FALSE statement about Brachial plexus
**Core Concept**
The brachial plexus is a complex network of nerves that originates from the spinal cord, specifically from the C5 to T1 nerve roots, and extends through the neck and shoulder region to innervate the muscles and skin of the upper limb.
**Why the Correct Answer is Right**
The brachial plexus is formed by the ventral rami of the C5 to T1 spinal nerves, which merge to form the superior, middle, and inferior trunks, and then further divide into anterior and posterior divisions. The nerves of the brachial plexus are responsible for controlling muscle movement, sensation, and reflexes in the upper limb. The most common injury to the brachial plexus occurs due to birth trauma (Erb's palsy) or a fall onto an outstretched hand, resulting in damage to the C5-C6 nerve roots.
**Why Each Wrong Option is Incorrect**
* **Option A:** This statement is incorrect because the brachial plexus is formed from the ventral rami of the C5 to T1 nerve roots, not the dorsal rami.
* **Option B:** This statement is incorrect because the brachial plexus is not formed from the cervical plexus; the cervical plexus is a separate network of nerves formed from the C1-C4 nerve roots.
* **Option D:** This statement is incorrect because the brachial plexus is not formed from the lumbar plexus; the lumbar plexus is a separate network of nerves formed from the L1-L4 nerve roots.
**Clinical Pearl / High-Yield Fact**
The Erb's palsy, a form of brachial plexus injury, typically presents with weakness or paralysis of the muscles of the upper arm (supraspinatus, infraspinatus, and deltoid), resulting in a characteristic "waiter's tip" deformity of the hand.
**Correct Answer:** B.