LARYNX

 Emryology  Development  Situation  Functions  Anatomy  Ligaments and membranes of larynx

Embrology :

Develops from TRACHEOBRONCHIAL DIVERTICULUM in ventral wall of primitive pharynx during 4th week just below hypobranchial eminence. Groove deepens (caudally to cranially)  septum  separates Tracheobronchial TUBE from pharynx and oesophagus forming oesophageotracheal septum. Airway epithelium develops from the ENDODERMAL lining of this tube. Caudally this tube only form 2 branches leading on to 2 main bronchii and also 2 lung buds develop Cranially  Primitive larynx, (bounded by caudal part of Hypobrachial eminence {forms Epiglottis} and laterally by ventral folds of 6th brachial arches) Arytenoid swellings develop on each side of tracheobroncheal groove, enlarge to come close to each other and to hypo brachial eminence (caudal portion). This converts the Vertical slit like cavity into a T shaped one Initially laryngeal cavity fully closed as cleft walls adhere, after 3rd month dissolution of clump of cells 4th and 6th arch nerves  Superior and recurrent laryngeal nerves Epiglottis originates by fusion of anterior extensions of 4th arches (hypobrachial eminence) indicating paired origin. Laryngeal inlet  midline epiglottic swelling, paired arytenoid swellings and lateral aryepiglottic folds Vocal cords form at 8th – 10th week (2 months) The epiglottis is last cartilaginous tissue to develop Hyoid bone  2nd n 3rd arches Each primary bronchus divided into 18 to 23 generations SO THYROID CARTILAGE, EPIGLOTTIS, CRICOTHYROID AND INFERIOR CONSTRICTOR BY 4th ARCH  Sup laryngeal nerve  

Development :

Hypobrachial eminence  epiglottis 4th arch  Thyroid cartilage 6th arch  all (corniculate (Santorini’s cartilage), cuneiform (Wrisberg), cricoid, arytenoids & tracheal cartilages)  Angiogenesis begins in the Mesenchyme which is localised in 2 planes i.e.  o External Constrictor– (4th arch)  analogous to Inf constrictor & Cricothyroid. o Internal Constrictor – (5th and 6th arches)  analogous to intrinsic muscles of larynx.  Thyroid, cricoid and most of arytenoid is are Hyaline cartilages whereas tip of arytenoid and rest all are fibroelastic.  RLN enters the sixth visceral arch on each side below 6th aortic arch artery, on left side arch artery retains its position as ductus arteriosus so the nerve is found below the ligamentum arteriosum after birth.  Rt side it lies below 4th arch artery which becomes the subclavian artery. Situation & Anatomy :

 2nd to 4th cervical vertebrae in children and 3rd to 6th cervical vertebrae in adults from laryngeal inlet to inferior border of cricoid cartilage  Higher in women  9 cartilages  Cuneiform, corniculate and arytenoids (ACC Paired) and Thyroid, cricoid and epiglottis (CET unpaired)  Larynx starts high up under the tongue in early life and with age assumes an increasingly lower position in neck.  AP diameter : men 36mm & women : 26mm after puberty  Supraglottis  Superiorly – Epiglottis & aryepiglottic folds that sweep down to the arytenoids ;; Inferiorly – false vocal cords (ventricular bands)  Glottis  below false cords i.e. includes true vocal cords and anterior and posterior commissure.  Subglottis starts at 5 to 10 mm below vocal cords (some say VC only). Subglottis becomes trachea at lower border of Cricoid only. Functions of Larynx :

Protection of lower airway Provision of controlled airway Phonation Generation of High intrathorasic pressure for coughing and lifting

Framework of Larynx :

 Hyoid Bone  2nd and 3rd arch  Only bone in body not to be attached to any other bone. Body anteriorly, greater cornu Posterolaterally, lesser cornu at junc. of both projecting superiorly.  Thyroid Cartilage LAMINA Angle 90 degree in men and 120 degree in women. Lamina prolonged posteriorly upwards as superior cornua and downwards as inferior cornua. Superior  attaches lateral thyrohyoid ligament Inferior  (shorter and thicker) has facet for attachment of Cricoid Cartilage  Oblique line on ext surface of Lamina from superior thyroid tubercle just infront of root of superior horn to the inferior thyroid tubercle (lower border of lamina) and marks attatchement of Sternothyroid, Inferior constrictor muscles and Thyrohyoid ( S I T )  In midline just below thyroid notch on inner aspect attaches Thyroepiglottic ligament and on each side below this attaches vestibular and vocal ligaments (i.e. Thyroarytenoid). Both vocal ligaments meet to form anterior commisure

CRICOID CARTILAGE

 Deep broad lamina posteriorly and narrow arch anteriorly, attaches to inferior cornu of thyroid near junction of arch and lamina  Only complete cartilaginous ring.  Lamina has sloping shoulders for attachment of arytenoids  Vertical ridge in midline of lamina gives attachment to longitudinal muscles of the oesophagus  Entire inner layer lined by mucous membrane

*** Remember : Vocal folds aka vocal cords and vocal ligaments are inferior thyroarytenoids enclosed within vocal folds. Vocalis muscle is the deeper and lower fibres of the THYROARYTENOID (Vocal ligament) muscles which attatches to vocal process of Arytenoid

ARYTENOIDS

 Three sided pyramids with forward projection (vocal process) attaches to vocal folds and lateral projection (muscular process) to which is attached posterior and lateral cricoarytenoid  Btw these two processes upper triangular area gives attachment to Vestibular ligament and lower gives attachment to Lateral cricoarytenoid muscles and also vocalis.  Apex articulates with corniculate cartilage.  Medial surface covered with mucous membrane forms lateral boundary of posterior glottis and posterior surface is covered by transverse arytenoid muscles  Articulates with corniculate (elastic fibro cartilage) with synovial joint, situated in posterior part of aryepiglottic fold  Base attaches to cricoid lamina with both rotatory movements and side to side gliding movements  Posterior cricoarytenoid ligament prevents forward movement of arytenoid cartilages  Cuneiform are 2 small elongated flakes of fibro cartilages one in each margin of aryepiglottic fold

EPIGLOTTIS

 Attached to thyroid cartilage just below thyroid notch in midline by THYROEPIGLOTTIC ligament and to hyoid by hyoepiglottic ligament and projects upwards behind the tongue and body of hyoid bone.  Preepiglottic space is space between these two (hyoepiglottic and thyroepiglottic ligaments)  Valleculae is space between tongue and Epiglottis. So epiglottis forms posterior wall of valleculae  Glossoepiglottic folds medial and lateral and aryepiglottic folds

EXTRINSIC LIGAMENTS

. Thyrohyoid  thyrohyoid membrane (fibrocartilagenous) reinforced by fibrous cartilage as median thyrohyoid ligament and posteriorly as Lateral thyrohyoid ligament . These may contain cartilage i.e. cartilage triticea . Memb. pierced by superior laryngeal nerve’s internal branch and sup laryngeal vessels . Cricotracheal ligament  is between cricoid and 1st tracheal ring

INTRINSIC LIGAMENTS

Quadrangular membrane arises from the lateral border of Epiglottis and arytenoid cartilages. Upper memb forms framework of aryepiglottic folds and lower margin is thickened to form the vestibular ligament underlying vestibular fold (false vocal cord) Cricovocal Ligament / Cricothyroid Ligament Or Conus Elasticus – Lower part of Quadrangular membrane is thickened & has elastic fibres. Upper Border of this membrane forms true vocal cords Anteriorly thickening of memb. called cricothyroid ligament.

Fibroelastic membrane divided into upper and lower part by the laryngeal ventricle.

MUSCLES OF LARYNX

 Intrinsic muscles of larynx are all paired 1. Posterior cricoarytenoid  opens glottis 2. Lateral cricoarytenoids  Adducts vocal cords 3. Transverse arytenoids (unpaired)  Adducts vocal cords 4. Oblique arytenoids  (posterior aspect of muscular process of arytenoids only but superficial to transverse arytenoids) 5. Vocalis / Thyroarytenoid  lies above n lateral to cricovocal ligament/conus elasticus. relaxer 6. Cricothyroid  Only intrinsic muscle which lies outside cartilaginous framework of thyroid. Cricothyroid muscle dysfunction may be implicated in vocal fold collapse (lengthens the vocal folds i.e. tensor) 7. Aryepiglotticus  continuation of oblique arytenoid (weak sphincter of laryngeal inlet) 8. Thyroepiglotticus  Widens inlet of larynx by pulling aryepiglottic folds slightly apart  Infrahyoid muscles  Thyrohyoid, Sternothyroid, Sternohyoid  Suprahyoid group  GSM D SPS , Geniohyoid, Stylohyoid, Mylohyoid, Digastric, Stylopharyngeus, Palatopharyngeus and Salpingopharyngeus  Both stylopharyngeus and salpingo elevate larynx whereas palato. Tilts larynx forwards  Vocal folds overlie Conus Elasticus.  Closers of laryngeal inlet are aryepiglotticus and Interarytenoid.  PRIMARY ELEVATORS  Stylopharyngeus, Salpingopharyngeus, Palatopharyngeus, thyrohyoid.  SECONDARY ELEVATORS  GSM D  VOCAL FOLDS are layered structures  superficial nonkeratinised stratified squamous epithelium, underlies lamina propria  3 layers  Rienkes space (Gelatin like), Intermediate (Elastin fibre rich) and deep (Collagen rich layer) forms vocal ligament.

 Anterior 3/5th of the vocal cord is within vocal folds and called intermembranous part of the vocal cord posterior 2/5th is called intercartilaginous  Mucous membrane lining larynx is CLOSELY attached over posterior surface of epiglottis, corniculate, cuneiform and vocal ligaments, elsewhere it is loosely attached and prone to oedema.  Most larynx lined by pseudostratified ciliated columnar respiratory type of epithelium.  Mucous glands numerous at posterior surface of epiglottis, lower aryepiglottic folds, saccules.  Vocal folds are lubricated not by own but mucous glands of saccules (OIL TANKS OF LARYNX)

SPACES WITHIN LARYNX

Preepiglottic space – wedge shaped –

Anterior  thyrohyoid ligament and hyoid bone

Posteriorly  Epiglottis

Superiorly  hyoepiglottic ligament (continues laterally with paraepiglottic space)

Inferiorly  thyroepiglottic ligament

Paraglottic space  laterally thyroid cartilage ;;;; medially conus elasticus and quadrangular membrane ;;;; posteriorly piriform fossa mucosa ::::: it encompasses laryngeal ventricles and saccules Nerve supply of larynx

 ** Some fibres of Vagus originate in Medulla in Nucleus Ambiguus and some at higher level. Fibres from upper section of NUCLEUS AMBIGUUS Join 9th nerve i.e. glossopharyngeal nerve and fibres from inferior portion of nucleus join ACCESORY NERVE i.e. XI nerve.  9 10 11 are intricately related nerves in medulla.  Vagus has superior and inferior ganglion  The vagus nerve leaves the skull base via the jugular foramen anterior to the jugular vein. The vagus then assumes a more posterior position medial to the jugular vein.  The vagus nerve has an inferior ganglion also known as the Nodose ganglion immediately below the jugular foramen.  The course taken by the vagus nerve differs between the right and the left sides. The left vagus nerve follows the carotid artery into the mediastinum crossing anterior to the aortic arch.  The anterior bronchoesophageal artery supplies the left vagus nerve.  The approximate length of the left recurrent laryangeal nerve is 12 cms, whereas the right nerve measures about 6 cms only.

 The blood supply to the recurrent laryngeal nerve comes from the inferior thyroid artery.  SLN arises from inf ganglion of vagus (nodose ganglion) below level of jugular foramen and receives branch from Superior cervical sympathetic ganglion  goes behind ICA to sides of pharynx at level of greater horn of hyoid bone divides into small ext and large int branch  External br. Supplies Cricothyroid (motor)  Internal pierces thyrohyoid and divides further into sensory and secretomotor.  Laryngeal inlet has max sensory innervation  Vocal folds have lower sensory innervation  3 branches from Internal Laryngeal nerve supply valleculae, epiglottis and pyriform fossa.  Also carries afferents for neuromuscular spindles and other stretch receptors in the larynx.  SLN ends by piercing inferior constrictor and joining asc. b/o recurrent laryngeal nerve (Galen’s anaestomosis and is purely sensory)  Recurrent Laryngeal Nerves   As the vagus nerve exits the medulla, the fibres of the recurrent laryngeal nerve are anteriorly situated in it.  As the vagus traverses inferiorly, the fibres of the recurrent laryngeal nerve starts to rotate medially until they are ultimately separated from the vagus nerve.  Rt originates from main trunk of vagus in front of subclavian and lt in front of Arch of Aorta. Lt more liable to injury.  Both run in the groove between trachea and oesophagus and divided into anterior and posterior branches before entering the larynx.  RLN pass deep to lower border of inferior constrictor muscles and enters larynx behind cricothyroid ligament.  divides into motor and sensory  sensory supplies below level of vocal folds and all muscles of larynx by motor. Arterial Supply

 Laryngeal artery  b/o Superior and inferior thyroid arteries  Cricothyroid  b/o superior thyroid artery  VENOUS  Above vocal fold and below vocal fold drainage.  Superior thyroid drains in internal jugular  INFERIOR THYROID VEIN drain into brachiocephalic vein