True about sternocleidomastoid are -a) It arises from sternum and clavicleb) Turns head to the opposite sidec) Shortened in congenital torticollisd) Supplied by the cranial accessory nervee) Supplied by occipital artery
## Core Concept
The sternocleidomastoid (SCM) muscle is a key muscle in the neck that plays a significant role in movements of the head and neck. It is one of the major muscles of the neck and is innervated by the accessory nerve (cranial nerve XI), which is a cranial nerve that also has a spinal root.
## Why the Correct Answer is Right
The SCM muscle indeed arises from the sternum and clavicle (a), which makes option a correct. When the SCM muscle contracts on one side, it helps to turn the head to the opposite side (b), making option b correct. In congenital torticollis, the SCM muscle is often shortened or contracted (c), leading to a characteristic tilting of the head, which makes option c correct. The SCM muscle is supplied by the cranial accessory nerve (d), which is correct. However, the SCM muscle is primarily supplied by the **occipital artery** and the **superior thyroid artery**, branches of the external carotid artery, making option e correct as well.
## Why Each Wrong Option is Incorrect
- **Option A:** Not all listed statements are incorrect, but without specifying which ones are true, it's hard to label it entirely wrong without context.
- **Option B:** This option is incorrect because not all the provided choices are accurate statements about the SCM muscle, given that some are indeed true.
- **Option D:** This could be considered incorrect in the context of the question if one or more of the statements provided are not accurate regarding the SCM muscle.
## Clinical Pearl / High-Yield Fact
A key clinical correlation to remember is that congenital torticollis, often identified in infancy, involves the SCM muscle and can lead to facial asymmetry if not treated. The condition is associated with a palpable mass or tightness in the SCM muscle.
## Correct Answer: C.