Vision Flashcards
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.
Describe the signal transduction after the light activation of rhodopsin.
The alpha subunit of transducin activates a phosphodiesterase (PDE), which converts cGMP to GMP. This inhibits the CNG channels, resulting in a hyperpolarization of the rods.
What happens in the rod cells during darkness, and how are the further signal transduction through the bipolar cells?
GTP is converted into cGMP by guanylyl cyclase. cGMP gates the CNG channels, resulting in depolarization and action potential of the rods, leading to the release of glutamate. Glu binds to mGluR6 on the bipolar cell, and the G-beta-gamma-i inhibits a constitutively active TRP channel (TRPM1), causing hyperpolarization of the bipolar cell (no further signal transduction)
Explain the signal transduction through the bipolar cells in the light.
The glutamate release by the rod cells are inhibited by the signal cascade following light activation of rhodopsin. This means that the mGluR6 is not activated, and thus cannot nhibit the constitutively active TRPM1 leaing to Na^+ influx, resulting in depolarization and action potential. GPR179 orphan R is requried for this signal trandution, and is binding RGs, that are deactivating the G-alfa-i.
What are the rods and cones involved in?
Image forming. Subsequently, the rods are sensing black/white, whilest the cones are sensing colors.
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).
What synthesis are the ipRGCs involved in?
The synthesis of melatonin.
