the superior surface of vocal folds
    • External laryngeal nerve:
      • Motor
      • Smaller of the 2 branches
      • Innervates the pharyngeal constrictor and cricothyroid muscle

Inferior laryngeal nerve:

  • Constitutes the main motor nerve of the larynx
  • Continuation of the recurrent laryngeal nerve (branch of the vagus)
    • The left recurrent laryngeal nerve originates in the thorax.
    • The right recurrent laryngeal nerve originates in the root of neck.
  • Accompanies the inferior laryngeal artery
  • Divides into anterior and posterior branches
    • Anterior branch supplies the following muscles:
      • Lateral cricoarytenoid 
      • Thyroarytenoid
      • Vocalis
    • Posterior branch supplies the following muscles:
      • Posterior cricoarytenoid
      • Transverse and oblique arytenoids

Mnemonics:

  • “The larynx is supplied by the Xth (10th) cranial nerve.”
  • SCAR:
    • Superior laryngeal nerve innervates the Cricothyroid muscle.
    • All other muscles are innervated by the Recurrent laryngeal nerve.

Microscopic Anatomy

  • Larynx: mucous membrane containing ciliated columnar epithelium (respiratory epithelium)
  • Folds:
    • Vestibular cords (plicae vestibulares):
      • Stratified nonkeratinizing squamous epithelium
      • Seromucous glands
    • Vocal cords (plicae vocales):
      • Stratified nonkeratinizing squamous 
      • No glands
      • Vocal ligament
      • Vocal muscle

Functions

Table: Functions of the larynx
MuscleFunction
Cricothyroid
  • Forward and downward rotation of the thyroid cartilage
  • Tautens and thins the vocal cords → production of higher-pitched sounds
Posterior cricoarytenoid
  • Abduction and external rotation of the arytenoid cartilages
  • Primary opener of the glottis
Lateral cricoarytenoid
  • Internal rotation of the arytenoid cartilages and adduction of the vocal cords
  • Closes the rima glottidis (“sphincter of the laryngeal inlet”)
  • Aids in the production of whispered phonation
Transverse arytenoid
  • Adduction of the arytenoid cartilages
  • Closes the rima glottidis (“sphincter of the laryngeal inlet”)
Oblique arytenoid
  • Adduction of the arytenoid cartilages and the aryepiglottic folds
  • Closes the rima glottidis (“sphincter of the laryngeal inlet”)
ThyroarytenoidSphincter of vestibule and laryngeal inlet
Vocal muscleAdjusts tension of the vocal folds

Movements of the larynx: 

Depending on the action (e.g., respiration, phonation, etc.), the laryngeal muscles regulate the movements of the vocal cords and determine the size of the rima glottidis, the opening between the vocal cords.

Table: Movements of the larynx
Movements
RespirationIn quiet respiration:
  • Arytenoid cartilages are abducted.
  • Laryngeal inlet is open.
  • Rima glottidis is open and triangle-shaped.
In forced inspiration:
  • Arytenoid cartilages are rotated laterally.
  • Vocal folds are abducted.
  • Rima glottidis is open wider.
Phonation
  • Arytenoid cartilages and vocal folds are adducted.
  • Air is forced through rima glottidis.
Effort closureRima glottidis is completely closed.
Swallowing
  • Laryngeal inlet is narrowed.
  • Rima glottidis is closed.
  • Larynx moves up and forward.
  • Epiglottis swings downward.
The functions of the intrinsic laryngeal muscles

The functions of the intrinsic laryngeal muscles:
Note the effects on the vocal cords and the rima glottidis.

Image by Lecturio.
Head and Neck Larynx and Epiglottis

Intrinsic muscles of the larynx

Image by Lecturio.

Clinical Relevance

Infectious disorders of the larynx

  • Laryngitis: acute inflammation of the larynx; can be infectious or noninfectious: Laryngitis results in fever, hoarseness, pain, or an irritating cough that worsens at night, along with a dry throat and malaise. Runny nose and headache may be associated symptoms.
  • Epiglottitis: acute inflammation of the epiglottis and surrounding structures in the supraglottic space: Epiglottitis is more life-threatening and sudden in onset than laryngitis. Haemophilus influenzae is the culprit in children. Patients present with dysphagia and sore throat, along with dyspnea with or without stridor.
  • Diphtheria: serious bacterial infection caused by Corynebacterium diphtheriae: Diphtheria affects the mucous membranes in the nose and throat, resulting in sore throat, fever, swollen glands, and weakness. 
  • Croup: Croup is a disease caused most commonly by a viral infection or rarely by a bacterial infection that results in swelling inside the trachea and interferes with normal breathing.

Congenital disorders of the larynx

Laryngomalacia: excessive flaccidity of the supraglottic larynx leads it to be sucked out of position during inspiration, which can produce stridor: This condition manifests at birth and disappears after 2 years of age.

Miscellaneous disorders of the larynx

Foreign body aspiration: potentially life-threatening emergency that most commonly occurs in children ages 1–3 years. Presents as sudden onset of coughing, choking, stridor, and dyspnea.

References

  1. Drake, R., et al. Gray’s Anatomy for Students E-Book. Elsevier Health Sciences, 2014.
  2. Standring, S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st ed. Edinburgh: Churchill Livingstone/Elsevier, 2016.

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