**Question:** All are branches of thyrocervical trunk except-

A. C4 spinal nerve
B. C5 spinal nerve
C. Anterior cutaneous branch of thoracoacromial artery
D. Posterior cutaneous branch of thoracoacromial artery

**Core Concept:** The thyrocervical trunk is a major trunk of the brachial plexus, which arises from the cervical spinal nerves C5, C6, and C7. It has several branches that supply various structures of the upper limb.

**Why the Correct Answer is Right:**

C4 spinal nerve is incorrect because it is a spinal nerve arising from the cervical spinal cord, specifically from C4, not a branch of the thyrocervical trunk.

A. C5 spinal nerve: Like C4, C5 is a spinal nerve originating from the cervical spinal cord, not a branch of the thyrocervical trunk.

B. C5 spinal nerve: Similar to C4, C5 is a spinal nerve originating from the cervical spinal cord, not a branch of the thyrocervical trunk.

**Why Each Wrong Option is Incorrect:**

C. Anterior cutaneous branch of thoracoacromial artery: This option is incorrect because the thoracoacromial artery is a branch of the internal mammary artery, not related to the thyrocervical trunk. The anterior cutaneous branch supplies the skin overlying the anterior chest wall.

D. Posterior cutaneous branch of thoracoacromial artery: Similar to option C, the thoracoacromial artery is a branch of the internal mammary artery, not related to the thyrocervical trunk. The posterior cutaneous branch supplies the skin overlying the posterior chest wall.

**Clinical Pearl:** The thyrocervical trunk is essential for understanding the anatomy and distribution of nerves and arteries in the upper limb. Familiarizing yourself with the branches of the thyrocervical trunk can aid in interpreting clinical findings and making accurate diagnoses in medical practice.