The long thoracic nerve, also called the axon reflex nerve, is a large group of nerves that run from the spinal cord to the shoulder and are involved in a hand, arm, and face movement. The long thoracic nerve also known as the axon reflex nerve, is important in the generation of pain and other sensations that are associated with bodily functions and movement. The long thoracic nerve, or Tendon reflex, is characterized by strong, pulsating, intermittent sensations that are felt below the neck, right behind the ears, in the shoulder, arms, legs, and feet. The sensations do not dissipate until they reach the brain, where they are interpreted as a variety of feelings from aching to tingling.
Location of Long Thoracic Nerve
The long thoracic nerve starts in the upper back near the lumbar spine, moving downward through the front of the body and down the length of the arms and into the chest cavity. It then passes through the side of the scapula to the neck and up to the shoulders. It continues to the shoulders and down again, following the direction of the acupoints, before it curves down through the hip joint and finally exits through the knee joint. The nerves in the sides of the torso appear to wrap around the entire upper half of the lungs, and the nerves at the back of the neck are responsible for the sensation of facial expression. Finally, the long thoracic nerve, or axon reflex nerve, divides into two nerves, the internal long thoracic nerve and the external long thoracic nerve.
Types of Long Thoracic Nerve
Two specific types of long thoracic nerve exist, depending on the location and nature of the problem. In the thoracic spine, the long fibers of the serratus anterior muscles attach to the lumbar vertebrae and originate above the sacral region of the heart. These muscles play an important role in providing stable thoracic posture. They help maintain the natural inward rotation of the torso, facilitating movement of the sacrum and ribs towards the hips, and facilitating the inward rotation of the lumbar spine. The long fiber of these muscles also provide strong support to the abdominal wall, facilitating movement of this cavity against the diaphragm.
On the other hand, in the thoracic spine to the long thoracic nerve, composed of three long fibers, attaches directly to the pelvic bone. This makes it possible to feel the sensation of winging or rolling in the thoracic region. This is due to the tension between the extensor muscles and the LTN, as well as between the sacral and thoracic discs. This muscle weakness can be felt as a pain behind the breastbone, or in the upper thighs, or behind or under the pectorals.
Causes of the Weakness of Long Thoracic Nerve
There are two prominent theories on the cause of the weakness of this long thoracic nerve. The first one is that it is due to a weakness of the gluteal muscles, or the external oblique. This theory can be tested for persons having a long right brachial ligament. In such patients the left external oblique muscle is weak along the border of the tendon, whereas the long thoracic nerve remains unaffected. If the patient has weak muscles in the middle and outer side of the quadriceps, the weak region may become affected between the third and fourth rib, or between the second and third ribs. The weakness may extend up into the upper left chest.
Another theory that has been theorized to explain the weakness of the LTN has it that it is caused by the development of the deep internal rotator cuff muscle at the level of the clavicle. This muscle exists at the base of the neck, just above the crest of the skull. It originates in the upper chest and extends down to the lateral aspect of the shoulder. The theory states that in a case where the long thoracic nerve becomes affected, the development of the deep internal rotator cuff muscles will result in its contraction and consequently, stretching of the nerve.
A third theory postulated on the causes of this weakness of the long thoracic nerve, has it that it is a result of an abnormal anatomy at the level of the lumbar spine. This abnormal anatomy is referred to as the c5-to-c8 curve. Specifically, the abnormal anatomy referred to involves a shortening of the lumbar spine at the level of the cervical spine. The theory proposes that the shortening of this lumbar spinal column will result in a weakness of the long thoracic nerve at its level of the cervical spine. Therefore, when the long thoracic nerve becomes affected, the weakness and pain will be felt in the area between the fifth and the sixth thoracic vertebrae.
These theories postulate that the long thoracic nerve may become affected when it has been repeatedly subjected to irritation, inflammation, or trauma. Such injuries include penetrating injuries, impact injuries, rotator cuff tears, as well as a superficial course of arthritis. In addition, one should also keep in mind that prolonged exposure to a compressive load can result in a weakening of the superficial course of the brachial plexus. Finally, it should be noted that the human body has a tendency to retain body fluids which can cause a weakening of the brachial plexus.