Lecture 6
One cone-to-one bipolar-to one ganglion cell relation in cone system contributes to ___.
One cone-to-one bipolar-to one ganglion cell relation in cone system contributes to visual acuity.
Phototransduction is the process by which ___ by the photopigment causes ___ of the photoreceptor cells. Changes in the ___ of photoreceptor cell causes changes in the ___.
process by which absorption of light by the photopigment causes gradual changes in the membrane potential of the photoreceptor cells. Changes in the membrane potential of photoreceptor cell causes changes in the rate of release of the transmitter.
A given orientation in the visual field (scene) is encoded in the activity of a distinct population of orientation-selective neurons in the primary visual cortex.
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Comparing the activity in different classes of cones is essential for color discrimination.
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Introduction to Sensory Systems: -Sensory receptors -Sensory modalities -types of sensory systems -sensory transduction -multisensory integration
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Retinal
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The axons of ganglion cells in the nasal retina of each eye cross in the optic chiasm. The xons of ganglion cells in the temporal retina do not cross.
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The genes for the three human cone pigments are highly homologous and localized on X chromosome (for red and green) and on Chromosome 7 (for blue).
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light hyperpolarizes the photoreceptor, decreasing the release of glutamate 2) the on-bipolar cell is depolarized (freed from inhibition) -the off-bipolar cell is hyperpolarized (less excitation)
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light spot in center of receptive field -> center cone low activity
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review 80-90 slides
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List the 5 steps to the Retinoid cycle in photoreceptors
1) Light absorption by cis-retinal 2) photoisomerization of retinal (cis to trans configuration) 3)Trans-retinal dissociates from the opsina nd is converted to trans-retinol 4)Trans-retinol is transported into the pigment epithelium were it is converted to a cis-retinal. 5) Cis-retinal is transported back into the outer segment where it recombines with opsins.
List the process of transduction that leads to behavioral response
1) stimulus detection, receptors activation 2) activation of downstream signaling cascades Signal amplification 3) Transformation of the signals to electrical signals that can be sent to the brain
A chromophore is the part of a molecule responsible for its ___. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.
A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.
Amplification in rods contributes to ___.
Amplification in rods contributes to detection of signal.
Binocular visual field consists of two ___. The vision on the periphery of field of view is strictly ___ (projected on most medial parts of the nasal retina)
Binocular visual field consists of two symmetrical visual hemifields. The vision on the periphery of field of view is strictly monocular (projected o most medial parts of the nasal retina)
Classes of neurons in the retina: 1) 2) 3) 4) 5)
Classes of neurons in the retina: 1) photoreceptors 2) bipolar cells 3) horizontal cells 4) amacrine cells 5) ganglion cells
Color vision is the result of spectral properties of the cone system: three photopigments are differentially sensitive to a light of different wavelengths (BLUE or short, GREEN or medium and RED or long.).
Color vision is the result of spectral properties of the cone system: three photopigments are differentially sensitive to a light of different wavelengths (BLUE or short, GREEN or medium and RED or long.).
___ makes rod system a better detector of light, but reduces ___.
Convergence makes rod system a better detector of light, but reduces spatial resolution.
Each ganglion cell responds to stimulation of a small circular patch of the retina, which defines the cell's ___.
Each ganglion cell responds to stimulation of a small circular patch of the retina, which defines the cell's receptive field.
Each retina and corresponding visual fields are divided ___. Lines intersect at ___ -- the point in visual space that falls on the ___.
Each retina and corresponding visual fields are divided into quadrants. Lines intersect at fixation points -- the point in visual space that falls on the fovea.
Highly specialized cells, ___, convert the signals associated with sensory stimuli into neural signals --___ sensory electrical signals that convey information to the CNS.
Highly specialized cells, sensory receptors, convert that signals associated with sensory stimuli into neural signals --afferent sensory electrical signals that convey information to the CNS.
Horizontal cell modulatory inputs generate the ___response.
Horizontal cell modulatory inputs generate the surround response.
LGN receives inputs from ___. These inputs are still ___ in separate layers in LGN. Individual LGN neurons are ___. The responses of neurons in LGN are similar to ___ cells responses --with a ___ recetive fields and selectivity to ___.
LGN receives inputs from both eyes. These inputs are still segregated in separate layers in LGN. Individual LGN neurons are monocular. The responses of neurons in LGN are similar to retinal ganglion cells responses --with a center-surround recetive fields and selectivity to luminance increases and decreases.
Layers in the LGN are distinguished on the basis of the cell size
Layers in the LGN are distinguished on the basis of the cell size
Rods and cones are both functional in which layer?
Mesopic
Myelin staining of the sections of the human brain through the occipital lobe reveals prominent myelinated band (___) of axons in layer ___ which receives dense projections from ___. The responses of neurons in Primary sensory cortex (___ cortex) are very different from responses of ___ cells and cells in the ___.
Myelin staining of the sections of the human brain through the occipital lobe reveals prominent myelinated band (stria) of axons in layer 4 which receives dense projections from LGN. The responses of neurons in Primary sensory cortex (Striate cortex) are very different from responses of retinal ganglion cells and cells in the LGN.
The cGMP channel allows the influx of which ions?
Na+ and Ca2+
Neurons in layer 4C send their axons to layers ___ and ___. Neurons in layer 4C receive ___ input from layer ___ .
Neurons in layer 4C send their axons to layers 4B and 2/3. Neurons in layer 4C receive intracortical input from layer 6.
New outer segment disks are formed near the ___ of the ___.
New outer segment disks are formed near the base of the outer segment.
Rods and Cones morphology: Outer segments are composed of ___. The photopigments which reside in the ___ contain ___ coupled to transmembrane proteins called ___. Inner segments contain the rest of the cell body and forms synaptic contacts with ___ and ___ cells.
Outer segments are composed of membranous discs. The photopigments reside in the disc membrane which contain chromophores coupled to transmembrane proteins called opsins. Inner segments contain the rest of the cell body and forms synaptic contacts with bipolar and horizontal cells.
Photosensitive retinal ganglion cells (RGCs) contain photopigment ___ and are ___ by light. The axons of these RGCs project to the ___ of the ___ --the central site of the circadian control of ___ functions.
Photosensitive retinal ganglion cells (RGCs) contain photopigment melanopsin and are depolarized by light. The axons of these RGCs project to the suprachiasmatic nucleus of the hypothalamus --the central site of the circadian control of homeostatic functions.
Pretectume is a coordinating center for the pupillary light reflex.
Pretectume is a coordinating center for the pupillary light reflex.
Primary properties of visible light are ___, ___ ___, ___ or wavelength spectrum, and ___.
Primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarization.
What is protanopia? Effects? deuteranopia
Protanopia - loss of long-wavelength sensitive cones), difficult to discriminate between red and green Deuteranopia - loss of medium-wavelength sensitive cones, difficult to discriminate between red and green
Receptive fields ___, so that every point in the retinal surface is analyzed by many ganglion cells.
Receptive fields overlap, so that every point in the retinal surface is analyzed by many ganglion cells.
Response properties of M, P and K ganglion cells: ___ 1) ___ ganglion cells have larger receptive fields than ___ cells 2) The axons of M cells have ___ than axons of the P cells 3) K cells send ___ to ___ layers of the LGN neurons. 4) M cells respond ___ to visual stimuli. P cells respond in a ___. 5) M cells do not transmit information about ___ of the visual stimuli because ___. 6) ___ cells convey color information because ___. As a results ___ cells are sensitive to the ___. 7) ___ cells might contribute to color vision as they receive information from ___ cones.
Response properties of M, P and K ganglion cells: 1) M ganglion cells have larger receptive fields than P cells 2) The axons of M cells have faster conduction velocity than axons of the P cells 3) K cells send fine-caliber axons to koniocellular layers of the LGN neurons. 4) M cells respond transiently to visual stimuli. P cells respond in a sustained fashion. 5) M cells do not transmit information about color of the visual stimuli because their receptive fields contain the same classes of cones in the center and in the surrounds. 6) P cells convey color information because their receptive field centers and surrounds contain different classes of cones (S, M, L). As a results P cells are sensitive to the differences in the wavelength of light falling on their center and surround of hte receptive field. 7) K cells might contribute to color vision as they receive information from S cones.
Superior colliculus pathways:
Retina -> optic nerve -> optic tract -> Superior colliculus -> gaze centers in the reticular formation
Pretectum pathways:
Retina -> optic nerve -> optic tract -> pretectum -> Ediger-Westphal nucleus -> ciliary ganglion -> pupillary constrictor muscles
___ is a part of the nervous system that forms the neural portion of the eye.
Retina is a part of the nervous system that forms the neural portion of the eye. The electrical activity of the retinal photoreceptors (specialized photosensitive neurons) is converted into action potentials that travel to central targets.
Rhodopsin is a ___-sensitive receptor protein. It is a biological ___ in ___ cells of the ___. Rhodopsin is the primary pigment found in ___ photoreceptors. Rhodopsins belong to the ___ family. They are extremely sensitive to light, enabling vision in ___ conditions.
Rhodopsin is a light-sensitive receptor protein. It is a biological pigment in photoreceptor cells of the retina. Rhodopsin is the primary pigment found in rod photoreceptors. Rhodopsins belong to the G-protein-coupled receptor (GPCR) family. They are extremely sensitive to light, enabling vision in low-light conditions.
Rods and cones are distinguished by:
Rods and cones are distinguished by: -Shape -Pattern of synaptic connections -Type of photopigment -Distribution across the retina
Rods have ___ sensitivity to light but ___ resolution during the ___. Cones have ___ sensitivity to light but ___ resolution during the ___. Cones are responsible for ___.
Rods have high sensitivity to light but low resolution during the night. Cones have low sensitivity to light but high resolution during the day. Cones are responsible for color vision.
Sensory systems ___ information (signal) generated by stimuli of different ___.
Sensory systems transduce information (signal) generated by stimuli of different modalities.
Steps of Phototransduction: 1) Photon of light is absorbed by ___ which is coupled to ___. 2) Absorption of light causes changes in ___ (from ___ to ___) 3) changes in ___ activates ___. 4) Transducin activates ___, which in turn hydrolyzes ___ reducing ___ level. 5) ___ channel is ___. 6) ___
Steps of Phototransduction: 1) Photon of light is absorbed by chromophore retinal which is coupled to GPCR-opsins. 2) Absorption of light causes changes in retinal configuration (from cis to trans) 3) changes in retinal configuration activates transducin. 4) Transducin activates PDE, which in turn hydrolyzes cGMP reducing cGMP level. 5) cGMP channel is closed. 6) Hyperpolarization
Summary (Visual system/part 1) 1) Light activates ___. 2) Retinal circuitry transforms the signal into the pattern of ___. 3) Two types of ___, on- and off-center cells, carry information about increases or decreases of ___ in the centers of their ___. 4) ___ axons convey the information to the visual centers in the brain. 5) The brain gets information about increase or decrease of luminance always in the form of ___ (action potentials) which is more reliable than decreased response.
Summary (Visual system/part 1) 1) Light activates photoreceptos 2) Retinal circuitry transforms the signal into the pattern of action potentials 3) Two types of ganglion cells, on- and off-center cells, carry information about increases or decreases of luminance in the centers of their receptive fields 4) Ganglion cell axons convey the information to the visual centers in the brain 5) The brain gets information about increase or decrease of luminance always in the form of increased activity (action potentials) which is more reliable than decreased response.
Summary (visual system pt 2) 1. Retinal ganglion cells project to: - - - - 2. The primary visual cortex is organized topographically and is characterized by ___ and ___ architecture.
Summary (visual system pt 2) 1. Retinal ganglion cells project to: -Pretectum -Hypothalamus -Superior colliculus -Thalamus (LGN) 2. The primary visual cortex is organized topographically and is characterized by laminar and columnar architecture.
___ receives visual input from the retina and sends a command signal to the gaze centers to initiate a ___. Neurons in the ___ layer of the SC make axodendritic contacts with the neurons in the ___ layer. The functional connections between neurons in the visual and motor layers are required for initiating the command for visually guided ___ eye movements. Vision is an ___ process in which eye movements shifts the view several times per second to selected parts of the scene to examine especially ___ features.
Superior colliculus receives visual input from the retina and sends a command signal to the gaze centers to initiate a saccade Neurons in the visual layer of the SC make axodendritic contacts with the neurons in the neurons in the motor layer. The functional connections between neurons in the visual and motor layers are required for initiating the command for visually guided saccadic eye movements. Vision is an active process in which eye movements shifts the view several times per second to selected parts of the scene to examine especially interesting features.
Th einputs from each eye remain segregated in cortical layer 4 individual neurons. Cortical layer 4 has eye-specific ocular dominance columns.
Th einputs from each eye remain segregated in cortical layer 4 individual neurons. Cortical layer 4 has eye-specific ocular dominance columns.
The cone receptors density is highest at ___, providing anatomical substrate for visual acuity.
The cone receptors density is highest at the center of macula (in the fovea), providing anatomical substrate for visual acuity.
The division point between crossing and non-crossing ganglion cells is in the ___. The retina receives visual information from the ___.
The division point between crossing and non-crossing ganglion cells is in the center of the fovea. The retina receives visual information from the visual field.
The human retina has (#) (with ___ present in rods, and three other opsins (___, ___, ___) in cones) that differ in their ___.
The human retina has four photopigments (with rhodopsin present in rods, and three other opsins (S, M, L) in cones) that differ in their absorption spectra.
The ___ of the visual cortex serves to segregate populations of neurons that are having distinct patterns of connections. Neurons in layer ___ receives input from ___.
The laminar organization of the visual cortex serves to segregate populations of neurons that are having distinct patterns of connections. Neurons in layer 4 receives input from LGN.
Lateral Geniculate Nucleus (LGN)
The lateral geniculate nucleus (LGN) (also called the lateral geniculate body or lateral geniculate complex) is a relay center in the thalamus for the visual pathway. It receives a major sensory input from the retina. The LGN is the main central connection for the optic nerve to the occipital lobe. Each LGN has six layers of neurons (grey matter) alternating with optic fibers (white matter).
The magnocellular (large neurons), parvocellular (small neurons), and koniocellular (small neurons) layers receive inputs from distinct populations of retinal ganglion cells, that exhibit corresponding differences in cell size: M, P and K retinal ganglion cells.
The magnocellular (large neurons), parvocellular (small neurons), and koniocellular (small neurons) layers receive inputs from distinct populations of retinal ganglion cells, that exhibit corresponding differences in cell size: M, P and K retinal ganglion cells.
The neurons in the visual cortex respond to a particular orientation of edges. the peak in the tuning curve indicates the preferred orientation.
The neurons in the visual cortex respond to a particular orientation of edges. the peak in the tuning curve indicates the preferred orientation.
Roles of the retinal pigment epithelium: 1) The oldest discs at the tip of the outer segment are ___ by pigment epithelium cells. Pigment epithelium regenerates ___ after light exposure. The chromophore (retinal/ol) cycles between ___ and ___.
The oldest discs at the tip of the outer segment are phagocytosed by pigment epithelium cells. Pigment epithelium regenerates photopigment after light exposure. The chromophore (retinal/ol) cycles between outer segment of the photoreceptor and the pigment epithelium cells.
The ___ tract contains the axons of ___ cells that originate in both eyes and represent the ___ visual field (right optic tract represents the left visual field, whereas, left optic tract represents the right visual field).
The optic tract contains the axons of ganglion cells that originate in both eyes and represent the contralateral visual field (right optic tract represents the left visual field, whereas, left optic tract represents the right visual field).
The photopigment is a coupling of ___ and ___.
The photopigment is a coupling of opsin and chromophore.
The two foveas align on a signle target in visual space (the fixation point) causing the ___ of left and right visual fields.
The two foveas align on a signle target in visual space (the fixation point) causing the overlap of left and right visual fields.
Visible light has a wavelength in the range of about ___ nm to about ___ nm -- between the invisible ___, with longer wavelenghts and the invisible ___, with shorter wavelenghths.
Visible light has a wavelength in the range of about 380 nm to about 740 nm -- between the invisible infrared, with longer wavelengths and the invisible untraviolet, with shorter wavelengths.
Visible light is emitted and absorbed in tiny "packets" called ___, and exhibits properties of both ___ and ___.
Visible light is emitted and absorbed in tiny "packets" called photons, and exhibits properties of both waves and particles.
What determines the functional differences between on and off-center ganglion cells?
What determines the functional differences between on and off-center ganglion cells?
Visual field The images of visual field projected onto the surface of the retina are ___.
a part of visual space seen by an eye. The images of visual field projected onto the surface of the retina are inverted.
saccade
a rapid movement of the eye between fixation points.
Left and Right visual fields are parts of the visual space seen by left and right eye, respectively. The images of each eye's visual field are projected onto the surface of the corresponding retina
left eye sees the left visual field? right eye sees the right visual field?
What are the two classes of ganglion cells (distinguished by their responses)?
on-center cells off-center cells
Optic radiation
portion of the internal capsule (large white matter tract) that comprises that axons of lateral geniculate neurons that carry visual information to the striate cortex.
slide 90
slide 90
Transduction
the process of converting the energy of a stimulus into an electrical signal
What is modality? what are the different types?
type of stimulus that is detected by a sensory system -somatic sensation (somatic sensory control) -light (vision) -sound ( hearing or audition) -smell (olfaction) -taste (gustation)
