Cranial Nerves and Their Functions

The entire human body is innervated by nerves that are a part of the nervous system. These nerves help us to sense all of our five senses. The cranial nerves emerge directly from the brain as against spinal nerves which emerge from segments of the spinal cord. In humans, there are a total of twelve pairs of cranial nerves.

Only the first and the second pair of nerves emerge directly from the cerebrum, whereas the remaining ten pairs emerge from the brainstem and related parts, like the pons and the border of the medulla.

• It contains the ganglion cells of retina.
• This nerve transmits visual information to the brain and is located in the optic canal.

• This is mainly a motor nerve, and it originates in the midbrain.
• It innervates levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which are all the muscles that collectively perform most eye movements. It also innervates sphincter pupillae. It is located in the superior orbital fissure.

• The trochlear nerve originates in the midbrain.
• This nerve innervates the superior oblique muscle, which depresses, rotates laterally around the optic axis, and helps in eyeball movement. It is located in the superior orbital fissure.

• The trigeminal nerve originates in the pons.
• This is a mixed nerve, that is, it contains both sensory and motor sensations. It receives sensation from the face and innervates the muscles of mastication. It is located in the superior orbital fissure (ophthalmic nerve - V1), foramen rotundum (maxillary nerve - V2), and foramen ovale (mandibular nerve - V3).

• The abducens nerve originates along the posterior margin of the pons.
• This nerve is mainly motor in nature. It innervates the lateral rectus, which helps to abduct the eye and is located in superior orbital fissure.

• The facial nerve originates in the pons.
• It is both sensory and motor in nature. The facial nerve is one of the most important nerves in the body.

It provides motor innervation to the muscles of facial expression, posterior belly of the digastric muscle, and the stapedius muscle, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland.

It is located and runs through the internal acoustic canal to facial canal and exits at the stylomastoid foramen.

The vestibulocochlear nerve has its origin along the cerebellopontine angle.
This nerve is mostly sensory in nature. As the name suggests, it senses sound, rotation, and gravity, which is essential for balance and movement.

The vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing. It is located in the internal acoustic canal.

The glossopharyngeal nerve originates in the medulla.
This nerve is both sensory and motor in nature. It receives taste from the posterior one-third of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus, which is essential for touch, pain, and thermal sensation.

Some of the sensation is also relayed to the brain from the palatine tonsils. Sensation is relayed to oppose the thalamus and some of the hypothalamic nuclei. This nerve is located in the jugular foramen.

The vagus nerve originates in the posterolateral sulcus of the medulla. This nerve is both sensory and motor in nature. It supplies branchiomotor innervation to most laryngeal and all pharyngeal muscles (except the stylopharyngeus, which is innervated by the glossopharyngeal nerve).

It also provides parasympathetic fibers to nearly all the thoracic and abdominal viscera down to the splenic flexure, and receives the special sense of taste from the epiglottis. A major function of this nerve is to control muscles for voice and resonance along with the soft palate. This nerve is also located in the jugular foramen.

The accessory nerve originates in the cranial and spinal roots. It controls sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve. This nerve is located in the jugular foramen.

The hypoglossal nerve originates in the medulla. It is mainly motor in nature. It provides motor innervation to muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) along with other glossal muscles. It is an important nerve for swallowing and speech articulation. It is located in the hypoglossal canal.

The functions of cranial nerves vary depending on the origin and the type of nerve. However, it is important to know everything about the various types of nerves and their functions, because any kind of problem that affects these nerves can lead to serious implications to the health of the person.