The twelve cranial nerves are typically covered in introductory anatomy courses, and memorizing their names is facilitated by numerous mnemonics developed by students over the years of this practice.
Three of the nerves are strictly responsible for special senses whereas four others contain fibers for special and general senses. The olfactory, optic, and vestibulocochlear nerves (cranial nerves I, II, and VIII) are dedicated to four of the special senses: smell, vision, equilibrium, and hearing, respectively.
The optic nerves from both sides enter the cranium through the respective optic canals and meet at the optic chiasm at which fibers sort such that the two halves of the visual field are processed by the opposite sides of the brain.
The vestibulocochlear nerve (CN VIII) carries both equilibrium and auditory sensations from the inner ear to the medulla. Balance or hearing deficits may be the result of damage to the middle or inner ear structures.
Tests of equilibrium are important for coordination and gait and are related to other aspects of the neurological exam. The trigeminal system of the head and neck is the equivalent of the ascending spinal cord systems of the dorsal column and the spinothalamic pathways.
Subtests for the sensory component of the trigeminal system are the same as those for the sensory exam targeting the spinal nerves. The three nerves that control the extraocular muscles are the oculomotor, trochlear, and abducens nerves, which are the third, fourth, and sixth cranial nerves. Coordinated movement of both eyes through different nuclei requires integrated processing through the brain stem. Testing eye movement is simply a matter of having the patient track the tip of a pen as it is passed through the visual field.
The final aspect of testing eye movements is to move the tip of the pen in toward the patient’s face. A crucial function of the cranial nerves is to keep visual stimuli centered on the fovea of the retina. An iconic part of a doctor’s visit is the inspection of the oral cavity and pharynx, suggested by the directive to “open your mouth and say ‘ah.’” This is followed by inspection, with the aid of a tongue depressor, of the back of the mouth, or the opening of the oral cavity into the pharynx known as the fauces. The facial and glossopharyngeal nerves are also responsible for the initiation of salivation. The hypoglossal nerve is the motor nerve that controls the muscles of the tongue, except for the palatoglossus muscle, which is controlled by the vagus nerve.
The accessory nerve, also referred to as the spinal accessory nerve, innervates the sternocleidomastoid and trapezius muscles ([link]). To test these muscles, the patient is asked to flex and extend the neck or shrug the shoulders against resistance, testing the strength of the muscles. The Pupillary Light Response The autonomic control of pupillary size in response to a bright light involves the sensory input of the optic nerve and the parasympathetic motor output of the oculomotor nerve. If light in the right eye only causes the left pupil to constrict, the direct reflex is lost and the consensual reflex is intact, which means that the right oculomotor nerve (or Eddinger–Westphal nucleus) is damaged.
The cranial nerves can be separated into four major groups associated with the subtests of the cranial nerve exam. The olfactory, optic, and vestibulocochlear nerves are strictly sensory nerves for smell, sight, and balance and hearing, whereas the trigeminal, facial, and glossopharyngeal nerves carry somatosensation of the face, and taste—separated between the anterior two-thirds of the tongue and the posterior one-third. The oculomotor, trochlear, and abducens nerves control the extraocular muscles and are connected by the medial longitudinal fasciculus to coordinate gaze. The trigeminal nerve controls the muscles of chewing, which are tested for stretch reflexes. Movement of the head and neck using the sternocleidomastoid and trapezius muscles is controlled by the accessory nerve. She has just demonstrated voluntary control by closing her eyes, but when he provides the resistance that she needs to hold tight against, she has already relaxed the muscles enough for him to pull them open.
Without olfactory sensation to complement gustatory stimuli, food will taste bland unless it is seasoned with which substance? If the person already has problems focusing on far objects, and wears corrective lenses to see farther objects, then as accommodation changes, focusing on a reading surface might still be in their naturally near-sighted range. The medulla is where the accessory nerve, which controls the sternocleidomastoid muscle, and the hypoglossal nerve, which controls the genioglossus muscle, are both located. Sign up and receive info about new releases, special promotions and exclusive deals right in your inbox! In Frankenstein effort, Gregoire Courtine, a researcher at the Ecole Polytechnique Federale in Lausanne, Switzerland, has developed a process that has helped a paralyzed rat in walking with a precise cadence.
With an aim of resurrecting life in the paralyzed limbs of people, the researcher has zapped spinal cords with electrical pulses.
Although doctors at the University of Louisville, California and Los Angeles, were working on epidural stimulation, which means implanting device for stimulating spinal cords, on four men, however, the effort did allow the patients to regain their limb movement in terms of exercises but the men were not able to walk independently. Limitation of epidural stimulation was due to the inability of electrical pulses to generate coordinated movements, which are complex by nature. Courtine also disclosed that he is looking forward to create a brain-machine interface, so that electrodes can be mounted inside the motor cortex of brain for recording intended movements that would further allow users to control their spinal stimulator. Pooja Kashyap likes reading and writing on topics related to scientific research and technology. Our brain is busy making sense of the data it collects in our over-stimulating environments. Applying muscular strength to sit or stand tall and lengthen upward with our torso requires both mental and physical energy. When we slouch, our head juts forward and tilts down, flexing anterior neck muscles and over stretching trapezius, splenius, and longissimus. The pectoralis major, pectoralis minor, subclavius, and sternalis muscles become hypertonic (excessively strong) and pull shoulder blades forward with an anterior rotation in the upper arm bones.
Nerves in our neck, collarbones, torso, between the ribs, and through our core can become impinged, lessening their ability to relay signals between our brain and body.
Clients and students walk away after completing these exercises with a greater ability to inhale deeply into the upper chest and feel a decrease of tension in their neck. Breathe and visualize that you are opening your front ribcage and reversing your slouching posture. Exhale while contracting your glute muscles toward your upper thighbones, creating length in your in low back and sacral-iliac joint. Begin with your elbows bent at ninety degrees and squeezing gently at side of your ribcage. Breathe with the following in mind: synchronize your breathing with your movement to strengthen your longissimus, illiocostalis, trapezius, and splenius, and expand your ribcage. Begin with your feet on the floor, knees bent, and hands holding your hips until you feel balanced. Feel your chest muscles stretching and your neck and head relaxing on the ball to stretch the front of your spine.
The resulting mental clarity will also help with daily productivity and keeping a positive outlook on life.
Willow Ryan specializes in helping people rewrite past stories from a present perspective to move forward for personal renaissance. But knowing the names of the nerves in order often leaves much to be desired in understanding what the nerves do.
Taste sensation is relayed to the brain stem through fibers of the facial and glossopharyngeal nerves. The patient should be able to recognize the smell of coffee or mint, indicating the proper functioning of the olfactory system. The Snellen chart ([link]) demonstrates visual acuity by presenting standard Roman letters in a variety of sizes. Deficits in visual field perception often suggest damage along the length of the optic pathway between the orbit and the diencephalon. Meniere's disease is a disorder that can affect both equilibrium and audition in a variety of ways. The Rinne test involves using a tuning fork to distinguish between conductive hearing and sensorineural hearing.
Somatosensation of the face is conveyed along the nerve to enter the brain stem at the level of the pons. As the name suggests, the abducens nerve is responsible for abducting the eye, which it controls through contraction of the lateral rectus muscle. In the midbrain, the superior colliculus integrates visual stimuli with motor responses to initiate eye movements. Movements are often at an angle, so some horizontal components are necessary, adding the medial and lateral rectus muscles to the movement.
This may appear similar to testing visual field deficits related to the optic nerve, but the difference is that the patient is asked to not move the eyes while the examiner moves a stimulus into the peripheral visual field. As visual stimuli move closer to the face, the two medial recti muscles cause the eyes to move in the one nonconjugate movement that is part of gaze control.
The vestibulo-ocular reflex (VOR) coordinates all of the components ([link]), both sensory and motor, that make this possible. Whereas this portion of a medical exam inspects for signs of infection, such as in tonsillitis, it is also the means to test the functions of the cranial nerves that are associated with the oral cavity. Testing this is as simple as introducing salty, sour, bitter, or sweet stimuli to either side of the tongue. Neurons in the salivary nuclei of the medulla project through these two nerves as preganglionic fibers, and synapse in ganglia located in the head.
When both the sternocleidomastoids contract, the head flexes forward; individually, they cause rotation to the opposite side. When light hits the retina, specialized photosensitive ganglion cells send a signal along the optic nerve to the pretectal nucleus in the superior midbrain. Damage to the right oculomotor connections will be evident when light is shined in the left eye. First are the sensory nerves, then the nerves that control eye movement, the nerves of the oral cavity and superior pharynx, and the nerve that controls movements of the neck.
Testing conjugate gaze is as simple as having the patient follow a visual target, like a pen tip, through the visual field ending with an approach toward the face to test convergence and accommodation. Motor functions of the facial nerve are usually obvious if facial expressions are compromised, but can be tested by having the patient raise their eyebrows, smile, and frown. Flexing of the neck and strength testing of those muscles reviews the function of that nerve.
She needs to squeeze them tighter to demonstrate the strength she has in the orbicular oculi.


If a person is already myopic (near-sighted), why would corrective lenses not be necessary to read a book or computer screen? The weakness of the left side of the neck, and the tendency of the tongue to point to that side, both show that the damage is on the left side of the brain stem. The neuroscientist has employed electronics to reinstate realistic movements to the disabled animal. These undulations will substitute the commands being sent by brain in normal condition however, the signals are disrupted with an injury in the spinal cord.
Along with that, these stimulators were manually controlled, which is quite different from Courtine’s system. In order to prove this, the researchers severed spinal cords of couple of rats and then mounted electrodes on the lower part of their spine.
He said that currently, epidural stimulation technology is at its infancy and the future versions must be in a position to balance out the automated routines with the actions decided by the user added Hunter Peckham researcher at Case Western Reserve University.
In this article, I aim to shed some light on the topic and explain why we should pay attention to our posture and how to reverse the slouch. Lights, sounds, smells, terrain all require a part of our brain to process and guide our actions. This causes the sternum and chest to pull inward toward the front spine and down toward the pelvis. The phrenic nerve is an important nerve branching off the spinal cord between the third and fifth cervical vertebrae. What I observe is that they are standing upright, with shoulders retracted back and down away from their neck.
This indicates the diaphragm is drawing down into your mid torso and pressurizing your lungs to receive deeper breaths. It helps build and maintain the strength required for our diaphragm and lungs to provide our brain and body with adequate air to stay alert and responsive to external stimuli.
The nerves can be categorized by functions, and subtests of the cranial nerve exam can clarify these functional groupings.
Four nerves connect to muscles of the face, oral cavity, and pharynx, controlling facial expressions, mastication, swallowing, and speech. The vagus nerve (cranial nerve X) has autonomic functions in the thoracic and superior abdominal cavities. The trigeminal nerve is a mixed nerve that carries the general somatic senses from the head, similar to those coming through spinal nerves from the rest of the body. Loss of the sense of smell is called anosmia and can be lost following blunt trauma to the head or through aging. Anosmia means that food will not seem to have the same taste, though the gustatory sense is intact, and food will often be described as being bland. The result of this test is a rough generalization of the acuity of a person based on the normal accepted acuity, such that a letter that subtends a visual angle of 5 minutes of an arc at 20 feet can be seen. For example, loss of peripheral vision may be the result of a pituitary tumor pressing on the optic chiasm ([link]). Problems with balance, such as vertigo, and deficits in hearing may both point to problems with the inner ear. The patient can suffer from vertigo, a low-frequency ringing in the ears, or a loss of hearing.
Balance and equilibrium, as tested by the Romberg test, are part of spinal and cerebellar processes and involved in those components of the neurological exam, as discussed later. Conductive hearing relies on vibrations being conducted through the ossicles of the middle ear. Synapses of those axons, however, are distributed across nuclei found throughout the brain stem. A cotton-tipped applicator, which is cotton attached to the end of a thin wooden stick, can be used easily for this. The trochlear nerve controls the superior oblique muscle to rotate the eye along its axis in the orbit medially, which is called intorsion, and is a component of focusing the eyes on an object close to the face.
The paramedian pontine reticular formation (PPRF) will initiate a rapid eye movement, or saccade, to bring the eyes to bear on a visual stimulus quickly.
The rapid movement of the eyes used to locate and direct the fovea onto visual stimuli is called a saccade.
When the two eyes move to look at something closer to the face, they both adduct, which is referred to as convergence. If the head rotates in one direction—for example, to the right—the horizontal pair of semicircular canals in the inner ear indicate the movement by increased activity on the right and decreased activity on the left. The patient should respond to the taste stimulus before retracting the tongue into the mouth. The parasympathetic fibers of the facial nerve synapse in the pterygopalatine ganglion, which projects to the submandibular gland and sublingual gland.
The extrinsic muscles of the tongue are connected to other structures, whereas the intrinsic muscles of the tongue are completely contained within the lingual tissues.
A neuron from this nucleus projects to the Eddinger–Westphal nuclei in the oculomotor complex in both sides of the midbrain. Light shined in one eye causes a constriction of that pupil, as well as constriction of the contralateral pupil. In that case, the direct reflex is intact but the consensual reflex is lost, meaning that the left pupil will constrict while the right does not.
General senses can be tested through sensory discrimination of touch versus painful stimuli.
Along with the vestibular functions of the eighth nerve, the vestibulo-ocular reflex stabilizes gaze during head movements by coordinating equilibrium sensations with the eye movement systems.
Movements of the tongue, soft palate, or superior pharynx can be observed directly while the patient swallows, while the gag reflex is elicited, or while the patient says repetitive consonant sounds. It delivers a complete set of brain stimulation exercises designed to keep your brain sharp, healthy and youthful, plus give you a more active and balanced lifestyle.
By filming on rats, the Swiss researchers noted that their innovative approach gave synchronized stepping movements. The rodents were then administered with serotonin agonist, a drug that allows spinal cord to communicate with the lower limbs, since it failed to coordinate after the injury. Mental stimulation has benefits, but too much is taxing on both our brain and postural alignment.
Vertebrae can be easily pulled out of alignment, creating curvature imbalances along the spine and in some cases causing nerve impingement. This adds more pressure on the diaphragm and inhibits its ability for an unrestricted inhalation. It runs along the neck and branches off to areas around the heart, pericardium, lungs, and diaphragm. I recommend it to most clients and teach it in the majority of my Forrest yoga classes to improve posture, alignment, and breathing capacity.
Additionally, they speak with more energy, which I would deduce is a result of alleviating breathing restrictions and increasing pulmonary circulation. Four nerves make up the cranial component of the parasympathetic nervous system responsible for pupillary constriction, salivation, and the regulation of the organs of the thoracic and upper abdominal cavities.
The special senses are served through the cranial nerves, as well as the general senses of the head and neck. The pituitary, seated in the sella turcica of the sphenoid bone, is directly inferior to the optic chiasm.
Sensorineural hearing is the transmission of sound stimuli through the neural components of the inner ear and cranial nerve. The mesencephalic nucleus processes proprioceptive information of the face, which is the movement and position of facial muscles. The wood of the applicator can be snapped so that a pointed end is opposite the soft cotton-tipped end.
The oculomotor nerve controls all the other extraocular muscles, as well as a muscle of the upper eyelid.
These areas are connected to the oculomotor, trochlear, and abducens nuclei by the medial longitudinal fasciculus (MLF) that runs through the majority of the brain stem. The examiner is watching for conjugate movements representing proper function of the related nuclei and the MLF. To keep the stimulus in focus, the eye also needs to change the shape of the lens, which is controlled through the parasympathetic fibers of the oculomotor nerve. The information is sent to the abducens nuclei and oculomotor nuclei on either side to coordinate the lateral and medial rectus muscles.
Stimuli applied to specific locations on the tongue will dissolve into the saliva and may stimulate taste buds connected to either the left or right of the nerves, masking any lateral deficits. The parasympathetic fibers of the glossopharyngeal nerve synapse in the otic ganglion, which projects to the parotid gland.
While examining the oral cavity, movement of the tongue will indicate whether hypoglossal function is impaired. These strength tests are common for the skeletal muscles controlled by spinal nerves and are a significant component of the motor exam. Neurons in this nucleus give rise to the preganglionic parasympathetic fibers that project through the oculomotor nerve to the ciliary ganglion in the posterior orbit. Shining a penlight in the eye of a patient is a very artificial situation, as both eyes are normally exposed to the same light sources. The motor control of the gag reflex is largely controlled by fibers in the vagus nerve and constitutes a test of that nerve because the parasympathetic functions of that nerve are involved in visceral regulation, such as regulating the heartbeat and digestion.
When we are well rested, strong and flexible, we remain more upright, with good spinal extension.
Finally, one nerve controls the muscles of the neck, assisting with spinal control of the movement of the head and neck.
The movement of the eyes, face, tongue, throat, and neck are all under the control of cranial nerves. The neurons in the olfactory epithelium have a limited life span, and new cells grow to replace the ones that die off. Testing the extent of the visual field means that the examiner can establish the boundaries of peripheral vision as simply as holding their hands out to either side and asking the patient when the fingers are no longer visible without moving the eyes to track them. The axons that decussate in the chiasm are from the medial retinae of either eye, and therefore carry information from the peripheral visual field.
The vestibule is the portion for equilibrium, composed of the utricle, saccule, and the three semicircular canals.


Additionally, within a single patient, the symptoms and signs may change as the disease progresses. A vibrating tuning fork is placed on the mastoid process and the patient indicates when the sound produced from this is no longer present. It is the sensory component of the jaw-jerk reflex, a stretch reflex of the masseter muscle. The cotton end provides a touch stimulus, while the pointed end provides a painful, or sharp, stimulus. Movements of the two eyes need to be coordinated to locate and track visual stimuli accurately. The MLF allows for conjugate gaze, or the movement of the eyes in the same direction, during horizontal movements that require the lateral and medial rectus muscles.
Failure of one eye to abduct while the other adducts in a horizontal movement is referred to as internuclear ophthalmoplegia. The left lateral rectus and right medial rectus muscles will contract, rotating the eyes in the opposite direction of the head, while nuclei controlling the right lateral rectus and left medial rectus muscles will be inhibited to reduce antagonism of the contracting muscles. Along with taste, the glossopharyngeal nerve relays general sensations from the pharyngeal walls.
Salivation in response to food in the oral cavity is based on a visceral reflex arc within the facial or glossopharyngeal nerves. But directed tests, especially for contraction against resistance, require a formal testing of the muscles.
Deficits associated with the accessory nerve may have an effect on orienting the head, as described with the VOR. The postganglionic parasympathetic fibers from the ganglion project to the iris, where they release acetylcholine onto circular fibers that constrict the pupil to reduce the amount of light hitting the retina. Testing this reflex can illustrate whether the optic nerve or the oculomotor nerve is damaged. Save TimeCombine your cardio and brain workouts in one time-saving, brain-and body-pumping session. All the rats were able to move methodically taking several successive steps despite being paralyzed. Our ribcage broadens, torso lengthens and taking deep, full breaths becomes easier without the weighty restrictions of anterior collapse compressing into our lungs. Preganglionic parasympathetic nerve fibers that control pupillary size, salivary glands, and the thoracic and upper abdominal viscera are found in four of the nerves. The axons from these neurons grow back into the CNS by following the existing axons—representing one of the few examples of such growth in the mature nervous system.
Use of the neurological exam subtests for the vestibulocochlear nerve illuminates the changes a patient may go through. Then the fork is immediately moved to just next to the ear canal so the sound travels through the air. The chief nucleus, located in the pons, receives information about light touch as well as proprioceptive information about the mandible, which are both relayed to the thalamus and, ultimately, to the postcentral gyrus of the parietal lobe.
While the patient’s eyes are closed, the examiner touches the two ends of the applicator to the patient’s face, alternating randomly between them.
When moving the eyes to locate an object in the horizontal plane, or to track movement horizontally in the visual field, the lateral rectus muscle of one eye and medial rectus muscle of the other eye are both active. Control of conjugate gaze strictly in the vertical direction is contained within the oculomotor complex.
Also, the superior and inferior rectus muscles are not perfectly oriented with the line of sight. When this occurs, the patient will experience diplopia, or double vision, as the two eyes are temporarily pointed at different stimuli. Accommodation ability changes with age; focusing on nearer objects, such as the written text of a book or on a computer screen, may require corrective lenses later in life. These actions stabilize the visual field by compensating for the head rotation with opposite rotation of the eyes in the orbits. Other stimuli that stimulate salivation are coordinated through the hypothalamus, such as the smell and sight of food.
Along with the spinal accessory nerve, these nerves contribute to elevating the scapula and clavicle through the trapezius, which is tested by asking the patient to shrug both shoulders, and watching for asymmetry. The sympathetic nervous system is responsible for dilating the pupil when light levels are low. If shining the light in one eye results in no changes in pupillary size but shining light in the opposite eye elicits a normal, bilateral response, the damage is associated with the optic nerve on the nonresponsive side. Tests of these functions can provide insight into damage to specific regions of the brain stem and may uncover deficits in adjacent regions. If all of the fibers are sheared when the brain moves within the cranium, such as in a motor vehicle accident, then no axons can find their way back to the olfactory bulb to re-establish connections. Physical inspection of the optic disk, or where the optic nerve emerges from the eye, can be accomplished by looking through the pupil with an ophthalmoscope. The sensory nerves from these two structures travel side-by-side as the vestibulocochlear nerve, though they are really separate divisions.
The disease appears to be the result of accumulation, or over-production, of fluid in the inner ear, in either the vestibule or cochlea. If the sound is not heard through the ear, meaning the sound is conducted better through the temporal bone than through the ossicles, a conductive hearing deficit is present. The spinal trigeminal nucleus, located in the medulla, receives information about crude touch, pain, and temperature to be relayed to the thalamus and cortex. The lateral rectus is controlled by neurons of the abducens nucleus in the superior medulla, whereas the medial rectus is controlled by neurons in the oculomotor nucleus of the midbrain.
To elevate the eyes, the oculomotor nerve on either side stimulates the contraction of both superior rectus muscles; to depress the eyes, the oculomotor nerve on either side stimulates the contraction of both inferior rectus muscles. The origin for both muscles is medial to their insertions, so elevation and depression may require the lateral rectus muscles to compensate for the slight adduction inherent in the contraction of those muscles, requiring MLF activity as well. Diplopia is not restricted to failure of the lateral rectus, because any of the extraocular muscles may fail to move one eye in perfect conjugation with the other. Coordination of the skeletal muscles for convergence and coordination of the smooth muscles of the ciliary body for accommodation are referred to as the accommodation–convergence reflex.
Deficits in the VOR may be related to vestibular damage, such as in Meniere’s disease, or from dorsal brain stem damage that would affect the eye movement nuclei or their connections through the MLF. If the examiner moves the tongue depressor to contact the lateral wall of the fauces, this should elicit the gag reflex. If the hypoglossal nerves on both sides are working properly, then the tongue will stick straight out.
The strength test in this video involves the patient squeezing her eyes shut and the examiner trying to pry her eyes open. For the sternocleidomastoid, those spinal nerves are primarily sensory projections, whereas the trapezius also has lateral insertions to the clavicle and scapula, and receives motor input from the spinal cord.
If light in either eye elicits a response in only one eye, the problem is with the oculomotor system.
So long as you're pedaling away on that recumbent bike, why not sharpen the old gray matter too? If the nerve is not completely severed, the anosmia may be temporary as new neurons can eventually reconnect.
They both emerge from the inner ear, pass through the internal auditory meatus, and synapse in nuclei of the superior medulla. The Weber test also uses a tuning fork to differentiate between conductive versus sensorineural hearing loss.
Essentially, the projection through the chief nucleus is analogous to the dorsal column pathway for the body, and the projection through the spinal trigeminal nucleus is analogous to the spinothalamic pathway.
If the nerve on one side has a deficit, the tongue will stick out to that side—pointing to the side with damage. Get your brain in top shape by combining exercise and brain training software (user must purchase software seperatley). Though they are part of distinct sensory systems, the vestibular nuclei and the cochlear nuclei are close neighbors with adjacent inputs.
In this test, the tuning fork is placed at the top of the skull, and the sound of the tuning fork reaches both inner ears by travelling through bone. Contact with the cotton tip of the applicator is a light touch, relayed by the chief nucleus, but contact with the pointed end of the applicator is a painful stimulus relayed by the spinal trigeminal nucleus. The motor response, through contraction of the muscles of the pharynx, is mediated through the vagus nerve. Though that is not precisely how the name originated, it does help make the association between the function of this nerve in controlling these muscles and the role these muscles play in movements of the trunk or shoulders.
Deficits in one or both systems could occur from damage that encompasses structures close to both. Additionally, because the location of the hypoglossal nerve and nucleus is near the cardiovascular center, inspiratory and expiratory areas for respiration, and the vagus nuclei that regulate digestive functions, a tongue that protrudes incorrectly can suggest damage in adjacent structures that have nothing to do with controlling the tongue. With unilateral conductive hearing loss, however, the tuning fork sounds louder in the ear with hearing loss. If a patient cannot recognize a painful stimulus, that might indicate damage to the spinal trigeminal nucleus in the medulla. The vagus nerve directly stimulates the contraction of skeletal muscles in the pharynx and larynx to contribute to the swallowing and speech functions. This is because the sound of the tuning fork has to compete with background noise coming from the outer ear, but in conductive hearing loss, the background noise is blocked in the damaged ear, allowing the tuning fork to sound relatively louder in that ear. The medulla also contains important regions that regulate the cardiovascular, respiratory, and digestive systems, as well as being the pathway for ascending and descending tracts between the brain and spinal cord.
Further testing of vagus motor function has the patient repeating consonant sounds that require movement of the muscles around the fauces. With unilateral sensorineural hearing loss, however, damage to the cochlea or associated nervous tissue means that the tuning fork sounds quieter in that ear. Damage, such as a stroke, that results in changes in sensory discrimination may indicate these unrelated regions are affected as well. The patient is asked to say “lah-kah-pah” or a similar set of alternating sounds while the examiner observes the movements of the soft palate and arches between the palate and tongue.



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