1. Sensory Receptors

2. Definition of Sensory Receptors:
Receptors are specialized cells / nerve endings which respond to stimuli.
These generate impulses which inform CNS about changes in internal & external environment.
Receptors are transducers, which convert various forms of energy into action potential or electrical energy.

3. STIMULUS: A change in environment.
TYPES OF STIMULUS: Electrical, Mechanical, Thermal, Chemical & Electromagnetic
Sensation: Becoming aware of a particular type of stimulus, e.g., tactile, thermal & pain sensations.

10. Non-encapsulated & encapsulated receptors:
Non-encapsulated: free nerve endings /
nociceptors, Merkel’s discs, hair follicle
receptors.
Encapsulated: Meissner’s corpuscles, Pacinian corpuscles, Ruffini’s end organs, Krause’s corpuscles.

11. Non-encapsulated: FREE NERVE ENDINGS: Widely distributed.
In epidermis, mucus membranes, joint ligaments, tendons, connective tissue, periosteum, peritoneum, pleural membrane, meninges, dental pulp.
Involved in crude touch, pressure, tickle & itch, pain & temperature sensation.

12. Non-encapsulated: MERKEL’S DISCS:
Present in clusters / groups in epidermis
(deeper part).
Stimulated when there is continuous touch or pressure. Example: holding a pen while writing.

13. Non-encapsulated: HAIR FOLLICLE RECEPTORS:
Wrapped around hair follicles.
Stimulated by bending of hair (if something is crawling on skin).

14. HAIR FOLLICLE
HAIR FOLLICLE

16. Adaptation in non-encapsulated receptors:
Free nerve endings & merkel’s discs  slow adaptation.
We feel the pen as long as we hold it.
Hair follicle receptors undergo rapid adaptation.
Insect starts crawling  we feel it  if it does not bite  we forget its presence.

17. Encapsulated: MEISSNER’S CORPUSCLES:
Meissner's corpuscles were discovered by the anatomist Georg Meissner ( ).
Rapid adaptation.
In dermal capillaries in skin of soul & palm
Nipple & external genitalia.
Under the capsule are flat modified schwann cells arranged concentically along long axis of corpuscles & end in expanded nerve endings.
Involved in: fine touch, 2 point tactile discrimination & vibration.

18. MEISSNER’S CORPUSCLE IN SKIN

19. Encapsulated: PACINIAN CORPUSCLE: Rapid adaptation.
In dermis of skin, C.T, ligaments, joint corpuscles, peritoneum etc.
Thick corpuscles, on section  onion like appearance.
Flattened cells arranged concentrically (in layers)
Involved in vibration & movement.

20. PACINIAN CORPUSCLE
PACINIAN CORPUSCLE

21. Encapsulated: RUFFINI’S END ORGANS: In dermis of skin.
Respond when skin is stretched / heavy pressure applied on skin.
Slow adaptation.

22. RUFFINI’S END ORGANS
RUFFINI’S END ORGANS

23. Encapsulated: KRAUSE’S CORPUSCLES: In the skin of external genitalia.
Respond to 2 point tactile discrimination.
Rapid adaptation.
Structure resembles  Meissner’s corpuscles.

24. KRAUSE’S END-BULBS / KRAUSE’S CORPUSCLES

25. OTHER CLASSIFICATION OF RECEPTORS:
4 TYPES:
EXTEROCEPTORS:
INTEROCEPTORS
TELOCEPTORS
PROPRIOCEPTORS

26. EXTEROCEPTORS:
In skin
Respond to external stimuli.

27. INTEROCEPTORS:
In body tissues.
Respond to internal stimuli.

28. TELOCEPTORS: Respond to stimuli at a distance.
EXAMPLE: Receptors in retina: rods & cones. Hearing receptors in ears.

29. PROPRIOCEPTORS:
Receptors involved in sensation of position & movement.
When a part of body is moved, they are stimulated.

30. Classification on the basis of nature of stimulus:
5 types:
MECHANORECEPTORS.
THERMORECEPTORS.
NOCICEPTORS.
CHEMORECEPTORS.
ELECTRO-MAGNETIC RECEPTORS.

31. MECHANORECEPTORS:
Respond to mechanical deformation of receptor membrane & of tissue, adjacent to receptor.
Large number of receptors are included.
EXAMPLES: Free nerve endings, Merkel’s disks, hair follicles, Meissner’s, Ruffini’s, Krause’s corpuscles, muscle spindle, golgi tendon organs, receptors in internal ear: in organ of corti, in semi-circular canals, in macula & vestibular apparatus. Baroreceptors are also included.

32. THERMORECEPTORS: Respond to temperature changes.
Include cold & warmth receptors.

33. NOCICEPTORS: Respond to noxious stimuli.
Receptors which detect tissue damage.
Nociceptors are free nerve endings.

34. CHEMORECEPTORS: Respond to chemical changes.
Include chemoreceptors in carotid & aortic bodies, chemosensitive area in medulla oblongata, olfactory receptors, taste receptors, osmoreceptors in hypothalamus & glucostat cells in satiety centre in hypothalamus.

35. ELECTROMAGNETIC RECEPTORS:
Respond to electromagnetic rays.
EXAMPLE: Rods & Cones in Retina.