Final answer:
The accessory nerve, or cranial nerve XI (CNXI), is classified as a motor nerve. It controls movements of the sternocleidomastoid and trapezius muscles in the head and neck.
Step-by-step explanation:
The accessory nerve, also known as cranial nerve XI (CNXI), is classified as a motor nerve. According to the basic functional grouping of cranial nerves, there are three types of nerves: sensory, motor, and both sensory and motor (mixed). The accessory nerve falls into the motor category, indicating its role is related to motor functions. Specifically, this nerve controls the movement of certain muscles in the head and neck, namely the sternocleidomastoid and trapezius muscles. It provides the motor input required for movements such as turning the head and shrugging the shoulders. The accessory nerve is one of five cranial nerves categorized as strictly motor, with the other four being the oculomotor (CNIII), trochlear (CNIV), abducens (CNVI), and hypoglossal (CNXII) nerves.