The Larynx

The larynx (plural larynges), colloquially known as the "voice box", is an organ in the neck of mammals involved in protecting of the trachea and sound production. It manipulates pitch and volume. The larynx houses the vocal folds, which are an essential component of phonation. The vocal folds are situated just below where the tract of the pharynx splits into the trachea and the esophagus.

The larynx is found in the anterior neck at the level of the C3-C6 vertebrea. It connects the inferior part of the pharynx (hypopharynx) with the trachea. The laryngeal skeleton consists of nine cartilages: three single (thyroid, cricoid, and epiglottic) and three paired (arytenoid, corniculate, and cuneiform). The hyoid bone is not part of the larynx, though it is connected to it. The larynx extends vertically from the tip of the epiglottis to the inferior border of the cricoid cartilage. The intristic and extrinsic muscles and paired and unpaired cartilages are listed and described below.

Sound is generated in the larynx, and that is where pitch and volume are manipulated. The strength of expiration from the lungs also contributes to loudness.

Fine manipulation of the larynx is used to generate a source sound with a particular fundamental frequency, or pitch. This source sound is altered as it travels through the vocal tract, configured differently based on the position of the tongue, lips, mouth, and pharynx. The process of altering a source sound as it passes through the filter of the vocal tract creates the many different vowel and consonant sounds of the world's languages as well as tone, certain realizations of stress and other types of linguistic prosody. The larynx also has a similar function as the lungs in creating pressure differences required for sound production; a constricted larynx can be raised or lowered affecting the volume of the oral cavity as necessary in glottalic consonants.

The vocal folds can be held close together (by adducting the arytenoid cartilages), so that they vibrate (see phonation). The muscles attached to the arytenoid cartilages control the degree of opening. Vocal fold length and tension can be controlled by rocking the thyroid cartilage forward and backward on the cricoid cartilage (either directly by contracting the cricothyroids or indirectly by changing the vertical position of the larynx), by manipulating the tension of the muscles within the vocal folds, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal cords are longer and with a greater mass, producing a deeper pitch.

The vocal apparatus consists of two pairs of mucosal folds. These folds are false vocal cords (vestibular folds) and true vocal cords (folds). The false vocal cords are covered by respiratory epithelium, while the true vocal cords are covered by stratified squamous epithelium. The false vocal cords are not responsible for sound production, but rather for resonance. The exceptions to this are found in Tibetan Chant and Kargyraa, a style of Tuvan Throat Singing. Both make use of the false vocal cords to create an undertone. These false vocal cords do not contain muscle, while the true vocal cords do have skeletal muscle.

During swallowing, the backward motion of the tongue forces the epiglottis over the glottis' opening to prevent swallowed material from entering the larynx which leads to the lungs; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex to protect the lungs.

The larynx is innervated by branches of the vagus nerve on each side. Sensory innervation to the glottis and laryngeal vestibule is by the internal branch of the superior laryngeal nerve. The external branch of the superior laryngeal nerve innervates the cricothyroid muscle. Motor innervation to all other muscles of the larynx and sensory innervation to the subglottis is by the recurrent laryngeal nerve. While the sensory input described above is (general) visceral sensation (diffuse, poorly localized), the vocal fold also receives general somatic sensory innervation (proprioceptive and touch) by the superior laryngeal nerve.

Injury to the external laryngeal nerve causes weakened phonation because the vocal cords cannot be tightened. Injury to one of the recurrent laryngeal nerves produces hoarseness, if both are damaged the voice may or may not be preserved, but breathing becomes difficult.

Intrinsic muscles associated with the larynx

Cricothyroid muscles lengthen and stretch the vocal folds.

Posterior cricoarytenoid muscles abduct and externally rotate the arytenoid cartilages, resulting in abducted vocal cords.

Lateral cricoarytenoid muscles adduct and internally rotate the arytenoid cartilages, which can result in adducted vocal folds.

Transverse arytenoid muscle adducts the arytenoid cartilages, resulting in adducted vocal cords.

Oblique arytenoid muscles narrow the laryngeal inlet by constricting the distance between the arytenoid cartilages and epiglottis.

Vocalis muscles adjust tension in vocal folds.

Thyroarytenoid muscles - sphincter of vestibule, narrowing the laryngeal inlet.

Notably, the only muscle capable of separating the vocal chords for normal breathing is the posterior cricoarytenoid. If this muscle is incapacitated on both sides, the inability to pull the vocal cords apart (abduct) will cause difficulty breathing. Bilateral injury to the recurrent laryngeal nerve would cause this condition. It is also worth noting that all muscles are innervated by the recurrent laryngeal branch of the vagus except the cricothyroid muscle, which is innervated by the external laryngeal branch of the vagus.

Extrinsic muscles associated with the larynx

Thyrohyoid muscles

Sternothyroid muscles

Inferior constrictor muscles

Digastric

Stylohyoid

Mylohyoid

Geniohyoid

Hyoglossus

In most animals, including infant humans and apes, the larynx is situated very high in the throat—a position that allows it to couple more easily with the nasal passages, so that breathing and eating are not done with the same apparatus. However, some aquatic mammals, large deer, and adult humans have descended larynges. An adult human, unlike apes, cannot raise the larynx enough to directly couple it to the nasal passage. Despite its presence in non-aquatic deer, proponents of the aquatic ape hypothesis claim that the similarity between the descended larynx in humans and aquatic mammals supports their theory.

Some linguists have suggested that the descended larynx, by extending the length of the vocal tract and thereby increasing the variety of sounds humans could produce, was a critical element in the development of speech and language. Others cite the presence of descended larynges in non-linguistic animals, as well as the ubiquity of nonverbal communication and language among humans, as counterevidence against this claim.

In most animals, including infant humans and apes, the larynx is situated very high in the throat—a position that allows it to couple more easily with the nasal passages, so that breathing and eating are not done with the same apparatus. However, some aquatic mammals, large deer, and adult humans have descended larynges. An adult human, unlike apes, cannot raise the larynx enough to directly couple it to the nasal passage. Despite its presence in non-aquatic deer, proponents of the aquatic ape hypothesis claim that the similarity between the descended larynx in humans and aquatic mammals supports their theory.

Some linguists have suggested that the descended larynx, by extending the length of the vocal tract and thereby increasing the variety of sounds humans could produce, was a critical element in the development of speech and language. Others cite the presence of descended larynges in non-linguistic animals, as well as the ubiquity of nonverbal communication and language among humans, as counterevidence against this claim.

There are several things that can cause a larynx to not function properly. Some symptoms are hoarseness, loss of voice, pain in the throat or ears, and breathing difficulties. The world's first successful larynx transplant took place in 1999 at the Cleveland Clinic.

Acute laryngitis is the sudden

Two , immature cartilage of the upper larynx collapses inward during inhalation, causing airway obstruction.

Most tetrapod species possess a larynx, but its structure is typically simpler than that found in mammals. The cartilages surrounding the larynx are apparently a remnant of the original gill arches in fish, and are a common feature, but not all are always present. For example, the thyroid cartilage is found only in mammals. Similarly, only mammals possess a true epiglottis, although a flap of non-cartilagenous mucosa is found in a similar position in many other groups. In modern amphibians, the laryngeal skeleton is considerably reduced; frogs have only the cricoid and arytenoid cartilages, while salamanders possess only the arytenoids.

Vocal cords are found only in mammals, and a few lizards. As a result, many reptiles and amphibians are essentially voiceless; frogs use ridges in the trachea to modulate sound, while birds have a separate sound-producing organ, the syrinx.