Phonation

• There are 6 cartilages:

  1. Thyroid Cartilage (unpaired)
  2. Cricoid Cartilage (unpaired)
  3. Epiglottis (unpaired)
  4. Arytenoids (paired)
  5. Corniculates (paired)
  6. Cuneiforms (paired)

  
• • Thyroid Cartilage (unpaired) this is what gives us Adam's apple / one of the biggest cartilage
  • Laryngeal Prominence (Adam's apple)
  • Superior Thyroid Notch - a small notch at the superior region where the thyroid plates do not completely join together.

  Primary function is to provide structure to support and protect the vocal cords

  
• Cricoid Cartilage (unpaired) not like a band all around, like a ring

  • Serves to maintain airway patency, forms part of the larynx, and provides an attachment point for key muscles, ligaments, and cartilages, which function in the opening and closing of the vocal cords for sound production. 

  
• Epiglottis (unpaired) close off air-way

  • broad, flat and attached to the medial surface of thyroid.
  • covers the airway when one swallows.
• Arytenoids (paired) on top of the cricoid cartilage ; pyramid like

  • are shaped like small pyramids placed on the signet portions of the cricoid ring.
  • three projections:

  1. Apex - at the top
  2. Muscular Process - at the side
  3. Vocal Process - The points toward the front

  *most important after epiglottis and cricoid*

  • vocal folds are directly attached to arytenoid vocal process to thyroid cartilage
  • helps vocal fold strengthen and contract

  
• • Corniculates (paired) above the arytenoid
  • rest on top of the arytenoids
• • Cuneiforms (paired) between the fold
  • embedded within the membrane of the aryepiglottic folds (on top of corniculate) 
• • extrinsic is attached within the larynx and the other part is attach outside the larynx and because they are outside it can pull the larynx up or down
  • Have one attachment to a laryngeal structure and one attachment to an external structure
  • It can be divided into 2 sets, depending on whether their external attachment is superior or inferior to the hyoid.

  1. Suprahyoid - elevate the larynx
  2. Infrahyoid - depress the larynx

  helps to elevate or pull (depress) the larynx

  larynx moving up or down leads to pitch changes
• Vocal fold structure, layers

  • anterior ⅗ of vocal folds is soft tissue know as membranous portion of VF
  • posterior ⅖ is known as cartilaginous portions of VF
  • the true vocal folds lie inferior to the false vocal folds. The 2 pairs are paralleled to each other and stretch across the airway.
  • they participate in phonation ; False VF, can helpful if true VF fail

  True and false VF are separated by a small cleft called the ventricle.
• 5 layers of tissue:

  1. Superficial epithelium (outermost layer)
  2. Elastin fibers
  3. Elastin fibers
  4. Collagen fibers
  5. Thyrovocalis muscle (inner most layer)

  1-3: cover of vocal folds

  4-5: body of vocal folds

  *complex in layers*
• True Vocal Folds

  Important in normal phonation

  Made up from mucous membrane, connective tissue & vocal muscle

  Space between true VF: Glottis
• False Vocal Folds

  Important only in vocal pathology

  Made up from mucous membrane and fibrous vestibular ligament

  Space between false VF: Rima Vestibuli
• • How is voice produced? Know the steps

  Vocal Fold Vibration (step in phonation)

  1. PCA contraction (& enlargement of thorax) leads to inflow of air into lungs through the open vocal folds
  2. Next, LCA, OA, & TA contraction leads to vocal folds adduction
  3. this results in increase in Ps (subglottic pressure)
  4. Vocalis & CT contraction leads to increase in vocal fold tension, this offers resistance to outflow of air
  5. Ps  continues to increase and ultimately when Psub is > Supra the resistance offered by the vocal fold tension is overcome and is blown apart
• • How is voice produced? Know the steps

  .Vocal Fold Vibration (step in phonation)

  6. thus a puff of air is released

  7. Elastic recoil brings the folds closer together (VF adducted with slight opening)

  8. Air now leaves through a narrow constriction

  9. This leads to a drop in pressure perpendicular to the air flow. Therefore vocal folds are further sucked together (Bernoulli’s effect)

  10. air stream is completely cut off allowing for the build of subglottal air pressure

  ~227 times/sec
• Bernoulli’s principle

  • Two aerodynamic forces are actually responsible for vibration

  1. Subglottal air Pressure (Ps) - cannot produce voice without this
  2. Bernoulli’s effect - when water or air travels through a narrow space; little space available will increase in velocity & decrease in pressure

  • Danielle Bernoulli (18th century)
  • When a gas or liquid current runs through a constricted passage, its velocity increases
  • Increase in velocity results in a drop in pressure exerted by the molecules of incoming gas. This drop in pressure is perpendicular to the direction of flow of molecules.
• Myoelastic Aerodynamic Theory of Phonation:

  • periodic opening and closing of the vocal folds is produced by interaction between the mass-tension of the folds and aerodynamic forces exerted on and around them by the exhaled air stream.
• Cover body theory of phonation:

  • vocal adjustments in speaking and singing are regulated by changing the mechanical properties of the different layers of tissue in the vocal folds. The talker or singer can change the stiffness of the layers of the vocal folds producing different vocal fold vibration.
• How can we change intensity of our voice? 

  Intensity:

  Increase in subglottal air pressure increases intensity.

  • When subglottal air pressure is greater, vocal folds are blown apart much wider.
  • Greater puff of air is released and the sound pressure wave has greater amplitude, thus greater intensity.
  • As intensity increases the amount if time for which vocal folds remain closed is also long
• • How can we change frequency of our voice? 

  Frequency:

  • refers to the rate at which vocal folds vibrate, F0 is constantly changing in speech
  • Thicker & longer VF’s naturally vibrate at lower frequencies compared to thinner and shorter vocal folds
  • VF’s vibrate faster when they are tense than slack. VF’s can be tensed by simply stretching them
  • BUT … within a speaker, if a person stretches his or her VF’s, to make it longer, the mass per unit length is lower leading to higher F0.
• How can we change frequency of our voice? 

  • (F0) changes is determined primarily by changes in VF tension. VF’s can be tensed by stretching (increase distance between thyroid and arytenoid cartilages). This is achieved by contracting the cricothyroid muscle.
  • Thus, for producing higher (F0), primarily CT muscle is contracted. For Falsetto voices, VF’s are pulled taut and forego their usual wave-like motion & vibrate more like strings.
  • F0 can be increased by:
  • increasing subglottal air pressure
  • elevating the larynx
• Instrumentations used in assessing phonation –  

  Endoscopy

  • Oral Rigid Laryngoscopy: Generally this technique is not tolerated well. Anesthesia may be required. Assessment of structure and function possible during sustained vowels only.
  • Flexible Nasendoscopy:  Can assess function during singing and speaking
• Instrumentations used in assessing phonation –

  Stroboscopy

  • Fiber Optic device that uses stroboscopic light to obtain sampled images of the vocal folds
  • Pictures are taken at a rate that approximates  the same frequency of vibration of an object. One picture taken per cycle. So, what appears to be a single cycle of vibration is in fact a product of many cycles.