Sensory: vision Flashcards
How many different opsins can the cones express, and how do they differ?
Three: OPN1SW (short waves=blue), OPN1MW (midlength waves=green), OPN1LW (long waves=red)
What is the function of rods and cones?
Rods: spatial resolution, more light sensitive
Cones: colour vision
What does the retinal molecules bind to?
Opsin
Describe the signaling pathway in cilliary photoreceptors
Photon stimulates the conversion of 11-cis-retinal bound to the opsin to all-trans-retinal –> release of retinal, and activation of the opsin receptor. Opsin is coupled to a Gt protein, and by activation the G_alpha is released from G-beta-gamma. G-alpha activates PDE –> reduction of cGMP –> inhibition of CNG Na+ channel –> inhibition of Ca^2+ influx (and AP) –> inhibition of glutamine release
How is the signal inhibited in cilliary cells, and when does this happen?
GRK1 phosphorylates opsin –> inactivation of opsin –> increase of cGMP –> increase of Ca^2+ –> depolarization of Vm –> release of glutamate
During darkness
What does the dynamic range of an eye refer to and how is it controlled in the human eye?
The number of photons the rods and cones can absorb depending on the brightness of a habitat.
It’s controlled by the number of active opsins in the retina (called adaptation), by controlling the process of conversion all-trans-retinal to 11-cis-retinal.
What is the lens involved in?
Accomodation: making sure the resolution matches the distance by contracting or extending the lens. Near/long sigthness is caused by a flaw in this mechanism.
What is the fovea?
Cones lined in the back of the eye directly in line with the lens (in the centre of the optical axis of the eye) not covered by any other cells –> no interference. It is packed densely with cone cells.
How does the pupil dialate, and which neuronss innervate the muscles responsible for this?
The radially smooth muscles of the iris (the dialator pupillae) contract, dialating the pupil. The dialator pupillae are innervated by adrenergic, sympathetic neurons
How does the pupil constrict, and which neuronss innervate the muscles responsible for this?
The circular smooth muscles of the iris (the sphincter pupillae) contract, constricting the pupil. The sphincter pupillae are innervated by cholinergic, parasympathetic neurons.
How many layers is the retina consisting?
3 layer: rods and cones in the back, bipolar, horizontal and amacrine cells in the middel and retinal ganglion cells in the front (+ ipRGCs)
Describe a rod cell.
Glutamatergic, rod-shaped neuron containing discs. Discs are organels lined with rhodopsin. The ros are depolarized in the darkness, and hyperpolarized in the light.
What is rhodopsin?
GPCR of the rods (opsin), with a bound retinal molecule (11´cis-retinal). They are light activated. When light hits the retinal, it converts from 11´cis- to all-trans-retinal, pushing the TM regions of the opsin. This configuration change activates the GPCR. Rhodopsin is tranducin coupled.
What are ipRGCs involved in?
The circadian rhytm and pupillary light reflexes.
Which regions of the brain does ipRGCs and rod cells project to, respectively.
ipGRCs project to the non-image forming center, the pineal gland (RHT -> suprachiasmatic nucleus -> paraventricular nucleus -> spinal cord -> SCG -> pineal gland).
Rod cells project to the image-forming center, the primary visual cortex (through the nucleus geniculatus).
How is the retina formed?
As an outpocekting of the diencephalon
What is accomodation?
When the eye is adjusted for sharp vision at short distances
How are the response to light?
Graded: mirroring the light intensity
What is the function of the pigment epithelium?
To move worn out photoreceptor discs
What is the center-surround organization?
Can either be center on/off
What type of NT does the horizotal cells use?
GABA
What type of NT does the bipolar cells use?
Glutamate
What type of NT does ganglion cells use?
Glutamate
What types of ganglion cells are there, and how do they differ?
3:
P-type: parvocellular cells/midget cells
- small RF and dendrite tree
- slowly adapting, slow conduction of APs, low light sensitivity
- 90 % of ganglion cells
- specializes in visual acuity
M-type: magnocellular cells/parasol cells
- large RF, and dendritic tree
- fast adaption and conduction of APs, high light sensitivity
- 5 % of ganglion cells
- specializes in movement
K-type
- non-P, non-M type cells
What is the term for having three types of cones?
Trichromat
Describe the signal route from the retina to the brain.
–> optic nerve –> optic chiasm –> optic tract –> hypothalamus/pretectum/superior colliculus/lateral geniculate nucleus –> optic radiation –> primary visual cortex
Which axons cross in the optic chiasm?
Axons from the nasal half of the retina
Describe layer IV of the primary visual cortex.
- main input layer for thalamic projections
- edge detectors
- oriented in ocular dominance columns (right/left eye) and orientation columns
- P- and M-type ganglion cells project to layer IV
Describe the non-input layers of V1.
- binocularity
- ON/OFF system convergence
- partial M/P systems
True/false: there are one visual area in the human brain.
False, there are multiple
What are some of the other visual layers called, and what are their function?
V2 (corners, surfaces), V3, V4 (complex shapes) and inferior temporal cortex (faces etc)
What are the dorsal and ventral stream perceiving, and where are they projecting to?
Dorsal: where? –> V1–> MT–> parietal lobe –> motor areas
Ventral: what? –> V1 –> V4–> inferior temporal lobe –> limbic system
What are cerebral akinetopsia, and what symptoms can it cause?
Bilateral damage to area MT from a stroke:
- dorsal stream defect –> lack of ability to perceive movement
- ventral stream defect –> lack of ability to perceive color
What are prosopagnosia, and what can it be caused by?
Face blindness
Can result from damage to the inferior temporal cortex (ventral stream)
