Question:  In preparation for my optometry admittance test, I have been studying the nervous system and how nerves function.  This led to a spiked interest in how the human eye transmits nerve impulses from the optic nerve to the brain for processing.  My question is:  How is the eye able to transmit visual information to the brain via the optic nerve?

Answer:It is known that the optic nerve is responsible for transmitting visual stimuli to the brain, but how this actually happens is an area that is being studied more and more.
Much interest in this type of research comes from glaucoma patients since glaucoma is a breakdown of the optic nerve due to an increase of intraocular pressure.   When the eyes see an image, the light is passed through the lens and focused on the retina.  The image on the retina is inverted and it is the optic nerve’s responsibility to flip the image right side up.  Once at the optic nerve, the light signals are transmitted to electrical signals to be sent to the brain.  Each eye has an optic nerve and the nerves cross behind the eye in the brain at the optic chiasm.  This crossing results in images seen in the left eye to be processed on the right side of the brain and vice versa.  After crossing, the optic nerve endings can end at one of four locations within the brain as seen in Figure 1.  Nerve fibers that end at the lateral geniculate nucleus of the thalamus are responsible for visual perception and fibers ending at the superior colliculus of the midbrain are responsible for the movement of the eye.  The light reflex of the pupil is controlled by the nerve ending at the pretectum of the midbrain and diurnal rhythms along with hormonal changes are detected by the suprachiasmatic nucleus in the hypothalamus.  These nerve endings are where the synapse occurs and sight is processed.  Each location contains a number of different types of cells and neurons responsible for the more intricate qualities of human sight such as color intensity and acuteness of visual reception.  All of the different tracks the optic nerve takes are always being processed and are some of the fastest processing nerves in the body.  The exact speed of nerve impulses to and from the brain is still a largely studied area.  Although the shape of the eye is what is responsible for capturing and focusing an image, the optic nerve is the powerhouse that physically processes and relays the visual information to the brain.

-Megan K.

Figure 1:  This figure shows two different views of the brain to illistrate the different paths of the optic nerve.  The nerve ends in four different places, each having a specific visual characteristic.

References

  • Dragoi, Valentin, PhD. “Visual Processing: Cortical Pathways (Section 2, Chapter 15) Neuroscience Online: An Electronic Textbook for the Neurosciences | Department of Neurobiology and Anatomy – The University of Texas Medical School at Houston.”Neuroscience Online. The University of Texas Medical School, Web. 15 June 2016.
  • “How Fast Do Nerves Send Signals to and from the Brain?”UCSB Science Line. National Science Foundation, 2015. Web. 15 June 2016.
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