The eighth cervical nerve, C8, originates from the cervical, or neck, region of the spinal cord. It transmits both sensory information and motor commands. The C8 nerve specifically contributes to the network that controls movement and sensation in the arms and hands.
Anatomical Home of the C8 Nerve
The C8 nerve occupies a unique position. Unlike cervical nerves C1 through C7, which exit above their corresponding vertebrae, C8 emerges below the seventh cervical vertebra (C7) and above the first thoracic vertebra (T1). This mixed nerve originates from the C8 spinal segment. After exiting the intervertebral foramen, its anterior branch contributes to the brachial plexus.
The brachial plexus is a network of nerves formed by spinal nerves C5 through T1. This network extends from the neck through the armpit, supplying the entire upper limb. The C8 nerve joins with the T1 nerve to form the lower trunk of the brachial plexus. This arrangement allows C8 to contribute to several peripheral nerves in the arm and hand.
What the C8 Nerve Does
The C8 nerve performs both motor and sensory functions for the upper limb. Its motor fibers signal muscles involved in finger flexion, which is important for handgrip strength and fine motor control. It also contributes to muscles responsible for thumb and wrist extension.
Beyond movement control, the C8 nerve transmits sensory information from specific skin areas. This sensory distribution, known as the C8 dermatome, includes the little finger, half of the ring finger, and the ulnar (pinky finger) side of the hand. It extends slightly up the palmar and dorsal aspects of the forearm. Testing sensation in the pad of the little finger assesses C8 nerve integrity.
Signs of C8 Nerve Involvement
When the C8 nerve experiences compression, irritation, or damage, various symptoms can manifest, often reflecting its motor and sensory roles. Weakness in the muscles it supplies is a common motor symptom, presenting as difficulty with finger flexion, impaired grip strength, or challenges with thumb extension. Individuals may also notice a loss of fine motor control, making everyday tasks difficult.
Sensory disturbances include numbness, tingling, or a “pins-and-needles” sensation. These sensations typically occur within the C8 dermatome, affecting the little finger, ring finger, and the ulnar side of the hand and forearm. Pain can accompany these symptoms, often radiating down the arm to the affected fingers. Symptoms can arise from conditions like disc herniation or spinal stenosis, where the nerve root is compressed as it exits the spinal column.