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Axons carrying impulses from the retina are bundled together at the posterior aspect of the eyeball and issue rfom the back of the eye as the optic nerve. At the optic chiasma, the fibers from the medial side of each eye cross over to the opposite side of the brain; the fiber tracts that result are the optic tracts. The optic tract fibers synapse with neurons in the thalamus, whose axons form the optic radiation, which runs to the optic cortex located in the occipital lobe of the brain
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ReneThe visual pathway refers to the series of neural connections that transmit visual information from the eyes to the brain for processing. This pathway involves the optic nerve, optic chiasm, optic tracts, lateral geniculate nucleus, optic radiations, and visual cortex in the brain. Information processed through this pathway enables us to see and interpret the visual world around us.
Signal transduction pathway
The signal transduction pathway is the mechanism by which the energy of a photon signals a mechanism in the cell that leads to its electrical polarization. This polarization ultimately leads to either the transmittance or inhibition of a neural signal that will be fed to the brain via the optic nerve. The steps, or signal transduction pathway, in the vertebrate eye's rod and cone photoreceptors are then:
1. The rhodopsin or iodopsin in the outer segment absorbs a photon, changing the configuration of a retinal Schiff base cofactor inside the protein from the cis-form to the trans-form, causing the retinal to change shape.
2. This results in a series of unstable intermediates, the last of which binds stronger to the G protein in the membrane and activates transducin, a protein inside the cell. This is the first amplification step - each photoactivated rhodopsin triggers activation of about 100 transducins. (The shape change in the opsin activates a G protein called transducin.)
3. Each transducin then activates the enzyme cGMP-specific phosphodiesterase (PDE).
4. PDE then catalyzes the hydrolysis of cGMP. This is the second amplification step, where a single PDE hydrolyses about 1000 cGMP molecules. (The enzyme hydrolyzes the second messenger cGMP to GMP)
5. With the intracellular concentration of cGMP reduced, the net result is closing of cyclic nucleotide-gated ion channels in the photoreceptor membrane because cGMP was keeping the channels open. (Because cGMP acts to keep Na+ ion channels open, the conversion of cGMP to GMP closes the channels.)
6. As a result, sodium ions can no longer enter the cell, and the photoreceptor hyperpolarizes (its charge inside the membrane becomes more negative). (The closing of Na+ channels hyperpolarizes the cell.)
7. This hyperpolarization means that less glutamate is released to the bipolar cell than before (see below). (The hyperpolarization of the cell slows the release of the neurotransmitter glutamate, which can either excite or inhibit the postsynaptic bipolar cells.)
8. Reduction in the release of glutamate means one population of bipolar cells will be depolarized and a separate population of bipolar cells will be hyperpolarized, depending on the nature of receptors (ionotropic or metabotropic) in the postsynaptic terminal (see receptive field).
Thus, a rod or cone photoreceptor actually releases less neurotransmitter when stimulated by light.
ATP provided by the inner segment powers the sodium-potassium pump. This pump is necessary to reset the initial state of the outer segment by taking the sodium ions that are entering the cell and pumping them back out.
Although photoreceptors are neurons, they do not conduct action potentials with the exception of the ganglion cell photoreceptor.
from Wikipedia
- M cells, with large center-surround receptive fields that are sensitive to depth, indifferent to color, and rapidly adapt to a stimulus;
- P cells, with smaller center-surround receptive fields that are sensitive to color and shape;
- K cells, with very large center-only receptive fields that are sensitive to color and indifferent to shape or depth;
- another population that is intrinsically photosensitive; and
- a final population that is used for eye movements.
The visual pathway is the pathway taken by a nerve impulse triggered by lightas it travels from the retina to the visual cortex, in the occipital lobe of the brain. An impulse originating on the nasal side crosses to oposite side in the brain. An impulse arising from the temporal side goes to the same side in the brain.
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In the visual pathways to the brain the optic radiations project to the what?
The optic radiations project from the lateral geniculate nucleus of the thalamus to the primary visual cortex in the occipital lobe of the brain. This pathway is essential for processing visual information received from the eyes.
What does optic nerve mean in the eye?
The optic nerve is a bundle of nerve fibers that carries visual information from the retina to the brain. It serves as the main pathway for transmitting visual signals for processing and interpretation. Damage to the optic nerve can result in vision impairment or loss.
The Krebs cycle is an example of which type of metabolic pathway?
The Krebs cycle is an example of an aerobic metabolic pathway, as it requires oxygen to function efficiently.
Where does the pentose phosphate pathway occur?
The pentose phosphate pathway occurs in the cytoplasm of cells. It is a metabolic pathway that generates NADPH and produces ribose-5-phosphate, which is important for nucleotide synthesis and other cellular processes.
The extrinsic pathway of blood clotting occurs much quicker than the intrinsic pathway true or false?
True. The extrinsic pathway of blood clotting is triggered by external factors and occurs more quickly than the intrinsic pathway, which is initiated by internal factors.
