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