Infrahyoid Muscles

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Original Editor - Manisha Shrestha Top Contributors - Areeba Raja, Manisha Shrestha and Nupur Smit Shah

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Top Contributors - Areeba Raja, Manisha Shrestha and Nupur Smit Shah  

Introduction

Anterior neck showing Infrahyoid muscles

Infrahyoid muscles are also known as “strap muscles” which connect hyoid, sternum, clavicle and scapula. They are located below the hyoid bone on the anterolateral surface of the thyroid gland(1) and are involved in movements of the hyoid bone and thyroid cartilage during vocalization, swallowing and mastication. They are composed of four paired muscles, organized into two layers as following :

• Superficial layer
• Deep layer

Superficial layer

The superficial layer consists of the following muscles:

• Sternohyoid
• Omohyoid

Sternohyoid

It is a thin, narrow strap and lies anterior to the remaining strap muscles and the thyroid gland.

Origin:

It originates from the posterior surface of the medial end of the clavicle, the posterior sternoclavicular ligament and the upper posterior aspect of the manubrium sterni.

Insertion:

It inserts at the inferior border of the body of the hyoid bone

Nerve Supply:

it is innervated by branches of ansa cervicalis (C1, C2, and C3).

Arterial Supply:

It arterial supply comes from the branches of superior thyroid artery. (An anatomical study of the arterial and nerve supply of the infrahyoid muscles)

Action

It depresses the hyoid bone after it has been elevated

Variation

It may be absent or double, augmented by clavicle slip (cleidohyoid), or interrupted by a tendinous intersection.

Omohyoid

The omohyoid muscle is found deep in the sternocleidomastoid and consist of two bellies (superior and inferior) united at an angle by an intermediate tendon.

Superior Belly

Origin:

It begins at the intermediate tendon

Insertion:

It inserts to the lower border of the hyoid bone

Nerve Supply:

It is innervated by the superior ramus of the ansa cervicalis and from hypoglossal nerve.

variation

It can be absent or double; It is sometimes fused with sternohyoid.

Inferior Belly

Origin:

It arises from the upper border of the scapula near the scapular notch and occasionally from superior transverse scapular ligament

Insertion:

It inserts into the intermediate tendon

Nerve Supply:

It is supplied by ansa cervicalis (C1, C2 and C3)

Variation:

It can be absent or double; it may be attached directly to the clavicle

Arterial Supply:

It is supplied by superior thyroid and lingual arteries(An anatomical study of the arterial and nerve supply of the infrahyoid muscles)

Action:

• It depresses the hyoid bone after it has been elevated.
• It tenses the lower part of the deep cervical fascia in prolonged inspiratory effort, reducing the tendency for soft parts to be sucked inward.

Deep layer

The deep layer consists of the following muscles:

• Sternothyroid
• Thyrohyoid

Sternothyroid

It is shorter and wider than sternohyoid and contacts the anterior surface of the thyroid gland.

Origin:

It arises from the posterior surface of the manubrium sterni and from the posterior edge of the first rib

Insertion:

It insert into the oblique line of the thyroid cartilage.

Nerve Supply:

It is innervated by branches of ansa cervicalis.

Arterial Supply:

It is supplied by superior thyroid and lingual arteries.

Action:

• It draws the larynx downwards after it has been elevated by swallowing or vocal movements.
• In low notes singing, this downward traction would be exerted with hyoid bone relatively fixed.

Variation:

An accessory belly can be present.

Thyrohyoid

It is a small quadrilateral muscle that may be regarded as an upward continuation of the sternothyroid muscle.

Origin:

the oblique line on the lamina of the thyroid cartilage.

Insertion:

attaches to the lower border of the greater cornu and adjacent part of the body of the hyoid bone.

Innervation:

It is innervated by fibers of the first cervical spinal nerve which branch of the hypoglossal nerve beyond the descendens hypoglossi.

Arterial Supply:

It is supplied by superior thyroid and lingual arteries.

Action

• it depresses the hyoid bone.
• when the high notes are sung it the thyrohyoid muscle pulls the larynx upwards with the hyoid bone stabilized.

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