LARYNX• It is the musculocartilaginous structure,• lined with mucous membrane,• connected to the superior part of the trachea and tothe pharynx.• inferior to the tongue and the hyoid bone;• the essential sphincter guarding theentrance into the trachea.• functioning secondarily as the organ of voice.• It is formed by nine cartilages connectedby ligaments and eight muscles.
The LarynxInspired (inhaled) air leaves the pharynx bypassing through a narrow opening, the glottis.The larynx begins at the level of vertebra C4 or C5and ends at the level of vertebra C7.It is essentially a cylinder whose cartilaginouswalls are stabilized by ligaments or skeletalmuscles or both.
External view of the larynx: (a) anterior aspect; (b) anterolateral aspect.
Cartilages of the LarynxThree large unpaired cartilages form the bodyof the larynx: the thyroid cartilage, the cricoid cartilage, the epiglottis. The thyroid and cricoid cartilages are hyalinecartilages;the epiglottic cartilage is an elastic cartilage
The Thyroid Cartilage The largest laryngeal cartilage is the thyroid (“shield-shaped”) cartilage. It forms most of the anterior and lateral walls of the larynx . The thyroid cartilage, when viewed in sagittal section, is incompleteposteriorly. The anterior surface of this cartilage bears a thick ridge, the laryngealprominence. This ridge is easily seen and felt, and the thyroid cartilage is commonlycalled the Adam’s apple. During embryological development, the thyroid cartilage is formed bytwo pieces of cartilage that meet in the anterior midline to form thelaryngeal prominence. The inferior surface of the thyroid cartilage articulates with thecricoid cartilage; the superior surface has ligamentous attachments to the epiglottis andsmaller laryngeal cartilages.
The Cricoid Cartilage The thyroid cartilage sits superior to the cricoid “ring-shaped”) cartilage. It is a complete ring whose posterior portion is greatlyexpanded, providing support in the absence of the thyroidcartilage. The cricoid and thyroid cartilages protect the glottis andthe entrance to the trachea, and their broad surfaces provide sites for the attachmentof important laryngeal muscles and ligaments. Ligaments attach the inferior surface of the cricoidcartilage to the first cartilage of the trachea. The superior surface of the cricoid cartilage articulateswith the small paired arytenoid cartilages.
The Epiglottis The shoehorn-shaped epiglottis projectssuperior to the glottis The epiglottic cartilage that supports it hasligamentous attachments to the anterior andsuperior borders of the thyroid cartilage and thehyoid bone. During swallowing, the larynx is elevated, andthe epiglottis folds back over the glottis,preventing the entry of liquids or solid food intothe respiratory passageways.
Paired Laryngeal Cartilages The larynx also contains three pairs ofsmaller cartilages:the arytenoid,corniculate,and cuneiform cartilages. The arytenoids and corniculates are hyalinecartilages;the cuneiforms are elastic cartilages.
The Three Paired Cartilages• The arytenoid "ladle-shaped” cartilages articulate withthe superior border of the enlarged portion of thecricoid cartilage.• The corniculate “horn-shaped”) cartilages articulatewith the arytenoid cartilages.• The corniculate and arytenoid cartilages play a role inthe opening and closing of the glottis and theproduction of sound.• Elongate, curving cuneiform “wedge-shaped”)cartilages lie within the aryepiglottic fold that extendsbetween the lateral aspect of each arytenoid cartilageand the epiglottis.
Laryngeal Ligaments• A series of intrinsic ligaments binds all ninecartilages together to form the larynx.• Extrinsic ligaments attach the thyroid cartilage tothe hyoid bone and the cricoid cartilage to thetrachea.• The vestibular ligaments and the vocal ligamentsextend between the thyroid cartilage and thearytenoids.• The vestibular and vocal ligaments are covered byfolds of laryngeal epithelium that project into theglottis.• The vestibular ligaments lie within the superior pairof folds, known as the vestibular folds.
The vestibular folds, which are relatively inelastic, helpprevent foreign objects from entering the glottis andprovide protection for the more delicate vocal folds.The vocal folds are highly elastic, because the vocalligament is a band of elastic tissue. The vocal folds are involved with the production of sounds,and for this reason they are known as the true vocal cords.Because the vestibular folds play no part in soundproduction, they are often called the false vocal cords.Laryngeal Ligaments (continue)
Sound Production• Air passing through the glottis vibrates the vocal folds andproduces sound waves.• The pitch of the sound produced depends on the diameter,length, and tension in the vocal folds.• The diameter and length are directly related to the size of thelarynx.• The tension is controlled by the contraction ofvoluntary muscles that change the relative positions of thethyroid and arytenoid cartilages.• When the distance increases, the vocal folds tense and thepitch rises; when the distance decreases, the vocal folds relaxand the pitch falls.• Children have slender, short vocal folds, and their voicestend to be high-pitched.
• At puberty the larynx of a male enlarges considerably morethan that of a female.• The true vocal cords of an adult male are thicker andlonger, and they produce lower tones than those of anadult female.• The entire larynx is involved in sound production becauseits walls vibrate, creating a composite sound.• Amplification and echoing of the sound occur within thepharynx, the oral cavity, the nasal cavity, and the paranasalsinuses.• The final production of distinct sounds depends onvoluntary movements of the tongue, lips, and cheeks.Sound Production (continue)
The Laryngeal Musculature• The larynx is associated with two different groups of muscles, the intrinsic laryngeal muscles. the extrinsic laryngeal muscles.The intrinsic laryngeal muscles have two majorfunctions: One group regulates tension in the vocal folds, while a second set opens and closes the glottis. Those involved with the vocal folds insert upon the thyroid,arytenoid, and corniculate cartilages. Opening or closing the glottis involves rotationalmovements of the arytenoids that move the vocal foldsapart or together.
Part of oblique arytenoid muscle: an inconstant fascicle of theoblique arytenoid muscle, originating from the apex of the arytenoidcartilage and inserting to the lateral margin of the epiglottis.
• During swallowing, both extrinsic and intrinsic musclescooperate to prevent food or drink from enteringthe glottis.• Before you swallow, the material is crushed and chewedinto a pasty mass known as a bolus.• Extrinsic muscles then elevate the larynx, bending theepiglottis over the entrance to the glottis, so that thebolus can glide across the epiglottis, rather than fallinginto the larynx.• While this movement is under way, intrinsic musclesclose the glottis.• Should any food particles or liquids touch the surfaces ofthe vestibular or vocal folds, the coughing reflex will betriggered.• Coughing usually prevents the material from entering theglottis.
Extrinsic Laryngeal muscles• The extrinsic laryngeal musculature positionsand stabilizes the larynx.• Three of the four strap muscles of the neck,the omohyoid, sternohyoid and thyrohyoid,find attachment to it, only the sternothyroidfailing to gain it.
Lymph Drainage (skip)• The vocal cords themselves act as a complete barrierseparating the two lymphatic areas, but posteriorlythere is free communication between them.• Above the vocal cords, some lymphatics passing viasmall nodes lying on the thyrohyoid membrane.• Below the vocal cords, drainage partially vianodes on the front of the larynx and trachea.
External view of the larynx: (a) anterior aspect; (b) anterolateral aspect.
Nerve supply• The nerve supply of the larynx is of great practicalimportance and comprises the superior and recurrentlaryngeal branches of the vagus nerve (X).• The superior laryngeal nerve passes deep to theinternal and external carotid arteries where it divides;• its internal branch pierces the thyrohyoid membranetogether with the superior laryngeal vessels to supplythe mucosa of the larynx down to the vocal cords.• The external branch passes deep to the superiorthyroid artery to supply the cricothyroid muscle.
• The right arises from the vagus as this crosses thefront of the subclavian artery, passes deep to andbehind this vessel, then ascends behind the commoncarotid to lie in the Tracheo-oesophageal grooveaccompanied by the inferior laryngeal vessels.• The nerve then passes deep to the inferior constrictormuscle of the pharynx to enter the larynx behind thecricothyroid articulation.The recurrent laryngeal nerve has a different course on each side.
• The left nerve arises on the arch of the aorta, windsbelow it, deep to the ligamentum arteriosum, andascends to the trachea. It then lies in the tracheo-oesophageal groove and is distributed as on the rightside.• The recurrent nerves supply all the intrinsiclaryngeal muscles, apart from the cricothyroid,(supplied by the superior laryngeal nerve), andthe mucosa below the vocal cords.The recurrent laryngeal nerve has a different course on each side.
Giraffes are silent animals, but, they are certainlynot mute. Sounds like the bleating of calves, andthe bellowing of cows, have been heard.