INTRODUCTION
The larynx is also known as voice box , it links the laryngopharynx and the trachea.it lies in front of the laryngopharynx and the 3rd ,4th,5th and 6th cervical vertebrae. Until puberty there is little difference in the size of the larynx between the sexes. Thereafter, it grows larger in the male, which explains the prominence of the 'Adam's apple' and the generally deeper voice.
POSITION
it links the laryngopharynx and the trachea.it lies in front of the laryngopharynx and the 3rd ,4th,5th and 6th cervical vertebrae. Until puberty there is little difference in the size of the larynx between the sexes. Thereafter, it grows larger in the male, which explains the prominence of the 'Adam's apple' and the generally deeper voice.
STRUCTURE
Structure associated with the larynx
Superiorly - the hyoid bone and the root of the tongue.
Inferiorly - it is continuously with the bacteria
Anteriorly - the muscles attached to the hyoid bone and the muscles of the neck.
Posteriorly - the laryngopharynx and 3rd-6th cervical vertebrae
Laterally - the lobes of the thyroid gland
cartilage
The larynx is composed of several irregularly shaped cartilages attached to each other by ligaments and membranes. The main cartilage are:
| Cartilage type | Main cartilage |
|---|---|
| 1 thyroid cartilage | hyalin cartilage |
| 1 cricoid cartilage | hyalin cartilage |
| 2 arytenoid cartilage | hyalin cartilage |
| 1 epiglottis | elastic fibrocartilage |
Several ligaments attach the cartilages to each other and the the hyoid bone .
The thyroid cartilage
This is the most common prominent of the laryngeal cartilages. Made of hyaline cartilage, it lies to the front of the neck. Its anterior wall projects into the soft tissues of the front of the throat, forming the laryngeal prominence or Adam's apple, which is easily felt and often visible in adults males. The anterior wall is party s divided by the thyroid notch. The cartilage is incomplete posteriorly , and is bound with ligaments to the hyoid bone above and the cricoid cartilage below.
The upper part of the thyroid cartilage is lined with stratified squamous epithelium like the larynx, and the lower part with ciliated columnar epithelium like the trachea. There are many muscles attached to its outer surface. The thyroid cartilage forms most of the anterior and the lateral walls of the larynx.
The cricoid cartilage
This lies below the thyroid cartilage and is composed of hyaline cartilage. It is shaped like a signet ring, completely encircling the larynx with the narrow part anteriorly and the broad part posteriorly. The broad posterior part articulates with the arytenoid cartilages and with the thyroid cartilage. It is lined with ciliated columnar epithelium and there are muscles and ligaments attached to the outer surface. The lower border of the cricoid cartilage marks the end of the upper respiratory tract.
The arytenoid cartilages
These are two roughly pyramid-shaped hyaline cartilage situated on top of the broad part of the cricoid cartilage forming part of the posterior wall of the larynx. They give attachment to the vocal cords and to muscles and are lined with ciliated columnar epithelium.
The epiglottis
This is a leaf-shaped fibroelastic cartilage attached on a flexible stalk of cartilage to the inner surface of the anterior wall of the thyroid cartilage immediately below the tongue and the body of the hyoid bone. It is covered with stratified squamous epithelium. If the larynx is likened to a box then the epiglottis acts as a the lid; it closes off the larynx during swallowing, protecting the lungs from accidental inhalation of foreign objects.
INTERIOR OF THE LARYNX
The vocal cords are two plate folds of mucous membrane with cord-like free edges, stretched across the laryngeal opening. They extend from the inner wall of the thyroid prominence anteriorly to the arytenoid cartilages posteriorly.
When the muscles controlling the vocal cords are relaxed, the vocal cords open and the passageway for air coming up through the larynx is clear; the vocal cords are said to be abducted. Vibrating the vocal cords in this position produces low-pitched sounds.
When the muscles controlling the vocal cords contract, the vocal cords are stretched to this extent, and are vibrated by air passing through from the lungs, the sound produced is high pitched. The pitch of the voice therefore determined by the tension applied to the vocal cords by the appropriate sets of muscles. When not in use, the vocal cords are adducted. The space between the vocal cords is called the glottis.
FUNCTIONS
Production of sound
- Sound has the properties of pitch, volume and resonance.
- Pitch of the voice depends upon the length and lightness of the cords. Shorter cords produce higher pitched sounds.
- At puberty, the male vocal cords begin to grow longer, hence the lower pitch of the adult male voice.
- Volume of the voice depends upon the force with which the cords vibrate. The greater the force of expired air;he more strongly the cords vibrate and the louder the sound emitted.
- Resonance, or tone, dependent upon the shape of the mouth, the position of the tongue and the lips, the facial muscles and the air in the paranasal sinuses.
Speech
- This is produced when the sounds produced by the vocal cords are amplified and manipulated by the tongue, cheeks and lips.
Protection of the lower respiratory tract
- During swallowing the larynx moves upwards, blocking the opening into it from the pharynx
- . In addition, the hinged epiglottis closes over the larynx. This ensures that food passes into the oesophagus and not into the trachea.
Passageway for air
- The larynx links the pharynx above with the trachea below.
Humidifying, filtering and warming
- These processes continue as inspired air travels through the larynx.
BLOOD supply
Blood is supplied to the larynx by the superior and inferior laryngeal arteries and drained by the thyroid veins, which join the internal jugular vein.
NERVE SUPPLY
The parasympathetic nerve supply is from the superior laryngeal and recurrent laryngeal nerves, which are branches of the vagus nerves. The sympathetic nerves are from the superior cervical ganglia, one on each side. These provide the motor nerve supply to the muscles of the larynx and the sensory fibres to the lining membrane.
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