Date post: | 13-Jan-2017 |
Category: |
Health & Medicine |
Upload: | drashwin-menon |
View: | 478 times |
Download: | 0 times |
PHYSIOLOGY OF PHONATION
Dr. Ashwin Menon
DEFINITION
Rapid, periodic opening and closing of the glottis through separation and apposition of the vocal cords that, accompanied by breath under lung pressure, constitutes a source of vocal sound.
Other functions of Larynx
Protection of lower airways
Respiration
Fixation of Chest wall
Biomechanics of Phonation
Vocal Folds abduct on inspiration. Vocal Folds slightly adduct on
expiration. Full abduction in forceful inspiration
Larynx descends with Inspiration and Asends with expiration.
The requirements of normal phonation are as follows: Active respiratory support Adequate glottic closure Normal mucosal covering of the vocal cord
Adequate control of vocal fold length and tension.
Anatomy: Physical parts of the vocal system
Creating sound requires numerous muscles, bones and organs of the body
Three main anatomical aspects: Actuators: Lungs/diaphragm/intercostal
muscles; these organs deal with breathing/“air management”
Vibrator: larynx; this deals with the creation of pitch in the form of a sound wave
Resonators: Throat (pharynx), mouth/lips/teeth, nose; these deal with the modification of sound into varying accents
Respiration: Demonstration
Movement of diaphragm Movement of ribs/lungs
Phonation The larynx acts as a transducer during
phonation converting the aerodynamic forces generated by the lungs, diaphragm, chest and abdominal muscles into acoustic energy.
The consonants of speech can be associated with particular anatomical sites responsible for their generation i.e. 'p' and 'b' are labials, 't' and 'd' are dentals and 'm' and 'n' are nasals.
Initiation of Voice
Before phonation, vocal folds rapidly abduct to allow intake of air-Pre Phonatory inspiratory Phase (‘’Wyke’’)
Vocal folds adducted- Lat cricoarytenoid M
Pulmonic air forced between adducted Vocal Folds – vocal note
Repeated vibratory movt of the vocal folds – production of vocal note- Vocal fold oscillation
Amount of air pressure required to begin voicing – Phonation threshold pressure
THEORIES OF VOICE PRODUCTION
1. PUFF THEORY-Puff of air emitted through Glottis- vibratory action- Voice
2. NEUROCHRONAXIC THEORY-ROUL HUSSON(1950)Central impulses stimulate the RLN(beat by beat) leading to the active contraction of the thyroarytenoid M – vocal cord vibration.
This theory was not accepted as- Tracheostomy patients cannot phonate. Left RLN longer than the right.
3. CAVITY TONE THEORY – WILLISHe developed a series of resonating cavities with different shapes and lengths & coupled them to a vibrating reed source. He observed that the sound heard represented a particular vowel & it mainly depended on the length of the resonating tube independent of the reed tone and its frequency.
4. HARMONIC THEORY(OVERTONE/STEADY STATE THEORY)CHARLES WHEATSTONE
He noticed that the vowels heard were a combination of the reed tone and its harmonics. This modulated reed tone can be further modified at the supra laryngeal level giving rise to special sounds. But this theory fails to take into account the dampening effect.
5. MYO ELASTIC AERODYNAMIC THEORY-JOHANNES MULLER(1843)AERO- Air pressure & flowDYNAMIC- Movt & changeMYO- Muscular movtELASTIC- Ability to return to original state
6. COVER BODY THEORY
7. BODY SOURCE THEORY
8. SOURCE TRANSFER THEORY
VIBRATORY CYCLE1. ADDUCTION
2. AERODYNAMIC SEPARATION
3. RECOIL
Manifestation of a mucosal wave travelling from the inferior to the superior surface of each Vocal Fold.
Mucosal Wave
Also important component of vocal fold vibration/ voice production
Explained by Body-Cover model of vocal fold vibration Diff vibratory properties of vocal fold
layers Vertical phase differenceConditions that change density
relationships between cover & body result in decreased mucosal wave.
The Glottic Cycle The vocal folds alternately trap
and release air; each trap/release is one cycle of vibration. This cycle is often referred to as the glottic cycle, and it is divided into phases:
I. opening phaseII. open phaseIII. closing phaseIV. closed phase
During the closed phase, the air pressure builds up below the vocal folds. When the glottis opens, the air explodes through the vocal folds, and that's the beginning of the sound wave. The strength of that explosion determines the loudness of the sound coming directly from the larynx.
First, the laryngeal muscles position the vocal cords in various degrees of adduction and place them under the appropriate longitudinal tension.
Next, muscular and passive forces of exhalation cause the subglottic air pressure to increase.
When this subglottic pressure reaches a point where it exceeds muscular opposition, the glottic chink is forced to open.
When the vocal cords start opening from complete closure, they open in a posterior to anterior direction with the posterior portion of the glottis opening first, reaching maximum excursion first, and recontacting each other at the end of the vibratory cycle prior to the anterior portion of the cords.
After release of the puff of air there is a reduction of sub glottic pressure, and the vocal cords approximate each other again (myo elastic forces of the vocal cords have exceeded the aerodynamic forces).
The myo elastic forces are enhanced because air current flowing through a narrow channel exerts a negative pressure on the channel walls; This is the basis of Bernoulli's Principle.
The vocal cords are thus sucked back together in an adducted state until the sub glottic air pressure can overcome the myo elastic forces of the re approximated cords, and the cycle is then repeated.
FEATURES OF SOUND:1. PITCH
It is the number of vibrations of vocal cords per second
Depends on:a. Length of VC.
b. Mass of VC.
c. Tension of VC.
In general, men's vocal folds can vibrate from 90 - 500 Hz, and they average about 115 Hz in conversation.
Women's vocal folds can vibrate from 150 -1000 Hz, and they average about 200 Hz in conversation.
PITCH = T L M
Vocal folds vibrate faster as they're pulled longer, thinner, and more taut and vibrate more slowly when they're shorter, thicker, and floppier.
The cricothyroid muscle and thyroarytenoid muscle coordinate with each other to create different pitches.
2. VOLUME(INTENSITY) & LENGTH(DURATION)
Depends on the air pressure created which is in turn dependent on the lung capacities.
3. QUALITY(TIMBER)
Depends on the overtones added by the resonators and articulators.
Vocal Register differences in mode of vibration of
vocal foldsRegister may include
Equivalent terms Vocal folds F0 range(Hz)
Loft registerHighest vocal freq
Falsetto Thin, tense, lengthened.Minimal vibration
275-1100
Modal registerUsual freq employed in speaking & singing
Chest, head, middle, heavy voice
Complete adduction
100-300
Pulse registerLowest range of vocal freq
Vocal fry, glottal fry, creaky voice
Long closed phase
20-60
Vocal Disorders Organic, Functional & Psychogenic. Puberphonia- Maintenance of the
childhood pitch despite having passed through puberty
Spasmodic Dysphonia Stuttering Phonasthenia Bogart-Bacall syndrome
Vocal Injury It is fairly easy to injure the vocal cords!
Forceful singing, yelling, screaming, loud talking can cause the vocal cords to hit very hard and result in injury to the cords - vocal abuse
Excessive amounts of phonation can also lead to injury - vocal overuse
Nodules, polyps, laryngitis and hemorrhage of the cords are possible effects of such vocal abuse
Smoking also has dramatic effects on the larynx!
Nodules
Nodules (also called “nodes”): A common injury that is essentially a small growth found on both of the cords (nodules are much like a callus on the hand or foot); Nodules keep the cords from fully closing, resulting in a harsh/breathy voice
Polyps Polyps are like nodules in that they
are also a growth on the cords that keep the cords from closing, but are more like a soft lesion than a hard callus
Polyps may be on either just one cord or both (typically on just one side); both abusive phonation and smoking are common reasons for polyps
Hemorrhage
A hemorrhage is where a blood vessel rupture due to excessive pressure
Laryngitis Laryngitis is the inflammation of
the vocal cords
It may be the result of reactions to allergies, bacterial or fungal infections, or the result of vocal overuse
With laryngitis, the vocal cords often swell too much to correctly close, resulting in the lack of phonation
Acid Reflux as irritant Reflux can cause significant irritation,
burning or swelling on vocal cords/larynx; Two types:
“GERD”: Gastroesophageal reflux disorder– is when acid backflows into esophagus Symptoms: Heartburn, regurgitation;
occurs while laying down
“LPR”: Laryngopharyngeal reflux– is when acid backflows into larynx/pharynx Symptoms: Too much mucous in throat,
need to clear throat often, sour taste in mouth, hoarse voice, feeling of a “lump” in the throat
CANCER
VIDEO STROBOSCOPY Invented by JAN G SVEC.
It has evolved as the most practical and useful technique for the clinical evaluation of the visco-elastic properties of the phonatory mucosa.
Done with topical anaesthesia.
Essential diagnostic procedure for the evaluation of laryngeal mucosa, vocal fold motion biomechanics & mucosal vibration.
It uses a synchronized, flashing light passed through a flexible or rigid telescope.
Flashes of light from the stroboscope are synchronized to the vocal fold vibration at a slightly slower speed, allowing the examiner to observe vocal fold vibration during sound production in what appears to be slow motion.
VIDEO STROBOSCOPY OF VOCAL CORDS
THANK YOU!!!