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THE VISUAL SYSTEM
D. C. MIKULECKYPROFESSOR OF PHYSIOLOGY
ANDFACULTY MENTORING PROGRAM
THE VISUAL SYSTEM SENSES ELEECTROMAGNETIC RADIATION
ELECTROMAGNETIC RADIATION (EMR) SPANS THE ELECTROMAGNETIC SPECTRUM (EMS)
FROM RADIO WAVES (VERY LONG) TO -RADIATION (VERY SHORT)
VISIBLE LIGHT IS A SMALL PORTION OF THE SPECTRUM
PHOTONS OF LIGHT INTERACT WITH MATTER
ANATOMICAL ORGANIZATION
THE EYECORNEA AND LENS: BEND LIGHT RAYS
AND FOCUS THEM ON THE RETINACILLIARY MUSCLES LOSSEN OR TIGHTEN
TO ADJUST LENS THICKNESSRETINA: SITE OF PHOTORECEPTORSFOVEA: MOST SENSITVE PART OF RETINA
TEAR DUCTANDDRAINAGECANAL
PUPIL IRISSCLERA
OPTIC DISC
OPTIC NERVE
BLOOD VESSELS
FOVEA
SCLERA
RETINA
CHOROID
VITREOUS HUMOR
AQUEOUS HUMOR
CORNEA
LENS
PUPIL
IRIS
CONJUNCTIVACILIARY BODY
SUSPENSORY LIGAMENTEXTERNAL EYEMUSCLE
STRUCTURE OF THE EYE
THE PHOTORECEPTORSRODS:
CYLLINDRICALLY SHAPED- BROAD RANGE OF WAVELENGTHS, NIGHT
CONES: CONICALLY SHAPED-NARROW WAVELENGTH RANGE, COLOR
BEFORE A PHOTON ARRIVES
SODIUM IS PUMPED AND LEAKS BACK THROUGH OPEN CHANNEL
CHANNEL’S OPENNESS DEPENDENT ON cGMP
MEMBRANE POLARIZED NORMALLY
AFTER A PHOTON ARRIVES
RHODOPSIN ABSORBS PHOTON AND CHANGES SHAPE
TRANSDUCIN ACTIVATED BY RHODOPSINPHOSPHODIESTERASE ACTIVATED BY
TRANSDUCINcGMP HYDROLIZEDSODIUM CHANNEL CLOSESMEMBRANE HYPERPOLARIZED
RETINA’S NEURAL NETWORK
GANGLION CELLS: DEPOLARIZED BY BIPOLAR CELLS, FORM OPTIC NERVE
BIPOLAR CELLS: DEPOLARIZED BY PHOTORECEPTOR CELLS
HORIZONTAL CELLS: INHIBITED BY PHOTORECEPTORS - DEPOLARIZE ADJACENT PHOTORECEPTORS(INHIBITING THEM)
HORIZONTAL CELLS INHIBIT ADJACENT PHOTORECEPTORS
A B A B
PHOTORECEPTORS PHOTORECEPTORS
HIGHRATE OFFIRING
GANGLION CELL LOW
RATE OFFIRING
GANGLION CELL
RECEPTIVE FIELDS
THE AREAS OF THE RETINA THAT EXCITE OR INHIBIT A GANGLION CELL MAKE UP THE RECEPTIVE FIELD FOR THAT CELL
RETINAL GANGLION CELLS HAVE ANNULAR RECEPTIVE FIELDS WITH DIFFERENT PATTERNS
PATERNS OF EXCITATION/INHIBITION
PHOTORECEPTOR
HORIZONTAL CELLS
BIPOLAR CELLS
+
- - --
+-
-+
PATHWAYS FOR VISUAL INFORMATION
OPTIC NERVE (GANGLION CELLS FROM RETINA)
LEAVES THROUGH “BLIND SPOT”LATERAL GENICULATE NUCLEUS:
PROJECTS TO CORTEXPRIMARY VISUAL CORTEX
ORGANIZATION OF PHOTORECEPTORS
ROD
CONE
HORIZONTALCELL
AMICRINE CELL
BIPOLARCELLS
GANGLIONCELLS
TOOPTICNERVE
RECEPIVE FIELDS IN THE LATERAL GENICULATE AND SENSORY CORTEX
LATERAL GENICULATE:LIKE GANGLION CELLS: ANNULAR(EXCITATORY RINGS OR INHIBITORY RINGS)
OVERLAP OF ANNULAR FIELDS FROM LG RESULT IN RECTANGULAR FIELDS ON THE CORTEX
VISUAL ORIENTATION COLUMNS
CELLS IN VARIOUS COLUMNS OF CORTEX RESPOND TO DIFFERENT ORIENTATIONS
THESE DEVELOP DURING THE EARLY VISUAL EXPERIENCES OF YOUNG ANIMALS
COLOR VISION
TRICHROMATIC: RED, BLUE, GREENPARVOCELLULAR NEURONS CARRY
INFORMATIONDIFFERENT CELL TYPESCOLOR CONTRAST
THREE KINDS OF CONES
RED, BLUE, AND GREEN
CONNECT TO SMALL GANGLION CELLS
TRANSMIT COLOR INFORMATION TO PARVOCELLULAR NEURONS IN LGN
COLOR NEURONS
BROAD BAND: SINGLE COLOR, + INSIDE, - OUT
SINGLE - OPPONENT: EXITED BY ONE COLOR IN CENTER, INHIBITED WHEN ANOTHER COLOR IN PERIPHERY
DOUBLE OPPONENT: OPPOSING COLORS IN BOTH CENTER AND PERIPHERY
ANNULAR FIELDS OVERLAP TO RECTANGULAR IN CORTEX
LENS DEFECTS
FOCUSING IN FRONT OF RETINANEARSIGHTEDNESS (MYOPIA)USUALLY DUE TO WEAK CILIARY
MUSCLESFOCUSING BEHIND THE RETINAFARSIGHTEDNESS(HYPEROPIA)LENS TOO STIFF (AGING)
NEARSIGHTEDNESS (MYOPIA)
UNCORRECTED
CORRECTED
FARSIGHTEDNESS (HYPEROPIA)
UNCORRECTED
CORRECTED
VISUAL FIELD DEFECTS
OPTIC NERVE:VISUAL FIELD ON SAME SIDEOPTIC CHIASM:OUTER HALF OF BOTH
VISUAL FIELDSOPTIC TRACT: OPPOSITE HALF IN BOTH
VISUAL FIELDSOPTIC RADIATIONS:LOWER OR UPPER
QUADRANT ON OPPOSITE SIDE