THE ANATOMY OF HUMAN LARYNX BY MBK .pptx

PPT

1. ANATOMY OF LARYNX DR. MIDHUN BHASKAR K

2. Functions of Larynx P rotects the lower respiratory tract P rovides a controlled airway A llows phonation A llows the generation of a high intrathoracic pressure for coughing and lifting

3. Embryology At four weeks of embryonic development, an outgrowth of the primitive foregut forms the primordial respiratory system. The epithelium of the larynx, trachea and bronchi is of endodermal origin T he other soft tissues arise from the surrounding splanchnic mesoderm (fourth and sixth branchial arches).

4. R espiratory diverticulum develops from the ventral aspect of the foregut and elongates, drawing out a stalk and giving rise to the trachea T he larynx, which is formed at the most cranial end of the respiratory tract, then leads to the trachea, bronchi and lungs. Arytenoid swellings appear on both sides of the tracheobronchial diverticulum

5. The rudimentary arytenoids swellings elongate cranially, creating a cleft that is open cranially and bounded laterally by the aryepiglottic folds. More ventrally, at the front of this cleft, the hypobranchial eminence becomes the epiglottis.

6. The glottis forms just above the level of the primitive aperture Surrounding this, the thyroid cartilage develops from the ventral ends of the cartilages formed in the mesoderm of the fourth pharyngeal arch It appears as two lateral plates, each of which possesses two chondrification centres

7. The cricoid cartilage and the cartilages of the trachea develop from the sixth arch during the sixth week of gestation The trachea rapidly increases in length in a craniocaudal direction from the fifth week of gestation onwards The mesoderm of each pharyngeal arch differentiates into the cartilage, muscle and vascular structures of that arch

8. E ach arch receives an afferent and efferent nerve supply for the skin, muscles and endodermal lining of that arch F ourth a rch - superior laryngeal branch of the vagus S ixth arches - recurrent laryngeal branch of the vagus

9. EXTEND The larynx extends from the laryngeal inlet to the inferior border of the cricoid cartilage In the absence of respiration it lies in front of the third to sixth cervical vertebrae It is little higher in women than in men.

10. Infantile vs Adult larynx The infantile larynx is proportionally smaller than that of the adult compared to body size Its narrowest part is at the junction of the subglottic larynx with the trachea N arrowest part of the adult larynx is the glottis The laryngeal cartilages are much softer in the infant than the adult and collapse more easily

11. The larynx starts high up under the tongue in early life and with age assumes an increasingly lower position in the neck As the larynx grows, there is little difference in its size between boys and girls until after puberty After puberty anterior– posterior (AP) diameter of the larynx almost doubles in men F inal AP dimension average of about 36 mm in men and 26 mm in women.

12. The larynx is divided anatomically into the supraglottis , glottis and subglottis by the false and true folds T he supraglottis commence s at the epiglottis and aryepiglottic folds. Its lower border is a horizontal line drawn through the apex of the laryngeal ventricle. The glottis extends caudally from this line and includes the vocal cords as well as anterior commissure and posterior commissure .

13. The line of demarcation between the glottis and the subglottis is a line drawn 1 cm below the free edge of the vocal folds. The subglottis becomes the trachea at the lower border of the cricoid.

14. FRAMEWORK OF THE LARYNX The framework of the larynx consists of the hyoid bone and a number of cartilages connected by ligaments and membranes, as well as intrinsic and extrinsic muscles It is lined with a mucous membrane that is continuous above with the pharynx and below with that of the trachea. The spaces around the larynx are filled with adipose tissue and loose connective tissue

15. HYOID BONE U shaped bone Suspended by suprahyoid muscles & ligaments from skull base & mandible provides superior attachment to extrinsic muscles of larynx - suspends larynx in neck consists of anterior - BODY GREATER CORNUA - projects backward from body on each side LESSER CORNUA - 2 small conical projections attached to upper aspect of body laterally - by fibrous band

16. THYROID CARTILAGE C omposed of two laminae that are fused in the midline anteriorly giving rise to the laryngeal prominence The angle of fusion is about 90 ° in men and 120 ° in women. The posterior border of each lamina is prolonged above and below to form the superior and inferior cornua

17. The superior cornu is long and narrow and curves upwards, backwards and medially, ending in a conical extremity To which the lateral thyroid ligament is attached

18. The inferior cornu is shorter and thicker and curves downwards and medially. On the medial surface of its lower end is a small oval facet joint for articulation with the cricoid cartilage. On the external surface of each lamina, an oblique line curves downwards and forwards from the superior thyroid tubercle to the inferior thyroid tubercle on the lower border of the lamina

19. This line marks the attachment of the thyrohyoid, sternothyroid and inferior constrictor muscles. On the inner aspect of the thyroid cartilage, just below the thyroid notch in the midline, is - thyroepiglottic ligament B elow this and on each side of the midline, are attached the vestibular and vocal ligaments and thyroarytenoid, thyroepiglottic and vocalis muscles

20. The fusion of the anterior ends of the two vocal ligaments produces the anterior commissure tendon The superior border of each lamina gives attachment to the thyrohyoid ligament T he inferior border on the medial portion of its inner aspect is attached to - cricothyroid l igament .

21. CRICOID CARTILAGE The cricoid cartilage is the only complete cartilaginous ring in the airway It forms the inferior part of the anterior and lateral walls and most of the posterior wall of the larynx

22. It has a deep broad lamina posteriorly Narrow arch anteriorly A facet for articulation with the inferior cornu of the thyroid cartilage, near the junction of the arch and lamina The lamina has sloping shoulders on which the articular facets for the arytenoid cartilages are found

23. The entire inner surface of the cricoid cartilage is lined with mucous membrane. The cricoarytenoid joint –with an associated functional PCA muscle – is a key functional unit of the larynx, facilitating vocal fold motility to ensure a patent airway when abducted and airway protection when adducted

24. ARYTENOID CARTILAGES I rregularly shaped, like a three-sided pyramid with a forward projection forward projection - the vocal process , to which the dorsal end of the vocal folds are attached A lateral projection, the muscular process , to which the posterior cricoarytenoid and lateral cricothyroid muscles attach Between these two processes, the anterolateral surface is irregular and divided into two fossae by a crest running from the apex

25. The upper triangular fossa gives attachment to the vestibular ligament and the lower to the vocalis and lateral cricoarytenoid muscles The apex is curved backwards and medially and is flattened for articulation with the corniculate cartilage .

26. The medial surfaces have no muscular attachments, are covered with mucous membrane and form the lateral boundary of the posterior glottis The posterior surface of each cartilage is covered by the transverse arytenoid muscle, which inserts onto each cartilage across the midline The base is concave and presents a smooth surface for articulation wit h upper border of the cricoid lamina.

27. CORNICULATE CARTILAGE The corniculate cartilages (of Santorini ) are two small conical nodules of elastic fibrocartilage, They articulate through a synovial joint with the apices of the arytenoid cartilages. They are situated in the posterior part of the aryepiglottic fold.

28. CUNEIFORM CARTILAGES The cuneiform cartilages (of Wisberg) are two small, elongated flakes of fibroelastic cartilage , one in each free margin of the aryepiglottic fold The function of these cartilages is uncertain

29. EPIGLOTTIS The epiglottis is a thin, leaf-like sheet of elastic fibrocartilage P rojects upwards behind the tongue and the body of the hyoid bone.

30. It is attached inferiorly to the thyroid cartilage, just below the thyroid notch in the midline, by the thyroepiglottic ligament Also, to the hyoid bone anteriorly by the hyoepiglottic ligament. The space between these ligaments forms the pre-epiglottic space. From the sides of the epiglottis, the aryepiglottic folds sweep downwards and backwards to the apex of the arytenoids

31. The posterior (laryngeal) surface of the cartilage is indented by numerous small pits into which mucus glands project. The anterior (lingual) surface of the epiglottis is covered with mucous membrane superiorly and forms the posterior wall of the vallecula. The mucous membrane overlying the epiglottis is reflected onto the base of the tongue, forming the gloss epiglottic fold in the midline and laterally the lateral gloss epiglottic folds.

32. Ligaments and membranes of the larynx EXTRINSIC LIGAMENTS connect the laryngeal cartilages to the hyoid above and trachea below Superiorly, the thyrohyoid membrane stretches between the upper border of the thyroid cartilage and the posterior surface of the body and greater cornua of the hyoid Reinforced by fibrous tissue in the midline as the median thyrohyoid ligament and posteriorly as the lateral thyrohyoid ligament

33. The ligaments often contain a small nodule of cartilage, the cartilage triticea. The cricotracheal ligament unites the lower border of the cricoid with the first tracheal ring

34. INTRINSIC LIGAMENTS C onnect the laryngeal cartilages together , strengthen the capsule of the intercartilaginous joints F orm a broad sheet of fibroelastic tissue, the fibroelastic membrane, which lies beneath the mucous membrane of the larynx forming an internal framework The fibroelastic membrane is divided into an upper and lower part by the laryngeal ventricle .

35. The upper quadrilateral membrane extends between the lateral border of the epiglottis and the arytenoid cartilages. the lower margin is thickened to form the vestibular ligament underlying the vestibular fold (false vocal fold)

36. The lower part is thicker, containing many elastic fibres. It is commonly called the cricovocal ligament, cricothyroid ligament or conus elasticus . The free upper border of this membrane constitutes the vocal ligament the framework of the (true) vocal fold Anteriorly, there is a thickening of the membrane, the cricothyroid ligament, which connects the cricoid and the thyroid cartilages in the midline.

37. Muscles of the larynx The extrinsic muscles of the larynx attach the larynx to neighbouring structures and maintain the position of the larynx in the neck The infrahyoid muscles work in synergy with the elevators of the larynx, one set of muscles relaxing (infrahyoid) whilst the other contracts (suprahyoid) to facilitate laryngeal elevation. Under normal physiological conditions, descent of the larynx is due to elastic recoil of the trachea and lower respiratory tract and therefore, relaxation of the suprahyoid musculature is the only requirement.

38. The intrinsic muscles are all paired and function in a coordinated fashion to move the cartilages of the larynx thereby governing laryngeal function They control the overall position and shape of the vocal folds as well as the elasticity and viscosity of each layer The majority of intrinsic muscles act to move the arytenoid at the cricoarytenoid joint The joint has a complex range of movements but broadly speaking the arytenoid rotates inwards and downwards to close and upwards and outwards to open the glottis.

39. INTRINSIC MUSCLES

40. EXTRINSIC MUSCLES

41. THE GLOTTIS The glottis lies between two horizontal lines, one drawn through the apex of the laryngeal ventricle, the other drawn 1cm below the medial free edge of the vocal fold when the larynx is at rest. Laterally between the vestibular and vocal ligaments, a horizontal slit opens into an elongated recess, the laryngeal ventricle. From the anterior part of the ventricle, the saccule of the larynx ascends between the vestibular ligament and the inner surface of the thyroid cartilage It occasionally protrudes through the thyrohyoid membrane

42. Dilatation of the saccule results in the formation of a laryngocele The vestibular folds are thick folds of mucous membrane scaffolded on a narrow band of fibrous tissue - t he vestibular ligament, which is the lower border of the upper quadrilateral membrane.

43. VOCAL FOLDS The vocal folds extend from the middle of the angle of the thyroid cartilage to the vocal process of the arytenoid cartilages and scaffolding them is the upper border of the conus elasticus. Each fold is a layered structure consisting of a superficial layer of nonkeratinizing, stratified squamous epithelium, beneath which is the lamina propria. This has three distinct layers. The superficial layer (Reinke’s space) contains a fibrous substance with similar characteristics to gelatin. The intermediate layer contains elastic fibres and the deep layer collagen fibres.

44. The intermediate and deep layers make up the vocal ligament. The vocalis muscle, which forms the main body of the vocal fold, lies lateral and deep. The loose areolar tissue of Reinke’s spaces allows lax movement of the overlying mucosa, giving rise to a mucosal waveform during phonation

45. At the anterior end of the vocal fold there is a mass of collagen fibres (anterior commissure tendon or Broyle’s ligament) They are connected to the inner perichondrium of the thyroid cartilage and to the deep layer of the lamina propria posteriorly. T here is another mass of elastic fibres continuous with the intermediate layer of the lamina propria called the anterior macula flava.

46. A similar structure is seen at the posterior end of the membranous part of the vocal fold. These structures appear to serve as cushions to protect the ends of the vocal folds from mechanical damage caused by vocal fold vibration. The anterior three-fifths of the vocal fold (from the anterior commissure to the tip of the vocal process) is the membranous part.

47. The remaining two-fifths posteriorly extend from the tip of vocal process to the face of the arytenoid cartilage, and are called the cartilaginous part of the vocal fold. The height of the vocal folds diminishes towards the anterior commissure mainly because the inferior edge of the vocal fold slopes upwards At the anterior commissure the lower edges of the vocal folds form the apex of a triangle via Broyle’s ligament to the epiglottis. The vocal folds are therefore almost wedge shaped, with the ‘blunted’ apex of the wedge anteriorly

48. Mucous membranes of the larynx The mucous membrane lining of the larynx is closely attached over the posterior surface of the epiglottis, the corniculate and cuneiform cartilages and over the vocal ligament Most of the larynx is lined by pseudostratified ciliated columnar ‘respiratory’-type epithelium. The upper half of the posterior surface of the epiglottis, the upperpart of the aryepiglottic fold, the posterior glottis and the vocal folds are covered with non-keratinizing stratified squamous epithelium .

49. Mucous glands are freely distributed throughout the mucous membranes and are numerous on the posterior surface of the epiglottis . The vocal folds do not possess any glands and the mucous membrane is lubricated by mucus from the glands within the saccules. .

50. SPACES WITHIN LARYNX PRE-EPIGLOTTIC SPACE wedge-shaped space with the point of the wedge inferiorly bounded anteriorly by the thyrohyoid ligament and hyoid bone and posteriorly by the epiglottis. Superiorly, the hyoepiglottic ligament connects the epiglottis to the hyoid bone The pre-epiglottic space is continuous laterally with the paraglottic space as no anatomical boundaries exist.

51. PARAGLOTTIC SPACE bounded laterally by the thyroid cartilage medially by the conus elasticus and quadrangular membrane posteriorly by the piriform fossa mucosa It contains the laryngeal ventricles and saccules

52. Nerve supply The motor and sensory nerves of the larynx are derived from the vagus by way of its superior and recurrent laryngeal nerves The superior laryngeal nerve arises from the inferior ganglion of the vagus It descends lateral to the pharynx behind the internal carotid artery A t the level of the greater horn of the hyoid divides into a small external branch and a larger internal branch. The external branch provides motor supply to the cricothyroid muscle

53. T he internal branch pierces the thyrohyoid membrane above the entrance of the superior laryngeal artery and divides into two main sensory and secretomotor branches. The  upper branch supplies the mucous membrane of the lower part of the pharynx, epiglottis, vallecula , vestibule of the larynx x T he lower branch descends in the medial wall of the piriform fossa beneath the mucous membran e It supplies the aryepiglottic fold and the mucous membrane of the larynx down to the level of the vocal folds

54. RECURRENT LARYNGEAL NV The primitive recurrent laryngeal nerve enters the sixth visceral arch on each side below the sixth aortic arch artery On the left side, the arch artery retains its position as the ductus arteriosus so the nerve is found below the ligamentum arteriosum after birth. On the right side, the dorsal part of the sixth arch artery and the whole of the fifth arch artery disappear, leaving the nerve below the fourth arch artery, which becomes the subclavian artery

55. Occasionally, the proximal portion of the fourth arch artery also disappears leaving nothing in contact with the right recurrent laryngeal nerve I nstead of being pulled down into its usual position, it passes directly from the main vagal trunk to enter the larynx, as the non-recurrent laryngeal nerve

56. The right recurrent laryngeal nerve leaves the Vagus as it crosses superficial to the right subclavian artery and loops under the artery, ascending in the tracheoesophageal groove to reach the larynx. left recurrent laryngeal nerve originates from the Vagus as it crosses the aortic arch. It then passes under the arch and the ligamentum arteriosum to reach the tracheoesophageal groove. In the neck, both nerves follow the same course and pass upwards accompanied by the laryngeal branch of the inferior thyroid artery.

57. They pass deep to the lower border of the inferior constrictor muscle and enter the larynx behind the cricothyroid joint. The recurrent laryngeal nerve then divides into motor and sensory branches The motor branch has fibres derived from the cranial root of the accessory nerve, which supply all the intrinsic muscles of the larynx except the cricothyroid. The sensory branch supplies the laryngeal mucosa below the level of the vocal folds and also carries afferent fibres from stretch receptors in the larynx

58. ARTERIAL SUPPLY The arterial supply of the larynx is derived from laryngeal branches of the superior and inferior thyroid arteries and the cricothyroid branch of the superior thyroid artery The superior laryngeal artery arises from the superior thyroid artery and passes deep to the thyrohyoid muscle. W ith the internal branch of the superior laryngeal nerve, it pierces the thyrohyoid membrane to supply the larynx The inferior laryngeal artery arises from the inferior thyroid artery at the level of the lower border of the thyroid gland and ascends on the trachea with the recurrent laryngeal nerve .

59. The inferior laryngeal artery arises from the inferior thyroid artery at the level of the lower border of the thyroid gland and ascends on the trachea with the recurrent laryngeal nerve. It enters the larynx beneath the lower border of the inferior constrictor to supply the larynx. The cricothyroid artery is a branch of the superior thyroid artery and passes across the upper part of the cricothyroid ligament to supply the larynx. The arteries of the larynx form a communicating plexus in the paraglottic space, which can be the source of brisk bleeding during endolaryngeal surgery.

60. VENOUS SUPPLY veins leaving the larynx accompany the arteries S uperior laryngeal veins --> superior thyroid or facial vein --> internal jugular vein The inferior laryngeal veins --> inferior thyroid veins --> brachiocephalic vein Some veins drain into the middle thyroid vein and then into the internal jugular vein.

61. LYMPHATIC DRAINAGE The lymphatic drainage of the larynx is separated, by the vocal folds, into upper and lower drainage systems A bove the vocal folds is drained by vessels that accompany the superior laryngeal vein emptying into the upper deep cervical lymph nodes The larynx below the vocal folds drains to the lower deep cervical chain, often through prelaryngeal (Delphian) and pretracheal nodes The vocal folds themselves are firmly bound down to the underlying vocal ligament and there are no lymphatics present in this plane.