the olfactory nerve is a sensory nerve responsible for transmitting information about olfaction or smell to the brain the nerve begins in the olfactory epithelium A specialized collection of cells that lines the nasal cavity in humans the olfactory epithelium contains millions of olfactory receptor cells the axons of the olfactory receptor cells for bundles called Fila that travel up through a structure called the CRI plate which is part of the bone called the ethmoid bone that separates the nasal cavity from the brain the CRI form plate has holes that allow the Fila to pass through it the Fila make up the olfactory nerve the olfactory nerve travels to an adjacent structure called the olfactory bulb where it forms synaptic connections with several types of olfactory bulb neurons like cells called mitro cells these olfactory bulb neurons carry information about smell to the olfactory cortex as part of the Ala tract damaged to the olfactory nerve can happen in a number of ways such as head trauma or tumors when the olfactory nerve is damaged the sense of smell is affected the deficits can include anosmia which is a complete loss of the sense of smell or varying levels of impaired or distorted olfaction olfactory nerve damage is also linked to abnormalities in flavor perception due to the role of the olfactory system in flavor the ability to smell can can be assessed through tests where patients are exposed to a variety of odorants and asked to identify them an impaired sense of smell alone however can be due to a number of causes and doesn't necessarily indicate olfactory nerve damage so more testing must be done to verify the cause of the deficit the optic nerve is a sensory nerve responsible for transmitting information about Vision to the brain the nerve begins in the retina as the axons of cells called retinal gangan cells these axons come together to leave the eye at a region called the optic dis and form the optic nerve the optic nerve leaves the eye and extends to a structure called the optic kaym where it meets the optic nerve from the other eye at the optic kaym the optic nerve fibers carrying information from the sides of the retina closest to the nose cross over to the other side of the brain while those carrying information from the sides of the retina closest to the temple remain on the side of the brain where they are after leaving the optic kaym the nerve fibers are referred to as the optic tract most of the nerve fibers in the optic tract end in the lateral geniculate nucleus of the thalamus and from there the information will be passed on to the visual CeX damage to the optic nerve can occur due to a variety of causes like trauma tumors stroke or glaucoma the deficit that occurs after damage depends depends on where the nerve is damaged and involves some degree of visual defect or anopsia if the damage occurs before the optic kaym then the patient will experience blindness in the eye suppli by that optic nerve damage to the middle of the optic kaym will cause loss of the lateral visual field of both eyes due to the way fibers from the nasal side of the retina cross over at this point if the optic tract is damaged one half of the visual field will be lost in both eyes the ocular motor nerve is responsible for supplying four of the six extraocular muscles the medial rectus which moves the eye towards the nose the superior rectus which moves the eye upwards the inferior rectus which moves the eye downwards and the inferior oblique which moves the eye up and out Additionally the nerve supplies the levator palri superioris which is the muscle that elevates the eyelid it also forms connections with neurons in the ciliary gangion which inates the pupilary sphincter to control the constriction of the pupil and the ciliary muscle which adjusts the shape of the lens to see clearly at close distances ocular motor nerve fibers originate in the ocular motor nucleus in the midbrain from here they travel to the orbit of the eye along the way separating into branches that control the different extraocular muscles the fibers that control the pupilary sphincter and ciliary muscle originate in the Edinger Westfall nucleus and travel with the ocular motor nerve damage to the ocul motor nerve causes deficits in the ipsilateral eye a common symptom is a deviation of the affected eye to the side and downwards due to the paralysis of the medior rectus and inferior oblique and the unopposed action of the unaffected extraocular muscles medial eye movements may also be impaired due to paralysis of the medial rectus and vertical eye movements may be impaired due to paralysis of the superior and inferior recti and inferior oblique diplopia or double vision is common tosis or drooping of the eyelid may occur due to paralysis of the levator palp superioris because of pupilary constriction muscle is impaired the pupil on the side of the damage May remain dilated a condition known as madas and the patient may have a difficult time focusing the lens for close-up vision due to effects on the ciliary muscle the trar nerve also known as cranial nerve 4 is responsible for supplying one of the extraocular muscles of the eye this Superior oblique muscle the superior oblique helps the eye to move down and out to create this type of movement the muscle passes through a pulley likee structure called the tra of the superior oblique which is where the nerve gets its name the trar nerve originates in a small nucleus in the midbrain the nerve fibers decate or cross over to the other side of the brain stem before leaving the brain stem near the junction of the midbrain and ponds the trar nerve is the only cranial nerve that leaves the brain stem from the back or posterior surface of the brain stem it's also the only cranial nerve to completely originate from a nucleus contralateral to the structure IT Supplies the trar nerve is a very delicate nerve that is relatively easily damaged damage can be congenital or occur due to other causes like trauma the symptoms of trar nerve policy however are typically not as noticeable as those that result from damage to the ocular motor or abducent nerve because the superior oblique helps to move the eye downwards when the nerve is damaged the eye tends to deviate upwards since there is no opposing Force coming from the superior oblique this can result in diplopia or double vision some patients will adopt a head tilt as a compensatory mechanism to better align the eyes and reduce the diplopia if the paly does not resolve on its own or through less invasive treatments patients May undergo surgery to weaken an opposing muscle usually the inferior oblique to minimize the Devi a the trigeminal nerve is the main sensory nerve of the head it carries information about touch pain temperature and proprioception or the awareness of the position of muscles and Joints it also controls the muscles involved with chewing as well as the tensor tempani a small muscle in the middle ear that helps to dampen the sound of loud noises and the tensor v palatini a muscle that both helps prevent food from entering the naso fairings during swallowing an opens a small tube called the ustan tube which connects the upper throat with the middle ear this helps to equalize pressure between the middle ear and outside air the trigeminal nerve has three divisions the Opthalmic maxillary and mandibular divisions which supply three different regions of the head and face as seen in the image the Opthalmic and maxillary divisions carry sensory information while the mandibular division has sensory and motor components there are three sensory nuclei and a motor nucleus associated with the trigeminal nerve they form a column of cells that reaches from the midbrain of the brain stem to the upper spinal cord the main sensory nucleus receives information from the head about touch and proprioception the spinal trigeminal nucleus receives information about pain and temperature Sensations the mesencephalic nucleus receives proprioceptive information from the Jaw and teeth to prevent damage while biting and chewing the motor nucleus controls the muscles of chewing and other muscles mentioned earlier damage to the trigeminal nerve or its Associated nuclei can cause varying levels of abnormal sensation the patient may experience decreased sensation increased pain and or weakening of the muscles of chewing trial nerve damage can also lead to a condition called trigeminal neuralgia in which patients experience short but intense bouts of Facial Pain the abducens nerve also known as cranial nerve 6 is a motor nerve responsible for supplying one of the extraocular muscles of the eye the lateral rectus muscle the lateral rectus muscle abducts the eye or moves it laterally toward the side of the head the abduc nerve originates in the abducens nucleus which is located in the ponds fibers from the facial nerve wrap around the abduc nucleus and the combination of the nucleus and facial nerve fibers creates a bulge in the floor of the fourth ventricle known as the facial calculus the abducent nerve fibers exit the brain stem at the junction between the ponds and medulla and Supply the lateral rectus muscle on the same side of the head neurons from the abduc nucleus also travel through a pathway called the medial longitudinal fulus to the ocular motor nucleus where they synapse on neurons that control the medial rectus muscle of the other eye the medial rectus moves the eye inward this pathway allows for coordination of eye movement as when your abducent nerve allows you to look laterally with your left eye the fibers that travel in the medial longitudinal facula cause your right eye to look medially damage the abducent nerve causes impairment in the ability of the eye the Nerf supplies to move laterally and a condition called esotropia in which the eye that's affected deviates medially in this case the medial deviation is due to the loss of abducent function and the unopposed action of the medial rectus muscle this also leads to diplopia or double vision the facial nerve also known as cranial nerve 7 is best known for its role in controlling the muscles of facial expression as well as a number of other muscles of the face and head such as certain muscles involved with swallowing and jaw movement muscles of the external ear and the stapedius muscle which is found in the middle ear and is involved with Dam in loud noises the facial nerve also receives sensory information from the outer ear and from the taste buds on the anterior 2/3 of the tongue and IT Supplies most major glands in the head including the lacal glands for tear production the submandibular and sublingual salivary glands and the mucous glands of the nose paranasal sinuses and pallet the facial nerve is associated with several nuclei in the brain stem the motor portion of the facial nerve originates in the facial motor nucleus in the ponds the portion of the nerve that supplies the glands mentioned previously originates from the superior salivatory nucleus in the ponds taste information travels to the nucleus of the solitary tract in the medola and the sensory information from the outer ear travels to the spinal trigeminal nucleus in the mola facial nerve damage can cause a variety of symptoms but the most recognizable of of them is weakness Andor paralysis of the muscles of facial expression on the same side of the head that the damaged nerve supplies the patient's mouth on the affected side May droop and he may be unable to close the eye on the affected side in most cases of facial nerve paly the cause of the dysfunction is not known when this is the case is referred to as Bell's paly the vestibular clear nerve consists of a vestibular and clear component which have the functions of carrying information to the brain from the vestibular system and the ca respectively the information from the ca deals with hearing while the information from the vestibular system deals with vestibular Sensations which include information about head position and movement this vestibular information enables us to keep our balance stabilize our head and body during movement and maintain posture the clear component of cranial nerve 8 begins with neurons that make connections with hair cells the sensory receptor cell of the auditory system when hair cells are activated they relay auditory signals to the clear portion of the nerve through changes in levels of neurotransmitter release the clear nerve travels from the ca to the dorsal and vental clear nuclei which are found at the junction between the ponds and mola from there the auditory information is sent to areas in the brain stem and cortex that are involved with auditory processing the vestibular component of the nerve also receives stimulation from hair cells but these cells are found in the vestibular apparatus from there the nerve travels to the vestibular nuclei in the pon and medulla the vestibular nuclei consists of four subnuclei the inferior medial lateral and Superior vestibular nuclei neurons leave each of these nuclei to project to various areas in the brain brain stem and spinal cord to coordinate head eye and body movements to maintain balance and equilibrium along with other related functions damage to the vestibular colear nerve can cause disruption of hearing and or vestibular functions generating symptoms like hearing loss tinitus dizziness loss of balance and nausea the glossop farial nerve is associated with the tongue and the ferx or throat and has both sensory and motor functions it carries sensory information about touch pain and temperature from the posterior third of the tongue the upper part of the throat the tonsil part of the outer ear the inner surface of the eardrum and the ustan tube it also conveys sensory information from the cored body and coted sinus structures that detect oxygen carbon dioxide and pH levels in the blood along with changes in blood pressure the nerve also conveys taste information from the posterior third of the tongue and carries motor signals to the styop Fus muscle which plays a role in swallowing and speech and it innervates the paraded gland the largest of our salivary glands the glossop farial nerve is associated with a number of nuclei in the medulla the fibers that Supply the styop ferious muscle originate in the nucleus ambiguous the sensory fibers that carry taste information and those that carry sensory information from the cored body and cored sinus synapse in the nucleus solitarius and the fibers that convey touch and pain synapse in the spinal trigeminal nucleus the fibers that inate the pared gland arise from the inferior Sal vatory nucleus damage to the glossop farial nerve can cause a variety of symptoms including a loss of taste on the posterior third of the tongue trouble swallowing and generally decreased sensation on the back of the tongue the soft pallet and fairings patients may also have a diminished gag reflex and the uula will often deviate to the side opposite from where the damage has occurred in rare cases patients may experience glossop farial neuralgia which involves brief but intense pain in the tongue and throat the vagus nerve is an extremely long nerve that travels from the brain stem to the colon and has a long list of functions it carries sensory information about pain touch and temperature from the throat parts of the inner and outer ear and the meninges near the back of the head it plays a very minor role in taste it also receives sensory information from internal organs in the neck chest and abdomen like the esophagus heart and digestive tract and it carries sensory information from both Barrel receptors in the aorta that detect changes in blood pressure and chemo receptors in the aorta that sense oxygen levels in the blood the Vagas nerve controls the movement of a number of muscles in the fenx soft pallet and larynx as well as one muscle in the tongue to play a critical role in the control of speaking and swallowing it is also the main parasympathetic nerve of the body providing parasympathetic innervation to organs throughout the neck thorax an abdomen contributing to a variety of functions such as the slowing of heart rate there are several nuclei in the medola associated with the vagus nerve and the different types of information it carries information about touch pain and temperature travels to the spinal trigeminal nucleus sensory information from internal organs or visceral sensory information travels to the solitary nucleus motor signals originate in the nucleus ambiguous parasympathetic fibers originate primarily in the dorsal V motor nucleus while some parasympathetic fibers that travel to the heart begin in the nucleus ambiguous symptoms of vagus nerve damage may include heness of the voice difficulty swallowing and a deficient gag reflex the uula May deviate away from the side where the damage has occurred because the nerve supplies a number of organs however damage can result in many other symptoms as well like abnormalities in heart rate or gastrointestinal problems the accessory nerve is primarily considered a motor nerve that supplies two muscles the sternomastoid muscle and the trapezius muscle the sternomastoid helps to turn your head to the side as well as bend your neck down or to the side the trapezius is involved with the movement of the neck and scapula or shoulder blade the trapezius is important to a variety of shoulder and arm movements such as shrugging your shoulders or raising your arms above your head traditionally the accessory nerve has been divided into a spinal component which originates in the accessory nucleus in the spinal cord and a cranial component which originates in the nucleus ambiguous in the medola the fibers that make up the spinal portion of the nerve leave the spinal cord as a series of rootlets which then come together to form what is known as the spinal root the spinal root ascends to join the cranial root that extends from the medola the cranial and spinal Roots travel together briefly as they exit the skull but then the cranial portion travels with the vag nerve while the spinal portion extends to the sternomastoid and trapezius muscles because the cranial portion can be functionally considered part of the vagus nerve often the spinal portion is considered the true accessory nerve damage to the accessory nerve can cause weakness or paralysis of the sternomastoid Andor trapezius muscles but trapezius dysfunction is typically the more incapacitating problem trapezius dysfunction May impair arm and shoulder movement cause the shoulder to to droop and cause the shoulder blade to abnormally protrude from the back a condition known as winged scapula the patient may also experience shoulder and neck pain along with muscle fatigue because other muscles in the shoulder and arm that are unaccustomed to supporting the shoulder must be utilized the hypoglossal nerve is a motor nerve that controls all the muscles of the tongue except for one the palog glossus which is controlled by the vagus nerve the tongue muscles consist of what are known as intrinsic muscles which control the shape of the tongue and extrinsic muscles which act to protrude retract Elevate and move the tongue side decide healthy function of the hypoglossal nerve is thus critical for things like eating swallowing and speaking the hypoglossal nuclei are found in the mola hypoglossal nerve fibers leave the hypoglossal nuclei on each side of the brain stem and descend to travel to the same side of the tongue to stimulate the muscles of the tongue from below hence the term hypoglossal which comes from the Greek for under the tongue there are three other branches that extend from the hypoglossal nerve to supply various other muscles in the neck as well as the Duram Mater at the back of the head only the fibers that Supply the tongue originate in the hypoglossal nucleus however and thus they are often considered the true hypoglossal nerve damage to the hypoglossal nerve can cause tongue weakness and impair tongue dexterity it may also lead to small muscle twitches or fasiculations in the tongue as as well as atrophy of the tongue especially at the tip or borders of the organ if the hypoglossal nerve on only one side is damaged then atrophy will typically be seen in the tongue muscles on that same side if the patient is asked to protrude his or her tongue the tongue will often deviate toward the side of the damaged nerve patients with damage to only one hypoglossal nerve however are often able to compensate for the deficiency of the tongue muscles on one side but if both nerves are damaged the patient may be unable to protrude the tongue at all and may experience severe problems with speech and swallowing