Lecture 9 Flashcards
what are the cells (neurons) of the retina
Photoreceptor cells Bipolar cells Ganglion cells Horizontal cells – Amacrine cells
what are the photoreceptor cells
– neurons responsible for the transduction of light; they project to bipolar cells.
what are the bipolar cells
– neurons that relay information from photoreceptor cells to ganglion cells.
what are the ganglion cells
– the only neurons in the retina that sends axons out of the eye. They receive information from bipolar cells and project to the rest of the brain; their axons give rise to the optic nerve, which leaves the retina through the optic disc (i.e., the blind spot of the retina).
what are the horizontal cells
neurons that interconnect and regulate the excitability of adjacent photoreceptor and bipolar cells. They adjust the sensitivity of these neurons to light in general.
what are the amacrine cells
– neurons that interconnect and regulate the excitability of adjacent bipolar and ganglion cells. There are many different types of amacrine cells and they have many functions.
Receptor proteins that are sensitive to light are known as what
opsins
We use four different types of opsin proteins to detect light, what are they
rhodopsin and the red, green, and blue cone opsins
We use four different types of opsin proteins to detect light: rhodopsin and the red, green, and blue cone opsins. Each of these opsins are what kind of receptors
inhibitory metabotropic receptors.
Each photoreceptor cell in our eye contains only one of these types of opsins, which means we have how many types of photoreceptor cells
four different types of photoreceptor cells: rod cells and the red, green, and blue cone cells.
When light activates the opsin proteins in a photoreceptor cell, they trigger what
a g-protein signalling cascade that closes open sodium ion channels. Thus, the activation of these opsin proteins causes photoreceptor cells to hyperpolarize, which causes them to release less glutamate
It doesn’t matter if it is a rod or cone photoreceptor cell, they all respond to light activation in the same way, by becoming what
less active and releasing less neurotransmitter.
To study neurons involved in visual processing, we record from them (typically with a metal wire) while the animal does what
stares at a computer screen and maintains focus on a particular spot in the center of the screen
We then light up different parts of the screen (using various orientations and colors of light) to see what when testing an animal
where on the screen light can change the activity of the neuron
The area of the computer screen where light is capable of changing the activity of the neuron is that neuron’s what
receptive field. It is that area of visual space
what happens with The first cell in the pathway
When the correct wavelength of light is presented in a photoreceptor cell’s receptive field, the photoreceptor cell hyperpolarizes and becomes less active (releases less glutamate).
what happens with the Second cell in the pathway:
There are two main types of bipolar cells (ON & OFF). When light is presented in the receptive field of ON bipolar cells, they depolarize and release more glutamate. When light is presented in the receptive field of OFF bipolar cells, they hyperpolarize and release less glutamate. They respond differently to the changes in photoreceptor cell activity because they have different kinds of glutamate receptors. ON bipolar cells only have inhibitory glutamate receptors; OFF bipolar cells have excitatory glutamate receptors.
what happens with the Third cell in the pathway:
Retinal ganglion cells generally integrate information from many ON and OFF bipolar cells. Their receptive fields often have a “center-surround” organization and they are called ON or OFF cells, depending on whether they show increased or decreased spiking activity when light is presented in the center of their receptive field.
Retinal ganglion cells that process color information tend to have what types of receptive fields
yellow on, blue off
blue on, yellow off
etc (the ON is in the centre)
Retinal ganglion cells project to where
the thalamus (LGN),
Retinal ganglion cells project to the thalamus (LGN), which in turn projects to where
the cerebral cortex ( V1):
Primary visual cortex
is also known as what
also known as area V1 or striate cortex
Neurons in V1 have larger receptive fields than what
the retinal ganglion cells
Neurons in V1 have larger receptive fields than the retinal ganglion cells. They are most activated when…
a line of light in a particular orientation is detected in the receptive field
Some neurons respond best to what kind of lines
vertical lines, some to horizontal lines, and some to lines oriented somewhere in between.
what are Simple cells
Simple cells in primary visual cortex are sensitive to lines of light, and their receptive fields are typically organized in a center-surround fashion
where are Complex cells found
primary visual Cortex
what are Complex cells
like simple cells but they have larger receptive fields and do not have an inhibitory surround region. Complex cells respond to particular line orientations, but they don’t care if the line reflects the absence or presence of light
Complex cells often respond best to what
moving lines, but only if the line moves in the direction perpendicular to the line orientation
Complex cells often respond best to moving lines, but only if the line moves in the direction perpendicular to the line orientation. Complex cells are mostly in V2. They receive input from what
many simple cells
Every little spot in your visual field is rigorously analyzed. Is there light in that spot and is it oriented this way or that way? The neurons are trying to identify areas where there are sharp transitions between light and dark (or between two colors). The neurons are trying to identify what
borders, edges, corners
The axons of retinal ganglion cells leave the eye and go to the:
Thalamus visual cortex (specifically the lateral geniculate nucleus)
Midbrain
or
Hypothalamus
Thalamus (specifically the lateral geniculate nucleus, which in turn projects where
to the primary visual cortex in the occipital lobe of the cerebrum
Thalamus (specifically the lateral geniculate nucleus, which in turn projects to the primary visual cortex in the occipital lobe of the cerebrum): Visual information is processed in this pathway to determine what
what you are looking at
Thalamus (specifically the lateral geniculate nucleus, which in turn projects to the primary visual cortex in the occipital lobe of the cerebrum): Visual information is processed in this pathway to determine what you are looking at. This pathway creates what
an internal (mental) representation of your entire visual space: the objects in it, their position and relative attentional value.
The axons of retinal ganglion cells leave the eye and go to themidbrain, but specifically where
specifically the superior colliculi
Midbrain (specifically the superior colliculi): Visual information is used here to do what
control fast visually-guided movements. The midbrain doesn’t really know what you are looking at, but it knows where light is moving in visual space.
what happens in the hypothalamus
Visual information is used here to control circadian rhythms (such as sleep-wake cycles). The hypothalamus doesn’t know what you are looking at, but it knows how much light is present in your environment
Visual information is organized in the thalamus before it gets to where
the cerebral cortex
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has how many layers of neurons
six layers of neurons
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons:
The inner two layers (layers 1 and 2) are known as what
the magnocellular layers
what does the the magnocellular layers do
This layer transmits information from rod cells and is necessary for the perception of form, movement, depth, and small differences in brightness.
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons: The outer layers (3-6) are known as what
parvocellular layers
what do the parvocellular layers do
They encode information from red and green cone cells.
Visual information is organized in the thalamus before it gets to the cerebral cortex. The lateral geniculate nucleus (LGN) of the thalamus has six layers of neurons:
Information from the blue cone cells gets encoded in what
koniocellular sublayers
what are the koniocellular sublayers
interspersed in between each of the other layers
Primary visual cortex (area V1) consists of six layers of neurons (and several sublayers), arranged in bands parallel to surface. These layers show up as what
bands of light or dark in sections of tissue that have been dyed with a cell-body stain.
Like the rest of the brain, the visual cortex is organized in modules which range in size from a few hundred thousand to what
a few million neurons
The modules in V1 overlay the images from the two eyes and do what
determine light orientation and color.
Modules in V2 combine activity from multiple V1 modules. Modules in V3 combine activity from multiple V2 modules. And on and on… This is called what
feedforward processing
Cytochrome oxidase (CO) is an enzyme whose expression levels scale with what
the metabolic rate of the cell
Cytochrome oxidase (CO) is an enzyme whose expression levels scale with the metabolic rate of the cell. essentially More action potentials =
More action potentials = more expression of CO protein
Cells with high expression of CO are found where
in clusters throughout the occipital cortex. These areas are known as the CO blobs
Cells with high expression of CO are found in clusters throughout the occipital cortex. These areas are known as the CO blobs.
These regions process input from the parvocellular/koniocellular cells of the thalamus (LGN) and are responsible for what
color vision
what are the important terms in Depth perception
Monocular vision:
Binocular vision:
Depth perception:
Stereopsis:
what is monocular vision
Some V1 neurons respond to visual input from just one eye.
