The Larynx - Complete Anatomy for Beginners

Key point: The PRIMARY function of the larynx is not voice production - it is the protection of the airway during swallowing. Voice production is a secondary, evolutionary bonus.

1. Position and Relations

• Above: connects to the pharynx (throat) and hangs from the hyoid bone
• Below: continuous with the trachea (windpipe)
• Posteriorly: the esophagus lies behind it

2. The Cartilaginous Framework

Unpaired Cartilages

A. Thyroid Cartilage (the largest)

• Formed by a right and left lamina that join in the front
• The point where they fuse projects forward as the laryngeal prominence ("Adam's apple")
• In men, the two laminae meet at a sharper angle (90°), making the Adam's apple more visible; in women it is 120°
• At the top, the superior thyroid notch separates the two laminae - palpable in the neck
• The posterior margin of each lamina extends as a superior horn (connects to hyoid) and an inferior horn (articulates with cricoid cartilage)
• Muscles attach along the oblique line on the outer surface

B. Cricoid Cartilage (the most important structurally)

• Sits below the thyroid cartilage and connects to the trachea below
• It is the only complete ring of cartilage in the entire airway - this makes it unique
• Shaped like a signet ring: broad plate (lamina) posteriorly, narrow arch anteriorly
• The posterior lamina has two oval depressions for the posterior crico-arytenoid muscles, separated by a ridge for the esophagus
• Has articular facets for both the arytenoid cartilages above and the inferior horns of the thyroid cartilage laterally

Clinical note: In children, the cricoid cartilage marks the narrowest part of the airway - this is why a breathing tube placed too tightly can damage this spot.

C. Epiglottis

• A leaf-shaped cartilage made of elastic (flexible) cartilage (not the rigid hyaline type)
• Attached below to the thyroid cartilage angle; its upper portion projects freely toward the base of the tongue
• During swallowing, it folds backward like a trap door to cover the laryngeal opening and prevent food/liquid from entering the airway
• Contains tiny perforations through which glands and nerves pass

Paired Cartilages

D. Arytenoid Cartilages (most functionally important pair)

• Pyramid-shaped cartilages sitting on the upper rim of the cricoid lamina posteriorly
• Each has:
  • A vocal process projecting anteriorly - the vocal ligament attaches here
  • A muscular process projecting laterally - most laryngeal muscles attach here
  • An apex pointing upward - the corniculate cartilage sits on top
• Movement of the arytenoids opens and closes the vocal folds - they can slide, rotate, and glide on the cricoid

E. Corniculate Cartilages

• Small horn-shaped cartilages sitting on top of each arytenoid apex
• They extend the arytenoids slightly and contribute to the aryepiglottic folds (lateral walls of the laryngeal opening)

F. Cuneiform Cartilages

• Small rod-shaped pieces inside the aryepiglottic folds, anterior to the corniculate cartilages
• Create small visible bumps (cuneiform tubercles) on the inlet

3. Ligaments and Membranes

Clinical note: The median cricothyroid ligament is the site of emergency cricothyrotomy - a life-saving cut to open the airway when normal intubation fails. It's accessible because it sits just below the Adam's apple, with no major vessels overlying it.

4. Cavity of the Larynx - The Three Regions

LARYNGEAL INLET (opening into pharynx)
         ↓
   ┌─── VESTIBULE (supraglottis) ───┐
   │  (above the vestibular folds)  │
   └─────────────────────────────────┘
         ↓
   VESTIBULAR FOLDS = FALSE VOCAL CORDS
         ↓
   ┌── MIDDLE CHAMBER (ventricle) ──┐
   │  (between false & true cords)  │
   └─────────────────────────────────┘
         ↓
   VOCAL FOLDS = TRUE VOCAL CORDS
         ↓
   ┌── INFRAGLOTTIC CAVITY (subglottis) ┐
   └────────────────────────────────────┘
         ↓
      TRACHEA

The Three Regions in Detail:

• From the laryngeal inlet down to the vestibular (false) folds
• Bounded laterally by the aryepiglottic folds
• The pre-epiglottic space is a fat-filled space anterior to the epiglottis

• The narrowest and most important part
• The rima glottidis is the actual opening between the two true vocal folds - this is what opens and closes for breathing vs. speaking
• On each side, between the false and true cords, is a small pocket called the laryngeal ventricle (sinus of Morgagni)
• A small diverticulum called the laryngeal saccule extends from each ventricle and contains mucous glands that lubricate the vocal folds

• Below the true vocal folds down to the lower border of the cricoid cartilage
• Widens to become the trachea

5. The Vocal Folds (True Vocal Cords)

• They appear white (unlike the pink surrounding mucosa)
• Each fold contains a vocal ligament (the upper free edge of the conus elasticus) and the vocalis muscle
• They meet anteriorly at the midline of the thyroid cartilage (called the anterior commissure)
• Posteriorly, each is attached to the vocal process of an arytenoid cartilage
• This arrangement creates a characteristic "V" shape when viewed from above

• Intermembranous part - between the ligamentous vocal folds anteriorly (about 3/5 of total length)
• Intercartilaginous part - between the arytenoid cartilages posteriorly (about 2/5)

6. Intrinsic Muscles of the Larynx

Key memory point: The Posterior Crico-Arytenoid is the ONLY abductor. If both recurrent laryngeal nerves are damaged (e.g., in thyroid surgery), only the adductors work - the vocal folds adduct and close the airway, causing respiratory distress.

7. Nerve Supply

• Arises from the vagus at the nodose ganglion
• Divides into:
  • Internal branch: purely sensory above the vocal folds (enters via thyrohyoid membrane)
  • External branch: motor to the cricothyroid muscle only

• Loops around the subclavian artery (right) or arch of aorta (left)
• Ascends in the tracheo-esophageal groove
• Provides sensory supply below the vocal folds + motor to all intrinsic muscles except cricothyroid

Clinical note: The RLN is at risk during thyroid surgery, carotid endarterectomy, and thoracic procedures. Unilateral damage causes a hoarse voice; bilateral damage can cause airway obstruction.

8. Blood Supply

9. How the Larynx Produces Sound (Phonation)

1. Air from the lungs builds pressure below the closed vocal folds
2. Pressure forces the folds apart - air rushes through
3. The Bernoulli effect and myoelastic recoil snap the folds back together
4. This vibration creates sound waves
5. Pitch is controlled by the tension/length of vocal folds:
   • Higher pitch = cricothyroid contracts → lengthens/tenses folds
   • Lower pitch = thyro-arytenoid contracts → shortens/relaxes folds
6. Volume depends on airflow pressure from the lungs
7. The sound is then shaped into words by the tongue, lips, teeth, and palate

10. How the Larynx Protects the Airway

1. Epiglottis folds back over the laryngeal inlet (pushed by the base of tongue)
2. Aryepiglottic folds constrict, narrowing the inlet
3. True and false vocal folds adduct tightly shut

Summary Diagram: At a Glance

HYOID BONE (not part of larynx but suspends it)
    |
Thyrohyoid membrane
    |
THYROID CARTILAGE (largest, "Adam's apple")
    ├── Epiglottis (attached inside, faces up/back)
    ├── Arytenoid cartilages (on cricoid, posteriorly)
    │       └── Vocal process (→ vocal ligament → vocal fold)
    │
Cricothyroid ligament (median part = emergency airway site)
    |
CRICOID CARTILAGE (only complete ring; marks C6)
    |
Cricotracheal ligament
    |
TRACHEA