Twelve Cranial Nerves

Nerves which emerge from the brain region are known as cranial nerves. Cranial nerves are completely different from spinal nerves. Spinal nerves are those nerves which emerge from spinal cord segments. Traditionally, there are twelve pairs of cranial nerves present in the human body. The first and second pair of cranial nerve emerges from the region of cerebrum and rest of ten pairs emerges from region of brainstem.

There are following twelve cranial nerves present in the humans and non-human vertebrates:

1.    Olfactory

2.    Optic

3.    Oculomotor

4.    Trochlear

5.    Trigeminal

6.    Abducens

7.    Facial

8.    Auditory or Vestibulocochlear

9.    Glossopharyngeal

10. Vagus

11. Spinal Accessory

12. Hypoglossal

Olfactory: Olfactory is a purely sensory nerve and originates from telencephalon. Olfactory nerves are present in anterior olfactory nucleus and its major function is to transmit the sense of smell received from the nasal cavity. It is located in olfactory foramen which is in cribriform plate of ethmoid.

Optic: Like olfactory, it is also a purely sensory nerve and originates from diencephalon. Optic nerves are present in ganglion cells of retina and it transmits signals which are visual from the retina present in the eye to the human brain. It is located in a passage which is known as optic canals.

Oculomotor: Unlike the first two cranial nerves it is mainly a motor. It can be easily understood by its name. It originates from two type of nucleus one is oculomotor nucleus and the other one is Edinger-Westphal Nucleus. Its major function is to innervate inferior oblique, superior medial rectus, inferior rectus and levator palpebral superioris.

Trochlear: It belongs to the family of oculomotor. It is also motor like oculomotor. It mainly originates from dorsal aspect of midbrain and it has trochlear nucleus present in the brain.

Trigeminal: Unlike the other four cranial nerves, trigeminal is both sensory and motor nerve. It originates from pons.

Abducens: It is a mainly motor nerve and originates from anterior margin of pons. Its nucleus is known as Abducens nucleus.

 Facial: It is the most commonly known cranial nerve. It acts as both sensory and motor nerve. It originates from pons or cerebellopontine angle which is located above olive.

Auditory: Auditory nerve is also known as Vestibulocochlear or acoustic or auditory vestibular nerve.

Glossopharyngeal: It functions as both sensory and motor nerve. It originates from medulla. Its nucleus is known as ambiguous nucleus. Some of the sensation received is also relayed to the brain and it is generally located in jugular foramen of the brain.

Vagus: Vagus also functions as sensory and motor nerve. It originates from poster lateral sulcus which is present in medulla. Its nucleus is known as ambiguous nucleus. The major function of Vagus is to supply innervation known as branchiomotor to most of the pharyngeal muscles and laryngeal muscles. Stylopharyngeus muscle is innervated by glossopharyngeal

Spinal Accessory: Spinal accessory nerve is also known as just accessory or cranial accessory nerve. In this paragraph, we will use the word accessory for it. Accessory is mainly a motor nerve. As the name suggest it originates from spinal roots and cranial roots.

Hypoglossal: Hypoglossal nerve mainly functions as motor. It originates from medulla and its nucleus is hypoglossal nucleus. The important function of hypoglossal is to provide motor innervation to tongue and motor. It doesn’t provide innervation to palatoglossus. Palatoglossus is innervated by vagus nerve. It also innervates other glossal nerves. It plays essential role in bolus formation, swallowing and articulation of speech. It is found in hypoglossal canal.