Receptor or Sensory Cell

•There are various type of the receptor cells. They are classified according to their sensitivity to different physical stimuli.
•For example chemical receptors only are stimulated by chemical stimuli.
•Photoreceptors are stimulated by light


•Mechanoreceptor by mechanical stimuli
•Baroreceptor by pressure
•Mechanical receptors are two type: phasic receptor (Paccini corpuscle), tonic mechanoreceptor (Strech receptor on the wall of urinary blood).


•Phasic receptor generate action potential only at the begining of stimuli, but tonic receptor is stimulated continously in the presence of stimuli.
•Photoreceptor found in the retina of eye.
•Baroreceptor found in the wall of blood vessel, they are free nerve ending


•Pain receptor is also free nerve ending and are stimulated chemical mediators relased from damaged cell.
•Chemoreceptors are found in tongue, olfactory nasal region.
•Receptors are localized in certain region of the body. Every receptor can be stimulated by the stimuli applied to region that they are localized.


•Information from around of the body are coded to the central nerveous system by the frequency of action potential.
•Olfactory stimuli is coded by the action potential frequency, since all receptor cell in olfactory region have more than one receptor molecule for different oder stimulant.


Intensity of pressure is also coded by action potential frequency