The cervical spine, located in the neck, is composed of seven vertebrae, from which eight pairs of spinal nerves emerge. The sixth cervical spinal nerve, C6, exits the spinal column above the sixth cervical vertebra. Every spinal nerve is a mixed nerve, carrying both motor fibers (controlling muscle movement) and sensory fibers (transmitting signals for touch, temperature, and pain). Understanding the specific regions C6 innervates is fundamental to diagnosing issues that affect upper limb strength and sensation.
Mapping Sensation to the Hand and Forearm
The sensory distribution of a single spinal nerve is called its dermatome, and the C6 dermatome covers a distinct area of the upper extremity. Sensation carried by the C6 nerve root typically begins along the lateral, or thumb side, of the forearm. This sensory territory extends into the hand, encompassing the skin over the thumb and index finger.
This pattern of sensory supply along the radial side of the arm and hand is a specific marker. When a person experiences numbness or tingling in this exact distribution, it provides a strong indication that the C6 nerve root may be involved. The precise mapping of this sensory area is an important diagnostic tool used by clinicians to localize nerve issues to the correct spinal level.
Muscles Powered by the C6 Root
The group of muscles controlled by the C6 nerve root is known as its myotome, responsible for specific functional movements of the arm. The two primary actions associated with C6 motor function are elbow flexion and wrist extension. Elbow flexion is largely powered by the biceps brachii and brachialis muscles.
C6 provides substantial innervation to the biceps brachii, which is why testing the biceps reflex is a standard way to assess C6 function. This reflex involves a quick contraction of the biceps muscle when its tendon is tapped, confirming the integrity of the C6 nerve pathway. The supinator muscle, which turns the forearm outward, also receives fibers from the C6 root.
C6 is also involved in controlling the wrist. It innervates the extensor carpi radialis longus, one of the main muscles responsible for extending the wrist. This ability to lift the hand upward is a defining motor function of the C6 root. Weakness in this motion can lead to a condition known as “wrist drop.”
C6’s Role in Forming Major Arm Nerves
The C6 nerve root contributes fibers to the brachial plexus, a complex network formed by the ventral rami of the C5 through T1 spinal nerves. The C6 root joins with the C5 root to form the superior trunk of the brachial plexus.
From this superior trunk, C6 fibers are distributed into several major peripheral nerves that travel down the arm. C6 contributes fibers to the musculocutaneous nerve, which supplies the biceps muscle, and to the radial nerve, which controls the wrist extensor muscles.
C6 fibers also become part of the median nerve, which controls most of the muscles in the forearm that flex the wrist and fingers. This intricate routing allows the C6 root to influence function across the entire upper limb.
What Happens When the C6 Nerve Root is Compressed?
When the C6 nerve root becomes irritated or compressed, C6 radiculopathy can occur. The most common causes of this compression include a herniated disc or narrowing of the spinal canal (stenosis) at the C5-C6 level. The primary symptom is pain that originates in the neck and radiates down the nerve path into the arm and forearm.
This radiating pain is often described as sharp, burning, or electric and may be worsened by certain neck movements. Sensory fibers are also affected, causing paresthesia, which is felt as numbness or a “pins and needles” sensation in the classic C6 dermatome. Patients typically notice this altered sensation most prominently in their thumb and index finger.
Motor impairment manifests as weakness in the muscle groups C6 innervates. A person with C6 radiculopathy may experience difficulty bending the elbow or reduced strength when extending the wrist. Testing the biceps reflex may show a diminished or absent response, which helps a physician confirm the C6 level of involvement.