The suprascapular nerve innervates specific muscles of the shoulder region. The functions of the nerve are explained by its location and the way it transmits signals. Mechanical and biochemical nerve damage can lead to diseases and conditions explained in more detail below.
What is the suprascapular nerve?
The suprascapular nerve is a sensorimotor nerve. Colloquially, it is referred to as a mixed nerve. Motor nerve fibers of the suprascapular nerve innervate muscles, while sensory fibers travel to the shoulder joint. The fibers that supply only skeletal muscles are called somatomotor fibers. The fibers that convey impulses from mucous membranes, skin, muscle spindles, and receptors in tendons and joint capsules are called general somatosensitive fibers. The suprascapular nerve is a peripheral nerve and, like most peripheral nerves, does not have only one of the conduction qualities mentioned. Due to the nature of innervation, the nerve has both somatomotor and general somatosensitive fibers or portions. The fibers of the nerve are parts of a nerve plexus, which in turn projects to the spinal nerves.
Anatomy and structure
The suprascapular nerve is part of the brachial plexus and has its roots in the superior truncus in the 5th and 6th cervical segments (C5-C6). The superior truncus is one of the three main trunks formed by the spinal nerves. The suprascapular nerve branches from the superior truncus and travels to the incisura scapulae. The nerve passes through the incisura and draws to the supraspinous fossa. Then the nerve passes along the supraspinous fossa and along the collum scapulae into the infraspinous fossa. There, the nerve forms motor and sensory branches. The motor fibers innervate the supraspinatus and infraspinatus muscles, while a sensitive nerve branch travels to the glenohumeral joint. The suprascapular nerve is a peripheral nerve. Like most peripheral nerves, the suprascapular nerve consists of multiple axons that are sheathed by medullary sheaths called Schwann cells. Schwann cells are peripheral glial cells that form the myelination of neuronal processes. Schwann cells are found exclusively in the peripheral nervous system and serve saltatory excitation conduction.
Function and Tasks
The somatomotor nerve fibers innervate the supraspinatus muscle and the infraspinatus muscle. As somatomotor nerve fibers, they transmit excitation from the CNS to the muscles. The innervated muscles respond to the excitation and perform their assigned tasks. The supraspinatus muscle provides for the abduction of the arm up to an angle of 15°. The muscle acts as an agonist. The abduction of the arm is also referred to medically as abduction. The further rotational and abduction movements are subsequently performed by two other muscles, the deltoid and infraspinatus muscles. No muscle can work without the innervation of a nerve. Therefore, the suprascapular nerve is responsible for the work of another muscle, the infraspinatus muscle. This muscle is located in the dorsal part of the shoulder muscles and, together with the above-mentioned muscles, is responsible for the rotational movement of the arm. The muscle primarily provides external rotation of the upper arm during rotational movement. The suprascapular nerve innervates the shoulder joint and conveys sensory information. The information may include pressure and pain information, for example, and is transmitted to the CNS via the spinal cord. Sensory information is mediated in response to receptors. If a receptor reacts, this reaction leads to the transmission of information to corresponding nerve cells. The trigger for a reaction of a receptor is of different nature. For example, pressure receptors respond only when a certain pressure is reached. In summary, the suprascapular nerve performs the following functions:
- Excitation transmission to innervated muscles.
- Abduction of the arm up to 15°.
- External rotation of the upper arm
- Sensory information transfer from the shoulder joint to the CNS.
Diseases
Discomfort in the shoulder area is common and may come from the suprascapular nerve. For example, carrying heavy objects on the shoulder can lead to suprascapular nerve compression syndrome. In compression syndrome, paralysis of the nerve occurs.Due to the paralysis of the nerve, the innervated muscles can no longer be moved. This leads to a failure of the rotator cuff and can result in dislocation of the shoulder joint. However, paralysis of the suprascapular nerve does not only occur in compression syndrome, but can also occur due to incisura scapulae syndrome. This syndrome also describes compression of the nerve, but the cause of the compression is different. The ossification of a ligament (ligamentum transversum scapulae superius)creates a bony canal. The nerve passes through this channel and suffers compression. The compression may be maximized by rotational movements of the shoulder. The result is paralysis of the suprascapular nerve. Of course, traction (compression or stretching) of the nerve can also occur from athletic activity as a result of overuse or misuse. Rupture of the rotator cuff would be conceivable as a result of athletic misuse. Traction also leads to discomfort. Starting from discomfort in the course of movement up to dislocation of the shoulder. If shoulder pain and problems with the movement of the shoulder occur, the orthopedist should be consulted. The orthopedist can either confirm or rule out a traction of the suprascapular nerve. Seeing a doctor in a timely manner will prevent permanent neuropathy as a result of an incorrect load or a sports-related injury. The orthopedist can also treat the consequences of age-related ossification of a ligament.