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VisionVision

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Processes Processes 1. Light energy is transduced into neural activity1. Light energy is transduced into neural activity2. Neural activity is processed by the brain2. Neural activity is processed by the brain  Note: By way of analogy, you can imagine takingNote: By way of analogy, you can imagine taking a picture with a camera. The eye is the camera, a picture with a camera. The eye is the camera, the retina, which is a specialized part of the brainthe retina, which is a specialized part of the brainat the back of the eye, is the film, and the parts ofat the back of the eye, is the film, and the parts ofthe brain that process visual information is the the brain that process visual information is the photoshop.photoshop.

Human visual systems permit light reflected off Human visual systems permit light reflected off distant objects to be:distant objects to be:1.1. Localized relative to the individual within his orLocalized relative to the individual within his orher environmenther environment2. Identified based on size, shape, color, and past2. Identified based on size, shape, color, and pastexperienceexperience3. Perceived to be moving (or not)3. Perceived to be moving (or not)4. Detected in a wide variety of lighting conditions4. Detected in a wide variety of lighting conditions

Sequence of eventsSequence of events1. Light entering the eye is focused on the retina1. Light entering the eye is focused on the retina2. Retina converts light energy into neuronal 2. Retina converts light energy into neuronal activityactivity3. Axons of the retinal neurons are bundled to 3. Axons of the retinal neurons are bundled to form the optic nervesform the optic nerves4. Visual information is distributed to several 4. Visual information is distributed to several brain structures that perform different functionsbrain structures that perform different functions

Anatomy of the EyeAnatomy of the Eye

Structural levelsStructural levels1. Gross anatomy1. Gross anatomy2. Opthalmoscopic appearance2. Opthalmoscopic appearance3. Cross-section anatomy3. Cross-section anatomy

Gross anatomyGross anatomy

1. External features of the eye1. External features of the eyea.a.Pupil--opening that allows light to reachPupil--opening that allows light to reachthe retinathe retinab. Iris--circular muscle that controls b. Iris--circular muscle that controls the diameter of the pupilthe diameter of the pupilc. Aqueous humor--fluid behind the corneac. Aqueous humor--fluid behind the cornead. Sclera--outermost layer that forms the d. Sclera--outermost layer that forms the eyeballeyeball

e. Extraocular muscles--attached to the e. Extraocular muscles--attached to the eye and skull and allow movementeye and skull and allow movementf. Conjunctiva--membrane inside the f. Conjunctiva--membrane inside the eyelid attached to the scleraeyelid attached to the sclerag. Optic nerve--axons of the retina leavingg. Optic nerve--axons of the retina leavingthe eyethe eyeh. Cornea--transparent surface coveringh. Cornea--transparent surface coveringthe iris and pupilthe iris and pupil

Opthalmoscopic appearanceOpthalmoscopic appearance

Retina as seen through the pupil Retina as seen through the pupil (aside: in photographs, the red (aside: in photographs, the red appearance of the eye is actuallyappearance of the eye is actuallythe retina photographed. Double the retina photographed. Double flash camera causes the pupil toflash camera causes the pupil toconstrict)constrict)

a.Optic disk (a.Optic disk (blind spot, no vision is possibleblind spot, no vision is possible)) i. Blood vessels originate here. The vessels i. Blood vessels originate here. The vessels shadow the retinashadow the retina ii. Optic nerve fibers exit hereii. Optic nerve fibers exit here iii. No photoreceptorsiii. No photoreceptorsb. Macula--area of the retina responsible for b. Macula--area of the retina responsible for central vision (vs. peripheral)central vision (vs. peripheral)c. Fovea--center of the retina (where most of c. Fovea--center of the retina (where most of the cones are)the cones are)

Cross sectional anatomy Cross sectional anatomy

a. Lens--transparent surface that contributes a. Lens--transparent surface that contributes to the formation of images.to the formation of images.

b. Ciliary muscles--change the shape of the b. Ciliary muscles--change the shape of the lens and allow focusinglens and allow focusing

c. Vitreous humor--more viscous than the c. Vitreous humor--more viscous than the aqueous humoraqueous humor

i. Lies between the lens and the retinai. Lies between the lens and the retina ii. Provides spherical shapeii. Provides spherical shaped. Retinad. Retina i. Inner most layer of cells at the back of the i. Inner most layer of cells at the back of the

eyeeye ii. Transduces light energy into neural ii. Transduces light energy into neural

activityactivity

Image FormationImage Formation

ProcessesProcesses1. Refraction by the cornea1. Refraction by the cornea2. Accommodation by the lens2. Accommodation by the lens3. Pupillary light reflex3. Pupillary light reflex

Refraction by corneaRefraction by cornea1. Distant objects1. Distant objectsa. Light rays run in parallela. Light rays run in parallel

2. Light rays slow2. Light rays slowa. Corneaa. Corneab. Aqueous humorb. Aqueous humor3. Light rays bend3. Light rays benda. Perpendicular to the angle (radius a. Perpendicular to the angle (radius

of the cornea) between the curve of of the cornea) between the curve of the cornea and the plane they are the cornea and the plane they are traveling ontraveling on

4. Focal distance4. Focal distancea. Distance between the refractive a. Distance between the refractive

surface and where the light rays surface and where the light rays convergeconverge

b. Depends on the curvature of the b. Depends on the curvature of the corneacornea

i. 2.4 cmi. 2.4 cm ii. Distance between the cornea and ii. Distance between the cornea and

the retinathe retina

Accommodation by the lensAccommodation by the lens

1. Objects within 9 meters1. Objects within 9 metersa. Light rays do not travel in parallela. Light rays do not travel in paralleli. Some divergei. Some diverge2. Lens adds refractive power2. Lens adds refractive powerProvided by changing the shape Provided by changing the shape of the lensof the lens

3. Contraction of ciliary muscles3. Contraction of ciliary musclesTension on the suspensory Tension on the suspensory

ligamentsligamentsis releasedis releasedb. Lens becomes roundedb. Lens becomes roundedc. Greater the curvature provides c. Greater the curvature provides

greatergreaterthe refractionthe refraction

Pupillary light reflexPupillary light reflex1. Pupil contribute to optical qualities 1. Pupil contribute to optical qualities

of the eyeof the eyea. Adjusts for different light levelsa. Adjusts for different light levelsb. Contributes to simultaneous b. Contributes to simultaneous

focusing on near and distant objectsfocusing on near and distant objects2. Accommodation alters light rays 2. Accommodation alters light rays

that would otherwise run in parallelthat would otherwise run in parallela. Light rays are no longer focused on a. Light rays are no longer focused on

the retina by the corneathe retina by the cornea

3. Closing the aperture of the pupil3. Closing the aperture of the pupila. Only light rays that are primarily in a. Only light rays that are primarily in

the center of the cornea and lens are the center of the cornea and lens are allowed inallowed in

b. These are generally not focusedb. These are generally not focusedc. Permits seeing things in the c. Permits seeing things in the

foreground and background in focusforeground and background in focus

Additional terms and conceptsAdditional terms and concepts

1. Visual field1. Visual fielda. Total space that can be viewed by a. Total space that can be viewed by

the retinathe retina i. 150 degreesi. 150 degrees ii. 90 on temporal sideii. 90 on temporal side iii. 60 on the nasal sideiii. 60 on the nasal side2. Image formed on the back of the 2. Image formed on the back of the

retina is reversed and invertedretina is reversed and inverted

3. Emmetropia (normal vision)3. Emmetropia (normal vision)a. Parallel light rays are focused on a. Parallel light rays are focused on

the retina without accommodationthe retina without accommodation

Hyperopia (farsightedness)Hyperopia (farsightedness)a. Eye ball is too short a. Eye ball is too short b. Image is focused at a point behind b. Image is focused at a point behind

the retinathe retinac. Lens can accommodate for distant c. Lens can accommodate for distant

objects but not for nearobjects but not for neard. Condition can be corrected with a d. Condition can be corrected with a

convex lens (e.g., increase convex lens (e.g., increase refractive power)refractive power)

Myopia (nearsightedness)Myopia (nearsightedness)a. Eye ball is too longa. Eye ball is too longb. Light rays converge in front of the b. Light rays converge in front of the

retinaretinac. Lens can accommodate for near c. Lens can accommodate for near

objects but not distantobjects but not distantd. Condition can be corrected with a d. Condition can be corrected with a

concave lensconcave lens

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VisionVision

Microscopic Anatomy of the RetinaMicroscopic Anatomy of the Retina

A.A.Specialized cells Specialized cells of the retina convertof the retina convertlight energy into light energy into neural activityneural activityB. Cellular architectureB. Cellular architectureOf the retinaOf the retina

Cell typesCell typesa.a.Photoreceptors--the only lightPhotoreceptors--the only lightsensitive cells in the retinasensitive cells in the retina i. Transduce light energy into neural i. Transduce light energy into neural signalssignalsb. Bipolar cells--connect photoreceptors b. Bipolar cells--connect photoreceptors to ganglion cellsto ganglion cells

c. Ganglion cells--fire action potential and c. Ganglion cells--fire action potential and send axons to the brainsend axons to the braind. Horizontal cells--receive inputs from Photod. Horizontal cells--receive inputs from Photoreceptors and project laterally to bipolar cellsreceptors and project laterally to bipolar cellse. Amacrine cells--receive inputs from bipolar e. Amacrine cells--receive inputs from bipolar cells and project laterally to ganglion cellscells and project laterally to ganglion cells

Layers (3 primary, but there are Layers (3 primary, but there are subdivisions)subdivisions)a. Ganglion cell layer--cell bodies of the a. Ganglion cell layer--cell bodies of the ganglion cellsganglion cellsb. Inner nuclear layer--cell bodies of the b. Inner nuclear layer--cell bodies of the bipolar cellsbipolar cellsc. Outer nuclear layer--cell bodies of the c. Outer nuclear layer--cell bodies of the photoreceptorsphotoreceptors

Characteristics:Characteristics:a. Photoreceptors are the only cells that a. Photoreceptors are the only cells that respond to lightrespond to lightb. Ganglion cells are the only output cellsb. Ganglion cells are the only output cellsc. Light travels through the other cell c. Light travels through the other cell layers to reach the photoreceptorslayers to reach the photoreceptorsd. At the back of the eye is a pigmented d. At the back of the eye is a pigmented epithelium that absorbs any light not epithelium that absorbs any light not absorbed by the photoreceptorsabsorbed by the photoreceptors

Side point: Inside many mammalian eyes,Side point: Inside many mammalian eyes,There is an additional layer of cells betweenThere is an additional layer of cells betweenThe photoreceptors and the epithelial layer The photoreceptors and the epithelial layer That reflects the light back out again. The That reflects the light back out again. The photoreceptors have two opportunities to photoreceptors have two opportunities to Be exposed--greatly enhances night vision.Be exposed--greatly enhances night vision.

C. Photoreceptors--two kinds based on C. Photoreceptors--two kinds based on appearance and functionappearance and function

1. Rods--long, cylindrical, many disks1. Rods--long, cylindrical, many disksa. Photopigment is in the diska. Photopigment is in the diskb. Rods have a much higher pigment b. Rods have a much higher pigment concentrationconcentrationc. 1000x more sensitive to light than c. 1000x more sensitive to light than conesconesd. Function in scotopic conditionsd. Function in scotopic conditions i. Nighttime lightingi. Nighttime lightinge. All rods have the same pigmente. All rods have the same pigment i. Rhodopsini. Rhodopsin

2. Cones--shorter, tapering outer 2. Cones--shorter, tapering outer segment, relatively few diskssegment, relatively few disksa. Photopic conditionsa. Photopic conditions i. Daytime lightingi. Daytime lighting ii. Primarily conesii. Primarily conesb. 3 different types of cones basedb. 3 different types of cones basedon type of photopigmenton type of photopigment i. Pigments are differentially i. Pigments are differentially sensitive to wavelength of lightsensitive to wavelength of light

3. Retina is therefore a duplex3. Retina is therefore a duplexa. Scotopic retina using only rodsa. Scotopic retina using only rodsb. Photopic retina using primarily conesb. Photopic retina using primarily cones

4. Distribution of rods and cones4. Distribution of rods and cones

4. Distribution of rods and conesa4. Distribution of rods and conesaa.a.Rods and cones are distributed Rods and cones are distributed regionallyregionallyb. Center of the eye (i.e., the fovea)b. Center of the eye (i.e., the fovea) i. Only conesi. Only conesc. Peripheral retinac. Peripheral retina i. Primarily rodsi. Primarily rods ii. Few conesii. Few cones

5. Connectivity5. Connectivitya. Central retinaa. Central retina i. 1:1 (approximately) correspondence i. 1:1 (approximately) correspondence between photoreceptor and ganglionbetween photoreceptor and ganglionb. Peripheral retinab. Peripheral retina i. Many photoreceptors (rods) converge i. Many photoreceptors (rods) converge on a single output ganglion cellon a single output ganglion cellc. Peripheral retina is more sensitivec. Peripheral retina is more sensitiveto lightto light

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PhototransductionPhototransduction

Photoreceptors transduce (change) light Photoreceptors transduce (change) light energy into changes in membrane potentialenergy into changes in membrane potential

1.1.Analogous to transduction of Analogous to transduction of chemical signals into electrical chemical signals into electrical signals that occurs during signals that occurs during synaptic transmission at synaptic transmission at G-protein coupled receptorsG-protein coupled receptors

2. Events at G-protein coupled receptors2. Events at G-protein coupled receptorsa. Binding of NT activates G-proteinsa. Binding of NT activates G-proteinsb. G-protein activation stimulates various b. G-protein activation stimulates various effector enzymeseffector enzymesc.Enzymes alter the intracellular concen-c.Enzymes alter the intracellular concen-tration of cytoplasmic second messengerstration of cytoplasmic second messengersd. 2nd messengers either directly or indirectly d. 2nd messengers either directly or indirectly alter membrane ion channels which alter alter membrane ion channels which alter membrane potentialmembrane potential

3. Events during phototransduction3. Events during phototransductiona. Light stimulation of photopigment activates a. Light stimulation of photopigment activates G-proteinsG-proteinsb. G-proteins activate various effector b. G-proteins activate various effector enzymesenzymesc. Enzymes decrease intracellular c. Enzymes decrease intracellular concentrations of 2nd messengers (cGMP)concentrations of 2nd messengers (cGMP)d. Change in 2nd messenger concentration d. Change in 2nd messenger concentration closes a Na+ channelcloses a Na+ channel

Functional considerationsFunctional considerations

1. In complete darkness there is a steady 1. In complete darkness there is a steady influx of Na+ which depolarizes the influx of Na+ which depolarizes the photoreceptor membranephotoreceptor membranea. Movement of + charge across the a. Movement of + charge across the membrane is called the dark currentmembrane is called the dark current2. Na+ channels responsible for this current 2. Na+ channels responsible for this current are gated by cGMP are gated by cGMP a. cGMP is produced continually in a. cGMP is produced continually in photoreceptorsphotoreceptors i. Na+ channels stay open in the darki. Na+ channels stay open in the dark

3. In the light3. In the lighta. cGMP is converted to GMP (phospho-a. cGMP is converted to GMP (phospho-diesterase hydrolyzes cGMP)diesterase hydrolyzes cGMP)b. Membrane hyperpolarizes in response to b. Membrane hyperpolarizes in response to light. Na+ channels closelight. Na+ channels close4. Rhodopsin (photopigment) located in 4. Rhodopsin (photopigment) located in stacked disks in the outer segment of rods. It stacked disks in the outer segment of rods. It is comprised of retinal and opsin. Opsin is comprised of retinal and opsin. Opsin absorbs lightabsorbs light

5. Bleaching5. Bleachinga. Photoreceptors no longer respond at a. Photoreceptors no longer respond at particular light intensitiesparticular light intensitiesb. Activation of rods by light bleaches the b. Activation of rods by light bleaches the photopigmentphotopigment i. Changes the wavelengths absorbed by i. Changes the wavelengths absorbed by rhodopsinrhodopsin

6. Cones also contain opsins6. Cones also contain opsinsa. Three different opsinsa. Three different opsins i. Each maximally activated i. Each maximally activated by different wavelengths of by different wavelengths of lightlight ii. Blue--430 nmii. Blue--430 nm iii. Green--530 nmiii. Green--530 nm iv. Red--560 nmiv. Red--560 nm

b. All colors are created by b. All colors are created by mixing the proper ratio of mixing the proper ratio of red, green and bluered, green and bluec. Colors are assigned by the c. Colors are assigned by the brain based on a comparison brain based on a comparison of the readout of the three of the readout of the three cone typescone typesi. White results from equal i. White results from equal activation of all threeactivation of all three

Dark and light adaptationDark and light adaptationNote: Most of have had the following Note: Most of have had the following experiences. Get up at night and turn experiences. Get up at night and turn on the bathroom light; leave a brightly on the bathroom light; leave a brightly lit room to go down the basement lit room to go down the basement when there are no lights on. when there are no lights on. Remember there are two different Remember there are two different visual systems--one for daytime that visual systems--one for daytime that utilizes all cones and one for nighttime utilizes all cones and one for nighttime that utilizes all rods. There is a time that utilizes all rods. There is a time course necessary for the course necessary for the photoreceptors to "come on line".photoreceptors to "come on line".

Changes associated with adaptationChanges associated with adaptationa. Pupil diameter changesa. Pupil diameter changesb. Regeneration (or generation) of unbleached b. Regeneration (or generation) of unbleached (bleached) rhodopsin(bleached) rhodopsinc. Change the functional circuits to allow 1:1 c. Change the functional circuits to allow 1:1 rod to ganglion or reverse that to allow 1:1000rod to ganglion or reverse that to allow 1:1000

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Connectivity in the RetinaConnectivity in the Retina

Communicating changes in Communicating changes in photoreceptor function to the brainphotoreceptor function to the brain1. Only ganglion cells fire action 1. Only ganglion cells fire action potentialspotentialsa. Axons of ganglion cells form the a. Axons of ganglion cells form the optic nerveoptic nerve

Photoreceptor receptors to ganglion cellsPhotoreceptor receptors to ganglion cells1. Light energy (or its absence) is 1. Light energy (or its absence) is transduced into a chemical signal. transduced into a chemical signal. a. In response to dark, photoreceptors are a. In response to dark, photoreceptors are depolarized and release NT (glutamate).depolarized and release NT (glutamate).2. Photoreceptors make synaptic contact 2. Photoreceptors make synaptic contact with bipolar cells either directly or with bipolar cells either directly or indirectly via horizontal cellsindirectly via horizontal cells

3. Bipolar cells, in response to the glutamate 3. Bipolar cells, in response to the glutamate released by photoreceptors, are either released by photoreceptors, are either depolarized or hyperpolarized.depolarized or hyperpolarized.a. Based on their response to glutamate, a. Based on their response to glutamate, bipolar cells can be classified as:bipolar cells can be classified as: i. OFF cells ("off" refers to light being off) i. OFF cells ("off" refers to light being off) depolarize when there is no light. In darkness, depolarize when there is no light. In darkness, the glutamate released by the photoreceptor the glutamate released by the photoreceptor causes an EPSP in the bipolar cellcauses an EPSP in the bipolar cell ii. ON cells ("on" refers to light being on) ii. ON cells ("on" refers to light being on) hyperpolarize when there is no light (they hyperpolarize when there is no light (they depolarize when there is light)depolarize when there is light)

b. In darkness, the glutamate released by the b. In darkness, the glutamate released by the photoreceptor causes an IPSP in the bipolar photoreceptor causes an IPSP in the bipolar cellcell

Ganglion cellsGanglion cells1. Output neurons of the retina1. Output neurons of the retina2. Types2. Typesa. M-type ganglion—largea. M-type ganglion—largeb. P-type ganglion—smallb. P-type ganglion—small

Neural CircuitryNeural Circuitry

PathwayPathway

1. Retina to LGN (lateral geniculate 1. Retina to LGN (lateral geniculate nucleus of the thalamus)nucleus of the thalamus)2. LGN to the primary visual cortex2. LGN to the primary visual cortex3. Primary visual cortex to other 3. Primary visual cortex to other cortical areascortical areas

Connection between eyes and brainConnection between eyes and brain

1. Optic nerve, optic chiasm, optic tract1. Optic nerve, optic chiasm, optic tract2. Functional considerations2. Functional considerationsa. Information from the right visual field a. Information from the right visual field crosses to the left side of the braincrosses to the left side of the brain i. Decussationi. Decussationb. Information from the left crosses to the b. Information from the left crosses to the rightrightc. Not all information crossesc. Not all information crosses i. Partial decussationi. Partial decussation

General considerationsGeneral considerations1. Left and right visual worlds are processed 1. Left and right visual worlds are processed contralaterallycontralaterallya. Information about the left visual field is a. Information about the left visual field is processed by the right side of the brainprocessed by the right side of the brainb. Information about the left that is seen by b. Information about the left that is seen by the right eye does not cross overthe right eye does not cross over2. Right and left eyes perceive parts of both 2. Right and left eyes perceive parts of both visual worldsvisual worlds3. Image is inverted and reversed3. Image is inverted and reversed

Exercise: Look straight ahead. Imagine a verticalExercise: Look straight ahead. Imagine a verticalline dividing the right and left side. line dividing the right and left side. 1.1.Objects appearing to the left are in the left visual Objects appearing to the left are in the left visual hemifield.hemifield.2. Objects appearing to the right are in the right2. Objects appearing to the right are in the rightvisual hemifield.visual hemifield.Close your left eye. Your right eye sees part of theClose your left eye. Your right eye sees part of theleft visual hemifield. Remember that images as seen left visual hemifield. Remember that images as seen on the retinal are reversed. Objects in the temporal on the retinal are reversed. Objects in the temporal part of the left hemifield are focused onto the nasal part of the left hemifield are focused onto the nasal retina of the left eye. Objects in the nasal part of the retina of the left eye. Objects in the nasal part of the right hemifield are focused on the temporal retina of right hemifield are focused on the temporal retina of the left eye. The temporal retinal output does not the left eye. The temporal retinal output does not cross over. cross over. 

Target of optic tractTarget of optic tract

1. Primary target is the LGN 1. Primary target is the LGN 2. 10% goes to the superior colliculus 2. 10% goes to the superior colliculus in the midbrainin the midbrain3. Hypothalamus (SCN-circadian 3. Hypothalamus (SCN-circadian rhythm)rhythm)4. Pretectum-reflex control of the 4. Pretectum-reflex control of the pupil and lens pupil and lens

Lateral geniculate nucleus (LGN)Lateral geniculate nucleus (LGN)1. Part of the dorsal thalamus1. Part of the dorsal thalamus2. Arranged in six (6) layers (Draw--bended 2. Arranged in six (6) layers (Draw--bended knee; 6 dorsal, 1 ventral)knee; 6 dorsal, 1 ventral)3. Layers 1 + 2 (most ventral) contain large 3. Layers 1 + 2 (most ventral) contain large neurons and are referred to as neurons and are referred to as magnocellular LGN layers. magnocellular LGN layers. 4. Layers 3 - 6 contain small neurons and 4. Layers 3 - 6 contain small neurons and are referred to as parvocellular LGN layers.are referred to as parvocellular LGN layers.

5. The information from the two separate 5. The information from the two separate eyes is kept separate by projecting to eyes is kept separate by projecting to different layers of the LGNdifferent layers of the LGNa. Remember the nasal retinal sees the a. Remember the nasal retinal sees the temporal part of the hemifields.temporal part of the hemifields.i. This information crosses overi. This information crosses overb. The temporal retina of the opposite eye b. The temporal retina of the opposite eye sees the retinal part of the opposite sees the retinal part of the opposite hemifieldhemifieldi. This information does not cross overi. This information does not cross over

Connection between retina and LGNConnection between retina and LGN(Given the left hemifield)(Given the left hemifield)1.Nasal retina projects to layers 1, 4 and 61.Nasal retina projects to layers 1, 4 and 6a. Information about the temporal part is a. Information about the temporal part is seen by the nasal retina of the left eye seen by the nasal retina of the left eye i. This information goes to the right LGN i. This information goes to the right LGN layers 1, 4 and 6layers 1, 4 and 6

ExerciseExerciseWhere would a P-type ganglion cells in Where would a P-type ganglion cells in the right nasal retina project?the right nasal retina project?

Where would a P-type ganglion cells in Where would a P-type ganglion cells in the left temporal retina project?the left temporal retina project?

Where would a M-type ganglion cells in Where would a M-type ganglion cells in the right nasal retina project?the right nasal retina project?

Where would a M-type ganglion cells in Where would a M-type ganglion cells in the left temporal retina project?the left temporal retina project?

(Left LGN layer 4 and 6)(Left LGN layer 4 and 6)

(Left LGN layer 3 and 5)(Left LGN layer 3 and 5)

(Left LGN layer 1)(Left LGN layer 1)

(Left LGN layer 2)(Left LGN layer 2)

Connection between LGN Connection between LGN and primary visual cortexand primary visual cortex

1.1.Cortical organizationCortical organizationArranged in 6 layersArranged in 6 layers,Layer IV is subdivided,Layer IV is subdividedinto three separate into three separate layers--IVA, B, and C. layers--IVA, B, and C. 2. LGN projects 2. LGN projects primarily to layer IVCprimarily to layer IVC

3. Layer IVC is divided into two tiers3. Layer IVC is divided into two tiersa. Alphaa. Alphab. Betab. Beta4. Magnocellular LGN layers project 4. Magnocellular LGN layers project to IVC alphato IVC alpha5. Parvocellular LGN layers project 5. Parvocellular LGN layers project to IVC betato IVC beta

ExerciseExerciseNow where would a P-type ganglion Now where would a P-type ganglion cells in the right nasal retina project?cells in the right nasal retina project?

Higher Level Cortical ProcessingHigher Level Cortical ProcessingNot DiscussedNot Discussed