Anatomy of Larynx in a Nuthsell

Anatomy of Larynx

• Larynx: aka Voice box

• • Is the organ of sound (for speech)
  • Is part of the respiratory system
  • Held open by cartilage
  • Is covered anteriorly by the infrahyoid muscles
  • Partially covered by the thyroid gland.
  • Normally: The larynx will be anterior to the laryngopharynx
    • Adjacent to levels C3-C6
    • C6 is level of cricoid cartilage
  • Externally seen as the laryngeal prominence (Adam’s apple) which is more so seen in males
  • Composed of cartilage / ligaments (sometimes called membranes)

Cartilages of the larynx: 3 paired and 3 unpaired

• Thyroid cartilage (unpaired)
  • Is the largest cartilage.
  • Made of 2 fused laminae
  • The most superior attachment projects slightly anteriorly as the laryngeal prominence
  • Is incomplete posteriorly. Has structures on posterior margin:

1. 1. • Superior horns = extensions of cartilage that articulate with hyoid bone
      • Inferior horns = articulate with cricoid cartilage

1. Cricoid cartilage (unpaired)
   • Is the only cartilage that forms a complete ring
   • Inferior most cartilage
   • Shaped like signet ring: portions

1. 1. • Lamina = larger flat portion, posterior aspect
      • Arch = the anterior aspect, much thinner

• • Along with thyroid cartilage, this serves as a point of attachment for the inferior constrictor muscle.
  • On the posterior-superior border, have important sight of communication with paired Arytnoid cartilages.
  • On lateral part: has point of articulation with inferior horn of thyroid cartilage.
• Epiglottis: (unpaired) most superior
  • Is leaf shaped fibro-elastic cartilage (all other cartilages are hyaline cartilage)
  • Is in contact with posterior 1/3 of tongue
  • The inferior pointed tip is attached to the internal surface of the thyroid cartilage.
• Arytenoid Cartilages: (paired)
  • Are pyramidal in shape
  • Articulate with cricoid cartilage
  • Key for changing spaces within voice box
  • Laterally projecting Muscular Process: Serves as attachment for intrinsic muscles of the larynx
  • Anteriorly projecting Vocal Process: serves as point of attachment for Vocal Ligaments (R and L)
• Corniculate Cartilages (paired)
• Cuneiform Cartilages (paired)

Membranes: (aka ligaments)

• Thyrohyoid membrane:
  • Stretches between the hyoid bone and the superior margin of the thyroid cartilage
  • Because of this ligament, every action on the hyoid affects the larynx
  • Pierced by 2 structures:

1. 1. • Internal laryngeal nerve (Branch of Vagus)
      • Superior laryngeal artery (Branch of Superior Thyroid artery from External Carotid)

• Cricothyroid membrane:
  • Can only see a portion externally
  • The majority is from extension internally into the larynx
• Cricotracheal ligament: attaches inferior border of cricoid cartilage and the first tracheal ring.

Membranes of Internal Anatomy:

• Quadrangular membrane (R and L)
  • Stretches from the lateral border of the epiglottis to the anterior-lateral surface of the Arytenoid cartilages
  • Has an inferior free margin

1. 1. • Base thickens as a band = Vestibular Ligament
      • This ligament is covered with mucous membrane coatà ligament + membrane = Vestibular Fold (aka False Vocal Folds / Cords)

• Conus Elasticus:
  • Is the internal continuation of the cricothyroid membrane (goes between the cricoid and the thyroid cartilages.
  • Normally seen on the internal side of the cricothyroid cartilage
  • It will end superiorly as a thickened band called the Vocal Ligament

1. 1. • Vocal ligament is covered with mucous membrane
      • Vocal ligament + mucous membrane = Vocal Fold

1. • Vestibular fold is Superior to the Vocal fold

Chambers of the Larynx (3)

• Vestibule:
  • Chamber superior the vestibular fold
  • Vestibular folds are inferior boundary
• Ventricle: Is the space between the vestibular and vocal folds
• Infraglottic Cavity: The space below (inferior) to the vocal folds
• Rima Glottis: The laryngeal inlet
• Rima Glottidis: The space / opening between the Vocal Folds / Cords

• • Extrinsic muscles of the larynx act on the entire larynx as a unit
    • Suprahyoid muscles especially  elevate the hyoid / larynx
    • Infrahyoid muscles depress the hyoid / larynx
  • Intrinsic muscles of the larynx act on the laryngeal cartilages so that they change the position of the vocal ligaments
    • Make the Rima Glottidis more open / closed
    • May slack / tighten the vocal ligaments / Vocal cords.

Intrinsic Muscles of the Larynx: All are innervated by CN X Vagus nerve

• Important articulation is the one between the Arytenoid cartilage and the cricoid cartilage
  • Arytenoids cartilages can pivot and glide
  • Vocal ligaments are adducted when they are touching (the space between them is closed)
• Posterior Cricoarytenoid muscle
  • Attaches posterior aspect of cricoid cartilageà inserts on lateral process on arytenoid cartilage
  • Action: Abduct vocal ligaments
  • This opens the Rima Glottidis
• Lateral Cricoarytenoid muscle
  • Origin: Arch of cricoid cartilage
  • Insert: lateral process of arytenoid cartilage
  • Action: adduct the vocal ligament
  • Closes the Rima Glottidis
• Oblique Arytenoid muscle and Transverse Arytenoid muscle
  • These glide the two vocal ligaments together
  • Act to adduct / close the space.
• Muscles that change the tension on vocal cords
  • Tighten them→pitch will goes higher
  • Loosen thempitch goes lower
  • Does not happen at the Arytenoid-Cricoid articulation, it happens at the Atriculation of the Thyroid cartilage and Arytenoid cartilage.
  • Cricothyroid muscle:

1. 1. • Pulls thyroid cartilage forward
      • Tenses the vocal ligaments

• • Thyroarytenoid muscle:
    • Pulls thyroid cartilage back
    • Loosens the vocal ligaments

Innervation of Larynx:

• Mucous membrane surface superior to vocal folds
  • Innervation from internal laryngeal nerve
  • Pierces thyrohyoid membrane to innervate down to the vocal folds
• External laryngeal branch goes to the Cricothyroid muscle.
• Remainder of mucous membrane is supplied by Vagus’ recurrent laryngeal nerve
  • Enter the larynx inferiorly
  • Responsible for supplying mucous membrane inferior to vocal folds, supplies sympathetics as well
  • Also supplies all intrinsic muscles of the larynx.

Blood supply to Larynx:

• Superior Laryngeal artery
  • Branch of superior thyroid artery
  • Supplies superior aspect of larynx
• Inferior laryngeal artery

1. • Branch of inferior thyroid artery (from the thyrocervical trunk)
   • Supplies inferior aspect of larynx

Phonation:

• During respiration, the vocal folds must be abducted. There is not enough space between adducted ligaments to breath.
• To speak: Inhale → adduct vocal ligaments → exhale → ligaments vibrate to create sound.
• The greater the volume of air that passes, the louder the sound will be.
• Laryngitis: Inflamed mucous membrane in the larynx → swollen and distended → folds can’t be opposed as tightly as they need to be to speak.
• Polyp on the larynx will have the same effect.

Swallowing:

• The laryngeal aperture must be closed off
• If it is not close off, material will go into the trachea
• The epiglottis is right next to the posterior 1/3 of the tongue
• Elevation of the larynx will push the epiglottis against the tongue, thus causing it to depress over the laryngeal aperture.
• Process also involves elevation of the soft palate to wall off the nasopharynx.

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