Which portion of the upper extremity is not innervated by the brachial plexus?

Which portion of the upper extremity is not innervated by the brachial plexus?

• A. Posterior medial portion of the arm
• B. Elbow
• C. Lateral portion of the forearm
• D. Medial portion of the forearm

Answer: (A)

The main idea is that the brachial plexus supplies almost all sensory innervation to the upper limb, but there is a notable exception: a strip of skin on the medial arm is supplied by the intercostobrachial nerve, which comes from the T2 spinal nerve in the thorax and not from the brachial plexus. That intercostobrachial nerve travels into the axilla and covers the medial aspect of the upper arm, sometimes extending to the posterior medial region. Because it isn’t a branch of the brachial plexus, that area is not innervated by it. In contrast, the elbow area, the lateral forearm, and the medial forearm all receive sensation from nerves that originate in the brachial plexus (such as the medial and lateral cutaneous branches of the arm and forearm, and the nerves supplying the posterior arm). So the only region not innervated by the brachial plexus in this set is the posterior medial portion of the arm, which is served by the intercostobrachial nerve from the thoracic nerves.

The main idea is that the brachial plexus supplies almost all sensory innervation to the upper limb, but there is a notable exception: a strip of skin on the medial arm is supplied by the intercostobrachial nerve, which comes from the T2 spinal nerve in the thorax and not from the brachial plexus. That intercostobrachial nerve travels into the axilla and covers the medial aspect of the upper arm, sometimes extending to the posterior medial region. Because it isn’t a branch of the brachial plexus, that area is not innervated by it.

In contrast, the elbow area, the lateral forearm, and the medial forearm all receive sensation from nerves that originate in the brachial plexus (such as the medial and lateral cutaneous branches of the arm and forearm, and the nerves supplying the posterior arm). So the only region not innervated by the brachial plexus in this set is the posterior medial portion of the arm, which is served by the intercostobrachial nerve from the thoracic nerves.