Ansa cervicalis

Ansa cervicalis is a loop of nerves in the neck that is part of the peripheral nervous system. It is formed from the branches of the cervical plexus, specifically from the ventral rami of the first four cervical nerves (C1-C4). The ansa cervicalis is crucial for providing motor innervation to several muscles in the infrahyoid region of the neck, which are important for swallowing and speech.

Structure

The ansa cervicalis is divided into two parts: the superior root (also known as the descendens hypoglossi) and the inferior root (also known as the descendens cervicalis).

• The superior root is formed by fibers from the first cervical nerve (C1), which travel with the hypoglossal nerve (CN XII) before branching off to join the ansa cervicalis.
• The inferior root consists of fibers from the second and third cervical nerves (C2 and C3), and sometimes fibers from the fourth cervical nerve (C4).

These roots join together to form a loop that lies on the carotid sheath, anterior to the sternocleidomastoid muscle.

Function

The primary function of the ansa cervicalis is to provide motor innervation to the infrahyoid muscles, except for the thyrohyoid muscle, which is innervated directly by fibers from the first cervical nerve (C1) through the hypoglossal nerve. The infrahyoid muscles include:

• Sternohyoid muscle
• Omohyoid muscle
• Sternothyroid muscle
• Thyrohyoid muscle (innervated by C1 fibers through the hypoglossal nerve, not part of the ansa cervicalis innervation)

These muscles play a significant role in the movement of the hyoid bone and larynx, facilitating swallowing and phonation.

Clinical Significance

Damage to the ansa cervicalis can result from surgical procedures in the neck, leading to weakness or paralysis of the infrahyoid muscles. This can affect swallowing and speech. Understanding the anatomy of the ansa cervicalis is crucial for surgeons operating in the cervical region to avoid nerve injury.

See Also

• Cervical plexus
• Peripheral nervous system
• Hypoglossal nerve
• Infrahyoid muscles