1. SPECIAL SENSES (Introduction)
We are usually told that we have five senses that keep us in touch with what is going on in the external world: touch, taste, smell, sight, and hearing. Actually, touch is a mixture of the general senses that we consider in the nervous system chapter the temperature, pressure, and pain receptors of the skin and the proprioceptors of muscles and joints. The other four “traditional” senses—smell, taste, sight, and hearing— are called special senses. Receptors for a fifth special sense, equilibrium, are housed in the ear, along with the organ of hearing. In contrast to the small and widely distributed general receptors, the special sense receptors are either large, complex sensory organs (eyes and ears) or localized clusters of receptors (taste buds and olfactory epithelium).
Table 1- Special Sense Organs
|Eye||Rods and Cons||Photoreceptor||Vision|
|Ear||Organ of Corti||Mechanoreceptor||Hearing|
|Taste buds||Gustatory cells||Chemoreceptor||Taste|
2. Types of Receptors
Sensory receptors are categorized into five types according to their sensitivities
Chemoreceptors : are stimulated by changes in the chemical concentration of substances.
Pain Receptors : are stimulated by tissue damage.
Thermoreceptors : are stimulated by changes in temperature.
Mechanoreceptors : are stimulated by changes in pressure or movement.
Photoreceptors : are stimulated by light energy.