The Eye
This week I will recap what we've been learning in class. Right now we are studying the eye and mechanisms of vision. In order to understand vision, it's important to understand the anatomy of the eye.
Parts of your eye
The pupil is the dark center of the eye at which light enters the eye. The iris is a muscle that controls the size of the pupil. The pupils of each eye must always be the same size; a difference in size is taken as an indication of serious neurological dysfunction, since it is the brain stem (a vitally important part of the brain) which controls the consensual aspect of the pupillary light reflex (in other words, it is resonsible for the fact that light shone on one pupil changes simulataneously the size of both pupils).
Your retina
The retina of the eye is where the photoreceptors are located; it is here that light energy is transduced to neural messages. It's interesting to note that the function of these photoreceptors is primarily inhibitory in nature: photoreceptors actually hyperpolarize in response to light. This can be better understood if one thinks of vision as a system whose function it is to detect differences: the photoreceptor hyperpolarizes when it detects something new in the visual field or when it detects something important for object discrimination, like an edge. So evolution created an economy of vision in that our eyes don't need to work more than necessary. Pretty cool.
What amazes me...
What amazes me is the incredible speed with which vision processing occurs. By simply looking, most people are able to see. We don't have to wait a second for our photoreceptors to communicate to the bipolar cells to communicate with the ganglion cells to communicate with the LGN of the thalamus. We just see. And THAT is another reason why YOUR BRAIN IS SO AMAZING. See you next week.