Spinal accessory nerve supplies –
**Core Concept**
The spinal accessory nerve, also known as the **eleventh cranial nerve**, plays a crucial role in the innervation of specific muscles in the neck. It is responsible for controlling the **sternocleidomastoid** and **trapezius muscles**. This nerve has a unique course, originating from the cranial and spinal roots.
**Why the Correct Answer is Right**
The correct answer is related to the muscles innervated by the spinal accessory nerve. The **sternocleidomastoid muscle** is involved in rotating the head and flexing the neck, while the **trapezius muscle** helps in elevating the shoulder and rotating the scapula. The spinal accessory nerve provides motor innervation to these muscles, facilitating their functions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct muscles innervated by the spinal accessory nerve.
**Option B:** This option is also incorrect as it does not accurately represent the muscles supplied by the spinal accessory nerve.
**Option C:** Similarly, this option is wrong because it fails to identify the sternocleidomastoid and trapezius muscles as the primary targets of the spinal accessory nerve.
**Option D:** This option is incorrect as it does not correctly state the muscles innervated by the spinal accessory nerve.
**Clinical Pearl / High-Yield Fact**
The spinal accessory nerve is clinically significant due to its role in neck and shoulder movements. Damage to this nerve can result in **shoulder drooping** and **weakness in neck rotation**, highlighting the importance of its motor functions.
**Correct Answer:** B. Sternocleidomastoid and Trapezius.