0519 - Larynx - CS

Question 1

1. Explain the functions of the larynx

Answer 1

1. Control inlet to the lungs - prevent food from being inspired
2. Vocalisation - song in birds, calling and distress signalling in mammals
3. Bracing the thorax during effort - muscular/abdominal straining/birthing
4. Adapted for speech in humans - has occurred through evolution

Question 2

1b. Describe the evolutionary changes of the human larynx that has enabled speech. What are the trade-offs of this adaptation?

Answer 2

1-shortening of ‘snout’ and cranial base

2-thicker more mobile tongue

3-vertical dentition

4-more caudal larynx

5-epiglottis and soft palate no longer meet to form a tight ‘lock up’ and sound able to pass through oral cavity

.. has led to ability to make wider range of sounds, more vocal control

BUT - higher risk of choking and sleep apnoea

Question 3

2. Describe the surface features of the larynx

Answer 3

Three large unpaired cartilages (epiglottis, cricoid, thyroid) and three pairs of smaller cartilages along with a fibro-elastic membrane and numerous intrinsic muscles

Epiglottis - ‘leaf shaped’ cartilage. Upper margin of epiglottis is behind the pharyngeal part of the tongue

Thyroid - largest laryngeal cartilage. Most superior point projects forward as the laryngeal prominence (‘adam’s apple’)

Cricoid - inferior laryngeal cartilage, encircles the airway

Central tubular cavity of larynx is lined by mucosa.

Two pairs of mucosal folds (vestibular and vocal folds) project medially from lateral walls of the cavity and constrict and divide the larynx cavity into three major regions - the vestibule, the middle chamber and the infraglottic cavity

Question 4

3. Explain how the position of the vocal folds changes the type of sounds produced in vocalization

Answer 4

Vocal folds assume different positions when we breathe (remaining open), when we swallow (closed), and when we speak.

When vocalising, vocal folds are adducted and air is forced through the closed rima glottidis which causes the vocal folds to vibrate.

When we speak the vocal folds adduct together but there generally remains a space between the vestibular folds. When we strain our voices, both sets of folds shorten and are opposed.

Question 5

4. One way of thinking about the muscles of the larynx is to divide them into THREE groups, each controlling a different action. What would be the three different actions? For BONUS points, what are the muscles in each action group called?

Answer 5

Group 1: Controls adduction (3) and abduction (1) of the vocal cords (4 muscles)

• Posterior crico arytenoidius (abducts)
• Inter-arytenoidius (adducts)
• Lateral crico-arytenoidius (adducts)
• Oblique arytenoidius (adducts)

Group 2: Controls lengthening and shortening of the vocal cords (2 muscles)

• Crico-thyroidius (lengthens)
• Thyro-artenoidius (shortens)

Group 3: Controls tension in the vocal cords (1 muscle)

-Vocalis

Question 6

5. Describe the nerve supply of the larynx

Answer 6

1. Superior laryngeal branch (of vagus nerve) branches into:
   - Internal laryngeal nerve - sensory, secretomotor (above and including vocal folds)
   - External laryngeal nerve - motor to a couple of muscles
2. Recurrent laryngeal nerve (branch from vagus) - motor to all other muscles, secretomotor below vocal folds

Question 7

5. Describe the blood supply of the larynx

Answer 7

Blood supply from:

• Superior laryngeal branch of superior thyroid artery (supplies above vocal folds)
• Inferior laryngeal branch of inferior thyroid artery(supplies below vocal folds)