|CN I – Olfactory
CN II – Optic
CN III – Oculomotor
CN IV – Trochlear
CN V – Trigeminal
CN VI – Abducens
CN VII – Facial
CN VIII – Auditory
CN IX – Glossopharyngeal
CN X – Vagus
CN XI – Accessory
CN XII – Hypoglossal
Most of the nerves originate from the spinal cord. The remaining nerves which originate directly from the Brain are called Cranial Nerves. 10 of 12 of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.
The cranial nerves are considered components of the peripheral nervous system (PNS), although on a structural level the olfactory, optic and terminal nerves are more accurately considered part of the central nervous system (CNS).
All the cranial nerves are paired and are present on both sides.
There are twelve cranial nerves pairs, which are assigned Roman numerals I–XII. Some experts argue that there are 13 cranial nerves including nerve ‘zero’. The numbering of the cranial nerves is based on the rostral-caudal (front to back) position in which they emerge from the brain.
The Cranial Nerve Zero is a very small terminal nerve (nerve N or O) existing in humans but may not be functional. In other animals, it appears to be important to sexual receptivity based on perceptions of pheromones.
Some Important Points to Remember
1. The only cranial nerve which arises on dorsal aspect – Trochlear nerve
2. The cranial nerve with longest intracranial course – Trochlear nerve
3. The cranial nerve with the longest course – Vagus ( Vagabond Nerve / Wandering Nerve )
4. The cranial nerve most commonly involved in raised intracranial tension – Abducens
5. The cranial nerve most commonly involved in basal skull fractures – Facial Nerve
6. Commonest cranial nerve affected in spinal anaesthesia – Abducens
7. Cranial nerves carrying parasympathetic fibres – 3, 7, 9, 10
8. Thinnest cranial nerve – Trochlear Nerve
9. Thickest cranial nerve – Trigeminal Nerve
10. Cranial nerve palsies in which deviation occurs to the healthy side (opposite side ) – VII and X
11. Cranial nerve palsies in which deviation occurs to same side (diseased side ) – V and XII
12. Cranial nerve involved in Bell’s palsy – VII
13. Cranial nerve involved in herpes zoster ophthalmicus – V
14. Cranial nerve involved in Ramsay hunt syndrome – VII
15. TIC Douloureux – Neuralgia of V nerve ( Trigeminal Neuralgia )
16. Neuralgic pain in the tongue, soft palate, pharynx – Neuralgia of glossopharyngeal nerve