As the late Lucy Gealy, a woman with a postoperative facial deformity due to surgery for a malignancy, explained: Testing the Gag Reflex:. As the cable moves away from the spinal cord, wires split off and head to different destinations. Contraction pulls normal tissue into the open area to achieve coverage. Have the seated patient steadily press their lower extremity into your hand against resistance.
Structure and Function
The parasympathetic side, which the vagus nerve is heavily involved in, decreases alertness, blood pressure, and heart rate, and helps with calmness, relaxation, and digestion. As a result, the vagus nerve also helps with defecation, urination, and sexual arousal. Stimulation of the vagus nerve is a medical procedure that is used to try to treat a variety of conditions.
It can be done either manually or through electrical pulses. The effectiveness of vagus nerve stimulation has been tested through clinical trials. In , the FDA allowed the use of vagus nerve stimulation for refractory epilepsy. This involves a small, electrical device, similar to a pacemaker, being placed in a person's chest. A thin wire known as a lead runs from the device to the vagus nerve. The device is placed in the body by surgery under general anesthetic.
It then sends electrical impulses at regular intervals, throughout the day, to the brain via the vagus nerve to reduce the severity, or even stop, seizures. People using this form of treatment should always tell their doctor if they are having any problems as there may be ways to reduce or stop these. In , the FDA approved the use of vagus nerve stimulation as a treatment for depression.
It has also been found to help with the following conditions:. With the vagus nerve having pathways to almost every organ in the body, researchers are looking to see if stimulation can help other conditions. In the case of rheumatoid arthritis, which affects 1. Individuals who had failed to respond to other treatment reported significant improvements, while no serious adverse side effects were noted.
This was considered a real breakthrough in how vagus nerve stimulation might not only treat rheumatoid arthritis but other inflammatory diseases, such as Crohn's, Parkinson's, and Alzheimer's.
Article last reviewed by Wed 28 June All references are available in the References tab. Editors of Encyclopedia Britannica. Current Behavioral Neuroscience Reports , 1 2 , Vagus nerve stimulation inhibits cytokine production and attenuates disease severity in rheumatoid arthritis.
PNAS , 29 , The vagus nerve CN X. Vagus nerve stimulation VNS therapy for epilepsy. What happens in vagus. MNT is the registered trade mark of Healthline Media. Any medical information published on this website is not intended as a substitute for informed medical advice and you should not take any action before consulting with a healthcare professional.
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Reviewed by Stacy Sampson, DO. Table of contents What is the vagus nerve? Stimulation Further research and considerations. The vagus nerve is one of the cranial nerves that connect the brain to the body. Vagus nerve stimulation for epilepsy may have some side effects including sore throat and difficulty swallowing.
Symptoms, causes, and treatment of epilepsy. Therefore, the muscles of the forehead i. Individuals can typically wrinkle their foreheads and close their eyes with unilateral lesions of the cerebral cortex.
On the other hand, as a result of supranuclear lesions, patients will not be able to raise the corners of their mouths or move their lips contralateral to the lesions. Thus, this distinction is characteristic of an upper motor neuron lesion with respect to the facial nerve and clearly different from a lower motor neuron lesion of this cranial nerve described in the following section.
A lower motor neuron paralysis may result from damage to the facial nerve, its peripheral branches, or the facial nucleus. The patient shows little or no facial expression. If muscle tone is lost, the affected side of the face may take on the appearance of an empty, smooth, mask-like expression.
The angle of the mouth on the affected side may also droop, and, when attempting to display their teeth, patients cannot bring the angle of the mouth laterally. Speech may also be affected, and patients are unable to whistle. These patients also cannot close the affected eye, and the eye-blink reflex is lost. Moreover, lesions of the facial nerve can also produce hyperacusis, which is an increase in sensitivity to sounds on the side of the lesion, because of a paralysis of the stapedius muscle.
These effects are commonly due to an external blow to the face or overexposure to cold weather and affect peripheral branches of the facial nerve after the nerve exits the skull. The effects of damage to the facial nerve upon sensory systems include primarily loss of taste sensation from the anterior two thirds of the tongue and loss of general sensation from the back of the ear and external auditory meatus.
The trigeminal nerve is very large and can be easily seen upon its emergence at the level of the middle of the pons near the position of emergence of the middle cerebellar peduncle. It contains a massive GSA component, which provides most of the somatosensory inputs from the region of the anterior two thirds of the head i. The SVE component, which innervates skeletal muscle from the mesenchyme of the first branchial arch, is much smaller in size than the sensory branches but provides motor innervation of the muscles of mastication.
Origin, Distribution, and Function. The cell bodies of the GSA component of the trigeminal nerve are located in the trigeminal also called the Gasserian or semilunar ganglion. The ganglion itself is located on a cleft of the petrous bone lateral to the cavernous sinus.
There are three principal divisions of the sensory components of the trigeminal nerve: Concerning the peripheral distribution of the ophthalmic division, nerve fibers supply the forehead, cornea, upper part of the eyelid, dorsal surface of the nose, and mucous membranes of the nasal and frontal sinuses.
The central processes of this branch enter the skull through the superior orbital fissure. The peripheral distribution of the maxillary division includes the lateral surface of the nose; upper teeth; hard palate; upper cheek; and mucous membranes of the upper teeth, nose, and roof of the mouth. This division enters the skull through the foramen rotundum. The third division, called the mandibular division, supplies the lower jaw, lower teeth, chin, parts of the posterior cheek, temple, external ear, anterior two thirds of the tongue, and floor of the mouth.
All branches of the trigeminal nerve innervate the dura. The mandibular division enters the skull through the foramen ovale. FIGURE A Distribution of the sensory general somatic afferent and motor special visceral efferent components of the trigeminal nerve, including the sensory arrangement of the sensory divisions of the trigeminal nerve.
Fibers conveying pain and thermal sensations are indicated in red; fibers conveying tactile and pressure sensations are indicated in blue; the motor root is indicated in black on the left side of figure, and the ascending lateral spinothalamic tract is shown in black on the right side of figure.
As noted earlier, the central processes of each of the divisions of the trigeminal nerve enter the skull through different foramina. However, upon entry into the pons, these first-order fibers may take one of two primary directions: Some trigeminal pain fibers associated with the posterior aspect of the face may even extend as far caudally as C2 of the spinal cord.
From both the main sensory and spinal nucleus, second-order neurons arise, and their axons are distributed to the VPM of the contralateral thalamus. Fibers that arise from the spinal nucleus are distributed to the contralateral VPM via the ventral trigemi-nothalamic tract. Fibers that issue from the main sensory nucleus are distributed bilaterally to the VPM. Those fibers that pass ipsilaterally do so in the dorsal trigeminothalamic tract, whereas fibers passing contralaterally do so in the ventral trigeminothalamic tract.
Collectively, it would certainly appear that the ventral trigeminothalamic tract is far more significant in transmitting sensory information from the trigeminal system to the thalamus. Third-order sensory fibers arising from the VPM then project to the ipsilateral face region of the postcentral gyrus Fig.
Both experimental and clinical studies have revealed that the fibers mediating pain and temperature sensation are distributed to the caudal aspect of the spinal nucleus, whereas conscious proprioception, pressure, and tactile sensation are distributed through the main sensory nucleus and possibly parts of the spinal nucleus.
Knowledge of the dissociation of pain fibers from other forms of somatosen-sory inputs has been applied clinically; for example, severing the sensory root fibers after they enter the spinal tract of CN V can alleviate intense forms of trigeminal neuralgia. The receptors for some of the fibers contained within the mandibular branch are muscle spindles.
These fibers mediate unconscious proprioceptive signals to the brain and terminate in the mesencephalic nucleus of CN V, which represents part of the first-order sensory neuron. For this reason, the unusual feature is that the mesencephalic nucleus, which appears to be similar in appearance to cells of the Gasserian ganglion, does not lie outside the CNS but, instead, is situated within it.
Although the mesen-cephalic nucleus is functionally similar to the dorsal root ganglion, it represents an anomaly in that it is the only sensory structure whose first-order cell bodies lie within the CNS and not in the periphery. Similar to neurons of the dorsal root ganglion, there is a second limb of the axon emanating from the mesencephalic nucleus, which transmits signals away from it to the motor nucleus of CN V. This provides the basis for a monosynaptic reflex that is sometimes referred to as the jaw-jerk reflex.
This is a stretch reflex because it occurs after stimulation of muscle spindles in the masseter muscle of the lower jaw.
Afferent impulses 1a fibers cause a discharge of neurons in the motor nucleus, which is then followed by a jaw-closing response. Other fibers from the mesencephalic nucleus project to the cerebellum, thus providing the cerebellum with information concerning the status of muscles of the lower jaw.
From this discussion, it is reasonable to conclude that fibers of the trigeminal system share parallel relationships with several of the sensory pathways of the spinal cord. For example, the pathways that mediate pain and temperature sensation from the head to the thalamus via the ventral trigeminothalamic tract can be likened to the lateral spi-nothalamic tract, the pathways that mediate conscious proprioception and tactile inputs to the thalamus via the dorsal trigeminothalamic tract can be likened to the medial lemniscus, and the pathway involving inputs to the mesencephalic nucleus and its projection to the cerebellum shares similarities with the posterior spinocerebel-lar tract.