The communication between Central Nervous System (CNS) and the external environment is influenced by the sensory receptors which help maintain homeostasis. These receptor cells are formed as dendrites at the distal of sensory neurons specifically designed for receiving certain kind of stimuli. The sense organs consists of epithelial cells and tissues connecting to the sensory neurons, which are comprised of receptor cells with functions of special senses e.g. vision, hearing, smell, taste and touch. Based on the stimulus locations these sensory receptor cells can be identified in three different regions in the body as exteroceptors, interoceptors, proprioceptors. The exteroceptor are the ones mostly located in the outer surface of the body (e.g. skin, eyes, oral cavity, nose and ears), and they are sensitive to external stimuli. (Pomfrett, 2009).
Basic awareness develops from our body's ability to touch, feel and maintain equilibrium. The receptors that respond to external stimuli are the exteroceptors which consists of cutaneous receptors in the skin. The cutaneous receptors are influenced by their dendritic endings which becomes sensitive to external stimuli. There are many receptors in the skin such as free dendritic endings (responds pain and temperature), merkel discs (responds to light touch receptors), root hair plexuses(light touch), meissner's corpuscles (light touch), ruffini's corpuscles (pressure and distortion of the skin) and pacinian corpuscles (deep pressure). These sensory receptors send nerve impulses to the brain which results in a stimulus response. .
Moreover, gustation and olfaction are controlled by chemoreceptors which relies on chemicals to produce the stimuli that regulate cell function. Gustation can be distinguished in to five simple tastes such as sweet, sour, salty, bitter and umami ("Meaty or savoury", taste receptors stimulated by MSG).
