Cervical nerves are nerves that pass from the spinal cord through openings between the vertebrae of the neck. There are eight cervical nerves, which are numbered C1 through C8 from the top of the neck to the shoulders. These nerves are vital to numerous functions in the head, shoulders, arms and trunk. Damage to a cervical nerve can manifest in numerous ways depending on whether sensory, motor or organ function is impaired.
Impaired Muscle Function
When the vertebra of the neck are fractured due to trauma, such as a motor vehicle or diving accident, damage to the cervical nerves can result. That damage can impair the functioning of the muscles those nerves supply. Dr. Peter F. Ullrich, Jr., M.D. explains that an injury of the C7 nerve can weaken the muscles of the hands and fingers. The muscles of the shoulders and biceps may weaken and even atrophy in response to long-term damage to the C4 and C5 vertebrae.
Damage to the sensory component of any of the cervical nerves can result in pain along the regions supplied by that nerve. Damage to the 6th cervical nerve caused, for example, by a herniated disc, can cause pain radiating down the arm and into the thumb, according to Ullrich.
Damage to a nerve may compromise its ability to provide sensory information from its associated body region, resulting in numbness. When the C6 nerve is damaged, numbness in the arm and thumb can result. C5 damage sometimes manifests as numbness over the shoulder region.
Ullrich states that when the first three cervical vertebrae are damaged, the diaphragm muscle, which they supply, can be weakened to the point where the patient needs medical assistance in order to breathe.
"Pins and Needles"
The sensation commonly known as "pins and needles" has a medical name as well–paresthesia. When the cervical nerves are damaged, paresthesia can result. An evaluation of paresthesias of the hand is sometimes useful in determining which cervical nerve is being affected. The neuroanatomy department at Wisconsin University reports that damage to the 7th cervical nerve can cause a pins and needles sensation to radiate into the middle finger, and David Magee, Ph.D. cites "C6 nerve root palsy" as a cause of thumb and index finger paresthesias. C8 nerve root injury can cause paresthesias in the middle, ring and little finger.