 This video will cover the anatomy of the special senses. Most of this material comes from chapters 14 and 15 of OpenStacks Anatomy and Physiology, and additional content was taken from Gray's Anatomy. As we go, we'll cover the following study objectives to describe the gustatory pathway from the gustatory receptor cells, which are in the tongue, to the primary gustatory cortex in the insular lobe of the cerebral cortex. We'll describe the olfactory pathway from the olfactory receptor cells in the superior nasal cavity to the primary olfactory cortex of the temporal lobe. We'll identify the major structures of the eye, including the components of the fibrous, vascular, and nervous tunics. We will look at the anterior and posterior cavities, which are separated by the lens. We'll identify accessory structures of the eye, including the palpebrae, paruncal, lacrimal apparatus, and eye muscles. We'll describe the visual pathway from photoreceptors to primary visual cortex in the occipital lobe. We'll identify the structures of the external, middle, and inner ear, and then describe the auditory pathway from the auditory hair cells of the inner ear to the primary auditory cortex of the temporal lobe. Here we can see an illustration showing the tongue and the different types of papillae that are found on the tongue. There are fungiform papillae that have a mushroom shape. There are philiform papillae that have a more elongated shape, and foliate papillae that have a broader shape. On the papillae are the taste buds. On the bottom right here we can see a high magnification view of a taste bud. And within the taste bud we can see there are gustatory cells, which are the receptor cells that detect chemicals dissolved in our saliva in order to provide the sense of taste. When a chemical like fructose binds to a specific receptor on a gustatory cell, it will change the permeability of that cell's membrane to ions like sodium and calcium, and that will affect the release of neurotransmitters from the gustatory cell onto the dendrites of spacial nerve, the cranial nerve number 7. Now we'll go through the gustatory pathway, which begins with the gustatory cell, the receptor cells in the taste buds that release neurotransmitters onto cranial nerve number 7, the facial nerve. Information travels through the facial nerve into the medulla oblongata, a nucleus of the medulla oblongata called the solitary nucleus. And then the pathway continues with a neuron from the solitary nucleus that extends its axon up to the thalamus. And then neurons in the thalamus will then relay this information from the thalamus over to the primary gustatory cortex in the insular lobe. So primary gustatory cortex is the first region of the cerebral cortex that receives the sense of taste and where the conscious perception of taste is initiated. Now we'll move on to studying olfaction or the sense of smell. You can see here the olfactory nerves, which extend into the superior nasal cavity through the cribriform plate of the ethmoid bone. And so the sensible faction is involving chemical receptors, chemoreceptors that are detecting chemicals dissolved in the mucus of the superior nasal cavity. In the illustration here we see the smell of a hot drink like a coffee that is being brought into the nasal cavity. Chemicals that were dissolved in the air will then dissolve into the mucus of the superior nasal cavity and bind to receptors on the dendrites of olfactory receptor cells. These olfactory receptor cells are embedded in the olfactory epithelium in the superior nasal cavity and extend axons in through the cribriform plate as cranial nerve number one, the olfactory nerve. Then carries that information into the olfactory bulb. Here we can see the olfactory pathway which starts with information coming from the olfactory receptor neurons through cranial nerve number one into the olfactory bulb. Then from the olfactory bulb, axons project out through the olfactory tract to reach primarial factory cortex in the temporal lobe where the conscious perception of smell will be initiated. Next we'll move on to study a vision starting by looking at the anatomy of the eye. The anterior clear outer layer of the eye is called the cornea and then the white outer layer of the eye is called the sclera. The eyelids are also known as palpebrae and there's a mucus membrane covering over the anterior of the eye and the inner surface of the eyelids known as conjunctiva. So there is a palpebral conjunctiva that covers the inner surface of the eyelids and there's also a bulbar conjunctiva which covers the sclera on the anterior of the eye. You can also see here the skeletal muscle leviter palpebrae superioris which contracts in order to pull open the superior palpebrae, the superior eyelid. That muscle is excited by the oculomotor nerve. We can also see here the orbicularis oculi muscle which is excited by the facial nerve and contracts in order to close the palpebrae, closing the eyelids. There are extra ocular muscles that are skeletal muscles that insert onto the sclera, the white part of the eye. We have superior rectus that will contract to direct the gaze upward. Inferior rectus that will contract to direct the gaze downward. Medial rectus will contract to direct the gaze towards the midline. We can see there are oblique muscles like the inferior oblique muscle that can rotate the eye in the socket. All of those muscles, superior rectus, inferior rectus, medial rectus and inferior oblique are all excited by cranial nerve number three, the oculomotor nerve. There's also a superior oblique muscle that attaches to a cartilage of the frontal bone known as the trochlea which functions as an anatomical pulley to redirect the force of the superior oblique muscle so that the eye can rotate within the socket when the superior oblique muscle contracts. It will cause the superior part of the eye to rotate towards the midline and the inferior part will rotate out laterally. This muscle is excited by the trochlea nerve. The trochlea is the cartilage that's the anatomical pulley for the superior oblique muscle and the trochlea nerve, cranial nerve four excites the superior oblique. The last of the extraocular muscles is another rectus known as the lateral rectus. The rectus muscles are all pulling straight, lateral rectus pulls straight on the lateral side of the eye in order to direct our gaze away from the midline. Directing our gaze away from the midline, just like moving a limb away from the midline can be called abduction, abduction. The nerve that excites lateral rectus is cranial nerve number six, the abducens nerve. The abducens nerve will excite lateral rectus to perform abduction of the eyeball to direct our gaze laterally. So here we can see a little more detailed view of the anatomy of the eye. There is an anterior cavity and a posterior cavity within the eye. The anterior cavity is between the cornea and the lens. The lens is a clear tissue that can focus light and the shape of the lens is controlled by smooth muscles known as the ciliary muscles. And then those ciliary muscles attach to the lens through suspensory ligaments. When the ciliary muscles contract, they have a circular shape and they will release the tension on the suspensory ligaments which allows the lens to bulge out becoming more convex. It has a biconvex shape, it bulges out on both sides and when the tension of the suspensory ligaments is released, it will bulge more which is important for accommodating our vision that is near point accommodation to see something that's close to the face. Now behind the lens is the posterior chamber. So everything between the lens and the cornea is the anterior chamber and everything posterior to the lens is the posterior chamber. The anterior chamber contains a liquid that has a watery substance it's known as the aqueous humor whereas the posterior chamber contains a more gelatinous thick liquid which is vitreous humor. So vitreous humor is filling the posterior cavity behind the lens. You can see the iris is surrounding the opening where light enters known as the pupil. So the dark spot in the middle of your eye is the pupil and the region that's surrounding the pupil that can be blue if your eyes are colored blue or brown if your eyes are colored brown is actually smooth muscle known as the iris. The iris can regulate the diameter of the pupil there are circular muscles in the iris the pupillary constrictor muscles that can contract in order to decrease the amount of light entering the pupil and there are radial muscles of the iris that can pull open the pupil pupillary dilator muscles that dilate the pupil in order to allow more light to enter the eye. There are three major tunics of the eye the outermost layer of the eye is known as the fibrous tunic which includes the sclera as well as the cornea so this is the outermost layer of the eye then the middle layer of the eye known as the vascular tunic includes the iris in the ciliary body as well as a layer on the posterior known as the coroid the coroid contains many blood vessels and so the name vascular tunic comes from the fact that there are blood vessels traveling through this middle layer of the eye, the coroid and there's also melanocytes in the coroid layer that produce a dark pigment melanin in order to prevent reflection of light within the eye the deepest layer of the eye is known as the retina and the retina contains the neurons inside of the eye and photoreceptor cells that detect light and so the retina is also known as the neural tunic and there's a neural layer of the retina which is the deepest layer as well as an epithelium which is the most superficial layer of the retina the retinal epithelium contains melanin so it's also known as the pigmented epithelium and that melanin also functions to reduce reflection of light inside of the eye to help give us sharper vision the neurons in the retina relay information out through the optic nerve the region where the optic nerve attaches to the retina is known as the optic disc and there are no photoreceptors in the optic disc and so this region of the eye is not sensitive to light and therefore gives us a blind spot there's no photoreceptors at the optic disc where the optic nerve attaches to the retina and so we have a blind spot of the retina and then we can see in this image just above the optic nerve attachment is a region known as the fovea centralis so fovea centralis contains only cone shaped photoreceptors so there are two different types of photoreceptors cones and rods and the cone shaped photoreceptors give us very high resolution, very detailed vision and color division and the fovea centralis contains only cones and no rods whereas as we move out from fovea centralis the concentration of rods becomes higher and the concentration of cones becomes lower there is a region surrounding fovea centralis and including fovea centralis known as the macula lutea which is literally translated as the yellow spot the macula lutea is a yellow circular region of the retina that has a high concentration of cones and a relatively low concentration of rods here we can see the layers of cells in the retina the most superficial layer of the retina is the pigment epithelium the pigmented epithelium contains epithelial cells that have granules of melanin in order to help reduce reflection of light then just deep to the pigmented epithelium are the photoreceptor cells in the photoreceptor cell layer these photoreceptors are the cells that detect light the rods detect a broad wavelength of light so they are responsible for just black and white vision they are very sensitive to low intensities of light contrast the cones have a narrow range of wavelength that they can respond to so there are cones that respond to red light cones that respond to green light and cones that respond to blue light and those three different types of cone photoreceptors provide us with colored vision the photoreceptor cells then form synapses with bipolar cells and the bipolar cells relay this information to ganglion cells of the retina and the ganglion cells extend their axons out through the optic nerve in order to carry visual information into the brain here we can see an illustration of a rod and inside of a rod there are membranous discs and embedded in the membranous discs are proteins called rod-opsin molecules rod-opsin is the specific protein found inside the rods there are also other types of opsin proteins found in the discs of cones and so the general idea of how a photoreceptor detects light is the same for rods and cones the only difference is the wavelength of light that's detected is more specific for the cones when a photon of light is detected by the opsin protein a chemical inside of the opsin changes shape this chemical is known as retinal and so during the resting state when there's no light being detected opsin contains a cis-shaped retinal and then the energy from a photon is absorbed by cis-retinal and converts that cis-shaped retinal into the trans-shaped retinal and as the retinal changes from the cis to the trans-isomer that changes the shape of the opsin which leads to a cascade of signaling events inside of the cell that will affect the release of neurotransmitters from the photoreceptor cell onto the bipolar cell and so this process is known as photoisomerization where retinal changes from the cis to the trans-isomer and then there's a process that can regenerate the cis-retinal where an enzyme, an isomerase enzyme uses ATP in order to convert trans-retinal back to cis in order to reassemble a opsin that can perform this cycle again so here we can see the color sensitivity of the different photopigments found in rods, blue cones, green cones, and red cones and you can see that the rods have a broader range of wavelengths that the photopigments respond to and that's why rods have a high sensitivity but produce only black and white vision instead the cones provide color vision where the blue cones respond to shorter wavelengths of light the green cones respond to a medium wavelength of light around 534 nanometers and the red cones respond to the longest wavelengths of light in the visual range around 564 nanometers is the highest sensitivity range for the red cones now we'll go through the visual pathway which starts with light entering through the pupil and landing on the retina and exciting the photoreceptor cells which release neurotransmitter onto bipolar cells that release neurotransmitter onto retinal ganglion cells and the retinal ganglion cells extend their axons in through the optic nerves now you can see here in the illustration that the information shown in the purple color corresponds to the left visual field the information in the right visual field is shown with a green color and the information regarding the right visual field will travel to the left hemisphere of the brain and the opposite is true information from the left visual field will travel to the right hemisphere of the brain information from the medial portion of the retina will have to cross the midline because the medial portion of the retina on the right eye will receive information about the right visual field whereas the lateral portion of the eye can stay on the same side because the lateral portion of the retina is detecting light that's coming from the contralateral visual field there is a region in the center of our visual field known as the binocular field where both the left and the right eye receive light and this binocular field allows our brain to compare information from the left and the right eye and small differences in that information can be used in order to calculate depth in order to perceive depth and that is giving us a three-dimensional picture of our visual field so let's follow the visual pathway where the information from the lateral part of the retina is going to travel down through the optic nerve and stay on the same hemisphere of the brain as it travels past the optic chiasm into the optic tract the optic tract will carry those axons of the retinal ganguin neurons all the way to the thalamus to a region of the thalamus known as the lateral geniculate nucleus, the LGN where they form synapses with neurons in the LGN and then the neurons of the lateral geniculate nucleus of the thalamus extend their axons through a tract known as the optic radiation which connects to the primary visual cortex in the occipital lobe and then we'll look at the medial portions of the retina on the left eye this is in purple and on the right eye this is in green the axons coming from the medial portions of the retina travel in through the optic nerve and then cross the midline at the optic chiasm in order to reach the lateral geniculate nucleus on the contralateral hemisphere and then from the lateral geniculate nucleus the visual pathway will be the same traveling out to the occipital lobe the primary visual cortex in the occipital lobe the retinal disparity is the difference between the images that are received by the left and the right eye within the binocular field because there are slight differences between the visual image that the two eyes receive the brain can extract depth perception just the two dimensional information that is received by the retina slight differences are used between the two eyes in order to calculate a three dimensional image with depth perception so here we can see the visual pathway that travels from the occipital lobe out into visual association areas higher levels of processing to perform more complex computations to understand either what we're viewing or where that is located and so the visual pathway that extends down the inferior or ventral part of the brain is known as the ventral visual stream and this processing pathway is important for distinguishing the identity of the object identifying what is the color what is the shape and do you recognize this object do you have a name for it have you previously encountered that object the superior pathway extending from the occipital lobe up towards the parietal lobe is known as the dorsal stream and this is important for processing the location of the object where is the object as well as is the object moving so we have a what visual stream and a where dorsal stream that are processing visual information here we can see the regulation of the iris by the autonomic nervous system to control the diameter of the pupil this is a reflex where visual information traveling in from the retina through the optic nerve is used in order to regulate the activity of the iris so information coming in through the visual pathway travels into a region of the midbrain and that region of the midbrain then regulates activities of the parasympathetic nervous system that where neurons extend their axons out through the ocular motor nerve into the iris in order to stimulate contraction of the pupillary constrictor muscles the circular muscles of the iris which will constrict the pupil decrease the diameter of the pupil in order to decrease the amount of light entering the eye and so if the intensity of the light striking the retina is too high the midbrain will activate this parasympathetic pathway to constrict the pupil and decrease the amount of light entering the eye in contrast if the light entering the eye is too dim then a sympathetic pathway will be activated and the sympathetic pathway will cause pupillary dilator muscles of the iris to contract pulling open the pupil increasing the diameter of the pupil so the pupils dilate allowing more light to enter the eye so here we can see the pupillary reflex pathway which starts with visual information entering into the retina through the optic nerve and traveling in to the midbrain and then from the midbrain where there's a control center that will process this information the efferent pathway travels out through either parasympathetic or sympathetic fibers that travel in to regulate the iris we can see here the ocular motor nerve is one of the efferent pathways that carries the parasympathetic fibers in order to constrict the pupil in response to a bright light now we're going to move on to study hearing we can see here the anatomy of the external middle and inner ear the external ear includes the outer region known as the oracle also known as the pinna of the ear the oracle or pinna functions to funnel sound waves into the ear canal or the external acoustic miatus of the temporal bone and that those sound waves will then cause vibration of the tympanic membrane the tympanic membrane attaches to three small bones in the middle ear the middle ear is an air filled cavity inside the petrous portion of the temporal bone the malleus, incus and stapes are the auditory ossicles the malleus is attached to the tympanic membrane so that as the tympanic membrane vibrates the malleus will vibrate and cause the incus to vibrate which then causes the stapes to vibrate as the stapes vibrates it will then produce vibration on the inner ear at a region known as the oval window now the inner ear is a labyrinth inside of the petrous part of the temporal bone that's filled with fluid we can also see that there is a eustachian tube that connects to the middle ear and this eustachian tube is a passageway allowing air to equalize pressure in the middle ear by connecting to the superior part of the throat the nasopharynx and so if you've ever experienced pressure in your ear as you go through a change in elevation either driving up and down a mountain or on an airplane you need to chew gum or yawn in order to try and open the elastic cartilage that's supporting the eustachian tube allowing air to equalize the pressure in the middle ear now we're going to move on to study the inner ear in more detail you can see the spiral shaped region of the inner ear known as the cochlea this region contains the receptors that detect sound and so the fluid inside of the cochlea vibrates as the stapes pushes on the oval window and because fluid is not compressible there is a round window that allows pressure to be relieved as the stapes pushes in on the oval window fluid will push out on the round window and as that fluid vibrates it's going to lead to changes in neurotransmitter release from auditory hair cells that are the receptor cells inside of the cochlea that release neurotransmitter onto the dendrites of bipolar neurons that are found in the cochlear division of the vestibular cochlear nerve cranial nerve number 8 and so the vestibular portion of the vestibular cochlear nerve is receiving information from a region of the inner ear known as the vestibule and the vestibule is important for detecting acceleration of the head can detect both linear and angular acceleration we'll see that there are ampullae where these large semicircular canals attached to the vestibule and that's important for detecting angular acceleration whereas there are otolith organs the utricle and saccule located within the vestibule that relay information out regarding linear acceleration so here we can see the bony labyrinth of the inner ear where the cochlea has a spiral shape and contains the auditory hair cells that are responsible for detecting sound the vestibule is the middle region where the semicircular canals attached and the cochlea attaches and so this middle region the vestibule is where the vestibular nerve connects to the inner ear and the semicircular canals attach at enlarged regions known as the ampullae so an ampule of each semicircular canal contains hair cells that are embedded inside of the cochlea that detects movement of fluid inside of the semicircular canals and that region is known as the crista ampularis inside of the ampule of the canals and then inside of the vestibule we'll see there are the maculee where hair cells are found inside of two regions of the vestibule known as the utricle and saccule that detect linear acceleration and this information about the acceleration of our head is related through the vestibular division of the vestibular cochlea nerve so this is filled with fluid and there is a fluid called perilymph filling the bony labyrinth and then suspended inside of the perilymph fluid is a membranous labyrinth that contains another fluid called endolymph so here we can see an illustration showing the membranous labyrinth of the inner ear that is filled with endolymph fluid and the illustration shows the spiral shaped membranous labyrinth inside of the cochlea known as ductus cochlearis or the cochlear duct and inside of this cochlear duct is where we'll find the auditory hair cells that detect sound and relay that information in through the cochlear division of the vestibular cochlear nerve then attached to the cochlear duct we can see a large chamber called the saccule and then the saccule is interconnected with another large chamber inside of the vestibule called the utricle so the saccule is closer to the cochlea and the utricle is closer to the semicircular canals the saccule and utricle are both found inside of the vestibule and then attached to the utricle we see the ampulee where the ampulee are where the semicircular ducts of the semicircular canals connect to the vestibule now we're going to go through a little more detail of how sound is relayed in to the auditory hair cells inside of the cochlear duct sound waves cause vibration of the tympanic membrane leading to vibration of the auditory ossicles and the stapes will push in on the oval window creating vibration inside of the perilum fluid the perilum fluid fills two different ducts that surround the membranous duct or cochlear duct inside of the cochlea the vestibular duct or scala vestibule attaches to the oval window and vibration of the perilum inside of this scala vestibule will be relayed down through the tympanic duct or scala tympani that connects to the round window as the fluid is vibrating inside of the perilum fluid it will cause vibration inside of the vest- inside of the cochlear duct that's filled with indolent fluid as the cochlear duct vibrates it's going to cause movement of a region inside of the cochlear duct known as the basilar membrane of the organ of quartii and the basilar membrane of the organ of quartii contains the auditory cells that will then send information out through the cochlear branch of the vestibular cochlear nerve now the width of the basilar membrane changes as we go along the cochlear duct so that there is a wider end and a narrower end and this wider end will respond to a different frequency of sound waves or a different pitch of sound waves than the narrower end and so the pressure will bend the membrane of the cochlear duct at a particular point where we have the maximum vibration for that frequency which will cause the hair cells in the basilar membrane to vibrate and then those hair cells will release neurotransmitter onto the dendrites of bipolar cells so here we can see a section through the cochlea showing the three ducts inside of the cochlea the scale of the vestibule the cochlear duct and the scale of timpani and as the perilum fluid inside of the scale of vestibule and the scale of timpani vibrates it causes vibration of the cochlear duct in the middle that's filled with endolent fluid we can see inside of the cochlear duct is structure known as the organ of corti the organ of corti consists of a basilar membrane where there are auditory hair cells that extend up to attach to the tectorial membrane the tectorial membrane is more rigid than the basilar membrane so as the fluid of the perilum is vibrating it will cause vibration of the basilar membrane relative to the tectorial membrane leading to bending of the auditory hair cells so here we can see a higher magnification view of the auditory hair cells in the organ of corti these hair cells have stereocilia that are extensions from the apical surface of the cell that attach to the tectorial membrane and so as the basilar membrane moves relative to the tectorial membrane it will cause bending of the stereocilia the stereocilia are connected by tethers called tip link proteins that open ion channels or close ion channels affecting the permeability of the hair cell membrane to ions which will affect the release of neurotransmitters from the hair cells onto the dendrites of bipolar cells these bipolar cells have their cell bodies found in the spiral ganglion that travels along the cochlea and extend axons in through the cochlear division of vestibulocochlear nerve here we can see a higher magnification view using a light microscope showing the organ of corti inside of the cochlea where the tectorial membrane is found attached to the auditory hair cells that are embedded in the basilar membrane so here we can see a schematic of the membranes inside of the cochlear duct where the basilar membrane contains the auditory hair cells and the tectorial membrane is attached to the auditory hair cells at the stereocilia and we can see that there's a apex and then a base of the basilar membrane as we move towards the apex the basilar membrane becomes wider and that wider basilar membrane will vibrate in response to lower frequencies of sound whereas the base that has a narrower width will vibrate to higher frequency and so the region of the basilar membrane that vibrates in response to a sound provides us with selectivity to the pitch or frequency of the sound a high frequency vibration corresponds to a high pitch sound whereas a low frequency vibration corresponds to a low pitch sound and then the neurons that connect to the auditory hair cells will conserve this information as they extend in through the auditory pathway so now we'll go through the auditory pathway that starts with the auditory hair cells inside of the cochlea that release neurotransmitter onto the vestibular cochlear nerve that travels in to the medulla oblongata to form synapses within the medulla oblongata at the cochlear and superior olivary nuclei within the medulla oblongata auditory information will be relayed across the midline so that information coming from the inner ear on the right side will cross over to be processed by the left half of the brain and then the opposite is true information coming in from the left vestibular cochlear nerve will be relayed over to the right hemisphere of the brain information will then travel from the medulla oblongata up to the inferior colliculus and then neurons in the inferior colliculus will relay the information up to the medial geniculate nucleus of the thalamus and then from the medial geniculate nucleus of the thalamus neurons will relay out to the primary auditory cortex in the temporal lobe where the perception of sound will be initiated now we're going to move on to the organs inside of the vestibule which is responsible for the sense of equilibrium important for balance and for regulating eye movements to help stabilize an image as our head moves and so inside of the vestibule we see the uterical which is closer to the semicircular canals and the saccule which is closer to the cochlea the uterical and saccule both contain a structure known as the macula and inside of the macula are auditory hair cells embedded in an oedolith where calcium carbonate crystals are found these calcium carbonate crystals will move in response to the force of gravity as we move the position of our head gravity will cause the oedolith to move bending the stereocilia of the hair cells inside of the macule and then these hair cells will relay information into the vestibular division of cranial nerve 8 and so while the uterical and saccule contain the macule responsible for detecting linear acceleration the ampula of the semicircular canals contain a structure known as the crista ampularis that detects rotation of the head as we rotate our head the endolimp fluid inside of the semicircular ducts will have a delayed response so that our head will move around the fluid because of inertia the fluid will stay put until the forces of friction can start to move the fluid along with our head but as head moves relative to the endolimp fluid of the semicircular canals a structure inside of the ampula known as the cupula will bend and the bending of the cupula causes the bending of stereocilia in the crista ampularis and these stereocilia bending causes a change in the permeability of the hair cells plasma membrane to ions which affects the release of neurotransmitter from the hair cells onto a ampulary nerve a division of the vestibulococlear nerve and so information will travel in regarding the angular movement of our head in response to motion of the hair cells in the crista ampularis of the ampula inside of our inner ear one of the functions of the vestibular information that's coming from the saccule utricle and semicircular canals will be to guide the movement of our eyes there is a reflex known as the vestibulocular reflex in which the information regarding movement of our head can be used to make compensating eye movements and so if our head is rotated counterclockwise the fluid inside of the semicircular canals will move relative to our head in the opposite direction so we can see it's moving clockwise as the fluids moving clockwise on the right side it's going to excite the fibers traveling through the vestibulococular nerve and on the left side we see it's inhibiting the fibers traveling through the vestibulococular nerve and this is going to lead to excitation of the lateral rectus on the left side and medial rectus on the right eye in opposite we will see inhibition coming from the left inner ear and this will then lead to inhibition of the lateral rectus of the right eye and medial rectus of the left eye and so you'll remember that the nerves that excite the lateral rectus are the abducens nerves and the nerves that excite the medial rectus are the ocular motor nerves and so we can see the pathway traveling out from the ocular motor nerve or from the ocular motor nucleus of the midbrain through the ocular motor nerve travels to the rectus and then the pathway traveling from the abducens nucleus of the pons travels out through the abducens nerve to the lateral rectus