Heidi A. Everett
The eyes are the critical organs that contain nearly half of the body's sensory receptors. A large portion of the cerebral cortex is designated to processing all of the sensory information that these receptors receive (Grabowski, 2000). The eyes are complex structures and only two key photoreceptors will be reviewed concerning the anatomy of an eye. The ability for us to see in dim light is due to the action of rod cells. Cone cells provide us with the ability to see color and cones provide this capability only in bright light. Together these cells allow for our vision to function when various amounts of light are present.
The ears are the critical organs that allow for our ability to hear the various sounds of our environment. The external ear is the structure that is most familiar, but it is what is inside the ear or auditory canal that allows for our ability to hear. The ear canal leads to the eardrum or tympanic membrane. Take time to review with students the meaning of the Greek root word that tympanic is derived from. The Greek word "tympanon" means drum and this definition may be helpful for students to remember the function of the tympanic membrane (Hopson, 2006). Sound is made of up waves of energy. These waves cause the ear drum to vibrate allowing for a change in the air pressure in the middle ear. This pressure change causes small bones within the middle ear to vibrate the oval window which then transfers the vibrations to the inner ear. The cochlea is located in the inner ear where hair cells are located at the base of the base of the spiraling cochlea. These hair cells are mechanoreceptors that activate the auditory nerve by initiating an action potential that is relayed to the temporal lobe where the main auditory processing centers are located in the brain (Hopson, 2006).
The mouth and nose work together to provide our sense of taste. Gustation or the sense of taste deals directly with the tongue and the four zones on the tongue that are distinct to bitter, sweet, salty, and sour chemical stimuli (Grabowski, 2000). Olfaction or the sense of smell deals with taste as well providing the bulk of what we taste rather then the receptors located on the tongue. The olfactory receptors are stimulated by odorant molecules that may be inhaled into the nasal cavity or may enter the nasal cavity from the mouth (Grabowski, 2000). The sensitivity of olfaction is really the basis for the multitude of tastes we encounter in life. This is why a loss of smell means a loss of taste as well (Grabowski, 2000).
