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Lec. (1)Larynx Lecturer: Dr. Saad Y. Sulaiman

THE LARYNX

The larynx lies in front of the hypopharynx opposite the third to sixth cervical vertebrae. In adult, the larynx ends at the lower border of C6 vertebra.
Laryngeal cartilages
Epiglottis: Leaf-like yellow elastic cartilage that never ossify.



Thyroid: Is the largest of all and consist of two alae meeting anteriorly at an angle, called "Adam's Apple". It's a hyaline cartilage, ossifies at 20-30 years of age, and begins in the inferior margin and progress cranially.




Cricoid: It is the only cartilage forming a complete ring. Its posterior part is expanded to form a lamina while anteriorly it is narrow forming an arch. It is also a hyaline cartilage and it ossifies after the thyroid cartilage, first part to be calcified being the superior portion (which can be mistaken for a foreign body) Calcification progresses caudally.



cricoid cartilage
Arytenoid cartilages: they are paired. Each is pyramidal in shape. It has:
Base---articulate with cricoid cartilage.
Muscular process---laterally and give attachment to intrinsic muscle.
Vocal process--- directed anteriorly, giving attachment to vocal cord.
Apex---support the corniculate cartilage.




Corniculate: small cartilages that lie over the arytenoids.

Cuneiform: Small cartilages that lie in the aryepiglottic fold.




Laryngeal Joints

Cricoarytenoid joint and cricothyroid joint. Both are synovial joints.

Laryngeal Muscles:

Extrinsic muscle:
The extrinsic muscles move the larynx as a whole. The  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" infrahyoid HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm"  muscles or straps ( HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" omohyoid,  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" sternohyoid, and  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" sternothyroid) are depressors of the hyoid bone and the larynx, whereas the  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" suprahyoid HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm"  muscles ( HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" stylohyoid,  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" digastric,  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" mylohyoid and  HYPERLINK "http://download.videohelp.com/vitualis/med/mm_neck.htm" geniohyoid) and the stylopharyngeus are elevator of the hyoid bone and larynx.
Intrinsic muscles: All are paired except interarytenoid muscle. They open and close the glottis; and they are of three groups:
Abductors: consist of posterior cricoarytenoid muscle. It opens the glottis and it is the most important muscle of the body. Paralysis of this muscle leads to adduction of the vocal cords and suffocation.
Adductors: Lateral cricoarytenoid, interarytenoid, thyroarytenoid (external part)
Tensors: cricothyroid and vocalis(internal part of thyroarytenoid )

Laryngeal compartments

The glottis: composed of the vocal cords from the extreme lateral edge of the cord to the inferior border of the medial surface.
The subglottis: from the lower border of the glottis to the inferior border of the cricoid. Below this is the trachea.
The supraglottis: extend from the upper border of the glottis inferiorly to the hyoid bone superiorly.


Histology
Lining epithelium: squamous over the vocal cord and the upper 1/4 of the posterior surface of the epiglottis and low columnar ciliated over the rest of the larynx. The latter type commonly undergoes squamous metaplasia in response to atmospheric pollution and smoking.
Mucous glands and lymphatics: rich in supraglottis, nil in glottis and very few in subglottis.
The mucosa of the glottis and supraglottis is firmly bound down to the underlying tissue, but not so in the subglottic region. Here, the laxity of tissue allows a dangerous degree of oedema, especially in children, where the diameter of the area is relatively smaller than in adult.

Nerve Supply:

The superior laryngeal nerve (from the vagus) divides into external and internal branches:
The external is motor to cricothyroid muscle only.
The internal pass through the thyrohyoid membrane and is sensory to supraglottic area.
Recurrent laryngeal nerve: supply all the intrinsic muscles (abductors and adductors), and also it is sensory to the subglottic area.
All muscles of the larynx are innervated by the recurrent laryngeal nerve, except cricothyroid muscle which is innervated by the external branch of the superior laryngeal nerve.





Blood supply and venous drainage:
The supraglottis is supplied and drained by the superior laryngeal artery and vein, which enter the larynx through thyrohyoid membrane. The glottis and subglottis are supplied and drained by the inferior laryngeal artery and vein( branches of the inferior thyroid artery).

Lymphatic Drainage:

The main lymphatic drainage is to the deep cervical lymph nodes. The glottic area has NO lymphatic network; that's why cancer of vocal cords does not give rise to lymph node enlargement.

Paediatric larynx

The larynx of an infant differs considerably from that of an adult and has great clinical significans:
It is positioned high in the neck opposite C3 or C4 (level of vocal cord) at rest and reaches C1 or c2 during swallowing.
The laryngeal cartilage are soft and collapse easily.
The thyroid cartilage in an infant is flat and the cricothyroid and thyrohyoid spaces are narrow.
It is small and conical in shape (while it is cylindrical in adult).
Submucosal tissues of infant's larynx are loose and easily undergo oedematous changes with trauma or inflammation leading to obstruction.







Adult larynx


Infant larynx





 Adult Infant

Physiology of the larynx

Protection: This is a vital function; it prevents entry of any substance into the air passages (e.g. food, F.B) , by sphincteric closure of laryngeal inlet and cough reflex.
Respiration: larynx regulates flow of air into the lungs. Vocal cords abduct during expiration and adduct during expiration.
Phonation (sound production): air column from the chest causes vibration of the adducted vocal cords thereby producing a sound.
Fixation of chest: closure of the glottis fixes the chest to give support to the powerful voluntary muscular use of the arms. Closure of the glottis fixes the diaphragm to assist in the act of straining.
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Aytenoid

Cricoid cartilage


Corniculate

Cuneiform

NOTE:
(The first three laryngeal cartilages are single while the rest are paired )