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THE VISUAL SYSTEM
D. C. MIKULECKY
PROFESSOR OF PHYSIOLOGY
AND
FACULTY 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 EYE
CORNEA AND LENS: BEND LIGHT RAYS AND
FOCUS THEM ON THE RETINA
CILLIARY MUSCLES LOSSEN OR TIGHTEN TO
ADJUST LENS THICKNESS
RETINA: SITE OF PHOTORECEPTORS
FOVEA: MOST SENSITVE PART OF RETINA
TEAR DUCT
AND
DRAINAGE
CANAL
PUPIL
IRIS
SCLERA
STRUCTURE OF THE EYE
SUSPENSORY LIGAMENT
CILIARY BODY
CONJUNCTIVA
IRIS
PUPIL
EXTERNAL EYE
MUSCLE
CHOROID
RETINA
SCLERA
FOVEA
LENS
CORNEA
AQUEOUS HUMOR
VITREOUS HUMOR
OPTIC NERVE
OPTIC DISC
BLOOD VESSELS
THE PHOTORECEPTORS
RODS:
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 RHODOPSIN
PHOSPHODIESTERASE ACTIVATED BY
TRANSDUCIN
cGMP HYDROLIZED
SODIUM CHANNEL CLOSES
MEMBRANE 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
PHOTORECEPTORS
A
GANGLION
CELL
B
PHOTORECEPTORS
A
HIGH
RATE
OF
FIRING
GANGLION
CELL
B
LOW
RATE
OF
FIRING
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 CORTEX
PRIMARY VISUAL CORTEX
ORGANIZATION OF
PHOTORECEPTORS
ROD
TO
OPTIC
NERVE
HORIZONTAL
CELL
AMICRINE CELL
CONE
BIPOLAR
CELLS
GANGLION
CELLS
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, GREEN
PARVOCELLULAR NEURONS CARRY
INFORMATION
DIFFERENT CELL TYPES
COLOR 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 RETINA
NEARSIGHTEDNESS (MYOPIA)
USUALLY DUE TO WEAK CILIARY
MUSCLES
FOCUSING BEHIND THE RETINA
FARSIGHTEDNESS(HYPEROPIA)
LENS TOO STIFF (AGING)
NEARSIGHTEDNESS
(MYOPIA)
UNCORRECTED
CORRECTED
FARSIGHTEDNESS
(HYPEROPIA)
UNCORRECTED
CORRECTED
VISUAL FIELD DEFECTS
OPTIC NERVE:VISUAL FIELD ON SAME SIDE
OPTIC CHIASM:OUTER HALF OF BOTH VISUAL
FIELDS
OPTIC TRACT: OPPOSITE HALF IN BOTH
VISUAL FIELDS
OPTIC RADIATIONS:LOWER OR UPPER
QUADRANT ON OPPOSITE SIDE