Anatomy and physiology of the Larynx

1. Anatomy and physiology of the Larynx February 3, 2014

2. Why do we need to know the anatomy and physiology of the larynx • A solid understanding of normal structure and function of the larynx basis for • Evaluating larynx and phonatory function • Impact of specific pathologies • Interpretation of evaluation findings • Development of appropriate voice treatment plans

3. Larynx • Larynx (http://www.youtube.com/watch?v=Or5vGSLvoiE&feature=fvsr), (http://www.youtube.com/watch?v=DfN5J0-WbzM&feature=relmfu) http://www.youtube.com/watch?v=jlgUbA2ozNYhttp://www.youtube.com/watch?v=TiCgex4dBH4

4. Larynx • Cartilaginous tube • Connects to the respiratory system (trachea and lungs) inferiorly • Superiorly to the vocal tract and oral cavity • Position important because of its relationship and integration between three subsystems • Pulmonary power house • Laryngeal valve • Supraglottic vocal tract resonator • Lungs are the power supply for aerodynamic (subglottic tracheal) pressure that blows vocal cords apart – sets them into vibration • Vocal cords oscillate in a series of compressions and rarefactions • Modulate the subglottic pressure or transglottal pressure of short pulses of sound energy to produce human voice

5. Laryngeal valve • Complex arrangement of muscles, mucous membrane, and connective tissue • Soft tissues responsible for airway preservation • Cartilage serves as a protective shield • Muscles and cartilages create three levels of folds or sphincters for communication and vegetative body functions • Epiglottis folds posteriorly and inferiorly over the laryngeal vestibule – separates the pharynx from the larynx – first line of defense for preserving the airway

6. Laryngeal valve • Second sphincter is formed by the ventricular folds (not active during phonation) become active during hyper function or effortful speech production and extreme vegetative closure • Cause increase in intra-thoracic pressure by blocking outflow of air from lungs • Tight compression with rapid contraction of the thoracic muscles during sneezing and coughing • Longer durations to stabilize the thorax during physical tasks (e.g., lifting, childbirth, defecation, etc.)

7. Laryngeal valve • Third and final layer is the true vocal cords • Vibration for speech production • Close tightly for non-speech and vegetative tasks such as coughing, throat clearing and grunting • Angles of closure are multidimensional • Horizontal (lateral to medial) • Vertical

8. Structural support for the larynx • Larynx is suspended from a single bone – hyoid or superior border • Six laryngeal cartilages • Three unpaired (epiglottis, thyroid and cricoid) • Three paired (arytenoid, corniculate, cuneiform) • Hyoid bone articulates with the superior cornu of the thyroid cartilage via the thyrohyoid membrane • Epiglottis cartilage – leaf shaped- attached to the inner portion of the anterior rim of the thyroid cartilage • Made up of elastic cartilage - does not ossify or harden with age – remains flexible to allow a pliable free edge to assist in closing airway and diverting foods and liquids towards the esophagus

9. Structural support for the larynx • Thyroid cartilage – three sided, saddle shaped curve • Anterior attachment of the true vocal cords at the internal rim of the anterior curve • Posteriorly are two cornu or horns that extend upward to articulate with the hyoid bone and inferiorly to articulate with cricoid cartilage • Made up of hyaline cartilage that ossifies – limits flexibility with age • Lateral walls form quadrilateral plates or laminae – meet in the midline in a thyroid notch or prominence • In newborns, the laminae form a curve of 130 degrees – angle becomes more acute with age • A fully matured thyroid cartilage is 90 degrees in males (Adam’s apple) and 110 degrees in females

11. Structural support for the larynx • Cricoid cartilage – hyaline cartilage – below the thyroid • Signet ring shaped – narrow anterior curve and broad posterior back • Two sets of paired facets (flat surfaces) that articulate with adjacent thyroid and arytenoid cartilages • The cricothyroid joint connects the lateral edges of the cricoid to the inferior cornu of the thyroid • Cricothyroid joints are positioned on the top of the posterior cricoid rim • Both joints are lined with a synovial membrane (or connective tissue cushion for the joint, supplies secretions for lubrication, blood supply, adipose cells and lymph tissue) • Do not display age related deterioration and gender differences • Inferior to the cricoid cartilage are the tracheal rings

12. Structural support for the larynx • Arytenoid cartilages are pyramidal in shape • Four surfaces – anterior, lateral, medial and a base • Anterior angle projects forward at the base forming the vocal process • Hyaline cartilage except for vocal process which is made up of elastin • Vocal process is the cartilaginous portion of the vocal folds • Lateral arytenoid angle is the muscular process – intrinsic muscles for abducting and adducting the vocal folds • Medial angle faces its arytenoid pair forms an even surface for midline glottic closure • Base is concave to allow smooth articulation with the humped (convex) surface of the posterior cricoid cartilage (half cylinder over a bar)

13. Structural support for the larynx • Cricoarytenoid joint – two basic motions • Rocks anteriorly and posteriorly over the cricoid surface • It also slides laterally • Causes adduction, abduction and stabilizes the vocal folds • Vocal process tips can be pulled medially or laterally to determine the size and shape of the glottis • Tips directed medially causes the vocal folds to meet in midline and close or adduct • When the vocal process tips are pointed laterally the vocal folds are drawn open and abduction occurs

14. Structural support for the larynx • Corniculate cartilages (cartilages of Santorini) are attached by a synovial joint to the superior tip of the arytenoids • The cuneiform cartilages (cartilages of Wrisberg) are embedded in the muscular complex superior to the corniculates • Hyaline cartilages • Add structure and stability to preserve the airway

15. Extrinsic and intrinsic muscles • Extrinsic laryngeal muscles - attached to a site on the larynx and an external point (hyoid bone, sternum, mandible or skull base) • Major function – to change the height and tension as a gross unit (swallowing, lifting, phonating and other vegetative acts) • Also alter the shape and filtering characteristic of the supraglottic vocal tract – modifies vocal pitch, loudness and quality • Intrinsic muscles – both ends attached within the larynx • Primary function – alter shape and configuration of the glottis to modify the position, tension and edge of the vocal folds • Adduction (closing), abduction (opening) and modifying vocal fold length, tension and thickness • Both sets of muscles also help with ventilation, airway protection, communication and laryngeal valving

16. Extrinsic laryngeal muscles • Suprahyoid (above the hyoid bone) and infrahyoid (below the hyoid bone) • Identified based on their names which describe their anatomical attachments • Knowing the attachments one can predict the effect of the individual muscle contraction (shortening) between the sites • Stylohyoid (styloid process of the temporal bone to the hyoid bone) - raises the hyoid bone posteriorly • Mylohyoid (mandible to the hyoid bone) – raises the hyoid bone anteriorly • Digastric anterior belly (mandible to the hyoid) – raises the hyoid bone anteriorly • Digastric posterior belly (mastoid process of the temporal bone to the hyoid) – raises the hyoid bone posteriorly • Geniohyoid (mandible to the hyoid) – raises the hyoid bone anteriorly • Raises the larynx during swallowing to protect airway • Laryngeal elevation during phonation is a sign of excessive extrinsic laryngeal muscle tension and a sign of hyperfunctional voice use

17. Extrinsic muscles of the larynx • Infrahyoid muscles • Sternohyoid (sternum to hyoid bone) – lowers the hyoid bone • Sternothyroid (sternum to thyroid cartilage) – lowers the thyroid cartilage • Omohyoid (scapula to the hyoid cartilage) – lowers the hyoid bone • Thyrohyoid (thyroid cartilage to the hyoid bone) – shortens the distance between the thyroid and hyoid bone • Sternocleidomastoid (forms a sheath between the mastoid process and the sternum) • Lower the larynx in the neck

18. Extrinsic laryngeal muscles

19. Intrinsic laryngeal muscles • 5 intrinsic muscles attaches to cartilages to modify the cricothyroid and cricoarytenoid joint relationships • Affect the position, length and tension of the vocal folds • Changing the position of the cartilage framework that house the vocal folds • Altering the shape and configuration of the glottis, the opening between the vocal folds

21. Intrinsic laryngeal muscles • Cricothyroid – broad, fan-shaped muscle – inferiorly to the cricoid cartilage and superiorly to the thyroid cartilage – decreases the distance between the two cartilages – lengthening the vocal cords • Pars recta (vertical belly) • Pars oblique (angled belly) • Reduces the vibrating mass of the vocal folds by increasing the longitudinal tension, limits the vibrations to the thinnest portion of the vocal fold located at the medial edge • Greatest contributor to the fundamental frequency control – higher tones

22. Intrinsic laryngeal muscles

23. Intrinsic laryngeal muscles • Thyroarytenoid – attached anteriorly to the internal angle of the thyroid cartilage and posteriorly to the vocal process of the arytenoid • Two compartments • Thyromuscularislateral component – adduction of the vocal cords – fast acting muscle fibers • Thyrovocalis(vocalis) medial component – greater control over phonation – slow acting muscle fibers • Body of the vocal fold – contraction shortens the fold length by pulling the arytenoid cartilages anteriorly and thickens the vocal cords by increasing the mass of the vibrating medial edge • Lowers the fundamental frequency, increases loudness and tightens the glottic closure • Control over the vocal fold shape and edge and glottic closure patterns

24. Intrinsic laryngeal muscles

25. Intrinsic laryngeal muscles • Lateral cricoarytenoid muscle – broad fan-shaped muscle – lateral side of the cricoid to the arytenoid muscular process • Rocks the arytenoids anteriorly and slides them laterally • Redirects the vocal process medially brings the membranous vocal folds to midline or adduction • Strongest vocal fold adductors • Interarytenoid muscles – two bellies • Transverse portion (only unpaired intrinsic laryngeal muscle) attaches to the posterior plane of each arytenoid • Oblique portion (crossed bellies) attached at a 45 degree angle from the inferior border of one arytenoid to the superior border of its contralateral pair • Shortens the distance between the arytenoid cartilages causing adduction – forceful closure of the posterior glottis

26. Intrinsic laryngeal muscles • Posterior cricoarytenoid– sole abductor of the vocal folds • Posterior lamina of the cricoid and the muscular (lateral) arytenoid cartilage • Contraction causes abduction (opens) the vocal folds • When the arytenoids rock posteriorly to redirect the vocal processes laterally and separate the membranous portions of the vocal folds • Abducts for respiration and quick glottal opening gestures during unvoiced sound productions

27. Intrinsic laryngeal muscles

28. Intrinsic laryngeal muscles • Exceptional rules • All muscles are paired (right with a left) except for the transverse interarytenoid which functions as one unit, bringing the arytenoid cartilages together • All intrinsic muscles server as adductors except for posterior cricoidarytenoid muscles or the sole abductor • All muscles are innervated by the recurrent laryngeal nerve except the cricothyroid which is innervated by the external branch of the superior laryngeal nerve

29. Intrinsic laryngeal muscles

30. Vocal cord Microstructure • Membranous portion of the vocal folds – 5 histologically discrete layers – vary in composition and mechanical properties • Membrane oscillates to create sound • Integrity of the vibration pattern for phonation relies on the pliable elastic structure • Different layers provide variable amounts of flexibility and stability

31. Vocal cord Microstructure • 5 layers are epithelium, 3 layers of the lamina propria (superficial, intermediate and deep) layers, and the vocalis muscle • Epithelium – mucosal covering of stratified squamous cells that wraps over the internal contents, thinnest layer, consists of 6-8 cell layers, described as a pliable capsule – needs a thin layer of slippery mucous lubrication to oscillate

32. Vocal cord microstructure • Next 3 layers form the lamina propria • Loose extracellular tissue (extracellular matrix) composed of lipids, carbohydrates and specialized proteins • The lamina is slightly more dense than the epithelium but still flexible and loose • Superficial layer or Reinke’s space is a gelatinlike soft, slippery substance which allows it to vibrate significantly during phonation which is violated by vocal cord pathology, forceful abduction • Intermediate layer is composed principally of elastic fibers which can stretch to twice its length

33. Vocal cord microstructure • Deep layer of the lamina propria is still denser and composed of collagen fibers • Tissues of the third and fourth layers form the vocal ligament-not present in the new born – appears between 1-4 years and continues to develop until maturity at puberty • Deep layer is interspersed by muscle fibers to join vocalis muscle and the deep layers together

34. Vocal cord microstructure • The fifth layer or the vocalis muscle forms main body of the vocal fold • Provides tonicity, stability and mass • It is the only true “active” tissue and is the only portion of the vocal cord that can contract and relax in response to neurologic control • The lamina propria and epithelium layers vibrate passively in response to aerodynamic breath support

35. Vocal cord microstructure • Extracellular matrix of the lamina propria • Composed of fibrous proteins, interstitial proteins, carbohydrates and lipids • Fibrous proteins • consists of elastin and collagen found in different concentration in different layers of the lamina and contributes to the vibratory properties of the vocal fold cover

36. Vocal cord microstructure • Elastin fibers predominate in the superficial and intermediate layers, collagen in the deep layer • Elastin lets the layers stretch and then return to its original shape • Collagen does not stretch easily but tolerates stress but offers strength to the extracellular matrix

37. Vocal cord microstructure • Interstitial proteins • Consists of proteoglycens and glycoproteins • Role in vocal cord vibration is related to control of tissue viscosity, layer thickness and internal fluid content • Hyaluronic acid appears in greater concentration in the intermediate layer • Attracts water to form large, space filling molecules that creates a gel – acts as a cushion and resists compressive and shearing forces during vibration

38. Vocal cord microstructure • Also protects cells from deterioration, assists in tissue repair and clotting • Exceeds in males to females (3:1) • Glycoproteins, lipids and carbohydrates • Consists of fibronectin found in normal and injured vocal cords – plays a role in wound healing

40. Vocal cord microstructure • Body cover theory of vocal fold vibration (Hirano) • Three vibratory divisions • Cover (epithelium and superficial layer of the lamina propria) • Transition (intermediate and deep layer of the lamina propria) • Body (vocalis muscle)

41. Vocal cord microstructure • The vibrating cover forms the compliant, fluid oscillation seen in the vocal vibratory patterns while the body provides stiffer underlying stability of the vocal fold mass and tonus • The transition serves as coupling between the superficial mucosa and the deep muscle tissue of the vocal folds during vibration • Undulation or oscillation of the superficial vocal fold layers creates a ripple of tissue deformation and recoil

42. Vocal cord microstructure • Three vibratory phases of wave motion seen in endoscopy • Horizontal (medial to lateral movements) as seen in the open and closing patterns of vibration – 1-2 mm • Longitudinal (anterior and posterior – zipperlike wave) seen in front-to-back travelling wave 3-5 mm • Vertical phase (inferior to superior opening and closing of the vocal folds) as seen in an upper versus lower lip differences – mostly unseen

43. Folds and cavities of the larynx • Major folds are true vocal folds • Superior and lateral to the true folds are the false or ventricular folds • Do not actually vibrate in normal voice production except at very low fundamental frequency (below 50 Hz) • Few muscle fibers – very difficult to regulate their tension, mass and length • Aryepiglottic folds form a sphincter enclosing the entrance to the larynx • During swallowing and protective acts these folds contract to reduce the diameter of the laryngeal entrance to protect the airway

44. Folds and cavities of the larynx • Supraglottal cavity • Lies above the vocal folds • Superior border is the aryepiglottic sphincter • Acts as a resonator of the sound produced by the vocal cords • Subglottal cavity • Lies beneath the vocal folds • Lower boundary is the first tracheal ring • Pressure increases beneath the closed vocal folds until it becomes sufficient to force the folds open and begin phonation

45. Folds and cavities of the larynx • Ventricles • Paired cavities lying above and slightly lateral to the true vocal cords • Opening is very small and little effect on the sound produced • However in some conditions of singing the opening is sufficient to permit meaningful resonance adding to the glottal tone

48. Developmental changes • Newborns the larynx is situated high in the neck – cricoid positioned at the level of C3 to C4 • Newborns breathe only through nasal passages in the first few months of life allowing them to breathe and swallow simultaneously • During the first year the larynx begins its descent in the neck as the pharynx lengthens and widens • By puberty the larynx is at the level of C6 or C7 • Accompanied by skeletal facial growth and development, creates an expanded vocal tract which contributes a drop in fundamental frequency

49. Developmental changes • Intrinsic larynx also undergoes dramatic changes from birth through puberty • Vocal fold length of boys and girls is similar until 10 years • Gradual and consistent gender development changes vocal cord length and ratio between membranous to cartilaginous portions of the vocal cords • In males with the rise in testosterone at puberty stimulates the anterior growth of the thyroid notch and wide growth of the pharynx • In newborns have no vocal ligament (intermediate and deep layers of the lamina propria) and therefore little stability, the greater ratio of cartilage to membrane length provides protection of the airway (vocal ligament emerges between 1-4 years)

50. Developmental changes