3/9/99

Physiology II

 

Vision

·        Uniqueness of rods and cones is that they hyperpolarize

·        Ganglion—relay b/w rods and cones and the optic nerve

·        Visual bleaching—looking at an image ex:  in a movie theater and have to go out the back door; go outside in the bright sunlight from the darkness; blinded for a period of time b/c pupils are dilated and too much light is getting into the eye; see black spots b/c we have to wait for transmitter to recycle esp. rhodopsin; this is only temporarily; could be permanent if exposed to too highly intense light

·        Scotomata—something has happened to the rods and cones away from the central blind spot and they develop blind spots ex:  looking at a solar eclipse, diabetes  (lose cones first and central vision—retinopathy

·        Try to keep images in the fovea—if an image moves out of the fovea, we move our eyes—Tracking

 

·        Visual signal comes in

·        Strikes the retina

·        Optic nerve and meet at the optic chiasm

·        Glaucoma has pressure on optic nerve just behind the eye—lose lots of fields of vision

·        Pituitary tumor—tunnel vision (bitemporal hemionopsia)—temporal fields (nasal retina) cross in the optic chiasm which can be compressed in a tumor

·        Can't lose binasal vision in normal circumstances b/c these fields do not cross and would need a very large lesion

·        Smell passes through this area and w/pituitary tumor have trouble transmitting to the CNS

·        Optic tracts lead from the optic chiasm

·        Lead to the lateral geniculate and superior colliculus

·        From here have optic radiations (projection fibers) which lead to the visual cortex in the occipital lobe of the cerebrum

·        If you lose your right visual field, would lose left temporal field and right nasal field

·        Make sure that you can draw from the eye to the visual cortex

·        Stroke could cause lose of vision but is not common

·        Old cortical areas—associated w/circadian rhythms, patterns of dark and light, deprived of periods of dark and light get aberrant behaviors

·        Pretectile nuclei affect focus

·         

·        Superior colliculus—follow fast moving objects (watching tennis) rapid directional changes

·        Ventrolateral geniculate nucleus of the thalamus—visual abbherations

·        New vision—direct tract to visual cortex

·        Form

·        Color

·        Depth

·        Conscious vision (trust what you see)

·        Respond to this type of stimulation

·        Relay point b/w optic tract and cortex, very accurate, ½ fibers come from each eye

·        6 layers in the visual cortex

·        gating

·        corticofugal signals—inhibitory input, dampen signal

·        mesencephalon—dampen or reduce transmission of the input

·        cellular processes

·        Y ganglion--rod, fast

·        Goes into layer 4

·        Layers 1 & 2 receive signal from layer 4 (magnocellular)--b&w perception of shape, form; not a lost of detail (Shadow puppets)

·        Layers 3-6—parvocellular—X ganglion—color blobs, collateral cortical cells that allow to discriminate color, good point to point delineation (discriminate detail); analyze meaning

·        Take in two signals—register—one from each eye; if not vision is skewed; learning disabilities; can use some colored filters that filter out the color that is causing the problem (someone who can not read black letters on white paper)

·        Black ink on yellow paper is easier for a person to delineate

 

Process a Signal

·        What do you see first

·        On the retina see an X (two crossed lines)

·        First thing we process is the two lines

·        To retina contrast borders

·        Simple cells—orientation of lines

·        Complex cells—displacement of lines in space

·        Depth—hypercomplex cells—shading; 3-D structure; stance and body language

·        Transmit signals to different areas of the brain

·        Field of vision is the one that you can see at any given time

·        Can lose parts of the field of vision

·        Retinitis pigmentosa—receptors present, lens fine, melanin is over areas, absorbing the signal so can't go to the cortex

·        Only special sense that we can tract is vision

·