Cranial Nerves : Function, Anatomy and Location

Cranial Nerves: Function, Anatomy, and Location: Cranial nerves are a group of nerves that arises from the brain. Cranial nerves are mainly of two types of conducting nerves; cranial nerves which arise from the brain and spinal nerves which arises from the spinal cord. They are mainly part of the peripheral nervous system i.e. helps in the transmission of information from the brain.

What are the Cranial Nerves?

The 12 pairs of nerves arise from the brain and brain stem that carries signals from the brain to different parts of the body mainly to the head and neck. They emerge from the foramina and fissure of the cranium or skull.  These 12 nerves are numbered from I to XII using Roman numerals according to the order in which they emerge from the front of the brain to the back of the brain. The cranial nerve I and II are considered to be the part of central nervous system whereas the rest i.e. III to XII are considered to be part of the peripheral nervous system. They can be sensory, motor, or both based on their function. The 12 cranial nerves are; Olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), vestibulocochlear nerve (VIII), glossopharyngeal (XI), vagus (X), accessory (XI), and hypoglossal (XII).

Origin of the Cranial Nerves

Here, we will look into the origin point of each of the cranial nerves.

Nerve No.	Name	Origin
I	Olfactory	Olfactory lobe or the bulb of the cerebrum
II	Optic	Optic lobe of the cerebrum
III	Oculomotor	Floor of midbrain
IV	Trochlear	Floor of midbrain
V	Trigeminal	Pons
VI	Abducens	Pons
VII	Facial	Pons
VIII	Auditory (acoustic/vestibulocochlear)	Pons
IX	Glossopharyngeal	Side of medulla
X	Vagus (pneumogastric)	Side of medulla
XI	Accessory (spinal)	Side of medulla
XII	Hypoglossal	Side of medulla

Distribution of the Cranial Nerves

Here, we will look into the distribution of the cranial nerves.

Nerve No.	Name	Distribution
I	Olfactory	Olfactory epithelium
II	Optic	Retina of eyeball
III	Oculomotor	Eye, and its four muscles i.e. extraocular muscles, intraocular muscles, protractor, and retractors.
IV	Trochlear	Superior oblique muscle of eyeball.
V	Trigeminal	Head, face, jaws, and teeth.
VI	Abducens	Lateral rectus of the eyeball.
VII	Facial	Salivary glands, taste buds of the anterior two-thirds of the tongue, facial muscles, muscles of the neck, and chewing.
VIII	Auditory (acoustic/vestibulocochlear)	Organ of Corti, and vestibular receptors of the internal ear.
IX	Glossopharyngeal	Taste buds of the posterior one-third of the tongue, mucous membrane, parotid glands, and muscles of the pharynx.
X	Vagus (pneumogastric)	Pharyngeal muscles, vocal cords, lungs, heart, esophagus, stomach, and intestines.
XI	Accessory (spinal)	Palatine muscles, larynx, vocal cords, neck, and shoulder.
XII	Hypoglossal	Muscles of tongue, and neck.

Nature of the cranial nerves

Here, we will look into the nature of the cranial nerves i.e. whether they are sensory, motor, or both.

Nerve No.	Name	Nature
I	Olfactory	Sensory
II	Optic	Sensory
III	Oculomotor	Motor
IV	Trochlear	Motor
V	Trigeminal	Sensory + motor
VI	Abducens	Motor
VII	Facial	Sensory + motor
VIII	Auditory (acoustic/vestibulocochlear)	Sensory
IX	Glossopharyngeal	Sensory + motor
X	Vagus (pneumogastric)	Sensory + motor
XI	Accessory (spinal)	Motor
XII	Hypoglossal	Motor

Function of the Cranial Nerves

Here, we will look into the functioning of the cranial nerves.

Nerve No.	Name	Function
I	Olfactory	Helps in the detection of smell.
II	Optic	Helps in sight.
III	Oculomotor	Helps in the movement of the eyeball, constriction of the pupil, and its accommodation.
IV	Trochlear	Helps in the rotation of the eyeball.
V	Trigeminal	The sensory part helps in the sensation of the forehead, scalp, upper eyelid, side of the nose, and teeth. The motor part helps in the movement of the tongue, and jaw muscles for chewing.
VI	Abducens	Helps in the rotation of the eyeball.
VII	Facial	The sensory part helps with taste. The motor part helps in facial expression, chewing, and movement of the neck.
VIII	Auditory (acoustic/vestibulocochlear)	Helps in hearing and maintaining equilibrium.
IX	Glossopharyngeal	The sensory part helps with taste and touch. The motor part helps in the movement of the pharynx.
X	Vagus (pneumogastric)	The sensory part helps in the sensation of the throat, larynx, thorax, and abdomen. The motor part helps in swallowing, voice, peristalsis, secretion of gastric glands, and slowing of the heart.
XI	Accessory (spinal)	Helps in the movement of the muscle in the pharynx, larynx, neck, and shoulder.
XII	Hypoglossal	Helps in the movement of the tongue.

FAQs on Cranial Nerve

Q: If a person complains of loss of smell, which cranial nerve is possibly affected?

Answer:

The cranial nerve that is possibly affected will be the olfactory nerve.

Q: What is the purpose of cranial nerves in the human body?

Answer:

Cranial nerves convey information from the brain to various body parts. The cranial nerve also facilitates the sense of vision, muscle movement, hearing, and smell.

Q: Why cranial nerve XI is called an accessory nerve?

Answer:

Because it arises from the cranial as well as spinal portion of the CNS and it acts as an accessory to the vagus nerve i.e. complements its function.

Q: List the cranial nerves that help in the control of eye movements.

Answer:

Four cranial nerves help in the control of eye movements, these are; the optic nerve, oculomotor nerve, trochlear nerve, and abducens nerve.