The trigeminal nerve is the fifth cranial nerve and is responsible for sensation in the face and motor functions such as biting and chewing. It has three main branches: the ophthalmic nerve, maxillary nerve, and mandibular nerve, each serving different areas of the face. This nerve plays a crucial role in transmitting sensory information from the face to the brain, including touch, pain, and temperature. It also controls the muscles involved in mastication, making it essential for everyday activities like eating and speaking.