Download SCRIPT: Human Eye: Retina. https://www.youtube.com/watch?v

SCRIPT: Human Eye: Retina.
https://www.youtube.com/watch?v=NfLgzTSL-U0
This video will deal with the retina in particular. This is a simplified version of the vertebrate eye showing the path of
light takes into it.
Here is a small section that has been highlighted and has been exploded into this larger diagram. This is what we will
focus on. The main part of which is the retina.
Choroid: the choroid, the vascular tunic is the middle layer of the eyeball lying between the outer sclera and the inner
retina.
Retina: the retina is the innermost layer of the eyeball, the neural tunic. It consists of an inner neural layer and an
outer pigmented layer. The inner neural layer of the retina contains the photoreceptors, both rods and cones, that
detect lights as well as the neurons that the photons receptor stimulate in order to send signals to the brain.
Pigmented epithelium: the outer pigmented layer of the retina, the pigmented epithelium, absorbs light to prevent
visual echoes and also recycles retina from the photoreceptors in the neural layer.
Photoreceptors: the photoreceptors, the cells that respond to light, are located in the outermost region of the neural
layer of the retina. The vertebrate eye has two types of photoreceptors, rods and cones. In the resting state,
photoreceptors constantly release neurotransmitter glutamate. On absorbing a photon, a complex series of reactions
occurs which leads to the photoreceptors cessation of glutamate release. Thus, photoreceptors indicate reception of
photon by temporarily not releasing neurotransmitter, the opposite of what one might expect.
Neurons: various neurons, retinal ganglion cells, bipolar cells, amacrine cells and horizontal cells exist in the inner
region of the neural layer of the retina. These neurons are located in front of the photoreceptors so light must pass
through the layer of neurons in order to reach the rods and cones.
Rods: rods are photoreceptors specialized for low light conditions. Unlike cones, rods are unable to detect different
colors, only rods are present around the periphery of the retina. Hence, rods are responsible for peripheral vision.
Cones: cones are photoreceptors specialized for detecting different colors that is different wavelengths of light.
However, they do not function under low-light conditions. Only cones, with their ability to detect different colors and
to form sharper images, are found in the fovea: the center of the visual field where the lens focuses light.
Retinal ganglion cells: retinal ganglion cells or RGCs, are the innermost neurons with bipolar cells synapsing with their
dendrites. After receiving information from bipolar cells, retinal ganglion cells transmit that information via action
potential along their axons to the brain.
Optic nerve axons: the optic nerve axons are the axons of the retinal ganglion cells. All of the RGC axons meet at the
optic disc where they form the optic nerve. From the optic disc, the optic nerve axons, the retinal ganglion cells axons,
run to the brain.
Amacrine cells: amacrine cells are neurons that run perpendicular to bipolar cells and are located where the bipolar
cells synapse with the retinal ganglion cells. Amacrine cells can facilitate or hinder signalling between the
photoreceptors and the ganglion cells.
Bipolar cells: bipolar cells are the neurons whose dendrites these photoreceptors synapse with and whose axons
synapse with retinal ganglion cells. When a photoreceptor absorbs a photon it hyperpolarizes and stops releasing
glutamate. The change is detected by the bipolar cells and the information is passed on to the ganglion cells.
Horizontal cells: horizontal cells are neurons that run perpendicular to bipolar cells and are located where the
photoreceptors synapse with a bipolar cells. Like the amacrine cells, horizontal cells can facilitate or inhibit signalling
between the photoreceptors and the retinal ganglion cells