4 Comments

  • Yes, Every photoreceptor releases the same neurotransmitter—glutamate. However, the effect of glutamate differs in the bipolar cells, depending upon the type of receptor imbedded in that cell’s membrane. When glutamate binds to an ionotropic receptor, the bipolar cell will depolarize (and therefore will hyperpolarize with light as less glutamate is released). On the other hand, binding of glutamate to a metabotropic receptor results in a hyperpolarization, so this bipolar cell will depolarize to light as less glutamate is released.

    In essence, this property allows for one population of bipolar cells that gets excited by light and another population that gets inhibited by it, even though all photoreceptors show the same response to light. This complexity becomes both important and necessary for detecting color, contrast, edges, etc.

    Further complexity arises from the various interconnections among bipolar cells, horizontal cells, and amacrine cells in the retina. The final result is differing population of ganglion cells in the retina, each which convey different information to the brain, for the final synthesis of a visual world.

    A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eye’s retina that is capable of phototransduction. More specifically, the photoreceptor sends signals to other neurons by a change in its membrane potential when it absorbs photons. Eventually, this information will be used by the visual system to form a complete representation of the visual world. There are 2 types of photoreceptors: rods are responsible for scotopic, or night vision, whereas cones are responsible for photopic, or daytime vision as well as color perception.
    A third class of photoreceptors was discovered during the 1990s: the photosensitive ganglion cells. These cells, found in the inner retina, have dendrites and long axons projecting to several areas of the brain.

    Pinealocytes in many non-mammalian vertebrates have a strong resemblance to the photoreceptor cells of the eye. Some evolutionary biologists believe that the vertebrate pineal cells share a common evolutionary ancestor with retinal cells.[8]

    In some vertebrates, exposure to light can set off a chain reaction of enzymatic events within the pineal gland that regulate circadian rhythms.[9] Some early vertebrate fossil skulls have a pineal foramen (opening). This correlates with the physiology of the modern “living fossils,” the lamprey and the tuatara, and some other vertebrates that have a parietal organ or “third eye,” which, in some of them, is photosensitive. The third eye represents evolution’s earlier approach to photoreception.

  • Hi ya Love

    Every cell in your body is photo-receptive some are photochemically reactive as well
    One can see with the heart through the eyes of knowledge!

  • The skin is often considered to be photo receptive. You can actually do your own experiments to verify this.

    One theory is that the pineal gland was once a third eye. Another theory is that the pineal gland is going to be a third eye.

Leave a Comment