Your cranial nerves are pairs of nerves that connect your brain to different parts of your head, neck, and trunk. There are 12 of them, each named for its function or structure. Show
Their functions are usually categorized as being either sensory or motor. Sensory nerves are involved with your senses, such as smell, hearing, and touch. Motor nerves control the movement and function of muscles or glands. Keep reading to learn more about each of the 12 cranial nerves and how they function. The cranial nerves are located within the skull, on the underside of the brain. They begin in the nuclei of the brain and travel different paths to help control your senses and movement. Each nerve has a corresponding Roman numeral between I and XII. This is based on their location from front to back. For example, your olfactory nerve is closest to the front of your head, so it’s designated as I. Conditions and disorders of the cranial nerves can affect processes that involve vision, smell, hearing, speaking, and balance. They can also change the way you perceive sensation on the face and prevent or alter the movement of the head, eyes, neck, shoulders, throat, and tongue. Cranial nerve palsy affects a motor nerve — one that controls movement. If a sensory nerve is affected, it can cause pain or reduced sensation. Conditions and disorders that affect the cranial nerves can include:
Injury, trauma, and whiplash can also cause damage to cranial nerves. Disorders affecting the cranial nerve can cause different symptoms, depending on which nerve is affected. If you experience pain in your face, a change in your ability to alter the movement of your head or eye, or changes in sensation relating to vision, hearing, smell, balance, or speaking, you may have a cranial nerve disorder. Symptoms of cranial nerve damage can include:
I. Olfactory nerveThe olfactory nerve sends sensory information to your brain about smells that you encounter. When you inhale molecules with a scent, known as aromatic molecules, they dissolve in a moist lining at the roof of your nasal cavity. This lining is called the olfactory epithelium. It stimulates receptors that generate nerve impulses that move to your olfactory bulb. Your olfactory bulb is an oval-shaped structure that 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 nerveThe 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 present in smaller numbers. They have a lower light sensitivity than rods and are more involved with color vision. 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. Through each optic tract, the nerve impulses eventually reach your visual cortex, which then processes the information. Your visual cortex is located in the back part of your brain. III. Oculomotor nerveThe oculomotor nerve has two different motor functions: muscle function and pupil response.
This nerve originates in the front part of your midbrain, which is a part of your brainstem. It moves forward from that area until it reaches the area of your eye sockets. IV. Trochlear nerveThe trochlear nerve controls your superior oblique muscle. This is the muscle that’s in charge of downward, outward, and inward eye movements. It emerges from the back part of your midbrain. Like your oculomotor nerve, it moves forward until it reaches your eye sockets, where it stimulates the superior oblique muscle. V. Trigeminal nerveThe trigeminal nerve is the largest of your cranial nerves and has both sensory and motor functions. The trigeminal nerve has three divisions, which are:
The trigeminal nerve originates from a group of nuclei — which is a collection of nerve cells — in the midbrain and medulla regions of your brainstem. Eventually, these nuclei form a separate sensory root and motor root. The sensory root of your trigeminal nerve branches into the ophthalmic, maxillary, and mandibular divisions. The motor root of your trigeminal nerve passes below the sensory root and only connects to the mandibular division. VI. Abducens nerveThe 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 nerveThe facial nerve provides both sensory and motor functions, including:
Your facial nerve has a very complex path. It originates in the pons area of your brainstem, where it has both a motor and sensory root. Eventually, the two nerves fuse together to form the facial nerve. Both within and outside of your skull, the facial nerve branches further into smaller nerve fibers that stimulate muscles and glands or provide sensory information. VIII. Vestibulocochlear nerveYour vestibulocochlear nerve has sensory functions involving hearing and balance. It consists of two parts, the cochlear portion and vestibular portion:
The cochlear and vestibular portions of your vestibulocochlear nerve originate in separate areas of the brain. The cochlear portion starts in an area of your brain called the inferior cerebellar peduncle. The vestibular portion begins in your pons and medulla. Both portions combine to form the vestibulocochlear nerve. IX. Glossopharyngeal nerveThe glossopharyngeal nerve has both motor and sensory functions, including:
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 nerveThe vagus nerve is a very diverse nerve. It has both sensory and motor functions, including:
Out of all of the cranial nerves, the vagus nerve has the longest pathway. It extends from your head all the way into your abdomen. It originates in the part of your brainstem called the medulla. XI. Accessory nerveYour 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. It’s divided into two parts: spinal and cranial. The spinal portion originates in the upper part of your spinal cord. The cranial part starts in your medulla oblongata. These parts meet briefly before the spinal part of the nerve moves to supply the muscles of your neck. The cranial part follows the vagus nerve. XII. Hypoglossal nerveYour 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 moves down into the jaw, where it reaches the tongue. Explore this interactive 3D diagram below to learn more about the 12 cranial nerves. Your brain has 12 cranial nerves that are involved with your sensory, motor, and autonomic functions. They’re located inside of your skull on the underside of the brain. They’re numbered according to their location. Which nerves carries sensory information?The sensory (afferent) division carries sensory signals by way of afferent nerve fibers from receptors in the central nervous system (CNS).
Which cranial nerves carries only sensory fibers?In addition, some cranial nerves carry only sensory fibers: I, II, and VIII. Cranial nerves that serve almost entirely as motor tracts are III, IV, VI, XI, and XII.
Which cranial nerve carry only motor information?Four cranial nerves are purely motor–the 3rd, 4th, 6th, and 12th. Cranial nerve 3 is called the oculomotor. It supplies four of the six muscles that move the eye. It also supplies the eyelid raising muscle and the muscles that focus the lens and constrict the pupil.
Do all cranial nerves carry sensory information?In contrast to the spinal nerves, however, not all cranial nerves carry both sensory and motor information. In fact, three cranial nerves carry purely sensory information and four cranial nerves carry almost entirely somatic motor information.
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