Anatomy of the Larynx
The skeleton of the larynx
§ The skeleton of the larynx consists of various cartilages plus the hyoid bone.
§ There are three unpaired cartilages:
(1) epiglottic,
(2) thyroid (‘shield’)
(3) cricoid.
§ Major paired cartilages are:
(1) arytenoid
(2) corniculate.
§ Pair of cuneiform cartilages within the aryepiglottic folds.
The cartilages function as points of origin and insertion of muscles,
but also provide two important points of articulation.
Joints
§ Two major points of articulation
between the cricoid and thyroid cartilages
between the cricoid and arytenoid cartilages.
§ Movements about the cricothyroid joint determine the length (or tension) of the vocal ligament
§ movements about the cricoarytenoid joints are responsible to the size of the space between the vocal folds – rima glottidis.
§ In addition, movements at this joint aid in tensing and relaxing the vocal ligaments.
Membranes
§ Externally and superiorly, the thyrohyoid membrane anchors the thyroid cartilage to hyoid bone, so that the laryngeal apparatus can be moved superiorly and inferiorly by the action of muscles directly on the hyoid bone.
§ Internally, the ‘true’ vocal folds are made by the draping of muscosa over the vocal ligaments.
§ The vocal ligament is really the medial extension of the cricothyroid membrane
§ common to use the term conus elasticus to referred to the vocal ligament plus the cricothyroid membrane in combination.
§ Similarly, the ‘false’ (i.e., vestibular) folds are formed by the draping of muscosa over the medial border of the thyroarytenoid muscle, penetrated by the downward extension of the quadrangular membrane.
§ Actually, the vocal ligament is the medial extension of the cricothyroid ligament.
Laryngeal Spaces
§ The ‘true’ and ‘false’ vocal folds partition the larynx into a series of spaces.
§ vestibule
the space between the laryngeal inlet down to the plane of the false folds.
This particular region has a rich sensory innervation within the muscosa
when irritated by some sort of foreign object, initiates a violent cough reflex.
§ rima vestibuli
interval between the vestibular folds.
§ ventricle
the space between the ‘false’ folds above, and the ‘true’ folds below.
This region serves as transitional territory for several different nervous innervation.
§ rima glottidis
The space between the ‘true’ vocal folds.
Abduction of the vocal folds widens the rima glottidis,
adduction of the vocal folds narrows the rima glottidis.
In relaxed respiration, the rima glottidis is rather narrow.
During whispering, the rima glottidis is essentially narrowed, except for the anteromost port.
In heavy respiration, the rima glottidis is relatively wide.
During normal phonation, the rima glottidis is quite narrowed.
§ Different tones are produced by altering the tenseness of the vocal ligament, as well as being into action different portions of the vocal ligament.
§ Subglottic space,
Inferior to the vocal ligament
which is a transition zone between the larynx and trachea.
It is of little interest to anatomists and of no interest to clinicians.
Muscles
Extrinsic
§ those that insert into the hyoid bone to elevate and depress the entire larynx in phonation but also importantly, in swallowing.
§ These are the suprahyoid and infrahyoid muscles.
Intrinsic
§ comprised of those muscles that are confined to the larynx; i.e., originating and inserting on the various cartilages.
§ grouped into two families according to function.
§ One group is mainly concerned with the protection of the laryngeal inlet
Consists of:
1) aryepiglottic
2) thyroepiglottic
3) thyroarytenoid,
4) oblique arytenoid.
This group is primarily responsible for the protection of the larynx and are sphincteric in function on the laryngeal inlet and vestibule.
§ Second group responsible for closing and widening the epiglottidis.
This group is concerned with the adjustment of the vocal ligaments during respiration and phonation.
Consits of:
1) cricothyroid
2) posterior cricothyroid
3) lateral cricothyroid
4) transverse cricothyroid
5) transverse arytenoid.
Nerve Supply
§ As a whole, the laryngeal muscles are innervated by cranial nerve X (Vagus)
§ but the fibers are actually those belonging to cranial rootlets and the internal ramus of cranial nerve XI (Accessory).
§ There is, however, a clinically important differential innervation of the various laryngeal muscles.
For instance, the cricothyroid muscle, which happens to be the only intrinsic muscle on the external surface of the larynx, is innervated by the external branch of the superior laryngeal nerve.
The remainder of the superior laryngeal nerve is sensory and parasympathetic to interior of the larynx to the ventricle and above.
§ The remaining muscles are innervated by the recurrent branch of the vagus
which also supplies sensory innervation to regions of the ventricle and below.
§ These two nerve supplies are vulnerable during surgical procedures of the thyroid gland.
§ Refer to Table 1 for the action and innervation of the laryngeal muscles.
|
Muscle |
Action |
Innervation |
|
Thyroepiglotticus |
Close the aditus |
Recurrent Laryngeal |
|
Aryepiglotticus |
Close the aditus |
Recurrent Laryngeal |
|
Oblique arytenoid |
Close the aditus |
Recurrent Laryngeal |
|
Thyroarytenoid |
Relaxation of vocal folds |
Recurrent Laryngeal |
|
Posterior cricoarytenoid |
Abduction of vocal folds |
Recurrent Laryngeal |
|
Lateral cricoarytenoid |
Adduction of vocal folds |
Recurrent Laryngeal |
|
Transverse arytenoid |
Adduction of vocal folds |
Recurrent Laryngeal |
|
Cricothyroid |
Adduction of vocal folds |
External Bnch of Superior Laryngeal |
|
Vocalis |
Regional tensing of the vocal ligament |
Recurrent Laryngeal |
Two important points
§ the posterior cricoarytenoid is the only intrinsic muscle capable of opening the rima glottides
§ (2) the recurrent laryngeal innervates all the intrinsic laryngeal muscles, except for the cricothyroid.
Blood Supply
§ The arterial supply to the larynx arises from the superior and inferior thyroid arteries.
Phonation
§ quiet respiration
the vocal ligaments are only slightly abducted
ypically bowed.
§ heavy respiration
the vocal ligaments are abducted
consequently, the rima glottis is widened.
§ Phonation
the vocal ligaments are straightened, and tensed, under the action of the cricothyroid, to approximate one another at the midline.
§ phonation, at conversational levels
air is released only through the anterior portion of the rima glottidis.
produces the changes in pitch that are subsequently modified by the structures and features of the oral and nasopharynx,
along with the tongue and lips to produce the wide range of sounds that make up human speech.
Clinical correlates
§ Hoarseness is pathognomic for problems at the level of the larynx.
This frequently occurs as the result of cancer
also result of surgery to the thyroid
§ During such a procedure, one of two unfortunate things can happen:
dissection of the external branch of the superior laryngeal nerve
which supplies the cricothyroid muscle.
In such an event, the cricothyroid muscle cannot stretch the vocal ligament on the affected side.
This results in a lack of overall tenseness along the vocal ligament and consequently the patient typically complains of ‘tiredness’ and ‘hoarseness.’
The second common complication is destruction of the recurrent laryngeal nerve.
When unilateral, the quality of the voice is poor because the vocal ligament on the affected side cannot be abducted or adducted.
When bilateral, there may be significant respiratory distress that may require a tracheotomy to save the patient.
Tags: aryepiglottic, arytenoid cartilages, corniculate, cricothyroid, epiglottic, Hoarseness, hyoid bone, laryngeal muscles, Laryngeal Spaces, larynx skeleton, nasopharynx, nerve supply, oblique arytenoid, Phonation, rima glottidis, suprahyoid and infrahyoid muscles, thyroarytenoid, Thyroepiglotticus, thyroid
