Investigation of cranial nerves. XI pair: accessory nerve (n. Accessorius)
Last reviewed: 23.04.2024
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XI pair: an additional nerve (n. Accessorius) is a purely motor nerve that innervates the sternocleidomastoid and trapezius muscles.
The investigation of the function of the additional nerve begins with the evaluation of the shape, size and symmetry of the sternocleidomastoid and trapezius muscles. It is usually enough to compare the right and left sides. When the nucleus or the trunk of the XI nerve is injured, the shoulder belt on the side of the paralysis is omitted, the scapula is somewhat shifted downward and laterally.
To assess the strength of the sternocleidomastoid muscle, the patient is asked to force his head to the side and slightly upward. The doctor counteracts this movement, putting pressure on the lower jaw of the patient. With a one-sided contraction, the sternocleidomastoid muscle produces a tilt of the head and neck in its direction and at the same time it additionally rotates the head in the opposite direction. Therefore, when testing the right muscle, lay your hand on the left half of the patient's lower jaw, and vice versa. Look at the contours and palpate the abdomen of this muscle during its contraction. To assess the strength of the trapezius muscle, the patient is asked to "shrug" ("raise the shoulders to the ears"). The doctor is resisting this movement.
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