WBR0328

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Head and Neck
Prompt	Prompt::A 42-year-old male patient presents to the physician's office with complaints of an inability to laterally flex his neck or rotate his head. Upon physical examination, which other finding is most likely demonstrated in this patient?
Answer A	AnswerA::Inability to elevate his shoulder
Answer A Explanation	AnswerAExp::Cranial nerve (CN) XI or the spinal accessory nerve innervates the trapezius, which is the muscle responsible for elevation or shrugging of the shoulder.
Answer B	AnswerB::Inability to open his jaw
Answer B Explanation	AnswerBExp::The lateral pterygoid is the main muscle responsible for opening the jaw. All jaw muscles are innervated by the trigeminal nerve - the mandibular branch (CN V3).
Answer C	AnswerC::Inability to protrude his tongue
Answer C Explanation	AnswerCExp::The CN XII, hypoglossal nerve, innervates the tongue.
Answer D	AnswerD::Inability to preform arm abduction
Answer D Explanation	AnswerDExp::Arm abduction relies on the deltoid muscles and the supraspinatus muscle. The deltoid muscle is innervated by the axillary (C5-C6) nerve. The supraspinatus muscle is innervated by the suprascapular (C5-C6) nerve.
Answer E	AnswerE::Inability to swallow
Answer E Explanation	AnswerEExp::Swallowing relies on the CN IX or the glossopharyngeal nerve.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient in this scenario most likely has an injury to his sternocleidomastoid muscle (SCM), which is responsible for the lateral flexion of the neck and the rotation of the head. The SCM is innervated by CN XI, or the spinal accessory nerve, which also innervates the trapezius, the main muscle responsible for shoulder shrugging. Educational Objective: Sternocleidomastoid laterally flexes the neck and rotates the head. It is innervated by CN XI. The trapezius muscle, which elevates the shoulder, is also innervated by CN XI. References: First Aid 2014 page 472]]
Approved	Approved::Yes
Keyword	WBRKeyword::trapezius, WBRKeyword::sternocleidomastoid, WBRKeyword::SCM, WBRKeyword::innervate, WBRKeyword::innervation, WBRKeyword::cranial nerves, WBRKeyword::accessory nerves
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::