The 12 Cranial Nerves
You have cranial nerves that control your sensory and motor functions. Your brain connects to different parts of the body.
Your brain is connected to different parts of your body with your cranial nerves. Each of them has a function or structure.
Their functions are usually categorized as either sensory or motor. Sensory nerves are involved with your senses. Motor nerves control the movement of muscles.
You can learn more about the cranial nerves by reading this.
The brain has cranial nerves on it. They begin in the brain and travel through different pathways to help control your senses.
The Roman numeral for each nerve is I and XII. This is based on where they are. The olfactory nerve is closest to the front of your head, so it is designated as I.
Disorders and conditions of the cranial nerves can affect processes that involve vision, smell, hearing, speaking, and balance. They can change the way you perceive sensation on the face and the movement of the head, eyes, neck, shoulders, throat, and tongue.
Motor nerves are affected by cranial nerve palsy.
If a sensory nerve is affected, it can cause pain or reduced sensation.
There are conditions and disorders that affect the cranial nerves.
- Third nerve palsy. This disorder can cause a closed or partially closed eyelid, an enlarged pupil, and the movement of the eye outward and downward.
- Trigeminal neuralgia. Trigeminal neuralgia is a disorder of the fifth cranial nerve and typically causes pain on one side of the face.
- Fourth nerve palsy or superior oblique palsy. This disorder can cause misalignment of the eyes and can affect one or both eyes.
- Sixth nerve palsy or abducens palsy. This type of palsy can cause the eye to cross inward toward the nose.
- Bell’s palsy. Bell’s palsy, a disorder of the seventh cranial nerve, can cause temporary weakness or paralysis in one side of the face.
- Hemifacial spasm. A hemifacial spasm happens when blood vessels constrict the seventh cranial nerve and cause a facial spasm or tic.
- Glossopharyngeal neuralgia. This condition affects the ninth cranial nerve and can cause pain at the base of the tongue that may travel to the ear and neck.
- Cranial base tumors. These are tumors that can form in the skull and affect different cranial nerves.
Injury, trauma, and whiplash can also cause damage to cranial nerves.
Different symptoms can be caused by disorders affecting the cranial nerve.
If you experience pain in your face, a change in your ability to move your head or eye, or a change in sensation relating to vision, hearing, smell, balance, or speaking, you may have a cranial nerve disorder.
Symptoms of cranial nerve damage can include:
- There is pain in the face, tongue, head, or neck.
- inability to focus on something
- An eye that moves one side or the other.
- There is weakness in the face.
- slurred speech
- Hearing loss or vision loss.
- Changes in vision.
I. Olfactory nerve
The olfactory nerve sends sensory information to your brain about smells that you encounter.
The aromatic molecule that you inhale when you smell it is dissolved in a moist lining at the roof of your nose.
The olfactory epithelium is a lining. Nerve impulses move to your olfactory bulb. The olfactory bulb is made of an oblong shape and contains specialized groups of nerve cells.
From the olfactory bulb, nerves pass into your olfactory tract, which is located below the frontal lobe of your brain. Nerve signals are then sent to areas of your brain concerned with memory and recognition of smells.
II. Optic nerve
The optic nerve is the sensory nerve that involves vision.
When light enters your eye, it comes into contact with special receptors in your retina called rods and cones. Rods are found in large numbers and are highly sensitive to light. They’re more specialized for black and white or night vision.
Cones are in smaller numbers. They have a lower light sensitivity than rods.
The information received by your rods and cones is sent from your retina to your optic nerve. Once inside your skull, both of your optic nerves meet to form something called the optic chiasm. At the optic chiasm, nerve fibers from half of each retina form two separate optic tracts.
The information reaches your visual cortex through the nerve impulses that reach each of the optic tracts. The back part of your brain is where your visual cortex is located.
III. Oculomotor nerve
The oculomotor nerve has two different motor functions: muscle function and pupil response.
- Muscle function. Your oculomotor nerve provides motor function to four of the six muscles around your eyes. These muscles help your eyes move and focus on objects.
- Pupil response. It also helps to control the size of your pupil as it responds to light.
The front part of your midbrain is where this nerve starts. It moves from that area to the area of your eye sockets.
IV. Trochlear nerve
The trochlear nerve controls your superior oblique muscle. This is the muscle that’s in charge of downward, outward, and inward eye movements.
It comes from the back part of your brain. It moves forward until it reaches your eye sockets, where it stimulates the superior oblique muscle.
V. Trigeminal nerve
The trigeminal nerve is the largest of your cranial nerves and has both sensory and motor functions.
The trigeminal nerve has three divisions.
- Ophthalmic. The ophthalmic division sends sensory information from the upper part of your face, including your forehead, scalp, and upper eyelids.
- Maxillary. This division communicates sensory information from the middle part of your face, including your cheeks, upper lip, and nasal cavity.
- Mandibular. The mandibular division has both a sensory and a motor function. It sends sensory information from your ears, lower lip, and chin. It also controls the movement of muscles within your jaw and ear.
The trigeminal nerve is a collection of nerve cells that are located in the midbrain and medulla regions of your brainstem. The sensory and motor root are formed by these nuclei.
The trigeminal nerve branches into the mandibular and Occidental divisions.
“The trigeminal nerve’s motor root goes below the sensory root and connects to the mandibular division.”
VI. Abducens nerve
The abducens nerve controls another muscle that’s associated with eye movement called the lateral rectus muscle. This muscle is involved in outward eye movement. For example, you would use it to look to the side.
This nerve, also called the abducens nerve, starts in the pons region of your brainstem. It eventually enters your eye socket, where it controls the lateral rectus muscle.
VII. Facial nerve
The facial nerve provides both sensory and motor functions, including:
- The muscles in your jaw are used for facial expressions.
- A sense of taste for most of your tongue.
- salivary glands and tear- producing glands are supplied in your head or neck area.
- The outer parts of your ear are sending sensations.
Your facial nerve is very complex. The motor and sensory root of your brain stem can be found in the pons area. The facial nerve is formed by the fusion of the two nerves.
The facial nerve branches into smaller nerve fibers that are used for muscles and sensory information.
VIII. Vestibulocochlear nerve
Your vestibulocochlear nerve has sensory functions involving hearing and balance. It consists of two parts, the cochlear portion and vestibular portion:
- Cochlear portion. Specialized cells within your ear detect vibrations from sound based on the sound’s loudness and pitch. This generates nerve impulses that are sent to the cochlear nerve.
- Vestibular portion. Another set of special cells in this portion can track both linear and rotational movements of your head. This information is transmitted to the vestibular nerve and used to adjust your balance and equilibrium.
“The vestibulocochlear nerve is found in the brain’s two parts.”
The inferior cerebellar peduncle is where the portion of the brain that is called the cochlear portion begins. The pons and medulla are where the vestibular portion begins. The portions combine to form the vestibulocochlear nerve.
IX. Glossopharyngeal nerve
The glossopharyngeal nerve has both motor and sensory functions, including:
- Sending information from your nose, your throat, your inner ear, and your tongue.
- The back part of your tongue has a sense of taste.
- The back of your throat is called the stylopharyngeus and it is a muscle.
The glossopharyngeal nerve originates in a part of your brainstem called the medulla oblongata. It eventually extends into your neck and throat region.
X. Vagus nerve
The vagus nerve is a very diverse nerve. It has both sensory and motor functions, including:
- It is possible to convey sensation information from your ear canal and throat.
- Sending information from your organs to your chest and trunk.
- Allowing your muscles to move.
- The muscles of your chest and trunk are used to move food through your bicyle.
- A sense of taste is found near the root of your tongue.
The longest pathway is the vagus nerve. It goes all the way into your abdomen. The medulla is the part of your brain that is located in the center of the body.
XI. Accessory nerve
Your accessory nerve is a motor nerve that controls the muscles in your neck. These muscles allow you to rotate, flex, and extend your neck and shoulders.
The spine and cranial parts are divided. The upper part of your spine is the spine. The medulla oblongata is where the cranial part begins.
The parts meet briefly before the nerve in your neck moves. The vagus nerve is followed by the cranial part.
XII. Hypoglossal nerve
Your hypoglossal nerve is the 12th cranial nerve. It’s responsible for the movement of most of the muscles in your tongue.
It starts in the medulla oblongata and goes down into the jaw.
You can help keep your cranial nerves healthy by following some healthy practices.
According to the
- getting about
7 to 9 hoursof quality sleep each night
- not smoking, or if you smoke, quitting smoking if possible
- treating diabetes, if you have it
- treating high blood pressure, if you have it
- eating a heart-healthy diet and aiming to keep your low-density lipoprotein (LDL) cholesterol within a healthy range
- getting regular exercise
The interactive 3D diagram below shows you more about the cranial nerves.
Your brain has 12 cranial nerves that are involved in sensory, motor, and autonomic functions. They are located on the underside of the brain. They are numbered according to their location.