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VOICE (Cranial Nerves (CNV: tensor veli palitini for raising velum…
VOICE
Cranial Nerves
CNV: tensor veli palitini for raising velum (resonance), two extrinsic suprahyoid muscles for increasing pitch
CNXII: extrinsic laryngeal muscles (genioglossus and hyoglossus) that elevate the larynx (increase pitch), one suprahyoid muscle
CNX: most important, adducts/abducts VFs via intrinsic laryngeal muscles. Also involved in respiration.
CNXI: sternocleidomastoid, accessory respiratory muscle
CNVII: extrinsic suprahyoid laryngeal muscles (posterior belly of digastricus, stylohyoid)
Theories
Cover-Body Model: modification of MEAT to include concept that Vertical Phase Difference sustains VF oscillation, not just Bernoulli effect and elasticity.
Source Filter Theory: describes speech production as a two stage process involving the generation of a sound source at VFs, with its own spectral shape and spectral fine structure, which is then shaped or filtered by the resonant properties of the vocal tract.
Myoelastic Aerodynamic Theory of Phonation: Bernoulli effect closes VFs. Continued air pressure from lungs builds up in subglottic space until it blows VFs outward. Lateral movement of VFs continues until natural elasticity of the tissue takes over, and VFs move back to original, closed position. Then, the cycle begins again. Each cycle produces a single small puff of air..
Bernoulli Effect: when VFs are closed, air creates pressure against them until they are blown apart. As air rushes through narrow opening, it must accelerate to get through. This high speed air creates suction perpendicular to the direction of its flow --this sucks VFs back together.
Vertical Phase Difference: asymmetry between convergent and divergent airflow causes wave like oscillations of VFs.
Larynx
Cartilages: nine in total. VFs are attached posteriorly to the arytenoid cartilages and anteriorly to the thyroid.
Muscles
Intrinsic laryngeal muscles responsible for vibration of VFs, via CNX. Bulk of VFs are made up of part of thyroarytenoids.
Extrinsic laryngeal muscles can affect pitch (suprahyoids and infrahyoids). Innervated by CNV, CNVII, CNXII and other nerves.
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Spaces: super-glottic space (above VFs), glottis (between VFs when open) and sub-glottic space (below VFs).
Purposes
Respiration, as air goes up the larynx from the trachea. Also Valsalver manoeuvre.
Protective mechanism during swallowing. Epiglottis redirects prandial to oesophagus, VFs adduct and cause coughing if prandial reaches them.
Phonation for voicing in speech, via adduction of VFs.
Vocal Folds
Adduction: method of phonation (vibrating in place). Muscles: lateral cricoarytenoids, interarytenoids (oblique and transverse).
Abduction: for breathing, controlled by posterior cricoarytenoids.
Vocal Tone: larynx can make two adjustments to change vocal tone, longitudinal and medial compression.
Medial: changes intensity/loudness. Tighter compression results in more subglottic pressure building, and larger puff of air being released when VFs are blown apart. And vice versa. Muscles: lateral cricoarytenoids, intrinsic only.
Longitudinal: relates to changes in pitch. Greater pressure increases length of VFs and decreases mass. Increases pitch. And vice versa. Muscles: cricothyroids (high) and thyroarytenoids (low). Highest and lowest pitches achieved via supra- and infrahyoids. So sum of intrinsic and extrinsic muscles.
Structure
1. Epithelium: most superficial, white in appearance.
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5. Thyroarytenoid muscle, aka vocalis m.
Systems
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Phonatory: system by which humans produce voice, responsible for vocal tone
Articulatory/resonance: modifies/transforms acoustic signal as it travels through vocal tract (speech more than voice)
Disorders
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Neuromuscular dysphonia: Disturbances in any of components of nervous system that control laryngeal function. Hoarseness, breathiness, etc.
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Hyolaryngeal excursion via suprahyoid muscles can increase pitch, while the infrahyoid muscles can decrease pitch.