Final Exam Objectives For Auditory Systems

Auditory Systems Describe the three regions of the ear and important structures found within each region o The three compartments of the ear are the outer ear, middle ear, and inner ear outer ear c...

Auditory Systems Describe the three regions of the ear and important structures found within each region o The three compartments of the ear are the outer ear, middle ear, and inner ear outer ear collects and transmits sound Outer (external) ear middle ear transmits and Main function is to collect and transmit sounds amplifies sound inner ear transforms sound to Air-filled compartment electric signal Components: o Auricle Cartilage covered with skin Main function is collecting sound o External auditory meatus A little tunnel between auricle and tympanic membrane Main function is sound transmission o Tympanic membrane Main function is transforming sound waves to mechanical vibrations tympanic membrane transforms sound waves to mechanical vibration Middle ear Main function is to transmit and amplify sounds Air-filled compartment Components: o Ossicles (Malleus, Incus, Stapes) Main function is to amplify the sound signal When sound waves hit the tympanic malleus is attached to membrane, these three bones move, and stapes hits the tympanic membrane cause fluid in the inner ear to move oval window to commence fluid o The bones connect the tympanic movement membrane to the oval window o Middle ear cavity stapedius muscle and tensor tympani have the effect of o Oval window channel into inner ear reduction of sound transmission upon contraction stapedius attaches to stapes, tensor A contact point between middle and inner ear tympani attaches to malleus When the oval window is hit, fluid movement in the inner ear begins o Round window channel out of inner ear A contact point between c the middle and inner ear Relieves pressure in the inner ear by acting as a passageway for fluid out of the inner ear Inner ear Main function is to transform sound to electric signals Fluid-filled compartment Components:  “spiral organ” o Cochlea Scala vestibuli Upper chamber of the cochlea, which is connected to the oval window o Stimulation of oval window begins the scala media ends before the apex; the fluid movement in inner ear region where the scala vestibuli becomes the Scala tympani scala tympani is known as the helicotrema Lower chamber of the cochlea, which is connected to the round window o Round window relieves pressure of fluid in inner ear Scala media (Cochlear duct) Membrane-enclosed, middle-chamber, sensory which contains Organ of Corti, the sensory receptor cells receptor system that produces nerve are never regenerated, so impulses in response to sound vibrations if you lose them o The tectorial membrane rests atop they’re gone the hair cells. There are three rows of outer hair cells and one row of inner hair cells. These hair cells have stereocilia inner hair cells have a major sensory 1 inner hair cell is innervated inner hair neurons cells are much reception system, leading to information to by ~20 spiral ganglion, while carry all the way to the brainstem; outer hair more cells are much less effective in terms of 10 outer hair cells are innervated than outer sensory reception, but they have an important innervated by ~1 spiral 1:20 roll in mechanical regulation of movement hair cells ganglion neurons 10:1 o The stereocilia of the hair cells can be stimulated in a way that either hyperpolarizes or depolarizes the cell when the basilar membrane moves down when the basilar membrane moves up When the stereocilia are deflected away from longer stereocilia, the hair cell when the membrane hyper-polarizes, basilar membrane and afferent nerve fibers of moves down spiral ganglion neurons are not stimulated (inhibition) When the stereocilia are deflected toward the longer when the stereocilia, there is an influx basilar of K+ ions, the hair cell membrane membrane depolarizes, moves up there is an influx of Ca2+ ions, longest cilia = kinocilium neurotransmitters are  released, and afferent nerve fibers of spiral ganglion neurons are stimulated o There is tonotopic localization in the certain regions Organ of Corti. this means that basilar membrane of the basilar acts as a sound prism membrane certain sections of the basilar responds membrane will oscillate in response at the same time, positively to certain to certain sound frequencies. certain areas, depending on the frequencies Complex sound involves multiple frequency, will frequencies, and so multiple parts of oscillate in the basilar membrane oscillate multiple locations thick, stiff thin, floppy Higher frequencies are detected at the base (closer to middle ear) of the cochlea, where the basilar membrane is stiff and thick Lower tones are detected closer to the apex of the cochlea (closer to helicotrema), where the basilar membrane is thin and floppy Describe the auditory pathways from the Organ of Corti to the primary auditory cortex organ of corti o Sound is relayed from the Organ of Corti to the medulla, pons, midbrain, medulla thalamus, and then primary auditory cortex cochlear axons pons 1) Axons of spiral ganglion, excited by hair cells in the Organ of Corti, travel via CN VIII (cochlear division) into the medulla, where they synapse on midbrain the ventral and dorsal cochlear nuclei in the open medulla thalamus o In the cochlea, the spiral ganglion neurons are bipolar neurons, which means they have a peripheral and a central process primary cochlear auditory cortex nuclei are The peripheral process innervates the hair cells shaped like a saddleback The central process bundles together with vestibular nerve fibers to form CN VIII The axons of the ventral and dorsal cochlear nuclei of the open medulla 2) and ascend and decussate to make a synaptic connection with the superior olivary nucleus in the pons o Some of the axons of the ventral and dorsal cochlear nuclei will cross back again, In the midline structure, the axons of the ventral and dorsal cochlear nuclei form the trapezoid body In the lateral structure, the auditory nerve fibers bundle together to form the lateral lemniscus, which is a white matter tract  3) Auditory axons from the superior olivary nucleus of the pons ascend the brainstem in the lateral lemniscus white matter tract and synapse in the inferior colliculus in the midbrain o The lateral lemniscus white matter tract includes information from both ears so does trapezoid body Inferior colliculus of the midbrain projects to the medial geniculate 4) nucleus (MGN) in the thalamus o Do not confuse MGN with LGN MGN involved in auditory processing; LGN involved in visual processing 5) Medial geniculate nucleus projects to the primary auditory cortex (i.e., transverse temporal gyri), which is located in the temporal lobe o The tonotopic organization in the auditory relay is maintained in the auditory cortex High frequency sounds are localized in the deep regions of the transverse temporal gyri Low frequency sounds are localized in the more superficial 6) regions of the transverse temporal gyri From the transverse temporal gyri, the information flows to the unimodal incorporating sound with association cortex and then the hetero-modal association cortex other sensory information o Types of information transmitted through the auditory pathway include tone, amplitude and sound localization tonotopic organization in Tone cochlea & tonotopic o High frequency versus low frequency organization in primary Amplitude auditory cortex o Loud sound versus quiet sound Via differential firing of afferent fibers ~20 spiral ganglion neurons innervate 1 inner hair cell, but those spiral ganglion neurons have different thresholds for firing this is called differential Soft sounds generally only trigger firing of a firing; each spiral ganglion neuron has a few spiral ganglion neurons slightly different threshold Loud sounds generally trigger firing of at which they will fire almost all twenty spiral ganglion neurons Sound localization sound localization: superior o Proximity and direction of sound olivary nucleus and trapezoid Detected by neurons in the superior olivary nucleus and body trapezoid body in the pons Describe the effects, if any, of lesions in the auditory pathway on hearing o Whether or not hearing loss will ensure is dependent on where the lesion in the lesion in cochlear division of CN auditory pathway occurs at VIII or dorsal and ventral cochlear nuclei : hearing loss in Unilateral lesions in the cochlear nuclei or in cochlear division of CN VIII ipsilateral o Can cause hearing loss in the ipsilateral ear (deafness)  Unilateral lesions above the cochlear nuclei (i.e. pons, midbrain, and cortex) o Do not produce deafness, but will result in an impairment in detecting sound direction and distance These lesions do not produce deafness because there are bilateral projections at multiple sites in the brainstem mechanism for regulating selective Describe the olivocochlear system in regulating hair cell sensitivity attention to certain sounds o The olivocochlear neurons in the superior olivary nuclei of the pons send efferent fibers back to the cochlea to act as a mechanism for regulating selective attention to certain sounds (auditory modulation) Olivocochlear efferent fibers from the superior olivary nuclei project back to the cochlea to: o Inhibit auditory nerve terminals on outer hair cells o Regulate hair cell sensitivity Know different types of hearing loss and diagnostic tests o There are two different types of hearing loss conductive hearing loss and sensory neural hearing loss Conductive hearing loss occurs when there is a defect in sound transmission (involves the outer or middle ear) o A defect in sound transmission can be caused by: Foreign bodies in the external acoustic meatus A perforated tympanic membrane Most cases can be healed by themselves, but certain extensive cases may require surgery Otitis media Otosclerosis oto = bone Overgrowth of bones around stapes Prevents stapes from hitting against the oval window to start the movement of fluid within the cochlea Cholesteatoma Overgrowth of desquamated keratin debris within the middle ear cavity Sensory neural hearing loss (involves inner ear and auditory pathway) can be congenital or acquired. o Congenital hearing loss can be due to genetic mutations or developmental insults o Acquired hearing loss can be attributed to various causes: Noisy induced hearing loss Damage to sterociliated cells in Organ of Corti Loss of high frequency hearing first, which occurs at the base of the cochlea Aging related progressive bilateral/symmetric sensorineural hearing loss  Destruction of hair cells at the cochlear base Often hearing loss of higher frequencies Lesions in auditory pathway Whether or not hearing loss will ensure is dependent on where the lesion occurs Unilateral lesions in cochlear nuclei or in CN VIII can cause ipsilateral hearing loss Unilateral lesions above the cochlear nuclei (i.e. pons, midbrain, and cortex) do not produce deafness, but will result in an impairment in detecting sound direction and distance These lesions do not produce deafness because there are bilateral projections at multiple sites in the brainstem o Conductive versus sensory neural hearing loss can be distinguished by diagnostic tests (Rinne Test and Weber Test) These tests involve understanding the difference between bone conduction and air conduction. Typically, air conduction is much longer and louder than bone conduction, which is shorter and softer. o Bone conduction Sound vibration can be transmitted through temporal bone vibration to inner ear Less efficient than air conduction o Air conduction Sound transmission through tympanic membrane vibration and ossicle movement More efficient than bone conduction The Rinne Test compares bone conduction and air conduction o measure air conduction. Next, the tuning fork is hit and placed onto the mastoid process of the temporal bone to measure bone conduction In the case of conductive hearing loss, bone conduction due to blockage in air will be more effective than air conduction conduction auditory pathway In the case of sensory neural hearing loss, air conduction is more effective than bone conduction The Weber Test only evaluates bone conduction o The tuning fork is hit and placed in the middle on the top of the head In the case of conductive hearing loss, sound is heard better in the affected ear There are two explanations for this:  Because the sound information was very weak due to blockage of sound transmission, now the inner ear (sensory system) becomes really sensitive Because of the blockage of the outer or middle ear, sound remains trapped in the inner ear longer, as the exit pathway is blocked In the case of sensory neural hearing loss, sound is heard better in the unaffected ear  how do the utricle and sacule detect movement? important structures of inner ear specialized cells that synapse with neurons from the vestibular ganglion. these hair cells have attached vestibular branch of CN VIII stereocilia, including one long one called the kinocilium. stereocilia are attached to each other with proteins vestibule called tip links YOUR semicircular canals ◦when tip links stretch due to movement of the stereocilia, channels on the tips of the stereocilia VESTIBULAR NEURONS open, allowing ions to enter into the cell ARE ‣ this causes depolarization of the cell and the release of neurotransmitter, which Vestibular System stimulates the vestibular neuron TONICALLY ACTIVE bending stereocilia away from kinocilium causes hyperpolarization Describe the structure of the vestibular labyrinth of the inner ear, including the vestibule and contains the semicircular canals perilymph ◦Vestibule: part of the outer bony labyrinth between the cochlea outer bony and the semicircular canals labyrinth is in ‣ Has an inner membranous layer that contains swellings orange FUNCTIONS OF THE called the utricle and saccule inner VESTIBULAR SYSTEM : ‣ These are filled with endolymph and contain hair cells similar membranous understand and maintain the contrast endolymph with perilymph, which fills the outer to those in the cochlea layer is in teal orientation of your body with bony labyrinth and is ionically similar to cerebrospinalfluid respect to gravity Endolymph: contained in certain areas of membranous contains takes advantage of a series of layer, is higher in positive ions, especially K+, which is endolymph flexible structures in your important for action of hair cells linear acceleration, deacceleration, translational inner ear that are oriented in ‣ The utricle and saccule detect: movements, anatomic position or static head tilt typically talking about when your different planes. when these linear acceleration/deacceleration: an object moving in a straight line body is being moved by outside forces move your head, gravity bends these structures, and that can ◦Horizontal: forces acting on you when you are sitting in a car and moving forward ex: when you cause electrical impulses to in a straight line slam on the fire ◦Vertical: forces acting on you when you are riding up or down on an elevator breaks or the helps us maintain balance, whether your head is in “anatomical position”-static head tilt gas, your head adjust our orientation, and (when you tilt your head and remain in the position for a while, will tilt forward react to gravity. it also and back, ex: looking up at the stars for a while) static head tilt controls reflexes that respond respectively; translational movements: movements shifting you in a straight to head movements this is line on a certain axis something the ◦Semicircular canals: outer bony labyrinths, and have inner again, filled with utricle and membranous labyrinths inside them called semicircular ducts endolymph saccule detect ‣ You have 3 semicircular canals that are oriented in such a way that they detect motion in any axis: because they are filled with fluid X: through nose and the fluid is going to slosh in make a finger gun Anterior out back of your different ways depending on which to visualize these Posterior head way you move your head three planes Horizontal Y: through your ‣ Semicircular ducts dump into dilations called ampullae (one ears Z: up and down ampulla for each canal) Inside the ampullae are detectors called cristae that work in a somewhat similar manner to maculae YOUR VESTIBULAR NEURONS ‣ Semicircular canals detect dynamic movement and angular acceleration ARE TONICALLY ACTIVE translational movements refer Dynamic movement: voluntarily tilting and rotating your head to forces act on you to move Angular acceleration: riding on the graviton spinning you, whereas dynamic dynamic movement: you moving roll: tilt head toward shoulder movement is you moving your your head at your own volition pitch: nod your head muscles to move yourself yaw: shake head like saying “the utricle and sacule work basically the exact same way, no they just have hair cells that are oriented in different planes” Compare and contrast the motion detected by maculae in the vestibule with the motion detected by cristae in the semicircular canals ◦Macula (internal structure that contains hair cells) detects translational movement ‣ Movement that happens when an outside force acts upon you, instead of you making a conscious effort to move ‣ Hair cells in the maculae are oriented in many different and opposing directions striola: dip in the membrane So that no matter which way you move or tilt, some hair cell will be analogy: sticking a block of jello on excited, thus the body can understand which way you are being moved top of a hairbrush; if you jiggle the ‣ This is centered around a midpoint in the membrane that demarcates the jello, the bristles will move different orientations called the strolls STRIOLA macula is the term for this whole structure gravity acts on otoconia/otoliths to jiggle this gelatinous membrane and influence hair cell bending THE HAIR CELLS IN A MACULA ARE ORIENTED IN MANY DIFFERENT AND OPPOSING DIRECTIONS ‣ In the Utricle: Macula is on the floor (horizontal wall) with its hair cells pointing mnemonic: sAccule on upwards the wAll, no a Thus, the utricle responds more specifically to linear acceleration in utricle, in the horizontal axis if you’re moving forward or backward, these hair cells situated on the floor can be bent forward or backward which is on ‣ In the Saccule: the floor, Maculae are on one of the vertical walls and its hair cells are pointing which also towards you doesn’t have an a Thus, the saccule responds more specifically to linear acceleration in the vertical direction if you’re moving up or down, these hair cells situated on the wall can be bent up or down ◦Cristae ‣ Are detectors found within the ampullae 1 ampulla per semicircular duct cupula is analogous to ‣ It is filled with endolymph, and contains a set up like the utricle- macula - the AMPULLA is filled with afferent fibers synapsing on hair cells that extend into a gelatinous gelatinous endolymph, not the cristae layer, which is called a cupula structure ‣ The cupula takes up the whole space in one direction- so endolymph doesn’t flow through it, but can deform it since it is flexible cupula will be ‣ When the head turns, the sloshing of the endolymph produces a deformed AWAY force across the cupula that deforms it from the direction ‣ This can bend the hair cells and stimulate the nerve of head rotation ‣ Within an individual ampulla, all hair cells are oriented in the same direction Different from the maculae that are oriented in many different and opposing directions ‣ Understanding of which direction your head is turning comes from the fact that ampullae on both sides of your head work in pairs one will bend how do we understand in what way Each semicircular canal works together with the toward we’re moving if all the hair cells in the partner on the other side of the head that is in the kinocilium, the ampulla are oriented in the same same plane other side bends direction? Canal pairs will have their hair cells aligned oppositely, so that when one is stimulated away from ◦EACH CANAL WORKS the other is inhabited. This signal can be compared to understand which way the head kinocilium WITH A PARTNER ON is turning THE OTHER SIDE PAIRS ‣ it is the partner in The 3 pairs: right horizontal the same plane ◦Both horizontal canals and left ◦Right superior (anterior) and left posterior horizontal canals right anterior ◦Left superior (anterior) and right posterior and left canals posterior EX Horizontal canal pairs: right posterior and left anterior ◦React to rotation in the horizontal plane (shaking head IN HORIZONTAL: in a no motion: “yaw”) HAIR CELLS DEPOLARIZE ON THE SIDE ◦Hair cells in the canal towards which the head is THE HEAD IS TURNING HAIR CELLS HYPERPOLARIZE ON THE turning are depolarized and the ones in the opposite SIDE OPPOSITE THE HEAD IS TURNING side are hyper polarized in this picture the head is turning to the right. the right side cupula is pushed in the direction of the kinocilium and right only applies for flexion side neurons are stimulated. the left side cupula is pushed away from the kinocilium and left side neurons are inhibited  Vestibular System Part Two Explain the circuitry that connects the vestibular system to the central nervous system o The axons synapsing with hair cells are connected to neurons in the vestibular ganglion, which is also called. These vestibular ganglion neurons are bipolar, so their axons bifurcate The peripheral projection synapses with the ampullae and maculae The central projection travels into the CNS. This projection travels in the vestibular portion of CN VIII and enters the brainstem at the ponto- medullary junction The central processes of vestibular ganglion neurons: A) o Synapse on vestibular nuclei in the pons and medulla first order neurons - (most). There are four vestibular nuclei superior, lateral, neurons in Scarpa’s medial, and inferior ganglion second order neurons - Vestibular nuclei axons ascend and descend vestibular nuclei o Descending projections travel to: OR neurons in the The spinal cord to form cerebellar cortex vestibulospinal tracts o Ascending projections travel to: The cortex to provide awareness of head position in space Travel to the cortex via the ventral posterior nucleus of the vestibular cortex is the thalamus unique in that it is Ventral posterior nucleus considered to be a number of different areas in the axons terminate in cortical cortex areas adjacent to face representation in somatosensory cortex and in the posterior parietal cortex Extraocular nuclei to trigger reflexive eye corrections when the head moves so that gaze can remain stable Travel to the nuclei of CNs III abducens and occulomotor nuclei and VI Help coordinate eye movements in response to head movements, which is very important as your head moves small amounts constantly B) o Travel through the inferior cerebellar peduncle to synapse on neurons in the cerebellar cortex (a few) Describe the vestibulo-ocular reflex and the circuitry underlying this reflex  o Compensatory eye movements to keep a stable gaze are referred to as the vestibulo-ocular reflex. This can be demonstrated by fixing on a single spot in the distance and then turning your head left and right, while staring at that spot Example When the head turns to the right, the eyes must move to the left. In this case, the turning of your head activated your right semicircular canal, and eye movements occur in response to that signal o This means that the left eye must abduct, and the right because both eye must adduct eyes move to the The left eye abducts via the lateral rectus muscle, left as a result controlled by CN VI (abducens). The right eye of the head turning to the adducts via the medial rectus muscle, controlled by right CN III (oculomotor) o The circuitry underlying these horizontal movements of the eyes is the same as the circuitry discussed for a horizontal gaze Compare and contrast physiological nystagmus with spontaneous nystagmus o Nystagmus is a two-part movement c a motion. There are two types of nystagmus: physiologic and spontaneous Physiologic nystagmus is a normal reflexive reaction A rapid movement of the eyes can occur during a vestibulo-ocular reflex. When the eyes reach the limit of their orbit during slow movement, they snap back to center in a rapid saccade o Saccade: a rapid simultaneous movement of both eyes between two points Example: o The head turns to the right So, endolymphatic flow is toward ampulla on right and away from ampulla on left o This increases firing in the vestibular nerve on the right and decreases firing in vestibular nerve on the left Increased firing in vestibular nerve on the right drives slow eye movement to the left (this is the vestibular ocular reflex) With continued turning of the head (rotation), the eys reach their limit of movement and return to center by a fast movement to the right Spontaneous nystagmus can occur if the vestibular system is damaged. This is where the tonic firing of the semicircular canals becomes important Both the vestibulo-ocular reflex and nystagmus can occur even when the head is not turning o This can repeat many times Example: o Lesion causing decreased firing from left horizontal canal The brain is confused, and the relative decreased firing from the left horizontal canal compared to the right horizontal canal stimulates the vestibular nuclei as if the head is turning to the right, even when it is not o The eye muscles are stimulated to begin the slow eye movement When the limit of the orbit is reached, fast eye movement occurs  innervation of the eye - sensory and motor sensory ◦special (vision): CN II this is the optic nerve! it’s very interesting ◦somatic: CN V that we have blood vessels running right motor through the middle of the optic nerve. the ◦somatic (extraocular): CNs III, IV, VI vessels are the central retinal artery Visual Pathways ◦visceral efferent (intraocular): autonomic (branch of ophthalmic artery) and vein (sympathetic and parasympathetic) the globe is situated within the Describe the general anatomy of the globe and orbit orbit, which is the bony place ◦Globe what your patient is going to call the eyeball, we can see deep into ‣ “Eyeball” we’re going to call the globe, anatomically optic nerve globe ‣ Spherical shape globe is in the pyramidal space of the orbit a very spherical shaped globe is The pyramidal space is filled with periorbital fat around positioned within a very pyramidal shape incongruency the globe allows for the ability shaped bony space, so that’s kind of improved with periorbital fat ‣ Gaze directed by extraocular muscles of the globe to move like a round peg in a square hole - it’s ‣ Held in place by fascia, skin and orbital fat around within the not a very good fit bony orbit ◦the body does what it ‣ Segments of the globe optic nerves are directed medially toward the can to adapt to that and Anterior Segment (AS): posterior portion of the eye that is the deposition of ◦Cornea peri orbital fat to fill the ◦Anterior chamber space between the round ◦Posterior chamber globe and the pyramidal ◦Iris shaped orbit ◦Ciliary body ◦Lens light passes through the Posterior Segment (PS): cornea, through the anterior chamber, through the lens,, ◦Vitreous chamber through the vitreous ◦Retina chamber, and will land back ◦Sclera on the retina, which is lining ◦Choroid the inside surface of the ◦Optic nerve globe ◦Fovea centralis ‣ 3 layers of the globe tunic: “coat”; we have these concentric rings of globe material neural tunic is also called the retina Fibrous Tunic (outermost) very dark because of the presence of Vascular Tunic melanin in this region and it is there sort Neural Tunic (innermost) of to be a backdrop to prevent light from ◦Retina lined externally most by the bouncing around inside globe outer most ‣ Retinal pigment epithelium (RPE)- ◦it’s like if you go into a theater layer of retina absorbs scattered light macula = area you’ll notice the theater is usually painted with walls that ‣ Neural retina contains: just inside the RPE, right around not many blood are black to prevent light from Photoreceptors towards the anterior fovea vessels near fovea portion of the globe bouncing around behind you fovea: “pit” Fovea within macula lutea really nicely lined up with the cornea rods - ◦Area of the retina with the highest concentration of cone and the pupil so that light coming in, peripheral and photoreceptors (used to see high acuity and color vision) will be preferentially directed what your patient is going to call the eye socket, we’re non color vision ◦ Area of sharpest vision in center of fovea (foveola) towards the fovea going to call the orbit, ◦Orbit ◦no retinal ganglion cells anatomically ‣ Pyramidal-shaped space ◦few inner nuclear ‣ Dense bone laterally layer cells ‣ Thin bone medially & inferiorly This area of bone is thin so that upon impact, it will “crumple” instead of driving up into the brain (blowout the thickness of the bone that fracture) comprises the orbit varies depending on where in the orbit we are talking about ◦laterally and superiorly there are lots of different bones making up the orbit, the bone is THICK and but we don’t need to know the details of that. what we DENSE should know is that ◦medially and inferiorly the the margin of the orbit (outisde rim) is very strong bone is THIN superiorly and laterally) (dense bone towards the medial and inferior aspects of the orbit analogous to the crumple zone of your the bones are more thin and are more easily ethmoid air cell sinus; car; they will accept the force and just fractured should be empty, but in crumple and crush rather than driving the patient there is gunk bone fragments into your skull and stuff filling the space ANOPSIA LESION IN OPTIC NERVE ON AFFECTED SIDE BITEMPORAL HEMIANOPSIA LESION IN OPTIC CHIASM CONTRALATERAL (HOMONYMOUS) HEMIANOPSIA LESION IN OPTIC TRACT ON NORMAL SIDE CONTRALATERAL SUPERIOR QUADRANTANOPSIA LESION IN SUBLENT. FIBERS OF NORMAL SIDE CONTRALATERAL HEMIANOPSIA WITH MACULAR SPARING LESION IN VISUAL CORTEX OF NORMAL SIDE  information that comes into the eyes gets detected by those light comes in through all of the transparent cell photoreceptors and then travels back through the bipolar layers of the retina, activates the photoreceptors in cells in the ganglion cells. the ganglion cell axons come the fovea, and then the signal is transmitted back all info from left visual field will together to form the optic nerve. some information will cross towards the surface of the retina (ganglion cells) pass in right optic tract; all at the optic chiasm, and so some information will pass ◦the ganglion cells have all these axons, information from right visual through to the other side and all of these axons of all of these field will pass in left optic tract ganglion cells are collecting together to Sequence the events involved in form the optic nerve ◦the path of light through the retina THE INFORMATION THAT HITS THE NASAL we detect it because that light that is reflecting off of ‣ Visual field : area outside of the body/extra-personal RETINA IS THE INFORMATION THAT WILL CROSS ‣ Eyes are staying focused on the fixation point TO THE OTEHR SIDE AT THE OPTIC CHIASM THIS IS OUR VISUAL these surfaces in our external environment is ‣ If fixed on a a single point, the light from that fixation point will pass through the eye and FIELDS! don’t confuse this with eye fields, going to pass into both of pupil and will land on the temporal portion of the retina of both eyes, right at the fovea which are cortical our eyes and then be ‣ While fixating on that point, there will be light coming in from both sides of the eye regions of the brain processed posterior to that Light from the left side of the body: AT THE FIXATION POINT: if your ◦Will pass through the right eye and hit the eyes are fixed on a single place the light temporal hemiretina that is going to pass into the right eye ◦Will pass through the left eye and hit the binocular vision in through the pupil will land on the part of nasal hemiretina points B and C the retina that is lateral (temporal heim ◦ The information that hits the left eye’s nasal monocular vision in retina). light passing into the left eye will OPTIC points A and D hit the temporal hemiretina CHIASM hemiretina will cross over at the optic SUPERIOR chiasm and joins the information from the AT POINT B: light passing through TO SELLA right eye’s temporal retina (optic nerve) that information the right eye will hit the temporal TURCICA continues ipsilaterally to the right optic tract coming from the hemiretina, but light passing left side will hit the through the left eye will hit the (binocular vision) right portions of nasal hemiretina, so now we’re Light from the far left periphery only reaches the the retina getting information in two different nasal hemiretina of the left eye (monocular vision) (temporal of right eyes Light from the right side of the body: eye, nasal of left superior view AT POINT A: light will pass through ◦ Will pass through the right eye and hit the nasal hemiretina eye), and information left eye and hit the nasal hemiretina, ◦ Will pass through the left eye and hit the temporal hemiretina coming from the light will not make it into the right eye ◦The information that hits the right eye’s nasal hemiretina will cross over at the right side will hit (nose is in the way) optic chiasm and joins the information from the left eye’s temporal retina (optic the left portions of AT POINT D: light will pass through nerve) that continues ipsilaterally to the left optic tract (binocular vision) the retina the right eye and land on the nasal Light from the far right periphery only reaches the nasal hemiretina of the right eye hemiretina, light will not make it into (monocular vision) information that hits temporal hemiretina stays ipsilateral macroadenoma in sella turcica invades optic chiasm left eye (nose in the way) information that hits nasal hemiretina crosses over bitemporal hemianopsia ◦see central vision (between B and C) ◦the visual signal pathway from photoreceptor to but the information out lateral to that is ‣ visual cortex blocked because that is the information central targets of RGC Retinal ganglion cells axons form CN II and pass through the optic tracts that hits the nasal portion of the retina axons include: ◦Have different central targets: we do not hypothalamus, pretectum prefecture, superior ‣ Hypothalamus (info goes to pineal gland visually colliculus for regulation of day and night & diurnal perceive the LGN of thalamus cycles), pretectum, superior colliculus information we do not visually Do not visually see the information going to the perceive this information that is sent to these targets hypothalamus ‣ Lateral geniculate nucleus of thalamus , pretectum, (LGN) blue line in pic not V1 and superior We see the information sent to this colliculus target (area 17, V1) from the optic The LGN projects mainly to the primary visual cortex nerve ◦Projects to the primary visual cortex by the retrolenticular and sublenticular optic radiations (see below objective for description) Primary Visual Cortex in the occipital lobe ◦Divided by the calcarine sulcus to form the cuneus and lingula  ‣ efferent limb of pupillary light reflex (not on quiz) Light level detected by retinal ganglion cells throughout retina, in both nasal and temporal parts ◦Nasal RGC axons project to contralateral pretectum ◦Temporal RGC axons project to ipsilateral pretectum effectors of Pretectum on each side projects bilaterally to Edinger- Edinger- Westphal nucleus (preganglionic parasympathetics) Westphal Edinger-Westphal neurons project to ciliary ganglion nucleus are (postganglionic parasympathetics) the lens and Edinger-Westphalia nucleus is nucleus of CN III the pupil i ◦Innervates constrictor muscles in pupillary light reflex pretectal area controls pupillary light reflex as we go away from fovea, cone Compare and contrast: population quickly decreases and is ◦Rod- & cone- photoreceptor distribution & function quickly replaced by rods responsible for non ‣ Rods: present at high density throughout retina, except for sharp color and peripheral vision decline in fovea ‣ Cones: present at low density throughout the retina, except for allow us to see color sharp peak in fovea the retina contains rods and cones and high acuity vision rods concentrated toward the periphery, sharp decline at fovea cones concentrated toward the center (fovea) , sharp incline at fovea as we get further away ◦Fovea & optic disk optic nerves are from the fovea we will start ‣ Both are specialized areas of the retina in a general sense, macula is highest visual acuity directed medially to see more rods, which are ‣ Fovea: shallow depression on surface of retina, within macula lutes for non-color and no blood vessels Only cells present are the photoreceptors (cones) peripheral vision around fovea because Region of highest visual acuity why would we want In center of fovea (foveola): blood vessels in our ◦No retinal ganglion cells region of highest ◦Few inner nuclear layer cells acuity ‣ Optic disc: Inside portion of the globe that is continuous with the optic nerve that is outside the globe nerve fiber layer collects and OPTIC DISC (axons bundled from the nerve fiber “Blind-spot” of the eye heads toward optic disc, which is layer all travel toward this ◦No photoreceptors the inside portion (inside the region called the optic disc) ◦Contains neuroganglia cell axons globe) that is continuous with the optic nerve outside of the globe IS OUR BLIND SPOT OF All blood vessels THE EYE ooo from central retinal cuneate, retrolenticular, lower visual field artery and vein lingula, sublenticular, upper visual field ◦Retrolenticular- & sublenticular- parts of optic radiations white matter fiber tracts ‣ Retrolenticular: Fibers from the lateral geniculate nucleus to the cuneate gyrus of the primary visual cortex that conveys the lower visual field Has a pathway that stays retro to the lenticular nucleus ‣ Sublenticular: Fibers from the lateral geniculate nucleus that form the sublenticular Meyer’s loop and then continue to the lingual gyrus of the = superior primary visual cortex to convey the upper visual field visual field Has a pathway that swoops anteriorly in an area under the lenticular nucleus, and then swoops to the lingual gyrus information coming from inferior retrolenticular fibers visual field will hit superior unimodal association area: photoreceptors of retina dedicated to one modality information coming from superior heteromodal association area: sublenticular fibers visual field will hit inferior blending or synthesizing of photoreceptors of retina information from different THIS INFO WILL STAY kinds of modalities SEGREGATED DURING ITS PATHWAY BACK TO THE LGN  ◦Accommodation reflex & Pupillary light reflex testing ‣ Accommodation Reflex (Near Reflex) Shifting gaze from distant to near object: ◦Convergence of the eyes when you shift your gaze ‣ Left and right medial recti muscles from distant to nearby ‣ Left and right CN III nuclei and nerves object, these three things ‣ Accommodation center in midbrain happen: ‣ Tested by bringing finger closer to the patients nose ◦Accommodation of lens ‣ Parasympathetics in CN III that goes to the ciliary body ‣ Lens changes its shape makes it fatter, so that you can focus on something that’s very nearby ‣ Can not be watched for testing ◦Pupillary constriction ‣ Parasympathetics in CN III ‣ As patient focuses on your finger moving closer to their nose, the pupils constrict so you can’t use this test to Entire reflex is lost in a CN III lesion look at patients in a coma, Patient has to be awake and able to follow commands to test this reflex but YOU CAN USE THE PUPILLARY LIGHT for example, when you shine a light into the left eye, REFLEX ‣ Pupillary Light Reflex the direct reflex is constriction of the left pupil, and Pupil constriction in response to increased illumination the consensual reflex is the constriction of the right ◦Direct reflex: ipsilateral constriction pupil ◦Consensual reflex: contra lateral constriction Neurological test ◦Tests for intact: ‣ Afferent limb: can you see the light (by CN II) ‣ Efferent limb: can your pupils react to that light (by CN III, light information is detected by specifically the Edinger-Westphal nucleus, the retina and transmitted parasympathetic pathway) through the optic nerve and back ◦Used in unconscious patients to detect midbrain damage to the optic chiasm Pathway ◦Light level detected by retinal ganglion cells throughout retina, in both nasal and in contrast to many other retinal temporal parts ganglion cells, these specific ◦Nasal RGC axons project to contralateral pretectum retinal ganglion cells do not ◦Temporal RGC axons project to ipsilateral synapse at the LGN. they pretectum synapse in the pretectal region ‣ Axons from both types of RGC do not synapse at the lateral geniculate nucleus, at the pretectal region, these they pass through to the pretectal region cells stimulate an inter neuron (where they synapse) ◦Pretectum on each side projects bilaterally to Edinger-Westphal nucleus (location of the the interneuron stimulates the Edinger-Westphal nucleus of preganglionic parasympathetic cell bodies) both the right and left portions of ‣ This is whats responsible for the consensual response the midbrain ◦ The axons from the Edinger-Westphal neurons project to the ipsilateral ciliary ganglion and synapse here on the postganglionic parasympathetic cell bodies ◦The fibers from the ciliary ganglion then synapse on the pupillary constrictor the axons leaving the Edinger- muscle to decrease the size of the pupil to limit the amount of light that comes Westphalia nucleus project to H the ipsilateral ciliary ganglion into the eye the axon leaving the ciliary ganglion (location of postganglionic parasympathetics) projects to the pupillary muscle  Detecting lesions (can be done in unconscious patients) ◦In the afferent limb of the pathway ‣ Lesion to right CN II Increased light level not detected by right eye when light is shown in the right eye, so there is no direct or consensual reflex When the light is shown in the left eye, there is direct and consensual reflex since the left eye’s afferent limb is intact, and both efferent limbs are intact ◦In the efferent limb of the pathway ‣ Lesion to right CN III When light is shown in the right eye, the signal is detected, so there is a constriction on the left side, but the right eye does not constrict due to the damaged efferent limb on the right When light is shown in the left eye, the left eye constricts, but the right eye still does not constrict due to lesion Right eye does not constrict regardless of what eye the light is shown to Pupillary Control ◦Parasympathetic: Accommodation & Pupillary Light Reflexes ‣ Constrictor muscles (sphincter shaped muscle, so when they contract they