Following block dissection of the neck, a person is unable to move his head upward and to side ways. Which of the following nerve is injured
## **Core Concept**
The question tests knowledge of the innervation of neck muscles, specifically those involved in head movement. The primary muscles responsible for moving the head upward and sideways are innervated by the **spinal accessory nerve (cranial nerve XI)**, which controls the sternocleidomastoid and trapezius muscles.
## **Why the Correct Answer is Right**
The spinal accessory nerve (cranial nerve XI) is responsible for innervating the sternocleidomastoid and trapezius muscles. The sternocleidomastoid muscle is key in rotating the head to the opposite side and flexing the neck. The trapezius muscle helps in elevating, depressing, and rotating the scapula, which in turn assists in moving the head upward and sideways. Injury to this nerve during block dissection of the neck would lead to weakness or paralysis of these muscles, resulting in the inability to perform these movements.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The **vagus nerve (cranial nerve X)** primarily controls parasympathetic functions in the thorax and abdomen and is not directly involved in the motor innervation of neck muscles responsible for head movement.
- **Option B:** The **glossopharyngeal nerve (cranial nerve IX)** is involved in swallowing, salivation, and taste sensation but not in the motor control of head movements.
- **Option D:** The **hypoglossal nerve (cranial nerve XII)** controls tongue movements and is not responsible for the movements of the head.
## **Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that the spinal accessory nerve (cranial nerve XI) can be damaged during surgical procedures in the neck, such as lymph node dissections or during the insertion of central venous catheters. This damage can result in shoulder droop and weakness in moving the head to the side.
## **Correct Answer:** . Accessory nerve