12 cranial nerves

Anatomy

Cranial nerves are the 12 nerves of the peripheral nervous system that emerge from the foramina and fissures of the cranium. Their numerical order (1-12) is determined by their skull exit location (rostral to caudal). All cranial nerves originate from nuclei in the brain. Two originate from the forebrain (Olfactory and Optic), one has a nucleus in the spinal cord (Accessory) while the remainder originate from the brainstem.

There's a LOT to learn about the cranial nerves. You might like to ease yourself into this topic with our cranial nerves quizzes and labeling exercises.

Cranial nerves supply sensory and motor information to structures of the head and neck, controlling the activity of this region. Only the vagus nerve extends beyond the neck, to innervate thoracic and abdominal viscera.

We’re sure that while reading textbooks, you encountered with terms such as afferent, efferent, mixed, general, visceral, special, somatic etc, these refer to modalities of the cranial nerves. They often bring confusion, so let’s explain them before proceeding.  

The function of a nerve is to carry sensory and/or motor information between the body and the brain. If the information goes from the brain to the periphery, then it is an efferent (motor) nerve. If it travels from the periphery to the brain, then it is an afferent (sensory) nerve. Nerves that do both are mixed nerves. Unlike spinal nerves which are always mixed, cranial nerves can be purely motor, purely sensory or mixed. 

Now let’s understand the terms special, general, somatic and visceral. The information is classified as special if it travels from our special senses (vision, smell, taste, hearing and balance), while general describes information to/from everywhere else. The information carried by a nerve is called somatic if it goes to/from the skin and skeletal muscles, or visceral if it travels to/from our internal organs. 

Combining these categories allows us to define the functional components of a nerve. For example, if the nerve fibers exclusively carry special sensory information, it is called a special afferent nerve. If it carries other types of sensory information, like touch, pressure, pain, temperature, then it is a general afferent nerve.

If the nerve carries information to smooth muscle, cardiac muscle or glands, then it is a visceral efferent nerve. If it carries information to skin or skeletal muscle, then it is a somatic efferent nerve. As the term visceral is often a synonym for autonomic (nervous system), note that general visceral nerves carry autonomic nerve fibers to/from the target organs. The exception to this are the special visceral efferent nerves, sometime described as branchial efferent (BE). These are motor nerves, named for the embryological origin of the fibres. Information of movement and position (proprioception) from somatic structures like muscles, tendons, and joints is carried by general somatic afferent nerves. Lastly, be aware that there is no special somatic efferent classification. 

So to conclude, considering the possible directions and modalities, cranial nerves can be:

1. General somatic afferent (GSA)
2. General somatic efferent (GSE)
3. General visceral afferent (GVA)
4. General visceral efferent (GVE)
5. Special somatic afferent (SSA)
6. Special visceral afferent (SVA)
7. Special visceral efferent (SVE)

Here is a cranial nerves starter pack for you:

12 cranial nerves list

To get familiar with these nerves, let’s list all them in one place. 

Test your knowledge about the cranial nerves by taking this quiz which is specially designed to cover the most important anatomy facts about the 12 cranial nerves!

Mnemonics

If we take the first letter of each nerve, we can build a mnemonic to help remember the cranial nerve names! 

Oh, Oh, Oh, To Touch And Feel Very Good Velvet, Such A Heaven

• Olfactory nerve (CN I)
• Optic nerve (CN II)
• Occulomotor nerve (CN III)
• Trochlear nerve (CN IV)
• Trigeminal nerve (CN V)
• Abducens nerve (CN VI)
• Facial nerve (CN VII)
• Vestibulocochlear nerve (CN VIII)
• Glossopharyngeal nerve (CN IX)
• Vagus nerve (CN X)
• Accessory nerve (CN XI)
• Hypoglossal nerve (CN XII)

Or, if you’re a member of the Harry Potter fandom, you can learn this one: On, On, On, They Traveled And Found Voldemort Guarding Very Ancient Horcruxes. Remember these, and you’ll always be able to recall the cranial nerves in their numerical order. 

In addition, to remember if a nerve is sensory, motor or both in numerical order, remember this:

"Some say money matters, but my brother says big brains matter most" 

• Sensory (CN I)
• Sensory (CN II)
• Motor (CN III)
• Motor (CN IV)
• Both (CN V)
• Motor (CN VI)
• Both (CN VII)
• Sensory (CN VIII)
• Both (CN IX)
• Both (CN X)
• Motor (CN XI)
• Motor (CN XII)

Now that we’ve learned the tricks on how to remember cranial nerves and their modalities, let’s get introduced to the anatomy of each one of them. 

Olfactory nerve (CN I)

Cranial nerve 1 is a special somatic afferent nerve which innervates the olfactory mucosa within the nasal cavity. It carries information about smell to the brain.

The many branches of the olfactory nerve, called fila olfactoria, pass from the nasal cavity through the cribriform plate of the ethmoid bone. They terminate in the olfactory bulb, which continues as the olfactory tract. Within the brain, the fibers of the olfactory tract disperse and end within the olfactory cortex (piriform cortex, amygdala, entorhinal cortex). 

The olfactory nerve doesn’t have a specific nucleus of its own. Instead its cell bodies are found in the olfactory area-the nasal mucosa that covers the roof of the nasal cavity. 

*Note that there is an ongoing discussion about the modality of the olfactory nerve. Some authors say it’s SSA, whilst the others classify it as SVA. In any case, you won't make a mistake if you simply say that it is a special afferent nerve.

Find out more about the olfactory nerve in the study unit below, or take the quiz to see what you've learned so far!

Optic nerve (CN II)

Cranial nerve 2 is a special somatic afferent nerve which innervates the retina of the eye and brings visual information to the brain. 

Neural fibers originate from the photoreceptors of the retina. They converge at the optic disc, forming the optic nerve. The optic nerve leaves the orbit through the optic canal.

On the floor of the middle cranial fossa, the nasal parts of each nerve cross to the opposite side forming the optic chiasm. The nerve fibers then continue as the two optic pathways. CN II also doesn’t have its own nuclei, but instead its cell bodies are found in the retina. The optic nerve synapses with the visual relay centers of the brain. 

Eager to learn everything about the optic nerve? Check out this study unit and quiz we have prepared for you.

Oculomotor nerve (CN III)

Cranial nerve 3 is both a somatic and visceral efferent motor nerve. This means it has two nuclei and carries two types of efferent fibers. As the name suggests, the oculomotor nerve is the chief motor nerve supplying the eye.

It originates from the midbrain and leaves the skull through the superior orbital fissure to enter the orbit where it enables eye movement, constriction of the pupil (miosis) and lens accommodation.

Solidify your knowledge about the oculomotor nerve with this study unit:

Trochlear nerve (CN IV)

Cranial nerve 4 is a general somatic motor nerve. The trochlear nerve originates from the midbrain and enters the orbit through the superior orbital fissure, supplying one extraocular muscle thus playing a role in eye movement.

We have you covered with the anatomy of the trochlear nerve in the study unit below. 

Trigeminal nerve (CN V)

Cranial nerve 5 is a mixed nerve, containing both special visceral and general somatic fibers. The fibers originate from the brainstem, forming the trigeminal ganglion near the apex of the petrous part of the temporal bone.

The trigeminal nerve divides into three divisions; ophthalmic nerve (CN V1), maxillary nerve (CN V2) and mandibular nerve (CN V3). Each of them leaves the skull through a different opening. Ophthalmic leaves through the superior orbital fissure, maxillary through the foramen rotundum and the mandibular nerve exits via the foramen ovale.

All three branches of the trigeminal nerve supply sensation to the facial skin. The areas of cutaneous innervation (dermatomes) are as follows; Ophthalmic nerve (CN V1 dermatome) supplies the forehead, orbit and nose, maxillary nerve (CN V2 dermatome) the zygomatic region and upper lip, while the mandibular nerve (CN V3 dermatome) innervates the buccal skin, lower lip and skin of the mandibular region.

To learn everything about the trigeminal nerve and its divisions, we recommend you go through the following study materials and custom quiz:

Abducens nerve (CN VI)

Cranial nerve 6 is a general somatic efferent nerve which innervates the lateral rectus muscle (extraocular). The abducens nerve originates from the brainstem and exits the skull via the superior orbital fissure.

Although it may seem the least relevant, the abducens nerve plays a very important role in eye movement. Just ask anyone with strabismus.

Learn all about this nerve in the study unit below and then test what you've learned so far about the oculomotor, trochlear and abducens nerve with our qustom quiz below!

Facial nerve (CN VII)

Cranial nerve 7 is a multimodal nerve, carrying both general and special fibers. It originates from the brainstem as two separate divisions; a larger primary root carrying motor fibers and a smaller intermediate nerve carrying sensory and parasympathetic fibers.

The two divisions leave the cranial cavity through the internal acoustic meatus and then travel through the facial canal. Here they join forming the facial nerve proper and leave the cranium together through the stylomastoid foramen. Once the facial nerve reaches the face it enables many functions, such as facial expression, secretion of glands and taste sensation.

Even though it may seem like a never ending story, the facial nerve isn’t so hard to learn if you have a good approach.

We offer you one with our study unit and custom quiz:

Vestibulocochlear nerve (CN VIII)

Cranial nerve 8 is a special somatic afferent nerve. It is comprised of two parts: the vestibular nerve and the cochlear nerve. The cochlear component enables hearing, while the vestibular part mediates balance and motion. At the fundus of internal acoustic meatus, both parts unite to form the vestibulocochlear nerve and enter the cranium through the internal acoustic meatus.

The two components synapse with their respective nuclei in the brainstem. To save you from confusion, note that dorsal and ventral cochlear nuclei terminology varies. Sometimes you’ll see them as anterior and posterior cochlear nuclei, and elsewhere simply grouped as the auditory nuclei. 

Master the vestibulocochlear nerve anatomy with our user resources:

Glossopharyngeal nerve (CN IX)

Cranial nerve 9 is another multimodal nerve. It originates from the brainstem and leaves the skull through the jugular foramen. It enables swallowing, salivation, and taste sensation, as well as visceral and general sensation in the oral cavity.

Fortify your knowledge about the glossopharyngeal nerve with these Kenhub resources.

Vagus nerve (CN X)

Cranial nerve 10 is also a multimodal nerve, It originates from multiple nuclei in the brainstem, and exits the skull through the jugular foramen. It is the longest cranial nerve and the only one to leave the head and neck region. The vagus nerve travels into the thoracic and abdominal cavities, providing parasympathetic supply to visceral organs. 

CN 10 has two ganglia, called the superior ganglion of the vagus nerve and the inferior ganglion of the vagus nerve (nodose ganglion). The former provides fibers for general sensory function, while the latter gives special sensory and visceral output.

The vagus nerve controls a large number of functions, including gland secretion, peristalsis, phonation, taste, visceral and general sensation of the head, thorax and abdomen. This cranial nerve is frequently tested in anatomy exams.

Use our content to swot up on the vagus nerve and ace your cranial nerve exams!

Accessory nerve (CN XI)

Cranial nerve 11 is an efferent nerve originating from the brainstem and spinal cord. It exits the skull through the jugular foramen, acting to enable phonation and movements of the head and shoulders.

Sensory fibers of the cervical plexus join the accessory nerve enabling general sensation for its target muscles. So when you feel comfortable while getting a shoulder massage, thank your cervical plexus for that.

The (spinal) accessory nerve is interesting in that anatomists still don’t agree on exactly where its nerve fibers originate from. *Some debate that it is a SVE nerve, believing the spinal accessory nucleus to be continuous with the nucleus ambiguus (which is SVE). Yet others describe it as a GSE nerve, providing motor innervation to the three muscles without nucleus ambiguus involvement. There are also anatomists who believe that the CN XI contains both SVE and GSE nerves, receiving fibers from both nuclei sources.

Learn everything about the accessory nerve with our Kenhub study materials.

Hypoglossal nerve (CN XII)

Cranial nerve 12 is a general somatic efferent nerve originating from the brainstem. It leaves the skull through the hypoglossal foramen. It’s function is to enable tongue movements.

The hypoglossal nerve is extremely important for smooth daily functioning of every person, as it plays a significant role in important mouth functions such as speech and swallowing. Similar to CN XI, the hypoglossal nerve also interacts with the cervical plexus. It receives GSE fibers from C1 and C2 spinal nerves, and GSA fibers from the spinal ganglion of C2 spinal nerve.

Master the hypoglossal nerve anatomy with our study material:

Related articles

Articles within this topic:

• Abducens nerve (cranial nerve VI)
• Accessory nerve
• Chorda tympani
• Clinical case: Malignancy along facial nerve
• Clinical case: Optic neuropathy due to optic nerve compression
• Cranial nerves examination: Optic nerve
• Cranial nerves examination: Trochlear & abducens nerves
• Cranial nerves quizzes and labeling exercises
• Facial nerve (cranial nerve VII)
• Glossopharyngeal nerve (Cranial nerve IX)
• Hypoglossal nerve
• Inferior alveolar nerve
• Mandibular nerve (CN V3)
• Maxillary branch of the trigeminal nerve
• Mixed cranial nerves
• Motor cranial nerves
• Ocular motor cranial nerves
• Oculomotor nerve
• Olfactory bulb
• Olfactory pathway and nerve
• Olfactory tract
• Ophthalmic nerve (CN V1)
• Optic chiasm
• Optic nerve
• Optic tract
• Parasympathetic ganglia
• Sensory cranial nerves
• Trigeminal nerve (CN V)
• Trochlear nerve (cranial nerve IV)
• Vagus nerve
• Vestibulocochlear nerve
• Visual pathway