Question
A 27-year-old man falls while ascending stairs and sustains an injury to his neck from an iron nail. Since then, he has been experiencing difficulty shrugging his shoulders and turning his head, suggesting damage to a structure involved in these movements. Which anatomical structure is most likely injured?
| A. |
Spinal accessory Nerve
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| B. |
Deltoid Muscle
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| C. |
Sternocleidomastoid Muscle
|
| D. |
Long thoracic Nerve
|
Show Answer
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Correct Answer � A
Explanation
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Functions of the Spinal Accessory Nerve (Cranial Nerve XI):
- The spinal accessory nerve innervates two key muscles:
- Sternocleidomastoid (SCM): Responsible for turning the head to the opposite side.
- Trapezius: Responsible for shrugging the shoulders and rotating the scapula during arm abduction.
- Damage to this nerve results in:
- Weakness in shoulder shrugging due to impaired trapezius function.
- Difficulty turning the head toward the uninjured side due to weakness in the sternocleidomastoid muscle.
Clinical Correlation:
- The spinal accessory nerve is superficial in the posterior triangle of the neck, making it vulnerable to trauma, such as puncture wounds or lacerations.
- In this patient, a penetrating injury from an iron nail in the neck region is highly likely to damage this nerve.
Reasons to rule out other options
Option B- Deltoid Muscle : Primarily involved in arm abduction, the deltoid muscle does not significantly contribute to shoulder shrugging or head turning. Injury to this muscle would more likely affect arm movement rather than the symptoms described.
Option C- Sternocleidomastoid Muscle: While this muscle does play a role in turning the head, an injury to it alone would not typically affect the ability to shrug the shoulders, as this action primarily involves the trapezius muscle, indicating that the problem lies in a structure that innervates both regions.
Option D- Long Thoracic Nerve : This nerve innervates the serratus anterior muscle, which is crucial for the movement of the scapula. Damage to the long thoracic nerve results in “winged scapula” but would not directly cause difficulty in shoulder shrugging or head turning as described.
