| Cranial Nerve XI - Accessory Nerve | Page 9 of 9 |
Clinical correlation
Damage to the spinal root of CN XI is a lower motor neuron lesion and results in weakness or flaccid paralysis of the sternocleidomastoid and/or trapezius muscles.
Sternocleidomastoid muscle
Contraction of the sternocleidomastoid muscle pulls the mastoid process toward the ipsilateral clavicle resulting in rotation of the head and an upward tilting of the chin to the opposite side. Weakness of the sternocleidomastoid will result in difficulty in turning the head opposite the side of the lesion. This will be most noticeable when attempted against resistance.
Trapezius muscle
Contraction of the trapezius raises and medially rotates the scapula.
Weakness of the trapezius will result in shoulder drop and downward displacement and lateral rotation of the scapula on the affected side.
Figure 11-9. Clinical correlation.
