Muscles of Larynx

Muscles of Larynx are divided in extrinsic and intrinsic muscles

1. Extrinsic
   • Sterno-thyro- hyoideus
   • Thyro-hyoideus (hyothyroideus)
   • Hyo-epiglotticus
2. Intrinsic
   • Crico-thyroideus
   • Crico-arytenoideus dorsalis
   • Crico-arytenoideus lateralis
   • Arytenoideus transversus
   • Thyro-arytenoideus

EXTRINSIC MUSCLES

1. Sternothyro- hyoideus
   • This is a long, slender muscle situated on the ventral face of the trachea.
   • Origin: Manubrium sterni.
     • The two side muscles are very close together at their origin and cover trachea at the lower third of the neck. About the middle of the neck, each muscles divide into two bands-the thyroid and hyoid bands which diverge from those of the opposite side from the upper third of the neck. Hence in the upper third of the neck, the ventral face of the trachea is not covered by any muscle. The thyroid band is the larger and the lateral of the two bands.
   • Insertion:Thyroid band is inserted to the thyroid cartilage of the larynx and the hyoid band to the body of the hyoid and lingual process.
   • Action: To depress the hyoid, larynx, and tongue during deglutition .
   • Blood supply: Carotid artery.
   • Nerve supply: First and second cervical spinal nerves .
2. Thyro-hyoideus
   • Thyro-hyoideu (hyothyroideus) which extends between thyroid cartilage and the body and the thyroid cornua of the hyoid bone.
   • It draws the larynx downwards and forwards.
   • It is supplied by anterior laryngeal artery and anterior laryngeal branch of the vagus.
3. Hyo-epiglotticus
   • Hyo-epiglotticus is a small bifid muscle enclosed in the glosso-epiglottic fold.
   • It arises from the body and the two small cornua and is inserted to the ventral half of the anterior face of the epiglottis.
   • It draws the epiglottis towards the root of tongue.
   • Blood supply: Lingual artery.
   • Nerve supply: Hypoglossal nerve.

INTRINSIC MUSCLES

1. Crico-thyroideus lies on the posterior part of the lateral surface of the larynx. It extends from the attachment of cricoid cartilage to the posterior cornu of the thyroid cartilage. It draws the thyroid cartilage and ventral part of cricoid cartilage together and tense the vocal folds in this action. The posterior laryngeal artery and anterior laryngeal nerve supply it.
2. Crico-arytenoideus dorsalis is on the dorsal surface of the cricoid cartilage. It extends between the lamina of cricoid and the muscular process of the arytenoid cartilage. It dilates the glottis and abducts the vocal process and fold. The posterior laryngeal artery and the posterior laryngeal nerve supplies the muscle.
3. Crico-arytenoideus lateralis is on the deep surface of the thyroid cartilage. It extends from the upper part of cricoid to the muscular process of the arytenoid cartilage. It closes the glottis by rotating the arytenoid cartilage medially. It is supplied by the posterior thyroid artery and posterior laryngeal nerve
4. Arytenoideus transversus is unpaired and lies on the dorsal face of the bodies of the arytenoid cartilage, between their lateral borders. It narrows the glottis. It is supplied by posterior laryngeal artery and posterior laryngeal nerve.
5. Thyro-arytenoideus extends from the medial face of lamina of thyroid cartilage to the muscular process of the arytenoid. It closes the glottis and slackens the vocal folds.
6. Blood supply and Nerve supply: Same as the preceding.