The cervical spine is the region of the spinal column that supports the neck. Eight nerves emerge from between the cervical spinal bones, or vertebrae. These cervical nerves are referred to as C1 through C8. Each cervical nerve leads to different parts of the body and supports sensory, motor or organ function. When a nerve is damaged, the specific areas of the body that it serves can show symptoms.
The C4 and C5 nerves supply motor function to the muscles of the shoulder and arm. When either of these nerves is compromised, muscle weakness can result. Specifically, the C4 nerve enervates the levator scapulae, trapezius and rhomboid muscles. Damage to the C4 nerve may result in difficulty in elevating the shoulders. The C5 nerve supplies the deltoid, supraspinatus, infraspinatus and biceps muscles. Damage to the C5 nerve can affect the ability to raise the arm or bend it at the elbow.
Pain, Numbness or Paresthesia
Each cervical nerve detects sensory information from specific areas of skin, called dermatomes. When pain, numbness or paresthesia -- tingling or a pins-and-needles sensation -- appears over a specific dermatome, it could signify damage to the corresponding cervical nerve. The C4 nerve receives sensory input from the dermatome that covers the shoulder, collarbone and shoulder blade. Pain, numbness or paresthesia in these areas can signal damage to the C4 nerve. The C5 nerve receives sensory input from the dermatome located over the deltoid muscle at the uppermost part of the arm as well as the outer, upper arm.
Doctors test tendon reflexes to determine the integrity of communication between the nerves in the extremities and the spinal cord or brainstem. A quick tap from a tendon hammer is used to test reflexes at specific sites in the body. The tap activates sensory receptors within the tendon, which sends a message stimulating a return message that causes the muscle to contract. There is no tendon reflex tested for the C4 nerve. Damage to the C5 cervical nerve can cause diminished tendon reflexes of the biceps and brachioradialis muscles. Tapping the brachioradialis tendon typically cause contraction of this muscle in the forearm, whereas tapping of the biceps tendon usually causes contraction of this muscle at the front of the arm above the elbow.
C4 and C5, along with C3, supply the diaphragm -- the muscle that separates the chest and abdominal cavities. This muscle assists with breathing by creating more space in the chest and pulling air into the lungs when it contracts. Damage to these nerves, particularly C4, can disrupt the normal function of the diaphragm and result in difficulty breathing. However, this is rare unless the nerve damage is severe.
Warnings and Precautions
Many conditions can damage your C4 and C5 nerves, most commonly a herniated disk or arthritis or traumatic injury to your neck. These conditions are usually treatable and you should not ignore your symptoms. See your doctor as soon as possible if you experience symptoms that might indicate damage to the C4 and C5 nerves. Seeking help sooner rather than later will typically speed your recovery.
Reviewed by: Tina M. St. John, M.D.