Infrahyoid Muscles vs. Suprahyoid

Attribute	Infrahyoid Muscles	Suprahyoid
Location	Located below the hyoid bone	Located above the hyoid bone
Function	Depresses the hyoid bone and larynx	Elevates the hyoid bone and larynx
Number of Muscles	Four muscles: sternohyoid, omohyoid, thyrohyoid, and sternothyroid	Four muscles: digastric, mylohyoid, geniohyoid, and stylohyoid
Innervation	Supplied by the ansa cervicalis, a branch of the cervical plexus	Innervated by the trigeminal nerve (V3) and facial nerve (VII)
Origin	Originates from various points on the sternum, clavicle, and scapula	Originates from the mandible and styloid process of the temporal bone
Insertion	Inserts onto the hyoid bone	Inserts onto the hyoid bone and tongue

Anatomy and Location

The infrahyoid muscles and suprahyoid muscles are two distinct groups of muscles located in the neck region. The infrahyoid muscles, also known as the strap muscles, consist of four muscles: the sternohyoid, omohyoid, thyrohyoid, and sternothyroid. These muscles are located below the hyoid bone, which is a U-shaped bone in the neck. On the other hand, the suprahyoid muscles are located above the hyoid bone and consist of four muscles: the digastric, stylohyoid, mylohyoid, and geniohyoid.

Function

The infrahyoid muscles play a crucial role in depressing the hyoid bone and larynx during swallowing and speaking. They assist in the movement of the hyoid bone downwards and stabilize it during these actions. Additionally, the infrahyoid muscles also contribute to the overall stability of the neck. In contrast, the suprahyoid muscles have a different function. They elevate the hyoid bone and larynx during swallowing and speaking. These muscles work in coordination to assist in the opening and closing of the mouth, as well as the movement of the tongue and larynx.

Innervation

The infrahyoid muscles are innervated by the ansa cervicalis, which is a nerve loop formed by branches of the cervical spinal nerves C1-C3. This nerve loop provides motor innervation to the infrahyoid muscles, allowing them to contract and perform their functions. On the other hand, the suprahyoid muscles receive their innervation from different nerves. The digastric and stylohyoid muscles are innervated by the facial nerve (cranial nerve VII), while the mylohyoid and geniohyoid muscles are innervated by the mandibular branch of the trigeminal nerve (cranial nerve V3).

Structure and Composition

The infrahyoid muscles are relatively long and slender muscles that run vertically along the front of the neck. They are composed of both superficial and deep layers. The superficial layer consists of the sternohyoid and omohyoid muscles, while the deep layer consists of the thyrohyoid and sternothyroid muscles. These muscles are primarily composed of skeletal muscle fibers, which are responsible for voluntary movements. In contrast, the suprahyoid muscles have a more complex structure. The digastric muscle consists of two bellies, anterior and posterior, connected by an intermediate tendon. The stylohyoid muscle is a slender muscle that extends from the styloid process of the temporal bone to the hyoid bone. The mylohyoid muscle forms the floor of the mouth, and the geniohyoid muscle runs from the chin to the hyoid bone.

Attachments

The infrahyoid muscles have various attachments that contribute to their function. The sternohyoid muscle originates from the manubrium of the sternum and inserts into the hyoid bone. The omohyoid muscle has two bellies, with the superior belly originating from the superior border of the scapula and the inferior belly inserting into the intermediate tendon. The thyrohyoid muscle originates from the thyroid cartilage and inserts into the hyoid bone, while the sternothyroid muscle originates from the sternum and inserts into the thyroid cartilage. In contrast, the suprahyoid muscles have different attachments. The digastric muscle has its anterior belly originating from the digastric fossa of the mandible and its posterior belly originating from the mastoid process of the temporal bone. The stylohyoid muscle originates from the styloid process of the temporal bone and inserts into the hyoid bone. The mylohyoid muscle originates from the mylohyoid line of the mandible and inserts into the hyoid bone. Lastly, the geniohyoid muscle originates from the mental spine of the mandible and inserts into the hyoid bone.

Summary

In conclusion, the infrahyoid muscles and suprahyoid muscles are two distinct groups of muscles located in the neck region. The infrahyoid muscles are located below the hyoid bone and play a role in depressing the hyoid bone and larynx, as well as stabilizing the neck. They are innervated by the ansa cervicalis and are composed of both superficial and deep layers. On the other hand, the suprahyoid muscles are located above the hyoid bone and elevate the hyoid bone and larynx. They have different innervation, with the digastric and stylohyoid muscles innervated by the facial nerve and the mylohyoid and geniohyoid muscles innervated by the mandibular branch of the trigeminal nerve. The suprahyoid muscles have a more complex structure and various attachments that contribute to their functions. Understanding the attributes of these muscles is essential for comprehending their roles in swallowing, speaking, and overall neck stability.