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longest cranial nerve in human body
The vagus nerve is the longest cranial nerve. It contains motor and sensory fibers and, because it passes through the neck and thorax to the abdomen, has the widest distribution in the body.
It contains somatic and visceral afferent fibers, as well as general and special visceral efferent fibers. (See Table 1, below.)
Vagus Nerve Anatomy
The vagus nerve is the longest cranial nerve. It contains motor and sensory fibers and, because it passes through the neck and thorax to the abdomen, has the widest distribution in the body. It contains somatic and visceral afferent fibers, as well as general and special visceral efferent fibers. (See Table 1, below.)
Neuroanatomy, Cranial Nerve 10 (Vagus Nerve)
The vagus nerve (cranial nerve [CN] X) is the longest cranial nerve in the body, containing both motor and sensory functions in both the afferent and efferent regards. The nerve travels widely throughout the body affecting several organ systems and regions of the body, such as the tongue, pharynx, heart, and gastrointestinal system. Because of the wide distribution of the nerve throughout the body, there are several clinical correlations of the vagus nerve.
Structure and Function
The vagus nerve has its origin in the medulla oblongata and exits the skull via the jugular foramen. There are two ganglia on the vagus nerve (superior and inferior) as it exits the jugular foramen; the spinal accessory nerve (CN XI) joins the vagus nerve just distal to the inferior ganglion.
The origin of cell bodies for the vagus nerve originates from the nucleus ambiguous; the dorsal motor nucleus of X, superior ganglion of X, and the inferior ganglion of X.
The nerve fibers from the nucleus ambiguous are efferent
special visceral (ESV) fibers which help to mediate swallowing and phonation. Fibers originating from the dorsal motor nucleus of X are efferent, general visceral (EGV) fibers which provide the involuntary muscle control of organs it innervates (cardiac, pulmonary, esophageal) .
and innervation to glands throughout the gastrointestinal tract. Superior ganglion of X provides afferent general somatic innervation to the external ear and tympanic membrane.
The inferior ganglion of X provides afferent general visceral fibers to the carotid and aortic bodies;
the efferent fibers of this nerve travel to the nucleus tractus solitarius; the inferior ganglion also provides taste sensation to the pharynx and relays this information to the nucleus tractus solitarius
What are cranial nerves?
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 their function or structure.
Each nerve also has a corresponding Roman numeral between I and XII. This is based off 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.
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 olfactory nerve transmits sensory information to your brain regarding smells that you encounter.
When you inhale aromatic molecules, they dissolve in a moist lining at the roof of your nasal cavity, called the olfactory epithelium. This 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.
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 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 transmitted 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.
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.
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.
The trochlear nerve controls your superior oblique muscle. This is the muscle that’s responsible for 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.
The trigeminal nerve is the largest of your cranial nerves and has both sensory and motor functions.
The trigeminal nerve has three divisions, which are:
- 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 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 is only distributed into the mandibular division.
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 abducent 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:
- moving muscles used for facial expressions as well as some muscles in your jaw
- providing a sense of taste for most of your tongue
- supplying glands in your head or neck area, such as salivary glands and tear-producing glands
- communicating sensations from the outer parts of your ear
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.
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The vagus nerve, historically cited as the pneumogastric nerve, is the tenth cranial nerve or CN X, and interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It actually comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively in the singular.