The Brachial Plexus Quiz

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Which set of spinal nerves forms the brachial plexus?

A C5, C6, C7, C8 and T1 ✓
B C3, C4, C5, C6 and C7
C C4, C5, C6, C7 and C8
D T1, T2, T3, T4 and T5
E C6, C7, C8, T1 and T2

The answer is A: C5, C6, C7, C8 and T1

Explanation

Why A is correct

See The Brachial Plexus. Option A is correct. The brachial plexus is a network of nerves that begins in the neck and runs into the axilla (the armpit) to supply the skin and muscles of the upper limb. It is built from the anterior rami of five spinal nerves, C5, C6, C7, C8 and T1. Each spinal nerve divides soon after it leaves the spine into an anterior ramus (the branch that heads forwards, towards the limbs and the front of the trunk) and a posterior ramus (the branch that heads backwards, to the muscles and skin of the back), and only the anterior rami join the plexus. They pass between the anterior and middle scalene muscles (two muscles at the side of the neck) and then divide and recombine in a fixed order. The pattern explains common injuries: damage to the upper roots (C5 and C6), often from a stretching injury during a difficult delivery, causes Erb's palsy, whereas damage to the lower roots (C8 and T1) causes the rarer Klumpke's palsy, with a clawed hand. A well-known memory aid for the five stages is 'Read That Damn Cadaver Book':

Roots (Read)
Trunks (That)
Divisions (Damn)
Cords (Cadaver)
Branches (Book)

Roots: the brachial plexus is built from the anterior rami of C5, C6, C7, C8 and T1.
Posterior rami: they do not join the plexus.
Injuries: damage to C5 and C6 causes Erb's palsy, and damage to C8 and T1 causes Klumpke's palsy.

Why the other options are incorrect

B. C3, C4, C5, C6 and C7: C3 and C4 contribute to the cervical plexus (C1 to C4), which supplies the neck, and this set leaves out C8 and T1, the roots that carry fibres to the hand. C3 to C5 also form the phrenic nerve to the diaphragm, which is not a brachial plexus nerve.
C. C4, C5, C6, C7 and C8: C4 is not a root of the plexus, and leaving out T1 would remove the fibres that reach the small muscles of the hand. The usual plexus runs from C5 to T1, not from C4 to C8.
D. T1, T2, T3, T4 and T5: T1 does join the plexus, but T2 to T5 are thoracic nerves that run as intercostal nerves between the ribs. This set contains no cervical roots, so it could not supply the shoulder or arm.
E. C6, C7, C8, T1 and T2: This set drops C5, which joins C6 to form the upper trunk, and adds T2, which does not normally join the plexus. It would not explain an Erb's palsy, which involves C5 and C6.

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More questions from this set. Start the quiz to answer them and see each explanation.

1
Which muscle is primarily innervated by the axillary nerve?
2
A 22-year-old university student sustains a deep laceration to the front of the upper arm during a sports injury. On examination, elbow flexion is weak and there is reduced sensation over the lateral side of the forearm. Which nerve is most likely to have been injured?

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