Axillary nerve supplies:
**Question:** Axillary nerve supplies:
A. Deltoid muscle
B. Pectoralis major muscle
C. Rhomboid muscles
D. Triceps brachii muscle
**Core Concept:**
The axillary nerve is a major peripheral nerve that originates from the brachial plexus. It plays a crucial role in the innervation of various muscles in the upper limb. The brachial plexus is formed by the union of the ventral rami of spinal nerves C5-C8 and T1.
**Why the Correct Answer is Right:**
The axillary nerve supplies the following muscles:
1. **Deltoid muscle:** The deltoid muscle is responsible for shoulder abduction and rotation. It is innervated by the axillary nerve, making option A the correct answer.
2. **Pectoralis major muscle:** This muscle is involved in shoulder flexion and chest wall depression. Although it is innervated by the pectoral branch of the thoracoacromial artery, it does not directly receive axillary nerve supply. Therefore, option B is incorrect.
3. **Rhomboid muscles:** These muscles are responsible for scapular retraction and are innervated by the long thoracic nerve, not the axillary nerve. Consequently, option C is incorrect.
4. **Triceps brachii muscle:** The triceps brachii muscle is involved in elbow extension and supination. It is innervated by the radial nerve, not the axillary nerve. Hence, option D is incorrect.
**Why Each Wrong Option is Incorrect:**
- Option C (Rhomboid muscles) is incorrect because the long thoracic nerve, not the axillary nerve, supplies the rhomboid muscles.
- Option D (Triceps brachii muscle) is incorrect because the axillary nerve supplies the triceps brachii muscle, not the radial nerve.
**Clinical Pearl:**
The axillary nerve innervates essential muscles for upper limb function, including the deltoid, biceps brachii, and brachialis muscles. A comprehensive understanding of upper limb anatomy and nerve innervation is crucial for both clinical practice and patient management.
**Correct Answer:**
The axillary nerve supplies the deltoid, biceps brachii, and brachialis muscles, making option A (deltoid muscle) the correct answer.