What muscles are innervated by the C5 and C6 (cervical 5 and cervical 6) nerve roots?

From the Guidelines

The cervical spinal nerves C5 and C6 primarily innervate the muscles of the upper limb, including the deltoid, biceps brachii, and brachialis, as well as providing sensory innervation to the lateral arm, lateral forearm, and the thumb and index finger. The brachial plexus, which is formed from the C5-T1 ventral rami, supplies motor and sensory innervation to the upper extremity 1. Key points about the innervation of C5 and C6 include:

• Motor function to the deltoid, biceps brachii, brachialis, and parts of the rotator cuff muscles
• Sensory innervation to the lateral arm, lateral forearm, and the thumb and index finger
• Contribution to the musculocutaneous nerve, axillary nerve, and parts of the median and radial nerves
• Clinical significance in injury resulting in weakness in shoulder abduction, elbow flexion, and forearm supination, along with sensory deficits in their distribution areas, as noted in the context of plexopathy and its various etiologies 1. In the context of plexopathy, which may manifest as neuropathic pain, dysesthesia, and/or burning or electric sensation occurring in >1 peripheral nerve distributions, the diagnosis of C5 and C6 involvement is crucial for appropriate management 1.

From the Research

C5 and C6 Innervation

• C5 and C6 spinal nerves contribute to the innervation of the deltoid muscle via the axillary nerve 2
• The axillary nerve branch to the deltoid muscle is most commonly made up of three spinal nerve segments, with C6 contributing the majority of fibers in 35% of cases, and C5 contributing the majority in 16% of cases 2
• C5 and C6 nerve fibers contribute equally to the innervation of the deltoid muscle in 10% of cases 2

Muscle Innervation

• C5 mainly innervates the deltoid, infraspinatus, biceps brachii, and brachioradialis muscles 3, 4
• C6 mainly innervates the wrist extensor, extensor carpi radialis longus, and pronator teres muscles 3
• The deltoid muscle is innervated by both C5 and C6 roots, with the amplitude ratio of compound muscle action potentials (CMAPs) differing individually depending on the symptomatic intervertebral levels of the spinal cord 5

Brachial Plexus Roots

• The brachial plexus is functionally divided into three groups: C5 and C6 innervate shoulder and elbow, C8 and T1 innervate the hand, and C7 innervates shoulder, elbow, wrist, and hand 4
• Nerve transfers can be used to bypass damaged areas of the brachial plexus, allowing patients to regain critical arm functions faster 6