Sensation

       Sensation is the bottom up processing by which our senses receive outside stimuli. The processing of sensory information goes through three steps reception, transduction and sending the information to various projection areas in the brain. Each sensory system has receptors that receive the stimuli, after that comes the role of transduction and it represents the process of the translation of physical energy into neural impulses or action potentials. When the transduction occurs the electrochemical energy is sent along various neural pathways into the projection area of the brain that will further analyze the information. To make it more clear let us discuss that in different examples.

  1. Vision

 

        Vision is one of the most important processes when it comes to sensation because nearly 70 percent of all the sensory receptors in ourwhole body are in our eyes.

          To understand this process you should know some information about the anatomy of the eye. Let me save you all the scientific terms and tell you just the important ones.

          The parts of the eye that anyone should be familiar with are the pupil, the cornea, the iris, the lens and the retina. Light comes in through the cornea and pupil and hits the lens. The lens focuses the light and projects it onto the retina which the back part of the inner area of the eyeball.

      After the reception of the information the retina which is composed of millions of photoreceptors take the information and translate it into electrochemical energy. And here we can talk about two types of photoreceptors rods and cones. Cones are basically used for color vision and for perceiving fine details; on the other hand rods function in reduced illumination and allow the perception of achromatic colors.

         When the light hits your posterior retina it spreads from the photoreceptors to the bipolar cells just beneath the “Rods and Cones” these cells also sends the information to the ganglion cells where the information is translated to action potential. The axon of theses ganglion cells is what creates the optic nerve which is responsible of sending theses impulses to the responsible projection area in the brain and in this case it would be the lateral geniculate cells of the thalamus and the the visual cortex in the occipital lobe which process the information further .

      2.Auditory system

        Obviously vision deals with light wile on the other hand the auditory system deals with the sound. The way we differentiate between different sounds is not something that we are going to talk about here since it is more related to pitch perception, a topic talked about in perception, than it is related to sensation.

        The ear is divided into three major areas the external or outer ear, middle ear and inner ear. The sound first reaches the part of the ear visible from the outside which is called the pinna its main function is to channel sound waves into the auditory canal which can be found in the outer ear. So the auditory canal takes the sound to the tympanic membrane also known as the eardrum. When the sound waves hit the eardrum they cause its vibration and this vibration passes to tiny bones in the middle ear.

 

          The middle ear has three tiny bones called the ossicles. These ossicles are known as hammer, anvil and stirrup and of course like anything in science they also have scientific names (malleus, incus and stapes). The job of these bones is the transmission of the vibrations of the eardrum to the inner ear.

 

         The inner ear contains the cochlea and actually there are number of membranes that run the length of the cochlea however the most important one is the basilar membrane which is capable of reading every single sound, within the range of human hearing of course, and communicating it immediately to the nervous system thanks to the organ Corti that rests on the basilar membrane.

 

         The organ of Corti is composed of hair cells which can be analogous to the cons and rods in the eye. So when the osicles take the vibration along the ear to the cochlea these hair cells starts bending which causes the transduction of the sound into electrochemical energy. This signal is then transmitted to the nerve fibers in the cochlea which connects to other nerve fibers in the auditory system. 

 

       Finally the auditory nerve projects to the superior olivary complex, inferior colliculus, the middle geniculate nucleus in the thalamus and last but not least the temporal cortex.      

See Also:

Threshold 

Perception

Perception and experience

Attention