The 12 Cranial Nerves: What are They and What Do They Do?
The cranial nerves are a set of 12 pairs of nerves that connect your brain to the rest of your body. They carry information from the central nervous system to the peripheral nervous system and vice versa. We'll give you a summary of what cranial nerves are, how many cranial nerves there are, and what they do.
Cranial nerves are a part of the peripheral nervous system. There are 12 cranial nerves in all, each with different functions. Some cranial nerves control facial muscle movement, others relay sensory information from the eyes or ears, and still, others help regulate vital body functions such as breathing and swallowing.
The cranial nerves play a major role in sensory perception, facial expression, eye movement, balance and coordination of the head and neck regions, as well as speech production. Some cranial nerve functions include olfaction, sense of taste, vision also called ophthalmic, sense of smell or nasal, hearing and balance or auditory, facial sensation and movement also called maxillary, mandibular, and cervical, and lastly speech and swallowing which can be called facial, and hypoglossal.
Cranial nerve damage can result in a wide variety of symptoms depending on the nerve involved. For example, cranial nerve VII, or the facial nerve, controls the muscles of facial expression. Damage to this nerve can cause facial palsy which is a weakness or paralysis on one side of the face, resulting in a droopy eyelid, a crooked smile, and difficulty chewing and swallowing.
Cranial nerves should not be confused with spinal nerves, which are also part of the peripheral nervous system. The spinal nerves exit the cranial cavity through openings between the cranial bones, but they do not go to your brain. They travel down from your skull and branch out to all areas of the body before connecting with spinal cord segments that then lead back up into the brain stem or down into the rest of your spine.
The 12 cranial nerves and their functions are as follows:
- I. Olfactory nerve: This cranial nerve carries smell information from the nose to the brain. It does this by connecting the olfactory receptors in the nose with the olfactory bulb, a part of the brain that is responsible for processing smells.
- II. Optic nerve: The optic nerve carries visual information from the eyes to the brain by connecting the retina with the optic disc, which is part of the brain.
- III. Oculomotor nerve: Some of the cranial nerves involved in eye movement are called the oculomotor nerve. This cranial nerve controls some of the eye muscles, including the pupil, the iris, and the lens.
- IV. Trochlear nerve: Yet another set of cranial nerves involved in eye movement are called the trochlear nerve. This cranial nerve controls the superior oblique muscle that moves the eyes downwards, inwards, and outwards.
- V. Trigeminal nerve: The trigeminal nerve carries sensory information from the face to the brain and is also involved in three major functions: ophthalmic, maxillary, and mandibular. The ophthalmic function sends sensory information from the upper portion of your face including your scalp, forehead, and upper eyelids. The maxillary function sends sensory information from the middle portion of your face including your cheeks, nasal cavity, and upper lip. Unlike the other two, the mandibular has two functions in that it sends sensory information from the bottom portion of your face including your ears, bottom lip, and chin. It also serves the motor function of controlling the muscles in your jaw and ears. This is also the cranial nerve that controls the muscles of mastication or chewing and it is the largest of the cranial nerves.
- VI. Abducens nerve: This cranial nerve plays a role in controlling the lateral rectus muscle of your eyes. These cranial nerve functions are responsible for moving your eye outwards, away from your nose.
- VII. Facial nerve: The cranial facial nerve has two functions also, both sensory functions and motor functions. It provides the movement of muscles in your jaw and the side of your face for facial expressions and also provides sensory information from the outer part of your ear. It controls taste sensation on the anterior two-thirds of your tongue and secretes saliva from the parotid glands while also controlling tear production.
- VIII. Vestibulocochlear nerve: This cranial nerve sends sensory information from both your inner ear and balance organs to the brain. This information is responsible for your sense of balance and hearing. Damage to this cranial nerve can result in vertigo or a sense of dizziness.
- IX. Glossopharyngeal nerve: This cranial nerve is responsible for carrying sensory information from your tongue, pharynx, and middle ear. It also controls the muscles of the soft palate and the throat.
- X. Vagus nerve: This cranial nerve is responsible for a lot of different things, both sensory and motor. It carries sensory information from your larynx, pharynx, and torso, including your heart and intestines. It also controls muscles of your throat and digestive tract that go down your torso while providing the sensory needed for taste on the back of your tongue.
- XI. Accessory nerve: The cranial spinal accessory nerve works by controlling the muscles of your neck and shoulder area, specifically trying to move your head.
- XII. Hypoglossal nerve: This cranial nerve is responsible for controlling the muscles of your tongue and helps with speech and swallowing.
Now that you know a little more about cranial nerves, what they do, and some of the functions they control, you can see how important they are for overall health and well-being. When one of these cranial nerves is damaged or not working properly, it can cause problems with movement, hearing, balance, taste, and other functions. If you experience any problems with any of your cranial nerves, be sure to speak to a doctor. They will be able to help diagnose the problem and provide the necessary treatment.
The twelve cranial nerves are responsible for relaying sensory information from all over your body to the brain. They also play a role in helping you coordinate many important voluntary movements like chewing or facial expressions. So, the next time you're having a conversation or trying to eat something with a nice smile, remember that it's all thanks to those cranial nerves. If you have any further questions regarding your cranial nerves, we recommend talking to your doctor or healthcare provider.
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