This document summarizes the different types of receptors in the human body. It describes exteroceptors, which respond to external stimuli, and interoceptors, which respond to internal stimuli. It provides details on cutaneous receptors for touch, pain, and temperature. It also describes receptors for senses like vision, hearing, and taste. Proprioceptors that detect muscle stretch and position are discussed. The document outlines the classification, functions, and properties of different receptors.

1. Receptors

2. Definition :
Specialised afferent nerve endings
designed to set up nerve impulse in response
to appropriate & adequate impulse
Convert various forms of energy  Action Potential
“TRANSDUCERS”

3. CLASSIFICATION
• EXTERORECEPTORS :
Respond to changes in external environment
• INTERORECEPTORS:
Excited by stimuli arising within body

4. EXTERORECEPTORS
• Cutaneous Receptors :
Touch, Pain, Temperature & Pressure
• Chemical Receptors :
Taste & Smell
• Tele-Receptors :
Excited from distance
Vision & Hearing

5. INTERORECEPTORS
• Stretch Receptors – Alveoli of Lungs
• Chemoreceptors – Aortic & Carotid Bodies
• Baroreceptors – Carotid Sinus & Aortic Arch
• Osmoreceptors – Hypothalamus
• Volume Receptors – Right Atrium
• Proprioceptors – Muscle Spindle ,Tendon Organs
• Visceroreceptors -
• Mechanoreceptors- Touch, Pressure, Muscle Stretch

6. CUTANEOUS SENSATIONS
• TOUCH & PRESSURE
• COLD
• WARMTH
• PAIN

7. RECEPTORS – TOUCH & PRESSURE
• Meissners Corpuscle
• Merkels Disc
• Basket Like Endings/ Hair End Organs
• Ruffini End Organs
• Krausse End Bulbs
• Pacinian Corpuscle
• Free Nerve Endings

9. • MEISSNERS CORPUSCLE :
Non Hairy parts of Skin
Rapidly Adapting
Light Touch & Low frequency vibrations
• MERKELS DISC :
3 or more cup shaped discs
Hairy skin also
Slowly Adapting
Continuous Touch Sensations

10. • BASKET LIKE ENDINGS/ HAIR END ORGANS:
Base of Hair Follicle
Rapidly Adapting
• RUFFINI END ORGANS:
Deeper layers of Skin & SC Tissue
Slowly adapting
Warmth, Strong touch & pressure

11. • KRAUSSE END BULBS:
Encapsulated
COLD
• PACINIAN CORPUSCLE :
Large Receptor
Touch , Pressure, High frequency vibrations
Rapidly Adapting

12. • FREE NERVE ENDINGS :
Touch & Pressure
Pain
Cold
Warmth

13. THERMORECEPTORS
• WARMTH :
Ruffini end organs
Free Nerve Endings – Dorsal Root C ( Type IV )
• COLD :
Krausse End Bulb
Aδ (Type III fibers)
Free Nerve Endings - Dorsal Root C ( Type IV )
• More cold receptors than warmth receptors

14. PROPERTIES
1. EXCITABILITY :
Adequate & Appropriate Stimulus
2. SPECIFICITY :
Each receptor responds maximally to one type of stimuli
3. REPITITIVE RESPONSE :
Repetitive burst of impulses

15. 4.EFFECT OF STRENGTH OF STIMULUS :
Increasing the strength of stimulus –
increases the Receptor Response
5. EFFECT OF EXTENT OF STIMULUS :
Stimulation of wider area activates more receptors

16. Spatial Summation –
Stronger signals spread to more fibers

17. Temporal Summation-
Increasing the frequency of impulses 
Transmits signals of increasing strength

18. 6.Localization & Projection
• Ability to locate the region stimulated
• 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
• Precise with cutaneous sensations

19. Quality or MODALITY of sensation
• Muller, 1845
• Doctrine of specific nerve energies
Sensory nerve from a receptor no matter
how or where along the pathway stimulated will
give rise to sensation for which the receptor is
specialized

20. LABELED LINE PRINCIPLE
• The specificity of nerve fibers for transmitting
only one modality of sensation

21. SENSORY UNIT :
One sensory neuron with all its peripheral branches
and receptors innervated by it.
RECEPTIVE FIELD :
Area from which response is produced in a sensory unit.

22. SENSORY CODING
• Converting a receptor stimulus to a
recognizable sensation is termed sensory
coding.
• All sensory systems code for four elementary
attributes of a stimulus:
Modality, location, Intensity, and Duration.

23. Modality - type of energy transmitted by the stimulus.
Intensity- is signalled by the response amplitude or
frequency of action potential generation.
Location - is the site on the body where the stimulus
originated.
Duration - the time from start to end of a response in
the receptor.

24. Weber–Fechner law :
• Magnitude of the sensation felt is proportional
to the log of the intensity of the stimulus .
• R = KSA
R is the sensation felt
S is the intensity of the stimulus
for any specific sensory modality, K and A are constants

25. ADAPTATION
Impulse discharge on stimulation decreases in
frequency but not in amplitude & later disappears
even though the stimulus is applied continuously
with same intensity

26. • Rapidly Adapting Receptors :
Rate/ Phasic/ Movement receptors
Touch receptors
Detect change in stimulus strength
• Slowly Adapting Receptors :
Tonic receptors
Transmit impulses as long as stimulus is present
Muscle spindle , Receptors in Macula,
Baroreceptors & Chemoreceptors
Detect Continuous Signal strength

27. INTENSITY OF SENSATION:
Frequency of impulses reaching the
sensory area & Number of receptors activated
FATIGUE :
Fresh stimulus fails to evoke response

28. RECEPTOR POTENTIAL
GENERATOR POTENTIAL
Not Action Potential – Do not obey All or None Law
Graded Response
Receptor Potential cannot be propagated

29. Pacinian Corpuscle
• Large receptor
• Concentric layers of
connective tissue capsule
• Easily accessible –
Mesentery
• Mechanoreceptor

32. ADAPTATION OF RECEPTORS
1. Fluid within the corpuscle redistributes –
receptor potential is not elicited
2. ACCOMODATION of the nerve fiber
Inactivation of Na channels

33. • Maximum amplitude of most sensory receptor
potential is 100 mV

34. Physiological Classification and
Functions of Nerve Fibers

35. 1. GENERAL SENSATIONS :
Superficial Sensations:
HEAD’CLASSIFICATION
Epicritic / Fine
Protopathic/Crude
Deep sensations:
2. SPECIAL SENSATIONS :
Vision, Hearing, Smell, Taste, Acceleration

36. 3.VISCERAL SENSATIONS
• Sensations that originate in visceral structures
• Do not have proprioceptors
• Very few touch & temperature receptors
• Fewer pain receptors are present
• Lung Inflation, Distension of stomach,
Change in arterial Pressure

37. EPICRITIC / FINE SENSATIONS :
• Fine Touch, Tactile Localization & Discrimination
• Temperatures ( 25 – 40 degree Celsius )
• Cerebral cortex
• Not associated with feelings

38. PROTOPATHIC/CRUDE SENSATIONS
• PAIN
• EXTREMES OF TEMPREATURE
( < 20 / > 40 degree Celsius )
• Associated with feelings – AFFECT
• Subcortical level

39. TACTILE SENSIBILITY
• Fine Touch :
Wisp of cotton
Von Frey’s Hair Aesthesiometer
• Crude Touch :
Pressing with your finger tip
• Tactile Localization :
Localize the part of body part with help of ballpoint pen

40. TWO POINT DISCRIMINATION
Compass Aesthesiometer
Minimum distance : Distance between two point when
the subject feels it as two points
Finger Tips – 2mm
Hands – 5mm
Back of the body – 60 -70mm
Power of discrimination diminishes from distal to
proximal parts

41. STEREOGNOSIS
• Ability to identify familiar objects without visual aid,
by feeling and handling them.
• Touch & Pressure receptors
• Cerebral Cortex
Inability to identify an object by Touch -Tactile Agnosia

42. • Conscious Proprioception :
Position sense & Joint Movement
• Vibration sense :
128 Hz
Bony prominences –
lower end of tibia, Malleoli ,
styloid process of radius
• Pallesthesia : ability to feel mechanical vibrations

43. PAIN SENSATION
• Superficial Pain :
Pin
• Deep Pain :
Applying pressure / squeezing muscle/ Achilles tendon
• ALGOMETER

44. TEMPERATURE
• 4 – 10 TIMES MORE cold receptors than warmth
• Cold receptors – 10 – 35 0C
• Warm receptors – 30 – 45 0C
• < 10 / > 400C - Pain

45. Each spinal nerve innervates a “segmental field”
of the skin called a DERMATOME

46. DORSAL/POSTERIOR COULMN/
TRACTS OF GOLL & BURDACH
• Epicritic Tactile Sensations
• Tactile Localization &
Discrimination
• Position Sense &
Joint Movement
• Vibration Sense
• Stereognosis

47. VENTRAL SPINOTHALAMIC TRACT
• Crude Touch
• Crude Localization
LATERAL SPINOTHALAMIC TRACT :
• Pain & Temperature,
• Visceral & Sexual Functions
• Itch

48. Iggo Dome Receptor
• Merkels disc are grouped
together in a receptor
organ which projects
upwards against the
underside of the
epithelium
• Localize Touch Sensation
• Determine texture of
what is felt

49. • The Na+ channel BNC1 is closely associated
with touch receptors. This channel is one of
the Degenerins
• When Hyper expressed 
cause the neurons they are in to degenerate