What is the Larynx? Function, Cartilages, Muscles, Ligaments
Location of the Larynx
The larynx is the short tube that connects the pharynx (throat) to the trachea (wind pipe). It runs at the front of the throat at the level of C3 to C6 vertebrae and lies anterior to the esophagus.
Function of the Larynx
- It allows air to be directed into the respiratory organs for gas exchange.
- The larynx is also the organ that is responsible for producing vocal sounds (phonation) and therefore it is commonly known as the voice box.
- In addition, the larynx also plays a role in preventing food and drink from entering the respiratory system.
What structures are inside the larynx?
The structure of the larynx is fairly complex compared to surrounding respiratory and alimentary organs.
Cartilages of the Larynx
The skeleton of the larynx consists of nine cartilages – three of which are single and three are paired (six).
Single laryngeal cartilages
- Signet ring shaped cartilage that is attached to the thyroid cartilage above it and the first tracheal ring through ligaments.
- Elastic cartilage lined by mucous membrane to form the epiglottis. This flap prevents food and fluid from entering the respiratory passages.
- Largest laryngeal cartilage and holds one end of the vocal ligament.
- Its anterior projection known as the laryngeal prominence is the Adam’s apple which is more visible in men.
- Attached to the hyoid bone by a ligament.
Paired laryngeal cartilages
- Pyramid shaped cartilages that holds the other end of the vocal ligament.
- It can slide, rotate and tilt to tense and relax the vocal folds (vocal cords).
- Attaches to the apex (tip) of the arytenoid cartilages.
- Does not attach to any cartilage but lies below the arytenoid cartilage.
Muscles of the Larynx
There are two groups of laryngeal muscles – extrinsic and intrinsic.
Extrinsic laryngeal muscles move the larynx as a whole.
- Laryngeal elevators
- Laryngeal depressors
Intrinsic laryngeal muscles move, stretch and relax the laryngeal cartilages and folds, which is necessary for phonation.
- Posterior cricoarytenoid
- Lateral cricoarytenoid
The tenth cranial nerve (CN X – vagus nerve) innervates these muscles. Apart from the cricothyroid muscle which is innervated by the external laryngeal branch, the rest are supplied by the inferior laryngeal branch of the recurrent laryngeal nerve.
Glottis (Voice Box)
The glottis which is the apparatus responsible for voice production is broadly made up of two structures – vocal folds and the rima glottidis.
- Also known as the vocal cords, it controls sound production.
- It is made up of the :
- Vocal ligament which is thick elastic tissue.
- Vocalis muscle which are very fine muscle fibers that attach at various levels along the length of the vocal ligament.
- This is the space between the two vocal cords.
- Variations in the width of the rima glottidis coupled with the tension and length of the vocal cords are responsible for changes in pitch of the voice.
Cavities in the Larynx
The laryngeal cavity extends from the laryngopharynx to the trachea. Parts of this cavity is divided according to the structures within the larynx.
- Laryngeal vestibule is the uppermost part of the cavity above the vestibular folds. The vestibular folds do not play any role in phonation but protect the vocal folds.
- Middle part of the laryngeal cavity is the area between the vestibular folds and vocal folds (vocal cords).
- Laryngeal ventricles are recesses that lie on either side of the middle part of the laryngeal cavity.
- Infraglottic cavity is the part of the cavity below the vocal cords that extends to the point where the cricoid cartilage connects with the first tracheal ring.