Receptor

1. RECEPTORS
DR. SARAN AJAY
DEPT. OF PHYSIOLOGY, GMCM
2

2. DEPT. OF PHYSIOLOGY, GMCM 3
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

3. Information about internaland externalenvironment reaches
CNS through a variety of sensory receptors.
DEPT. OF PHYSIOLOGY, GMCM 4

4. Receptors detect sensory stimuli such as
•Touch and Pain
•Sound and Light
•Cold and Warmth
•Blood Pressure and Linear Acceleration
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5. These sensations are conveyed to CNS by means of
sensory nerve impulses.
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6. Receptors
•Receptorsaretransducers.
•Thatconvertvariousformsofenergyinthe
environmentintoactionpotentialsinthesensory
neurons
•i.e.mechanical,thermal,electromagnetic,chemical.
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7. Sensory receptor may be
1.Specialized dendritic endings of sensory nerve fibers
2.Free nerve endings
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8. Sense Organ
Receptoris sometimes associated with non neuronal cells
that surround it and forms a sense organ. e.g. Eye
DEPT. OF PHYSIOLOGY, GMCM 9

9. Sensory Modality
Type of energy transmitted by the stimulus
e.g.: touch, pain, temperature etc.
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10. DEPT. OF PHYSIOLOGY, GMCM 13
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

11. A. Classification–Traditional
1.Special senses
•Vision ,hearing, smell, taste, rotational and linear
acceleration (vestibular apparatus)
•Information carried by cranial nerves
•Located close to CNS
DEPT. OF PHYSIOLOGY, GMCM 14

12. 2. Cutaneous senses
•Receptors in the skin
•Touch-pressure, pain ,warmth, cold
•Information is carried by cutaneous branches of
spinal nerves.
DEPT. OF PHYSIOLOGY, GMCM 15

13. a. Epicritic
•Mild/light sensations, perceived more accurately
•Fine touch, tactile localization, tactile discrimination
b. Protopathic
•Crude type of sensations
•Pressure, pain, extremes of temperature
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14. 3. Deep senses
•from deep body tissues
•e.g. from joints, muscles and tendons
•Carried by spinal or cranial nerves
4. Visceral senses
•those concerned with perception of internal environment
•Carried by autonomic nerves
•Pain from viscera
DEPT. OF PHYSIOLOGY, GMCM 17

15. B. Classification–Type of Stimulus
1.Mechanoreceptors
2.Thermoreceptors
3.Nociceptors
4.Electromagnetic (photo) receptors
5.Chemoreceptors
DEPT. OF PHYSIOLOGY, GMCM 18

16. 1. Mechanoreceptors
Activatedbymechanicaldistortion(compressionor
stretching)ofreceptororoftissuesadjacenttothe
receptor.
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17. •Cutaneous receptors for touch –pressure
•Proprioceptors
•Sound receptors of cochlea
•Vestibular receptors
•Baroreceptors of carotid sinuses and aorta
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18. 2. Thermoreceptors
Respond to temperature changes
•Cold–cold receptors
•Warmth–warm receptors
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19. 3. Nociceptors
•Free nerve endings
•Mediates potentially harmful stimuli
•Pain, extreme heat, extreme cold
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20. 4. Electromagnetic receptors
(Photoreceptors)
•Respond to light.
•Rods & cones in retina
DEPT. OF PHYSIOLOGY, GMCM 23

21. 5. Chemoreceptors
Receptorsstimulatedbyachangeinthechemical
compositionoftheenvironmentinwhichtheyare
located.
•TasteandSmell
•Osmolalityofblood(osmoreceptorsinHT)
DEPT. OF PHYSIOLOGY, GMCM 24

22. C. Classification –location of stimulus
1.Teleceptors
2.Exteroceptors
3.Interoceptors
4.Proprioceptors
DEPT. OF PHYSIOLOGY, GMCM 25

23. 1. Teleceptors
Concerned with events at a distance.
•Visual receptors
•Auditory receptors
•Receptors for smell
DEPT. OF PHYSIOLOGY, GMCM 26

24. 2. Interoceptors
Concerned with internal environment.
•Pulmonary stretch receptors –alveoli, bronchioles
•Central chemoreceptors –medullary
•Peripheral chemoreceptors-aortic & carotid body
•Osmoreceptors –HT
DEPT. OF PHYSIOLOGY, GMCM 27

25. 3. Proprioceptors
Provide information about the position of body in space
at any given instant
•Muscle spindle -muscle length
•Golgi tendon organ-muscle tension
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26. 4. Exteroceptors
•Concerned with external environment near at hand.
•Cutaneous receptor
•Theyarefreenerveendings,expandednerve
endingsorencapsulatednerveendingsseenin
skinorsubcutaneoustissues
DEPT. OF PHYSIOLOGY, GMCM 29

27. 4 Cutaneous senses
1.Touch –Pressure mechanoreceptors
2.Pain –Nociceptors
3.Cold –cold receptors
4.Warmth –warm receptors
DEPT. OF PHYSIOLOGY, GMCM 30

28. DEPT. OF PHYSIOLOGY, GMCM 31
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

29. Cutaneous Mechanoreceptors
Touch
•Stimulation of tactile receptors in skin or in tissues
immediately beneath the skin
Pressureis sustained touch
•Deformation of deeper tissues
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30. DEPT. OF PHYSIOLOGY, GMCM 33

31. 1. Meissner’s corpuscle
•Endings of myelinated Type Aβ
sensory nerve fibers
•Encapsulated
•Rapidly adapting
DEPT. OF PHYSIOLOGY, GMCM 34

32. Location
•Abundantinfingertips,lips,nipple
•Smallreceptive field –precise
localization of sensation
Stimulus
•Movementofobjectsoverskin
•Slowvibration
DEPT. OF PHYSIOLOGY, GMCM 35

33. 2. Pacinian Corpuscle
•Encapsulated
•Unmyelinateddendriticendingofsensorynervefiber(Aβ)
-2mmindiameter
•Surroundedbyconcentriclamellaeofconnective
tissue–appearanceofonion
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34. •1
st
node of Ranvier –inside the capsule
•2
nd
near the point at which the nerve fiber leaves the capsule
DEPT. OF PHYSIOLOGY, GMCM 37

35. Location
•Dermis of glabrous and hairy skin
•Intramuscular connective tissues
•Periosteum and mesentery
Stimulus
•Deep pressure
•Fast tissue vibrations
Adaptation
•Rapidly adapting
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36. 3. Ruffini’s Corpuscle/ End organ
•Multi branched ,enlarged, dendritic ending of Aβfibers
•Elongated capsule
Location
•Deeper layers of skin & internal tissues
•Joint capsule
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37. Stimulus
•Sustained touch & pressure
•Signals degree of joint rotation
•Slowly adapting
Nerve
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38. 4. Merkel’s disc /cells
•Expandeddendriticending
•InnervatedbyAbfibers
Location
•Epidermisofglabrousskin,moderate
numbersinhairypartsoftheskin.
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39. Stimulus
•Sustained pressure & touch
•Helps to determine continuous touch
of objects on the skin
Adaptation
•Slowly adapting
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40. 5. Krause’s End Bulb
•Spherical mechanoreceptors
•Afferent fibers –Adgroup
•Encapsulated
•Respond to touch & pressure
Location-Conjunctiva , Papillae of lips
and tongue, Skin of genitalia
DEPT. OF PHYSIOLOGY, GMCM 43

41. 6. Hair End Organ
•Constituted by each hair & its basal
nerve fiber -Aβ
•Rapidly adapting
Stimulus
•Detects movement of objects on
surface of the body
Nerve
Hair
DEPT. OF PHYSIOLOGY, GMCM 44

42. Free Nerve Endings
•Found everywhere in skin & many
other tissues
•Terminal branches of thin,
unmyelinated Ad& C fibers.
•Detect touch, pain & temperature
DEPT. OF PHYSIOLOGY, GMCM 45

43. Receptor Sensation Location Features Adaptation
Meisner's
Corpuscle
Slow vibration
Movement of
object over skin
Epidermis of
glabrous skin
Abundant in
fingertips, lips,
nipple
Encapsulated
branched
dendrites in
connective tissue
Fast Adapting
Pacinian
Corpuscle
Fast vibration,
deep pressure
Dermis of
glabrous and
hairy skim
Largest receptor,
encapsulated
nerve ending
Fast Adapting
Merkel's Disc Touch, Sustained
Pressure
Epidermis of
glabrous skin
Expanded
dendritic endings
Slow Adapting
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44. Receptor Sensation LocationFeatures Adaptation
Ruffini’s endings Sustained touch
and pressure
Signals degree of
joint rotation
Dermis of
glabrous skin
Enlarged dendritic
endings,
multibranched
within capsule
Slow adapting
Krause End BulbTouch and
Pressure
Conjunctiva,
tongue, skin of
genitalia
Spherical
encapsulated
mechanoreceptors
Fast Adapting
Hair end organs Detects movt. of
objects on body
surface
hair & its basal
nerve fiber -Aβ
Rapidly adapting
Free Nerve
Endings
Pain, Temp,
Touch
Everywhere in
skin
Terminal branchesSlow adapting
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45. DEPT. OF PHYSIOLOGY, GMCM 48
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

46. Free (Naked) nerve endings
•Endings of AδandCfibers
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47. Location
•Widespread in superficial layers of skin
•Certain internal tissues
Periosteum
Arterial walls
Joint surfaces
•Most other deep tissues →only sparsely supplied with
pain endings
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48. Stimulus
•Respond to noxious stimuli
•Polymodal receptors
•Pain can be elicited by multiple types of stimuli
mechanical, thermal & chemical
Adaptation
•Non adapting
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49. DEPT. OF PHYSIOLOGY, GMCM 52
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

50. Thermoreceptors
•Discriminate thermal gradations
•Cold receptors
•Warm receptors
•Cold & warmth receptors are sub-epithelial located at
discrete spots.
DEPT. OF PHYSIOLOGY, GMCM 53
Innocuous

51. 1. Cold Receptors
•Dendritic endings of Aδ& C fibers
•Inactive at temp. of 40 °C
•Steadily ↑ their firing rate as skin temperature falls to about
24°C.
•Further ↓in temperature -firing rate ↓ until 10 °C
•Below that receptors inactive & cold becomes a local
anesthetic.
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52. DEPT. OF PHYSIOLOGY, GMCM 55

53. 2. Warm Receptors
•OnCfibers
•Thefiringrateofwarmreceptorscan↑astheskin
temperaturereachesabout45°C.
•Theybecomesilentifskintemperatureisfurther↑to
induceasensationofpain.
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54. DEPT. OF PHYSIOLOGY, GMCM 57

55. DEPT. OF PHYSIOLOGY, GMCM 58
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

56. •Whenastimulusisappliedcertainchangesoccurinthe
receptor.
•Immediateeffectisthechangeinmembrane
permeabilitytoions.
•Itleadstochangeinmembranepotentialofthe
receptor.
DEPT. OF PHYSIOLOGY, GMCM 59
Receptor Potential

57. •NonpropagateddepolarizingpotentialcalledReceptor
Potential.
•ItresemblesEPSP.
•Thisleadstothegenerationofactionpotentialinthe
sensoryneuron.
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58. Generation of impulses in Cutaneous Receptors
Paciniancorpusclehasbeenstudiedindetail
1.Largesize.
2.Easilyaccessibleinthemesenteryofexperimental
animals.
3.Canbeisolated,studiedwithmicroelectrodes&
subjectedtomicrodissection.
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59. DEPT. OF PHYSIOLOGY, GMCM 62

60. Structure of Pacinian Corpuscle
•Centralunmyelinatednervefiber
•Dendriticendingofsensorynervefiber(Aβ)
•Encapsulated
•Surroundedbymultipleconcentriclamellaeof
connectivetissue
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61. •Myelin sheath begins inside capsule
•1st node of Ranvier inside capsule
•2nd node –near the point at which nerve fibre
leaves the corpuscle
•Compressionanywhereontheoutsideofcapsule
elongate,indentordeformthenervefibre.
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62. •Whenagradedpressureisappliedtocorpuscle.
1.Smallamountofpressure→Nonpropagated
depolarizingpotential-Generatorpotential(GP)or
Receptorpotential.
•Thereceptorconvertsmechanicalenergyinto
electricalresponse.
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63. DEPT. OF PHYSIOLOGY, GMCM 66
Generator Potential

64. 2.Aspressureisincreased→Magnitudeof
GeneratorPotentialis↑.
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65. DEPT. OF PHYSIOLOGY, GMCM 68
Generator Potentials
Magnitude ↑

66. The magnitude of GP is proportionate to the intensity
of stimulus –graded RP.
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67. DEPT. OF PHYSIOLOGY, GMCM 70

68. 3.WhenmagnitudeofRPis>10mV→anAction
Potential(AP)isgeneratedinsensorynerve.
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69. DEPT. OF PHYSIOLOGY, GMCM 72
Generator Potentials
Action Potential

70. •GPisproducedinnon-myelinatednerveterminal.
•GPinturndepolarizesthesensorynerveat1stnodeof
Ranvier.
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71. DEPT. OF PHYSIOLOGY, GMCM 74

72. •Whenfiringlevelisreached–APisproducedinthe
1stnodeandthemembranethenrepolarizes.
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73. •IftheGPisgreatenoughneuronfiresagainassoonas
itrepolarizes.
•ItcontinuestofireiftheGPislargeenoughtobringthe
membranepotentialofthenodetothefiringlevel
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74. Thenodeconvertsthegradedresponseofthereceptorinto
actionpotentials.
Thefrequencyofwhichisproportionaltothemagnitudeof
theappliedstimulus.
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75. DEPT. OF PHYSIOLOGY, GMCM 78

76. Mechanism of production of GP & AP in Pacinian Corpuscle
Stimuli causes compression of Pacinian Corpuscle
↓
Mechanical distortion of the lamellas and small area of nerve terminal
↓
Stretch sensitive Sodium Ion channelsin membrane are opened
↓
Na+ diffuses to interior
↓
Increased positivity inside fiber
↓
Generator potential
79

77. Generator potential
↓
Local circuitof current flow
↓
Spreadsalong nerve fiber
↓
At 1st node of Ranvier, local current flow sets off Action Potential
↓
Transmittedalong nerve fiber to CNS
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78. DEPT. OF PHYSIOLOGY, GMCM 81
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

79. Sensory Coding
Converting a sensory stimulus to recognizable sensation
is called sensory coding.
DEPT. OF PHYSIOLOGY, GMCM 82

80. 4 attributes of a stimulus
•Modality–type of energy transmitted by stimulus
•Location–site on body or space where stimulus originated
•Intensity–signaled by amplitude of response or frequency
of action potential generated
•Duration–time from start to end of response
DEPT. OF PHYSIOLOGY, GMCM 83

81. Whateverbethestimulusapplied,thenervefiberfrom
receptortransmitsonlyAP.
AParesimilarinallnerves.
Howdoesstimulationoftouchreceptorevoketouch
sensation?
DEPT. OF PHYSIOLOGY, GMCM 84

82. •Howcan we differentiate between different intensities
of the same stimulus?
•How do we localize the stimulus ?
DEPT. OF PHYSIOLOGY, GMCM 85

83. DEPT. OF PHYSIOLOGY, GMCM 86
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

84. Properties of Receptor
1.Adequatestimulus
2.Adaptation
3.Muller’s Doctrine of specific nerve energies
4.Law of projection
5.Receptive field
6.Law of intensity discrimination
DEPT. OF PHYSIOLOGY, GMCM 87

85. 1. Law of adequate stimulus
•Specificityofresponse
•Eachreceptorisspecializedtorespondtooneparticular
formofenergy.
•Theparticularformofenergytowhichareceptoris
mostsensitive–adequatestimulus.
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86. •Receptorscanrespondtoformsofenergyotherthan
theiradequatestimulus.
•Butthethresholdofthesereceptorsfornonspecific
responsesismuchhigher.
DEPT. OF PHYSIOLOGY, GMCM 89

87. •Retinal receptors –light, but deep pressure on eye ball
can also stimulate the receptor
•Muscle spindle –stretch
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88. 2. Adaptation / Desensitization
•Ifastimulusofconstantstrengthismaintainedona
sensoryreceptor,itbecomesaccustomedtothe
stimulus.
•ThefrequencyofAPinitssensorynervedeclines
overtime–receptoradaptation.
DEPT. OF PHYSIOLOGY, GMCM 91

89. •Thedegreetowhichadaptationoccursvarieswiththe
typeofsenseorgan.
•Basedonthis,receptorscanbeclassifiedas
1.Phasic–rapidlyadapting
2.Tonic–slowlyadapting
DEPT. OF PHYSIOLOGY, GMCM 92

90. a. Phasic / Rate / Movement receptors
•Rapidlyadapting.
•e.g.Paciniancorpuscle,Meissner’scorpuscle
•Stimulatedonlyonchangeinstimulusstrength.
•Cannotbeusedtotransmitacontinuoussignal,butreact
stronglywhenachangeoccurs.
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91. b. Tonic receptors
•Slowlyadapting.
•Transmitimpulsesaslongasstimulusispresent.
•Awarenessofthestatusofthebodyanditsrelationto
surroundings.
•Examples–Merkelcells,Ruffini’sendorgan,
musclespindleetc.
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92. Advantages of Adaptation
1.Lighttouchwouldbedistractingifitwerepersistent.
2.Slowadaptationofspindleinputisneededtomaintain
posture.
3.Inputfromnociceptorsprovidesawarningthatwould
belostifthereceptoradaptedrapidly.
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93. DEPT. OF PHYSIOLOGY, GMCM 96

94. DEPT. OF PHYSIOLOGY, GMCM 97

95. Mechanism of Adaptation
Adaptation occurs in 2 ways in mechanoceptors
a.Receptors
b.Nerve Fiber
DEPT. OF PHYSIOLOGY, GMCM 98

96. a. Receptor Phenomenon
e.g. in Pacinian Corpuscle and Rods and Cones
•Pacinian Corpuscle is a viscoelasticstructure.
•When distorting force is applied to one side of corpuscle, it
is transmitted to the nerve fiber, eliciting a GP.
•Immediately, the fluid within the corpuscle redistributes,
and GP is no longer elicited.
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97. In eye, rods and cones adapt by changing the concentration
of light –sensitive chemicals.
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98. b. Nerve fibre accommodation
•Slower
•Tipofnervefibergraduallybecomeaccommodatedto
thestimulus
•ResultsfromprogressiveinactivationofNa
+
channelsinnervefibremembrane.
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99. 3. Muller’s doctrine of specific nerve energies
•Law of specific energies
•Specific sensory pathways are discrete from sense organ
to cortex.
•Achieved early during development of CNS.
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100. •Whenasenseorganornervepathwayfromaparticular
senseorganisstimulated,thesensationevokedisthatfor
whichthereceptorisspecialized.
•Nomatterhoworwherealongthepathway,activityis
initiated.
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101. •Thiswas1
st
establishedbyMullerin1835.
•IfthesensorynervefromaPaciniancorpuscleinthe
handisstimulatedbypressureattheelbowthe
sensationevokedistouch.
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102. Labeled Line Principle
•Specificnervefiberstransmitonlyonemodalityof
sensation
•Thespecificityofnervefibersfortransmittingonlyone
modalityofsensation–LabeledLinePrinciple
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103. 4. Law of Projection
Nomatterwhereaparticularsensorypathwayis
stimulatedalongitscoursetothecortex,theconscious
sensationproducedisreferredtothelocationofthe
receptor.
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104. Duringneurosurgicalproceduresonconsciouspatientswhen
thecorticalareareceivingimpulsesfromlefthandis
stimulatedthepatientreportofsensationinthelefthand,
notinthehead.
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105. Phantom Limb
•Seeninamputees.
•50-80%ofamputeesexperiencephantomsensationsin
theregionoftheiramputatedlimb.
•Patientcomplainsofpainandproprioceptive
sensationsinabsentlimb.
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106. •Theendsofnervecutatthetimeofamputation-
neuroma.
•Dischargespontaneouslyorwhenpressureisputon
them.
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107. Sincethenervefiberspreviouslycamefromthesense
organintheamputatedlimb,sensationisprojectedto
wherethereceptorsusedtobe.
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108. •Newerevidencesuggestsplasticityinsensorysystems
withintheCNSasthereasonforphantomlimb
phenomenon.
•Remappingofsomatosensorycortexoccurswhensensory
inputiscutoff.
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109. 5. Receptive Field
•Asinglesensorynervefiberanditsperipheral
branchesisasensoryunit.
•Receptivefieldofasensoryunitistheareafrom
whichastimulusproducesaresponseinthatunit
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110. DEPT. OF PHYSIOLOGY, GMCM 113

111. •Areceptorfiresonlywhentheskinclosetoits
receptivefieldisstimulated.
•Receptorfieldsdifferinsizeandresponse.
•Theareasuppliedbyoneunitmayoverlapand
interdigitatewithareassuppliedbyother.
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112. DEPT. OF PHYSIOLOGY, GMCM 115

113. MerkelcellsandMeissnercorpusclesprovidethemost
preciselocalizationastheyhavethesmallestreceptive
fields.
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114. 5. Law of Intensity Discrimination
How is it possible to tell whether touch is light or heavy
or whether pain is mild , moderate or severe?
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115. Two mechanisms
1.ByvariationinthefrequencyofAPgeneratedby
activityinagivenreceptor.
2.Byvariationinthenumberofreceptorsactivated.
DEPT. OF PHYSIOLOGY, GMCM 118

116. •Intensityofsensationfeltisdeterminedbythe
intensityofstimulusappliedtoareceptor.
•Greatertheintensityofappliedstimulus,largerwillbe
themagnitudeofReceptorPotential(RP).
1.
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117. •GreaterthemagnitudeofRP,greaterwillbethe
frequencyofActionPotentialsinsensorynerves.
•Theseareinterpretedinbrainasanincreasein
intensityofsensation.
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118. DEPT. OF PHYSIOLOGY, GMCM 121

119. •Greater intensity of stimulus will also activate receptors
with higher threshold in the same sensory unit.
•Recruits more receptors in surrounding areas into the
receptive field –recruitment of sensory units.
2.
DEPT. OF PHYSIOLOGY, GMCM 122

120. Asthestrengthofstimulusisincreasedleadsto
recruitmentofsensoryunits.
•Weakstimulus-activatereceptorswithlowthreshold
•Strongstimulus-activatereceptorswithhigher
thresholdaswell
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121. DEPT. OF PHYSIOLOGY, GMCM 124

122. Weber Fechner Law
Themagnitudeofsensationfeltisproportionatetothe
logofintensityofthestimulus.
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123. Perceived Intensity = K. log S
K = constant
S = intensity of the stimulus
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124. Stevens Power Law
Now, it is known that a power functionmore accurately
describes this relation.
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125. R = K.S
A
R = sensation felt
S = intensity of stimulus
K and A are constants for any sensory modality
DEPT. OF PHYSIOLOGY, GMCM 128

126. DEPT. OF PHYSIOLOGY, GMCM 129
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

127. Action Potential Receptor Potential
Produced by thresholdstimulus By subthreshold stimulus
Always depolarising Can be de/hyper polarising
Propagatedalong entire length of
cell without decrement
Can be conductedwith
decrementfor a short distance
Has constant size and shape as it
travels along the fiber
Size of the potential decreases
with distance
DEPT. OF PHYSIOLOGY, GMCM 130

128. Obeys “All or None” law
Size of AP does not ↑ with ↑in
stimulus strength
Does not obey
Amplitude of GP is proportionate to
strength of stimulus
Exhibits refractory period
So cannotbe summated
Do not exhibit refractory period
So they can be summated
DEPT. OF PHYSIOLOGY, GMCM 131

129. DEPT. OF PHYSIOLOGY, GMCM 132
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

130. DEPT. OF PHYSIOLOGY, GMCM 133

131. DEPT. OF PHYSIOLOGY, GMCM 134
Specific Learning Objectives
•Introduction
•Classification of Receptors
•Cutaneous Mechanoreceptors
•Cutaneous Nociceptors
•Cutaneous Thermoreceptors
•Receptor Potential
•Sensory Coding
•Properties of Receptor
•Difference between AP and RP
•Summary
DEPT. OF PHYSIOLOGY, GMCM

132. [email protected]
DEPT. OF PHYSIOLOGY, GMCM 135