Anatomy & Physiology of Phonation PDF

Anatomy & Physiology of Phonation Phonation Phonation, also known as voicing, is the product of vibrating vocal folds and occurs within the larynx As respiration is the source of energy for speech, phonation is the source of voice for speech Respiration is the energy source that permits phonation...

Anatomy & Physiology of Phonation Phonation Phonation, also known as voicing, is the product of vibrating vocal folds and occurs within the larynx As respiration is the source of energy for speech, phonation is the source of voice for speech Respiration is the energy source that permits phonation to occur; without respiration there would be no voicing Framework of the Larynx The larynx is a musculocartilaginous structure located at the superior end of the trachea Comprised of 3 unpaired and 3 paired cartilages bound together by ligaments and lined with mucous membranes Adjacent to vertebrae 4 through 6 in the adult (the larynx of an infant will be higher) Average length of larynx is 44mm (males) and 36mm (females) Overview of Framework of Larynx Cricoid Cartilage: complete ring resting atop the trachea; most inferior of laryngeal cartilages Thyroid Cartilage: Largest of cartilages; articulates with cricoid below by means of paired processes that let it rock forward and backward at the joint Arytenoid Cartilages: paired, ride on the high-backed upper surface of cricoid, forming posterior point of attachment for VFs Corniculate Cartilages: ride on superior surface of each arytenoid and are prominent landmarks in the aryepiglottic folds Cuneiform Cartilages: reside within the aryepiglottic folds, provides a degree of rigidity to the folds Epiglottis: Leaf-like structure, protective structure that drops to cover larynx during swallow Structures of the Larynx Cartilages of the Larynx: Cricoid Cricoid cartilage is a complete ring resting atop the trachea (most inferior of laryngeal cartilages) The low, anterior cricoid arch provides clearance for the vocal folds that will pass over that point. The posterior elevation, the superior surface of the posterior quadrate lamina, provides the point of articulation for the arytenoid cartilage The cricoid and thyroid cartilages articulate at the cricothyroid joint (a pivoting joint that permits rotation of the two structures) Cartilages of the Larynx: Thyroid Thyroid cartilage is the largest of the laryngeal cartilages ◦ Has a prominent anterior surface made up of 2 plates called thyroid laminae, joined by the thyroid angle Articulates with the cricoid cartilage below by means of paired processes that lets it rock forward and backward at that joint Thyroid articulates with the hyoid bone by means of a pair of superior processes. Medial to the thyroid and hyoid bone is the epiglottis Cartilages of the Larynx: Arytenoids Arytenoid cartilages are a paired cartilages that ride on the high-backed upper surface of the cricoid cartilage, forming the posterior point of attachment for the vocal folds Among the most important cartilages of the larynx Provides the mechanical structure that permits onset and offset of voicing Each cartilage has 2 processes and four surfaces. ◦ Vocal process: where posterior portion of VFs attach ◦ Muscular process: point of attachment for muscles that adduct/abduct the VFs Cartilages of the Larynx: Epiglottis Leaf-like structure that arises from the inner surface of the angle of the thyroid cartilage just below the notch, attached by the thyroepiglottic ligament Projects upward beyond larynx and above hyoid bone Attaches to root of the tongue by the glosso-epiglottic fold and paired lateral glosso-epiglottic ligaments. This juncture produces the vallecular space (important in swallowing) Attaches to hyoid bone via hyoepiglottic ligament Drops down to cover the larynx during swallowing Other Cartilages of Larynx Corniculate cartilages attach to the upper margin of the arytenoids; are prominent landmarks in the aryepiglottic folds Cuneiform cartilages, embedded within the aryepiglottic folds, provides a degree of rigidity to the folds Corniculate Cartilage Hyoid Bone Hyoid bone forms the union between the tongue and the laryngeal structure Only bone of the body that is not attached to another bone Three major elements: ◦ Corpus or body-prominent, shield-like structure forming front of bone; point of attachment for 6 muscles ◦ Greater Cornu- arises on lateral surface of corpus, projects posteriorly ◦ Lesser Cornu- arises from junction of corpus and greater cornu ◦ 3 additional muscles attach to the greater and lesser cornu Video: Cartilages of the Larynx Inner Larynx: Ligaments & Membranes Inner Larynx The cartilages are combined with the trachea and the airway above the larynx to form a rough tube-like space with a constriction caused by the cartilages The vocal folds are bands of mucous membrane, connective tissue and thyrovocalis muscle that are slung between the arytenoid cartilages and thyroid cartilage so that they may be moved in and out of the airstream Muscles attached to arytenoids provide both adductory and abductory functions, with which we control the degree of airflow by means of muscular contraction Laryngeal Membranes Larynx is a constricted tube with a smooth and aerodynamic surface Extrinsic ligaments provide attachment between hyoid bone or trachea and cartilages of the larynx Intrinsic ligaments connect the cartilages of the larynx and form the support structure for the cavity of the larynx, as well as that of the vocal folds Extrinsic Ligaments Thyrohyoid membrane, Lateral thyrohyoid and Median thyrohyoid ligament together connect the larynx to the hyoid bone Hyoepiglottic ligament and thyroepiglottic ligament attach the epiglottis to corpus hyoid and inner thyroid cartilage Lateral and median glossoepiglottic ligaments attaches epiglottis to tongue Cricotracheal ligament attaches trachea to larynx Intrinsic Ligaments Fibroelastic membrane of larynx is composed of: ◦ Upper quadrangular membranes (layer of connective tissue running from arytenoids to epiglottis and thyroid; lower free border forms the false VFs) ◦ Aryepiglottic fold (course from epiglottis to side of arytenoids) ◦ Lower conus elasticus (extending between cricoid and the vocal ligament) ◦ Vocal ligament (attached in front to the angle of thyroid cartilage and behind to vocal process of arytenoid; part of layers of VFs; formed by the thickened free border of the cricothyroid membrane) Video: Ligaments & Membranes of the Larynx Fine Structures of Vocal Folds Vocal Folds are composed of 5 layers of tissue: ◦ Most superficial layer is a protective layer of squamous epithelium (~.1mm thick); aids in keeping the tissues moist by fluid retention ◦ Next layer is superficial lamina propria (SLP) made up of elastin fibers; the fibrous and elastic elements cushion the VFs ◦ Intermediate lamina propria (ILP); ~1-2mm thick; composed of elastin fibers running in an anterior-posterior direction (making them cross-layered with the SLP) ◦ Deep lamina propria is primarily supportive; ~1-2mm thick; made up of collagen fibers that prohibit extension. The ILP and DLP combine to make up the vocal ligament ◦ Thyroarytenoid muscle (thyrovocalis and thyromuscularis) makes up the bulk of the VFs ◦ Depending on other muscle action, this muscle can act as an adductor, a tensor or a relaxer. Cavities of the Larynx Aditus-is the entry to the larynx from the pharynx above Vestibule-the first cavity of the larynx; space between the aditus and the ventricular folds (false VFs) Aryepiglottic folds-comprise the lateral walls of the larynx Laryngeal ventricle (laryngeal sinus)-middle space of the larynx that lies between the false and true VFs Glottis-space between the VFs. The length of the glottis at rest is approx. 20mm in adults from the anterior commissure (anterior-most opening posterior to angle of thyroid cartilage) to the posterior commissure (between the arytenoid cartilages) Vocal Fold Hydration VFs are sensitive to internal/external environment Problems arise when VFs are subject to abuse such as: ◦ Contact ulcers ◦ Vocal nodules Hydration therapy ◦ Effort of phonation (e.g., airflow required) increases as individuals become dehydrated ◦ Tell clients to increase environmental humidity, drink plenty of fluids Laryngeal Musculature Intrinsic & Extrinsic Laryngeal Muscles Intrinsic: ◦ Means they have origin and insertion on the laryngeal cartilages ◦ Makes fine adjustments to the vocal mechanism itself ◦ Assume responsibility for opening, closing, tensing and relaxing the vocal folds. Extrinsic: ◦ Have one attachment on laryngeal cartilages and other attachment on a nonlaryngeal structure ◦ Makes major adjustments to the larynx (such as elevating or depressing it) ◦ Tend to work in concert with the articulatory motions of the tongue and many are important in swallowing Laryngeal Musculature: Intrinsic Laryngeal Muscles Adductors: ◦ Lateral cricoarytenoid ◦ Transverse arytenoid ◦ Oblique arytenoid Abductors: ◦ Posterior cricoarytenoid muscle Glottal Tensors: ◦ Cricothyroid muscle ◦ Thyrovocalis muscle Relaxers: ◦ Thyromuscularis Auxiliary Muscles: ◦ Thyroepiglotticus ◦ Superior thyroarytenoid ◦ Aryepiglotticus Intrinsic Laryngeal Muscles: Adductors Lateral cricoarytenoid ◦ Originates from lateral surface of cricoid and inserts into muscular process of arytenoid ◦ Moves arytenoids towards adduction Transverse arytenoid ◦ Attaches on each side to dorsal surface of arytenoids ◦ Adducts vocal folds Oblique arytenoid ◦ Originates from muscular processes of arytenoids and crosses to insert into apex of opposite arytenoid ◦ Adducts vocal folds Intrinsic Laryngeal Muscles: Abductors ◦ Posterior cricoarytenoid ◦ Originates from lateral half of cricoid lamina and insert onto arytenoid cartilages ◦ Direct antagonist to lateral cricoarytenoid ◦ Sole abductor of the vocal folds Intrinsic Laryngeal Muscles: Glottal Tensors Cricothyroid ◦ Primary tensor of vocal folds ◦ Achieves its function by rocking thyroid forward relative to cricoid ◦ Composed of two heads: pars recta and pars oblique ◦ Contraction of this muscle would lengthen (tense) the vocal folds Thyrovocalis ◦ The medial muscle of vocal folds ◦ Contraction of this muscle tenses the vocal folds by drawing the thyroid and cricoid cartilages apart in front Intrinsic Laryngeal Muscles: Relaxers Thyromuscularis ◦ Considered to be the muscle mass lateral to thyrovocalis, which together make up the thyroarytenoid muscle (the bulk of the VFs) ◦ Contraction will adduct and lengthen the vocal folds; however, contraction of the medial fibers may relax the vocal folds as well Extrinsic Laryngeal Muscles Muscles with one attachment to a laryngeal cartilage (include suprahyoid and infrahyoid muscles) Hyoid and Laryngeal Elevators: ◦ Digastricus anterior and posterior ◦ Stylohyoid ◦ Mylohyoid ◦ Geniohyoid ◦ Genioglossus ◦ Hyoglossus ◦ Thyropharyngeus muscle Hyoid and Laryngeal Depressors: ◦ Sternohyoid ◦ Omohyoid ◦ Sternothyroid ◦ Thyrohyoid Extrinsic Laryngeal Muscles: Hyoid and Laryngeal Elevators ◦ Suprahyoid Muscles-muscles that extend superiorly from the hyoid bone and form a sling from mandible to hyoid to posterior base of cranium: ◦ Digastricus anterior and posterior-work together to elevate hyoid ◦ Stylohyoid- Moves hyoid posteriorly ◦ Mylohyoid-Elevates hyoid; depresses mandible ◦ Geniohyoid-Elevates hyoid; depresses mandible ◦ Genioglossus-Elevates hyoid ◦ Hyoglossus- Elevates hyoid, depresses tongue ◦ Thyropharyngeal or inferior pharyngeal constrictor-Constricts pharynx and elevates larynx Extrinsic Laryngeal Muscles: Hyoid and Laryngeal Depressors ◦ Infrahyoid Muscles-muscles extend from hyoid bone to the shoulder girdle; hyoid to larynx; shoulder girdle to larynx: ◦ Sternohyoid-Depresses hyoid ◦ Omohyoid-Depresses hyoid ◦ Sternothyroid-Depresses thyroid cartilage ◦ Thyrohyoid-Depresses hyoid or elevates larynx Movement of the Cartilages Movements of the Cartilages Cricothyroid and cricoarytenoid joints are the only functionally mobile points of the larynx Rocking motion of the cricothyroid joint provides the major adjustment for change in pitch Rocking action of cricoarytenoid joint brings the two vocal folds toward each other, permitting the VFs to make contact; provides the mechanism for vocal fold approximation and abduction Videos: Movement of the Cartilages Video: Muscles of Larynx Part 1 Video: Muscles of Larynx Part 2 References Seikel, J.A., Douglas, W.K., & Drumright, D.G. (2010). Anatomy and physiology for speech, language, and hearing. Clifton Park, NY: Delmar.