The ansa cervicalis is a nerve loop that lies under the sternocleidomastoid muscle in the neck. Without addition, the medicine with the Ansa cervicalis usually means the Ansa cervicalis profunda, as the original name of the noose is.
The anatomy earlier distinguished between the superficial cervical nerve sling (Ansa cervicalis superficialis) and the deep cervical nerve sling (Ansa cervicalis profunda). The ansa cervicalis superficialis represents a connection of two nerves: it is not below but on the sternocleidomastoid muscle and connects the transversus colli with the ramus colli nervi facialis. The latter represents a branch of the facial nerve (facial nerve). This corresponds to the seventh cranial nerve. The name Ansa cervicalis superficialis no longer exists in the new nomenclature. The anatomy of the ansa cervicalis is more rarely called Ansa hypoglossi, because it runs in the carotid triangle (trigonum caroticum) next to the hypoglossal nerve.
On the basis of their fibers, two roots of the ansa cervicalis can be anatomically distinguished: the inferior radix and the superior radix. The nerves that belong to the inferior radix have their origin in the cervical spinal cord segments C2 and C3.
In contrast, the superior radix consists of fibers associated with the spinal cord segments C1 and C2. Both roots of the ansa cervicalis contain nerve cords that originate from the cervical plexus and contain both motor and sensory fibers. The cervical plexus is a neural network in the human neck and includes not only axons from segments C1 to C3 but also C4 and (to a lesser extent) C5.
The ansa cervicalis is located under the sternocleidomastoid muscle, which participates in certain head movements and supports breathing as an auxiliary muscle. In its course in the neck, the ansa cervicalis first passes through the internal jugular vein and then the scalenus anterior muscle before it reaches the carotid triangle (trigonum caroticum). There she encounters the hypoglossal nerve (hypoglossal nerve or 12th cranial nerve), to which the ansa cervicalis does not maintain any anatomical or functional connection.
Nerve fibers from the ansa cervicalis control the movements of the lower hyoid muscles. It is also known as the infrahyoid muscle and consists of the omohyoid muscle, the sternohyoid muscle, the sternothyroid muscle, and the thyrohyoid muscle. As a group, the lower hyoid muscles work together with other muscles (for example, the upper hyoid muscles or suprahyoid muscles) in the process of swallowing, which requires precise coordination of the movements.
The complex interaction of the muscles succeeds in healthy people thanks to the swallowing centers in the brainstem and cerebrum as well as the interconnection of the innervating peripheral nerves.
These motor nerve fibers are efferent pathways that descend from the brain through the spinal cord and eventually enter the peripheral nervous system via the spinal nerves. The neuronal signal changes from one nerve cell to the next, crossing biochemical synapses. At such a switching point nerves can charge information that arrive at their membrane. Activating (excitatory) and inhibitory (action) action potentials are included in this calculation according to the summation principle, which also takes into account their respective strengths. On muscle cells, the motor end plate forms the connection to the supplying nerve.
The joint innervation of the infrahyoid muscles by the Ansa cervicalis helps to coordinate their movements during the swallowing process: muscles that contract at the same time can receive the electrical signals from the same nerve tract, which divides into individual fibers at a later time and on these Way different muscle cells responds. In addition, the interaction helps to automatically inhibit certain muscles while others are active. Such inhibition prevents the muscles from hindering each other.
Damage to the ansa cervicalis may affect the function of the infrahyoid muscles and lead to the development of dysphagia.
Masses of tumors, injuries and infections in the tissue can directly damage the ansa cervicalis. Since their nerve fibers originate from the cervical plexus, a lesion of the plexus also affects the ansa cervicalis. Radiation therapy for the treatment of breast cancer can in some cases damage the cervical plexus and lead to the loss of nerve fibers that also pass through the ansa cervicalis.
However, missing or defective information transmission in the cervical nerve loop may also be due to neuromuscular diseases such as myasthenia gravis. Blocked acetylcholine receptors interfere with signal transmission at the motor end plate in this disease. Myasthenia gravis typically first affects the eye muscles before the muscles that hold the head and facial muscles also suffer from paralysis. The neuromuscular disorder can spread to other muscles, including the respiratory muscles. Possible neuromuscular causes of dysphagia include Guillain-Barré syndrome (which relies on inflammation of the nerves) and myotonic dystonia (which causes tonus disorders).
Still further up the hierarchy of information processing, brain diseases can cause the ansa cervicalis to get inadequate nerve signals and show dysphagia. Neurodegenerative diseases such as Alzheimer's, Parkinson's, ALS and Huntington's can be considered as well as tumors, strokes and hemorrhages in the brain.