The axillary nerve provides sensory, cutaneous innervation to the skin within which set of dermatomes?

Question

BlackTom AI · Accepted Answer

The axillary nerve arises from the posterior cord of the brachial plexus with root contributions from the C5 and C6 spinal nerves and gives rise to the superior lateral cutaneous nerve of the arm, which supplies the skin over the deltoid ("regimental badge") area. These root contributions determine the dermatomal territory the axillary nerve carries sensory fibers for—namely C5 and C6.

1) Relevant knowledge points:
- Brachial plexus roots and peripheral nerves: the axillary nerve is composed of fibers from C5–C6.
- Peripheral nerve vs dermatome: a peripheral nerve’s cutaneous branch supplies a patch of skin that reflects contributions from specific spinal dermatomes.
- The axillary nerve’s sensory branch is the superior lateral cutaneous nerve of the arm, supplying the lateral shoulder region.

2) Step-by-step reasoning:
- Step 1: Identify nerve origin: axillary nerve = posterior cord with root fibers from C5 and C6.
- Step 2: Identify cutaneous branch: axillary → superior lateral cutaneous nerve of arm, innervates skin over deltoid.
- Step 3: Map to dermatomes: sensory fibers carried by the axillary nerve come from C5 and C6 spinal nerves, so the cutaneous area corresponds to C5–C6 dermatomes.

3) Intermediate mapping steps shown:
- Axillary nerve = motor to deltoid/teres minor + sensory via superior lateral cutaneous nerve.
- Superior lateral cutaneous nerve fibers originate from C5–C6 roots → therefore skin supplied = dermatome levels C5 and C6.

4) Why the correct answer is correct:
Because the axillary nerve’s neuronal cell bodies and root fibers are from C5 and C6, the cutaneous territory it innervates reflects those dermatomes.

5) Why other options are incorrect:
- "The axillary nerve does not provide cutaneous innervation." Incorrect — it does via the superior lateral cutaneous nerve of the arm.
- "C4, C5 and C6." Incorrect — axillary nerve does not contain C4 fibers.
- "C4 and C5." Incorrect — axillary nerve lacks C4 and also includes C6, so this pair is incomplete.

Conclusion: The axillary nerve provides cutaneous innervation corresponding to dermatomes C5 and C6, matching the given correct answer.

The axillary nerve provides sensory, cutaneous innervation to the skin within which set of dermatomes?单项选择题

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