[Biology Class Notes] on Cranial Nerves Pdf

The pair of nerves that connects mainly the neck region and other parts of head to the brain are called cranial nerves. The main functions of each cranial nerves are motor and sensory. Some of the nerves conjointly perform both sensory and motor function. The nerves are numbered in roman numerical from 1 – 12. The numbers correspond to the position of these nerves in brain.

Let us have a close look at each of the cranial nerve names.

Types of Cranial Nerves 

So, you know what are cranial nerves and that there are 12 cranial nerves in the human body, each of which performs a different function. Refer to the diagram given before to gain an idea about the position of each cranial nerve names.

The cranial nerves and their functions have been listed below – 

1. Olfactory Nerve –  

This nerve, shortest among all the cranial nerves is responsible for smell. The receptor neurons are located in olfactory mucosa at upper parts of nasal cavity. These neurons grow throughout life. 

The nerves are stimulated during inhalation and converted into electrical impulses in olfactory bulb. It then transmits the impulses to other parts of olfactory nerve and central nervous system via the olfactory tract.

2. Optic Nerve – 

The optic nerve records visual information via photoreceptors from the retina to the brain’s occipital lobe through the optic canal. Even though this nerve is related to the eye; it is a part of the central nervous system. One of the most common illness that can damage these nerves is Glaucoma.

3. Oculomotor Nerve – 

This nerve controls muscle movement of the eye such as the pupil constriction and adjustment depending on the availability of light. It also controls the ciliary muscles which aid the eye lens to see objects at short or long distance.

It begins at superior colliculus, goes through the superior orbital fissure to control the muscles responsible for holding the eyelid open.

4.  Trochlear Nerve

This is a motor nerve linked to the superior oblique muscle of the eye. This muscle prevents the eye from going into the eye socket and controls downward eye movement. Damage to this nerve can result in an inability to move the eye downward, which leads in vertical diplopia or double vision.

5.  Trigeminal Nerve – 

The sensory functions of these nerves record pain sensation of face and mouth and provide motion, position and tactile sense. It also has motor functions and facilitate movement of jaw, mouth and inner ear. 

It has three main branches which are – (i) ophthalmic nerve, (ii) maxillary nerve(iii) mandibular nerve. They converge on trigeminal ganglion within the trigeminal cave in brain. 

6. Abducens Nerve – 

This nerve controls the lateral rectus eye muscle. This muscle helps in outward eye movement.  It has one of the longest intracranial sequence among all the nerves and therefore is much more exposed to injuries. Several factors can cause damage to this nerve such as tumour growth, meningitis infection, diabetic neuropathy and so on.

7. Facial Nerve – 

These nerves control the muscles in our face, thereby controlling our facial expression. The nerves pass through the facial canal, then parotid gland and separates into six parts. These are – 

• Intracranial segment.

• Meatal segment.

• Labyrinthine segment.

• Tympanic segment.

• Mastoid segment. 

• Extratemporal segment.

8. Vestibulocochlear Nerve – 

Its job is to transmit information of sound from inner ear to brain. It comprises of two nerves which are cochlear nerve and vestibular nerve. The first is a sensory nerve whose function is to provide surrounding information to brain. The latter works to transmit sounds and balance information from inner ear to brain.

9. Glossopharyngeal Nerve – 

This nerve performs several essential functions, such as controlling some part of sense for taste and saliva production. Also, it regulates upper throat and oral cavity muscles. It comprises of vestibular nerve and cochlear nerve. The former fuses with the semi-circular canals through vestibular ganglion to receive positional information. While the latter gives information about our surroundings to brain.

10. Vagus Nerve – 

This is one of the essential cranial nerves. It starts from medullary pyramid, and inferior cerebellar peduncle goes through the carotid sheath to neck, chest and abdomen and aids in the innervation of viscera. 

It also conveys sensory information regarding our body’s organs to CNs because most of its nerves are sensory nerves. It controls some skeletal muscles, some of which are – larynx muscle, palatoglossus muscle, cricothyroid muscle etc. besides sending parasympathetic nerve fibres to all organs. 

11. Spinal Accessory – 

It controls the sternocleidomastoid and trapezius muscles of neck. The former is used for tilting and rotating the head and the latter’s function is shoulder elevation, depression and adduction, among others. It originates from Central nervous system and exits the cranium via foramen. It is the only nerve that enters and exits the skull.

12. Hypoglossal Nerve – 

Its function is to control the movements of tongue while speaking, eating and swallowing food. This nerve connects motor fibres to all tongue muscles except palatoglossus muscle. It performs a voluntary function, which means conscious thought is required for the above activities, cortinuclear nerves help in unconscious tongue movements during speech. This nerve enables us to move our tongue to pronounce difficult speech sounds 

Given below is a cranial nerve and their function table. 

Cranial Nerve Functions Table

The cranial nerves chart above will enable you to understand the type of function performed by each nerve.

You will find a detailed study guide with maps on cranial nerves and functions and diagrams on the nervous system on ’s website. It will enable you to gain a better understanding of cranial nerves and the difference between cranial nerves and spinal nerves. You can go through it online or download a PDF version of it via our app.

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