We will discuss in this essay the workings of the Photoreceptors and how they determine vision, the perception of light. Also we will briefly discuss how photoreceptors work in other animals and how they work, if at all, in humans without sight.

Photoreceptors                                                                                                                     1

              The peripheral nervous system is described as all parts of the nervous system

except the brain and spinal cord, which is considered the part of the central nervous

system.   The peripheral nervous system, or the PNS, connects   the central nervous

system (CNS) to the remainder of the body, and is the conduit through which neural

signals are transmitted to and from the CNS. (Gale Encyclopedia of Neurological

Disorders, Hoyle and Arthur, 2005).

                These neurons are broken down into three categories, sensory, motor and

associated neurons. Motor neurons control the muscles and glands, the sensory neurons

are associated with the eyes, ears and skin, while the associated neurons connect the two.

(The Living World, Johnson and Lobos, 2010) We will concentrate on a particular part of

the PNS, the sensory receptors, and in this case, the photoreceptors. Photoreceptors

respond to light, which is what vision is, the perception of light. Eyes contain sensory

receptors called rods and cones that respond to photons of light. The light energy is

absorbed by the pigments in the rods and cones, which respond by triggering nerve

impulses in sensory neurons, sending it to the CNS, particularly the brain.

          After sending these signals from the photoreceptors through the   retina (the

eyeballs, the locations of the rods and cones) to the cerebral cortex, the brain interprets

this information and provides the images of what we are seeing....