NROC64H3 Study Guide - Final Guide: Retinal Ganglion Cell, Optic Disc, Receptive Field

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Published on 8 Oct 2011
School
UTSC
Department
Neuroscience
Course
NROC64H3
Neuroscience-Sensory Processing
Neuroscience Exam # 3
Study Guide
-Sensory Experience and Sensory Reality
Sound as we perceive it does not exist without a brain to create
it. The only reason that we experience sound is that the
information from the ear goes to a region of the brain that
converts the neural activity into what we then perceive to be
sound.
Synesthesia: the capacity to join sensory experiences across
modalities. A particular sound will also produce a color or taste.
Winderickx study: provided the first evidence that normal
variation in our mental world is traceable to normal variation in
our genes.
-Analyzing Sensory Information
The brain processes visual information in multiple ways. Some
processing allows us to consciously analyze visual stimuli,
whereas other processing happens unconsciously.
The brain dissects the object, analyzes the various parts
separately, and then produces what appears to be a unified
perception of the whole.
-Anatomy of the visual system
Retina: light sensitive surface at the back of the eye consisting of
neurons and photoreceptor cells.
-Structure of the eye:
The cornea and lens of the eye focus light rays to project a
backward, inverted image on the receptive surface, the retina.
The optic nerve conveys information from the eye o the brain.
The fovea is the region of best vision and is characterized by the
densest distribution of photoreceptor cells..
The region in the eye where the blood vessels enter ad the axons
of the ganglion cells leave is called the optic disc and has no
receptors and thus forms a blind spot.
-Photoreceptors
Convert light energy into chemical energy and then into neural
activity.
Rods: longer and cylindrically shaped at one end, more
numerous than cones, and are more sensitive to dim light. They
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are used mainly for night vision.
Cones: shorter and have a tapered end, responsive to bright
light. They are responsible for color vision and our ability to see
fine detail.(have three different pigment types)
The fovea only has cones, but in lower density at either side-
vision is not so sharp at edges of visual field.
-Retinal Neuron Types
Retinal ganglion cells: neural cells of the retina that give rise to
the optic nerve. The axons of the ganglion cells collect in a
bundle at the optic disc and leavethe eye to form the optic
nerve.
oM-Cells: larger and receive their input primarily from rods
and are sensitive to light but not to color. Found
throughout the retina including the periphery where we are
sensitive to movement but not color.
oP-Cells: smaller and receive their input primarily from
cones and are sensitive to color. Found largely in the
fovea.
-Visual Pathways
Optic nerves: one exiting from each eye, they are formed by the
axons of ganglion cells leaving the retina. Just before entering
the brain they partly cross forming the optic chiasm.
The left half of each optic nerve goes to the left side of the brain,
and the right halves go to the brain’s right side.
The nasal or medial path cross to the opposite side, while the
lateral or temporal go straight back on the same side.
Geniculostriate system: after entering the brain the axons of the
ganglion cells separate, forming two distinct pathways. This one
goes from the retinal to the LGN of the thalamus and then to
layer IV of the primary visual cortex in the occipital lobes.
Tectopulvinar system: retina to the superior colliculus to the
pulvinar.
Geniculostriate Pathway (detailed)
Retinal ganglion cell fibers from the two eyes distribute their
connections to the two LGN of the thalamus. Fibers from the left
half of each retina go to the left LGN and those from the right
half go to the right LGN.
Each LGN has six layers, and projections from two eyes go to
different layers- layers 2,3,5 receive ipsilateral fibers and 1,4,6
receive contralateral fibers.
oThis serves to combine the information from the two eyes
and segregate the information from the P and M ganglion
cells.
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P-cells go to layers 3-6 and M cells go to layers 1-2.
Layer IV of the visual cortex has sublayers, IVCa and IVCB.
oIVCa-layers 1 and 2
oIVCb-layers 3-6
-Occipital Cortex
Composed of at least six different visual regions, V1-V6. V1 is
the primary visual cortex or the striate cortex.
Region V1: Neurons in the blobs take part in color perception,
whereas neurons in the interblobs participate in form and motion
perception.
Region V2: thick stripes receive input from the movement
sensitive neurons in region V1, thin stripes receive input from
V1’s color sensitive neurons, pale ones receive input from V1’s
form sensitive neurons.
Dorsal and Ventral Visual Streams
Two pathways that originate in the striate cortex. Pathway to
the temporal lobe is the ventral stream, to the parietal lobe is
the dorsal stream.
Dorsal: goes to the parietal lobe ad controls visual action
Ventral: goes to temporal lobe, controls object recognition.
-Location in the Visual World
The coding of location begins in the retina and is maintained
throughout all the visual pathways.
Visual field: region of the visual world that is seen by the eyes,
can be divided into two halves to form the left and right visual
fields.
The input from the right field goes to left hemisphere and vice
versa.
-Coding Location in the Retina
Receptive field: the patch of the retina in which each ganglion
cell responds if stimulated. It is a region of the retina on which it
is possible to influence that cell’s firing, it represents the outer
world as seen by a single cell.
-Location in the LGN and Cortical Region V1
The information from a receptive field retains its spatial relation
when it is sent to the lateral geniculate nucleus.
The receptive fields of many retinal ganglion cells combine to
form the receptive field of a single LGN cell. The receptive fields
of many LGn cells combine to form the receptive field of a single
V1 cell.
-The Visual Corpus Callosum
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Document Summary

Sensory experience and sensory reality: sound as we perceive it does not exist without a brain to create it. A particular sound will also produce a color or taste: winderickx study: provided the first evidence that normal variation in our mental world is traceable to normal variation in our genes. Analyzing sensory information: the brain processes visual information in multiple ways. Some processing allows us to consciously analyze visual stimuli, whereas other processing happens unconsciously: the brain dissects the object, analyzes the various parts separately, and then produces what appears to be a unified perception of the whole. Anatomy of the visual system: retina: light sensitive surface at the back of the eye consisting of neurons and photoreceptor cells. Photoreceptors activity: convert light energy into chemical energy and then into neural, rods: longer and cylindrically shaped at one end, more numerous than cones, and are more sensitive to dim light.