The ansa cervicalis is a loop of nerves found in the neck, part of the peripheral nervous system. It is a structure formed by the fusion of fibers from the cervical spinal nerves, specifically from C1 to C3. The ansa cervicalis gives off motor branches to several muscles in the neck, such as the omohyoid, sternohyoid, and sternothyroid muscles, which are involved in actions like swallowing and stabilizing the hyoid bone and larynx.
The nerve loop of the ansa cervicalis is often categorized into a “superior root” and an “inferior root”. The superior root is primarily formed by fibers from the C1 spinal nerve, while the inferior root is mainly contributed by fibers from C2 and C3.
The ansa cervicalis itself doesn’t have sensory functions; it is strictly a motor nerve loop. It is often seen as a component of the cervical plexus, a network of nerve fibers that originate from the upper cervical spinal nerves.
Structure of Ansa Cervicalis
The ansa cervicalis is a loop of nerves that is part of the cervical plexus. It is composed of two main roots:
- Superior Root: This root is derived from the descending branch of the hypoglossal nerve (cranial nerve XII) but carries fibers from the C1 spinal nerve.
- Inferior Root: This root comes directly from the cervical plexus, usually consisting of fibers from the C2 and C3 spinal nerves.
These two roots merge to form a loop-like structure, the ansa cervicalis, which then gives off several motor branches to supply specific muscles in the neck.
Location
- Neck Region: The ansa cervicalis is situated within the carotid triangle of the neck.
- Muscular Bed: It generally lies superficial to the internal jugular vein and the common carotid artery. It is also situated on the surface of the carotid sheath that envelops these vascular structures.
- Anatomical Relations: The superior root of the ansa cervicalis is closely related to the hypoglossal nerve from which it descends. The inferior root generally emerges from the cervical plexus deeper within the neck.
- Target Muscles: The branches of the ansa cervicalis typically innervate infrahyoid muscles, including the sternohyoid, sternothyroid, and omohyoid muscles.
The ansa cervicalis is a unique and identifiable part of the cervical plexus, notable for its loop-like structure and specific muscular innervation in the neck.
Functions
The primary function of the ansa cervicalis is motor innervation to specific muscles in the neck. Unlike many other nerves that either serve sensory or mixed functions, the ansa cervicalis is predominantly motor in function.
Motor Innervation
Infrahyoid Muscles: The ansa cervicalis supplies a group of muscles below the hyoid bone, commonly referred to as the infrahyoid muscles. These muscles include the sternohyoid, sternothyroid, and omohyoid muscles.
Muscle Actions:
- Sternohyoid: This muscle helps to depress the hyoid bone, aiding in swallowing and speaking.
- Sternothyroid: This muscle helps in depressing the thyroid cartilage, thereby playing a role in vocalization.
- Omohyoid: This muscle also depresses the hyoid bone and assists in actions like swallowing and speaking.
Coordination and Control:
- Swallowing: By controlling the infrahyoid muscles, the ansa cervicalis plays an indirect but important role in the process of swallowing. The depression of the hyoid bone allows for a smoother transit of food and liquids through the throat.
- Speech: Similarly, the muscles innervated by the ansa cervicalis contribute to vocalization by influencing the position of the hyoid bone and thyroid cartilage.
Clinical significance
The ansa cervicalis holds clinical importance primarily for its role in motor control of specific neck muscles, particularly the infrahyoid muscles. Here are some key points on its clinical significance:
- Surgical Procedures: During surgeries involving the neck, particularly thyroid surgeries or dissections of the carotid triangle, care must be taken to avoid damage to the ansa cervicalis to prevent post-operative swallowing or speech issues.
- Nerve Blocks: In some anesthetic procedures involving the neck, the ansa cervicalis may be targeted for nerve blocks. Accurate knowledge of its location and branches is essential for effective anesthesia.
- Diagnostic Assessment: Damage or dysfunction of the ansa cervicalis can result in weakness or dysfunction of the infrahyoid muscles. This can be significant in diagnostic assessments of neck injuries or pathologies.
- Anatomical Landmark: The ansa cervicalis serves as an important anatomical landmark during surgical procedures and radiological evaluations, owing to its distinct loop-like structure and location near major vascular structures.
