Download Topic 11

Biology 463 - Neurobiology
Topic 11
The Central Visual System
Lange
The Retinofugal Projection
The retinofugal projection consists of the Optic Nerve, Optic Chiasm, and
Optic Tract
The Retinofugal Projection
• Right and Left Visual Hemifields
– Left hemifield projects to right side of brain and right to the left
Visual deficits from lesions in
the retinofugal projection are
shown in these images.
Notice the specific types of loss shown in
black as compared to the intact fields
Nonthalamic Targets of the Optic Tract are areas that will use visual input
but not in the sense of SEEING OBJECTS.
– Hypothalamus: Biological rhythms, including sleep and
wakefulness
– Pretectum: Size of the pupil; certain types of eye movement
– Superior colliculus: Orients the eyes in response to new stimuli
X
X
X
The Lateral Geniculate Nucleus
(LGN)
The pathways occur in alternating
layers.
Contralateral = on the other side
Ipsilateral = on the same side
Parvocellular Cells
•
•
•
Parvocellular cells, also called P-cells, are neurons located within the
parvocellular layers of the lateral geniculate nucleus (LGN) of the
thalamus.
"Parvus" means "small" in Latin, and the name "parvocellular" refers to
the small size of the cell compared to the larger magnocellular cells.
The parvocellular neurons are sensitive to color, and are more capable
of discriminating fine details than their magnocellular counterparts.
Parvocellular cells have greater spatial resolution, but lower temporal
resolution, than the magnocellular cells.
Magnocellular Cells
•
•
•
Magnocellular neurosecretory cells are large cells within the supraoptic
nucleus and paraventricular nucleus of the hypothalamus.
There are two types of magnocellular neurosecretory cells, oxytocinproducing cells and vasopressin-producing cells, but a small number
can produce both hormones.
These cells are neuroendocrine neurons, they are electrically excitable,
and generate action potentials in response to afferent stimulation.
The Lateral Geniculate Nucleus (LGN)
Inputs Segregated by Eye and Ganglion Cell Type
P type = (also known as beta or midget ganglion cells) are believed to be
responsible for detecting details in vision.
M type = (also known as alpha or parasol ganglion cells) are believed to be
responsible for detecting motion.
nonM-nonP type =are a diverse group of cell types that make up the remaining 5%
of RGCs. Their roles in vision are less understood than M- and P-type ganglion
cells, but it is known that some non-M, non-P type cells are involved in color
vision.
Anatomy of the
Striate Cortex
The calcarine sulcus is
where the primary visual
cortex is concentrated. The
central visual field is located
in posterior portion of the
calcarine sulcus and the
peripheral visual field in the
anterior portion.
Anatomy of the Striate Cortex
Retinotopy
– Map of the visual field onto a target structure (retina, LGN,
superior colliculus, striate cortex)
– Central visual field overrepresented
– Discrete point of light: Activates many cells in the target
structure due to overlapping receptive fields
– Perception: Based on the brain’s interpretation of distributed
patterns of activity
Anatomy of the Striate Cortex
Inputs to the Striate Cortex
– First binocular neurons found in striate cortex - most
layer III neurons are binocular (but not layer IV)
Anatomy of the Striate Cortex
Outputs of the Striate
Cortex:
– Layers II, III, and
IVB: Projects to
other cortical
areas
– Layer V: Projects
to the superior
colliculus and pons
– Layer VI: Projects
back to the LGN
Anatomy of the Striate Cortex
Cytochrome Oxidase Blobs
– Cytochrome oxidase:
mitochondrial enzyme
used for cell metabolism
– Blobs: Cytochrome
oxidase staining in
striate cortex
– Each blob centered on an
ocular dominance column
in layer IV
– Receive koniocellular
inputs from LGN
Physiology of the Striate Cortex
• Monocular Receptive Fields
– Layer IVC: Similar to LGN cells
– Layer IVC: Insensitive to the wavelength
– Layer IVC: Center-surround color opponency
• Binocular Receptive Fields
– Layers superficial to IVC: First binocular receptive fields
in the visual pathway
– Two receptive fields - one for each eye
Physiology of the Striate Cortex
Cortical Receptive Fields
– Orientation Selectivity
Physiology of the Striate Cortex
Cortical Receptive Fields
– Direction Selectivity
» Neuron fires action potentials in response to moving bar
of light
Physiology of the Striate Cortex
Cortical Receptive Fields
– Simple cells: Binocular; Orientation-selective; Elongated on-off
region with antagonistic flanks responds to optimally oriented bar of
light
– Possibly composed of three LGN cell axons with center-surround
receptive fields
Physiology of the Striate Cortex
Cortical Receptive Fields
– Complex cells: Binocular; Orientation-selective; ON and OFF
responses to the bar of light but unlike simple cells, no distinct on-off
regions
Physiology of the Striate Cortex
Cortical Receptive Fields
– Blob Receptive Fields:
• Circular
• Monocular
• No orientation or direction selectivity
• Majority of color-sensitive neurons outside layer IVC
• Specialized for analysis of object color
Physiology of the Striate Cortex
Parallel Pathways: Magnocellular; Koniocellular; Parvocellular
Physiology of the Striate Cortex
Cortical Module
– Each module capable of analyzing every aspect of a portion of the
visual field
END.