Receptors are specialized sensory nerve endings that respond to specific stimuli. They are classified based on the type of stimulus, anatomical location, location of the stimulus, and rate of adaptation. Receptors include mechanoreceptors, chemoreceptors, thermoreceptors, nociceptors, and photoreceptors. Cutaneous sensations include tactile, thermal, and pain sensations detected by various receptors like Merkel's discs. Receptors demonstrate properties such as specificity of response, adaptation, and generator potentials. Sensory information is coded according to Muller's doctrine of specific nerve energies and the laws of projection and intensity discrimination.

1. RECEPTORS

2. Definition
It is a specialized/modified sensory nerve
epithelial ending which undergoes depolarisation
in response to a specific stimulus.
It acts as a ‘biological transducer’.

3. Classification
I. Based on type of stimulus
II. Based on anatomical location
III. Based on location of stimulus
IV. Based on rapidity of adaptation

4. I. Based on type of stimulus
 Mechanoreceptors
 Chemoreceptors
 Thermoreceptors
 Nociceptors
 Photoreceptors

5. II. Based on anatomical location
 Special Senses
 Superficial Senses/Cutaneous Senses
 Deep Senses
 Visceral Senses

6. III. Based on location of stimulus
 Telereceptors
 Exteroceptors
 Interoceptors

7. IV. Based on rapidity of adaptation
 Tonic Receptors
 Phasic Receptors

8. Cutaneous Senstaions
 Tactile Sensations
 Thermal Sensations
 Pain Sensations

10. Tactile Sensations
 Merkel’s discs & Meissner’s corpuscle
 Pacinian corpuscle
 Ruffini’s end organs
 Krause’s end bulbs
 Free nerve endings

11. Thermal Sensations
 Cold Receptors
 Warm Receptors

12. Pain Sensations
 Nociceptors
 Free Nerve Endings

13. Properties :
 Specificity of Response
(or) Law of Adequate
Stimulus
 Weber and Fechner’s Law
 Adaptation
 Generator Potential

14. Specificity of Response (or)
Law of Adequate Stimulus
The form of energy to which a
receptor is most sensitive is called its
‘adequate stimulus’.

15. Weber Fechner’s Law
The magnitude of the sensation felt is
proportionate to the
log of intensity of stimulus.

16. Adaptation (or) Desensitization

17. Generator Potential

18. Coding of Sensory Information
Muller’s Doctrine of Specific Nerve
Energies
Law of Projection
Law of Intensity Discrimination

19. Muller’s Doctrine of
Specific Nerve Energies
When the nerve pathways from a particular
sense organ are stimulated, the sensation produced
is that for which the receptor is specialized no matter
how or where along the pathway the activity is
originated.
Stimulation of the receptors or the sensory
pathway anywhere along its course will produce same
sensation as normally perceived by stimulation of the
receptor.

20. Law of Projection
No matter where a particular sensory
pathway is stimulated along its course to the
cortex, the conscious sensation produced is
referred to the location of the receptor. This
principle is called the ‘law of projection’.
Phantom Limb

21. Law of
Intensity Discrimination
 No. of action potentials
 Recruitment of sensory units