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Sternocleidomastoid and Trapezius Muscles (CN XI)

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Ask the patient to shrug their shoulders, turn their head in both directions, and raise their head from the bed, flexing forward against the force of your hands.

46. CNXI Testing

Sequence

What is Being Tested?

Weakness in the sternocleidomastoid or trapezius muscles can be caused by lesions in the muscles, neuromuscular junction, or lower motor neurons of the accessory spinal nerve (CN XI). Unilateral upper motor neuron lesions in the cortex or descending pathways cause contralateral weakness of the trapezius, with relative sparing of sternocleidomastoid strength. This may be explained by bilateral upper motor neuron projections controlling the sternocleidomastoid, in analogy to the bilateral projections controlling the upper face.

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