Exciting Facts about Human Anatomy!

Which two muscles are innervated by the accessory nerve?

A. Deltoid and biceps brachii

B. Sternocleidomastoid and trapezius

C. Quadriceps and hamstrings

D. Gluteus maximus and pectoralis major

Answer:

The accessory nerve or spinal accessory nerve innervates the sternocleidomastoid and trapezius muscles.

The accessory nerve, also known as the spinal accessory nerve, plays a crucial role in innervating the sternocleidomastoid and trapezius muscles. These muscles are essential for various movements involving the head, neck, and shoulders.

The sternocleidomastoid muscles, when contracted, enable forward flexion of the head or rotation toward the opposite side when contracted individually. On the other hand, the trapezius muscle serves as an antagonist to the sternocleidomastoids by allowing extension and hyperextension of the neck.

Both muscles are vital for orienting the position of the head and play a role in movements related to the trunk and shoulders. They are responsible for actions such as elevating the scapula and clavicle. These muscles are typically tested by having a patient perform movements like flexing and extending the neck or shrugging the shoulders against resistance to assess the function and strength associated with the accessory nerve.