SENSORY RECEPTORS. Physiology , 1st year mbbs/bhms/etc

A PowerPoint presentation by our respected HOD ma'am. Well made with ample information. Will give you good understanding

1. SENSORY RECEPTORS
and
SENSATIONS
By: Dr. Hetal Desai
Professor and Head, Physiology, SMIMER
1

2. •QUOTE OF THE DAY
Dr. Hetal Desai

3. SENSORY RECEPTORS
Learning Objectives:
1.Define and Classify Receptor
2.Describe structure and functions of each
receptor
3.Describe mechanism of Receptor
Potential
4.Enumerate and Describe Properties of
Receptors
3
Dr. Hetal Desai

4. SENSATIONS
Learning Objectives:
•Define Sensation
(is basic recognition of a stimulus)
(Aesthesia: Greek word = Feeling)
•Classify Sensations (Somatic, Visceral,
Special)
•Describe Dimensions of Sensations
•Define terms:
–Aesthesia, Anaesthesia, Paraesthesia,
Hyperaesthesia, Somaesthesia, Kinesthesia4
Dr. Hetal Desai

5. AfferentDivision of
the Nervous System
•Sensory Receptors
•Sensory neurons
•Sensory pathways
EfferentDivision of
the Nervous System
•Nuclei
•Motor neurons
•Motor tracts
Dr. Hetal Desai
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6. 6
1. SENSORY
RECEPTOR
2. SENSORY
NEURON
3. SENSORY
PATHWAY
AfferentDivision of
the Nervous System
Dr. Hetal Desai

7. Definition:
•Sensory Receptors are a part of neuron
or specialized cell.
•It is a specialized or modified sensory
nerve ending which undergoes
depolarisation in response to a specific
Stimulus and in turn, sends information
to CNS.
•Sensory Receptors convey information
from outside worldor within bodyto
CNS.
Dr. Hetal Desai
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8. Sensory Receptor acts as TRANSDUCER,
converts various forms of energy in env.
into electrical energy.
-These different energies include:
•Mechanical (Touch, Pressure,
Vibration)
•Chemical (Smell, Taste, O
2& CO
2
content of blood)
•Thermal (degrees of Warmth, Cold)
•Electromagnetic (Light)
Dr. Hetal Desai
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9. Receptor with surrounding non-neuronal
cell is called SENSE-ORGAN.
•DIFFERENTIAL SENSITIVITY of Receptors:
Each type of receptor is
-highly sensitive to only one type of sensory
Stimulus for which it is designed &
-is almost non-responsive to other types of
sensory stimuli.
•The specificity of nerve fibers for
transmitting only one MODALITY of sensation
is called LABELLED LINE PRINCIPLE.
Dr. Hetal Desai
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10. CLASSIFICATION OF
RECEPTORS:
1. According to
TYPE OF STIMULUS
2.CLINICAL / ANATOMICAL
Classification
3. According to
LOCATION/source OF
STIMULUS
Dr. Hetal Desai
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11. 1. According to TYPE OF STIMULUS
RECEPTOR--------------------------STIMULUS
1.Mechanoreceptors—mechanical:Touch, Pressure
e.g. Pacinian corpuscle,
golgi tendon organ (GTO)
proprioceptor.
2.Chemoreceptors—chemical stimulus
Taste, Smell,
O
2&CO
2content of blood,
osmolality (osmoreceptors)
3. Thermorecptors –---Hot, Cold temp.
4. Nociceptors-----------Pain.
5. Photoreceptors /Electromagnetic Receptors--Light.
Dr. Hetal Desai
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12. 2.According to CLINICAL / ANATOMICAL
Classification
1.Receptors for Special senses
2.Receptors for Cutaneousor
Superficial senses
3.Receptors for Deep senses
4.Receptors for Visceral Senses
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Dr. Hetal Desai

13. 2.According to CLINICAL / ANATOMICAL
Classification
1.Receptors for Special senses-
•Highly specific for only one modality of
sensation
•Eg. Auditory R, Visual R, Taste R, Smell or
Olfactory R, R for Linear & Rotational Motion .
•Transmit impulses through Cranial n.
•Lie in CNS.
Dr. Hetal Desai
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14. 2. According to CLINICAL/ ANATOMICAL
Classification
4. Receptors for VISCERAL
SENSES: present in visceral
organs
•Carry info. about internal env. of
body.
•Transmit impulses via ANS.
•Eg. Deep Pain from different
viscera, Blood Glucose conc., etc.
Dr. Hetal Desai
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15. 2.Receptors for Cutaneous / Superficial senses:
•Lie superficially on Skin.
•Carry Impulses through cutaneous branches of
spinal nerves. Eg. Touch, Pain, Pressure,
Temp. R.
3.Receptors for Deep senses:
•Lie in deep tissues & Provide Sensation from
joint, muscle, tendon, subcutaneous tissue.
•Transmit impulses through muscular branches
of spinal / cranial nerves.
•Eg. Muscle Spindle, Golgi Tendon Organ
(GTO), Joint Receptors.
2. According to CLINICAL/ ANATOMICAL
Classification
Dr. Hetal Desai
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16. 1.TELERECEPTORS : Perceive sensory stimulus
at a distance. Eg. Light, Sound, Smell.
2.EXTEROCEPTORS : Perceive changes in
External env. Outside of body. Eg.Touch, Pain,
Pressure, Temp.
3.INTEROCEPTORS : Perceive changes in Internal
env. Inside of body. Eg.
(a)PROPRIOCEPTOR
(b)BARORECEPTORS
(c)OSMORECEPTORS
(d)GLUCORECEPTORS
(e)CHEMORECEPTORS
3.According to LOCATION/ SOURCE OF STIMULUS
(Sherrington’s classification)
Dr. Hetal Desai
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17. INTEROCEPTORS : Perceive changes in Internal
env. of body :-
(a)PROPRIOCEPTORS : Inform about position of
of limb/ body in space & force of muscle
contraction at particular instant.
E.g. Muscle spindle, Golgi tendon organ (GTO),
Joint recepors, Vestibular Receptors
(b)BARORECEPTORS : respond to/ measure
Blood Pressure
(c)OSMORECEPTORS: respond to Osmotic
pressure of Plasma
(d)GLUCORECEPTORS: respond to
arteriovenous blood glucose difference
(e)CHEMORECEPTORS : Eg. Taste receptors,
O
2&CO
2content of blood, Glucoreceptors.
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Dr. Hetal Desai

18. Cutaneous Receptors
•MECHANORECEPTORS
•THERMORECEPTORS
•NOCICEPTORS
Dr. Hetal Desai
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19. CUTANEOUS RECEPTORS
•MECHANORECEPTORS : are concerned
with Touch & Pressure sensation.
consist of unmyelinated axon surrounded by
lamellated connective tissue.
1.MERKEL’S DISCS & MEISSNER’S
CORPUSCLES
2.PACINIAN CORPUSCLES
3.RUFFINI’S END ORGANS
4.KRAUSSE’S END ORGANS
5.HAIR END ORGANS
6.FREE NERVE ENDINGS
Dr. Hetal Desai
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20. Cutaneous Receptors in the Human Skin
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Dr. Hetal Desai

21. MERKEL’S DISCS
Dr. Hetal Desai
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22. MEISSNER’S CORPUSCLES
Dr. Hetal Desai
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23. MERKEL’S DISCS & MEISSNER’S CORPUSCLES
•Are tactile receptors. (Touch & Vibration sense)
•M.D. form expanded discs &
•M.C. form encapsulated corpuscles on
afferent nerve terminals of mye. Aβ(30-70m/s)and
Aδfibers (5-30m/s).
•Occur in groups in cutaneous papillae.
•Maximum density in skin of :
•Fingertips, Lips, nipples, orifices of body, around
base of hair follicles.
•Are RAPIDLYADAPTINGreceptors.
Eg. Why we don’t feel clothes once they are put on?
Dr. Hetal Desai
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24. PACINIAN CORPUSCLES
Dr. Hetal Desai
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25. PACINIAN CORPUSCLES
•Are nerve terminals of mye.Aβfibres (30-70m/s).
•Are Large receptors, resemble onion in shape, have
lamellated C.T.
•Found maximally in:
•skin, subcutaneous tissue, mesentery, near tendons &
joints.
•Respond to Deformation caused by firm pressure.
•Detect Pressure Touch, tissue Vibration.
•Are RAPIDLY ADAPTING receptors.
•Eg. Why we do not feel seat pressure when sitting?
Dr. Hetal Desai
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26. PACINIAN CORPUSCLES
RAPID ADAPTATION : Respond only to CHANGES in Pressure
(Deformation), NO response to Sustained Pressure.
Dr. Hetal Desai
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27. Key concept: Receptive field of a nerve fiber or neuron
Dr. Hetal Desai
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28. Paciniancorpuscles have large receptive fields.
Black dots = locations of
Paciniancorpuscles
grey areas = receptive
Fields.
Large receptive fields
are correlated with
poor spatial resolution.
Dr. Hetal Desai
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29. Large versus small receptive
fields
The more closely spaced
the receptors are and the
smaller their receptive
fields, the better the ability
to resolve two pressure
points on the skin
Large receptive fields collect
and integrate information
over a large area of sensory
space.
Spatial resolution is low.
Small receptive fields collect
information from a restricted
area of sensory space.
Spatial resolution is high.
Dr. Hetal Desai
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30. RUFFINI’S END ORGANS
Dr. Hetal Desai
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31. RUFFINI’S END ORGANS
•Encapsulated & expanded endings of
myelinated Aδ& unmyelinated Cfibres.
•Function :Mecahanoreceptors(detect
stretch, deformation within joint &
warmth) THERMORECEPTORS ,
Perception of degree of Warmth,
•Located in Dermis.
•Are Tonic Receptors,
very SLOWLYADAPTINGreceptors.
•RECEPTIVE FIELD SIZE is LARGE.
Dr. Hetal Desai
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32. 32
KRAUSSE’S END BULB or ORGANS
Dr. Hetal Desai

33. KRAUSSE’S END BULB or ORGANS
•Are spherical Mechanoreceptors
•Endings of Aδfibres.
•Located in conjunctiva, Papillae of
Lips & Tongue, skin of genitalia, &
in sheath of Nerves.
•Function: TOUCH & Pressure.
•RAPIDLY ADAPTING
Dr. Hetal Desai
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34. FREE NERVE ENDINGS
Dr. Hetal Desai
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35. FREE NERVE ENDINGS
•Are terminals of myelinated Aδ(5-30m/s)
& unmyelinated C fibres (2m/s).
•Function: NOCICEPTORS (Pain
perception)
•STIMULUS: Noxious stimuli, Tissue
damage
•Can also convey Touch & Pressure.
•Eg. Light contact with cornea of eye –
Corneal Reflex
•Cornea contains only free n. endings.
Dr. Hetal Desai
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36. HAIR END ORGAN
Dr. Hetal Desai
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37. HAIR END ORGAN
•Includes Hair & it’s basal nerve mye. Aβ
(30-70m/s).
•RECEPTIVE FIELD SIZE is SMALL.
•Function:
1.MOVEMENT OF OBJECT ON SURFACE
OF BODY.
2. INITIAL CONTACT WITH BODY.
•RAPIDLY ADAPTING receptors.
Dr. Hetal Desai
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38. PROPRIOCEPTORS
•Monitor:
–position of joints
–tension in tendons and ligaments
–state of muscular contraction
Dr. Hetal Desai
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39. PROPRIOCEPTION
•Is a purely somatic sensation
•No proprioceptors in the visceral
organs of the thoracic and
abdominopelvic cavities
•You cannot tell where your spleen,
appendix, or pancreas is at the
moment
Dr. Hetal Desai
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40. Major Groups of Proprioceptors
•Muscle spindles:-monitor skeletal muscle length
–trigger stretch reflexes
•Golgi tendon organs:-located at the junction between
skeletal muscle and its tendon
–monitor external tensiondeveloped during muscle
contraction
•Joint Receptors : Situated in joint Ligament & capsule
—Are Pacinian corpuscles, Golgi tendon organs,
Ruffini’s End organs.
—Are RAPIDLY ADAPTING receptors.
—Are endings of Gp.1 n. fibers.
—Encode changes in joint angle at extremes of angular
excursion
Dr. Hetal Desai
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41. Thermoreceptors
•Also called temperature receptors
•Are free nerve endings of Aδ& C fibres located
in:
–the dermis
–skeletal muscles
–the liver
–the hypothalamus
•Number of :
Cold receptors are 4-10 times > Warm receptors
•Never Adapt 100%
•STIMULUS: Changein Temp.
Adapt at same Temp.
Dr. Hetal Desai
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42. THERMORECEPTORS
•COLD RECEPTORS
1.Ending of Aδnerve
fib., 2.5μm dia.,
2.Fire with “steady”
discharge at any one
tissue temp.
between 10-35°C
3.Maximal frequency
of steady discharge
is at tissue temp.
25-30°C
•WARM RECEPTORS
1.Endings of unmye.C
fib., 0.4-1.2 μm dia.
2.Fire with “steady”
discharge at any one
tissue temp.
between 35-45°C
3.Maximal frequency
of steady discharge
is at tissue temp.
38-43°C
Dr. Hetal Desai
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43. Thermoreceptors
•Both warm & cold R. respond to temp. of
tissues surrounding them
•So, stimulus of 35°C will feel:
warm if skin is at 30°C &
cool if skin is at 40°C.
•This explains why cold metal objects feel
colder than wooden objects of same temp.:
Be’coz metal conducts heat away from skin
more rapidly.
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Dr. Hetal Desai

44. PARADOXICAL COLD FIBRE DISCHARGE
•If tissue temp. is ↑ed to >45°C, Warm R. do not respond but
Cold R. discharge at ↑ing rate producing a mixed sensation
of cold & pain called PARADOXICAL COLD FIBRE
DISCHARGE.
•CAUSE: At 45°C tissue damage begins to occur.
Dr. Hetal Desai
44→Skin temp. degree C.
25°C 40°C50°C
COLD FIBRE
WARM FIBRE

45. ELECTRICAL / IONIC EVENTS IN
RECEPTORS
•RECEPTOR CONVERTS STIMULUS
ENERGY INTO ELECTRICAL ENERGY
•Take Eg. Of Pacinian Corpuscle
•PARTS OF PACINIAN CORPUSCLE :[Fig]
Apply one electrode on unmye. N. end &
other at 2
nd
node of Ranvier outside capsule
↓
Mechanical deformation by rod causes opening of
Na
+
channels, produces localized memb pot.
[GENERATOR POT.]
↓
Depol. Spreads to n.fib. A.P. is propagated.
↓
Source of generator pot.
If capsule removed: Gen. Pot.+ A.P.+
1
st
node of Ranvier blocked: Gen. Pot.+ A.P.-
If n. cut, degenerated: Gen .Pot.-A.P.-
↓
►Generator pot. Is produced by change in memb.
Pot. of unmye. N. terminal.
►At 1
st
node of Ranvier, graded Generator pot. Is
converted into A.P.
↓
►Generator potential is similar to EPP &
EPSP.
►Generator potential & Receptor potential
Dr. Hetal Desai
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46. Dr. Hetal Desai

47. 47

48. PATTERNS OF TRANSMISSION
Dr. Hetal Desai
48
•Generator potential
–free nerve endings, encapsulated nerve endings
& olfactory receptorsproduce generator potentials,
–when large enough, it generates a nerve impulse
in a first order neuron

49. 49
•Receptor potential
–vision, hearing, equilibrium and taste
receptorsproduce receptor potentials
–receptor cells release
neurotransmitter molecules on first
order neurons producing postsynaptic
potentials
–PSP may trigger a nerve impulse
SPIKE-INITIATING ZONE
RECEPTOR POTENTIAL
Dr. Hetal Desai

50. Molecular Mechanism of Visual Reception
FINAL STEP IS OPENING & CLOSING OF ION CHANNELS
Dr. Hetal Desai
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51. Chemoreceptor Mechanisms
Dr. Hetal Desai
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52. Differences
RECEPTOR/GENERATOR P.
1.Is gradedresponse.
2.↑ intensity of stimulus =
↑magnitude of response.
3.No Refractory period.
4.cannot be propagated.
It is a LOCAL response.
5.Duration is greater
≈ 5-10ms.
6. Can be depolarizing or
hyperpolarizing.
7. Can be produced
spontaneously or in
response to electrical,
thermal, mechanical,
chemical stimuli.
•ACTION POTENTIAL
1.Follows All or None law.
2.↑ intensity of stimulus =
↑ frequency of A.P.
3.Refractory period = 1ms.
4.A.P. is propagated.
5.Duration = 1-2ms.
6. Is ALWAYS depolarizing.
7. Is produced only in
response to membrane
depolarization.
Dr. Hetal Desai
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53. 2.↑ intensity of stimulus= ↑ frequency of A.P.
Dr. Hetal Desai
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54. PROPERTIES OF RECEPTORS
1.EXCITABILITY.
2.SPECIFICITY OF RESPONSE / LAW OF
ADEQUATE STIMULUS.
3.GENERATION OF RECEPTOR/GENERATOR
POTENTIAL.
4.ADAPTATION
TONIC
PHASIC.
5.MULLER’S DOCTRINE OF SPECIFIC NERVE
ENERGIES.
6.LAW OF PROJECTION.
7.INTENSITY DISCRIMINATION:
BY FREQ. OF A.P. GENERATED IN N. FIB.
RECRUITMENT OF SENSORY UNITS.
Dr. Hetal Desai
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55. 1. EXCITABILITY
•Each receptor is an Excitable unit.
•It responds to External / Internal
stimulus by depolarization &
production of Generator / Receptor
potential.
Dr. Hetal Desai
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56. 2. SPECIFICITY OF RESPONSE /
LAW OF ADEQUATE STIMULUS.
•Each receptor is easily stimulated by
only one type of adequate stimulus.
•Adequate stimulus: Form of Energy
(Stimulus) to which receptor is most
sensitive.
•Receptor of a particular sense organ
has very low threshold for its Adequate
Stimulus.
Dr. Hetal Desai
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57. ♦RECEPTOR-------------------♦ADEQUATE STIMULUS
Rods and Cones----------+ce ofsingle Photon of Light
Ruffini’s receptors--------Warm temp. (water)
Tactile receptors----------Deformation
Golgi Tendon Organ-----Stretch
Cochlea---------------------Sound (vibrations of basement
membrane)
Pressure on eyeballs can also stimulate Retinal receptors but
their threshold to pressure is much higher than threshold of
pressure receptors of skin.
Hot water can also stimulate naked nerve endings of PAIN,
but response produced is not complete.
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2. SPECIFICITY OF RESPONSE /
LAW OF ADEQUATE STIMULUS.
Dr. Hetal Desai

58. 3. GENERATION OF
(RECEPTOR)/ GENERATOR POTENTIAL
•Each Receptor produces Generator pot.
when stimulated by Adequate Stimulus.
•When Generator pot. rises above threshold,
A.P. is produced in N. fib. Attached to receptor.
•Adequate Sti. →Na+ channels open →Na+ influx
→Generator pot. →Threshold →A.P. in sensory n.
Dr. Hetal Desai
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59. 4. Adaptation(desensitization)
•Reduction in sensitivity to a constantstimulus
•Nervous system quickly adapts to stimuli that are
painless and constant
•On basis of Adaptation receptors are classified as:
1.Slowly Adapting Receptors / TONIC Receptors
•Eg. Muscle Spindle, discharges continually to
maintain Posture.
•Pain & Cold R. will lose its warning value if they adapt.
•BaroR & ChemoR fire continually to regulate B.P.
2.Rapidly Adapting Receptors/PHASIC Receptors/
Movement Receptors
•Touch, Pressure, Olfactory(smell) receptors.
•Eg. We don’t feel clothes once they are put on.
59
Dr. Hetal Desai

60. FUNCTION OF ADAPTATION
•To Decrease the amount of sensory information
Reaching the Brain.
CAUSE OF ADAPTATION
1.Receptor fails to maintain Generator potential despite
constant Stimulus Application
2.Generator potential is present, but A.P. fails to develop,
because of ↓ excitability of nerve membrane.
(Na+ channel inactivation, ↑K+ conductance, Na+K+
pump activity)
3. Mechanoreceptors adapt due to redistribution of fluid.
4. Rods and cones adapt by changing their chemical
composition.
Dr. Hetal Desai
60

61. Stimulation of touch R. produces
touch sensation & not Warmth.
Why?
Because:
•each type of R. is specialized for
one specific type of sensation
•this specific sensation is carried
by its unique/seperate pathway to
cortex.
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5. MULLER’S DOCTRINE OF SPECIFIC
NERVE ENERGIES.
Dr. Hetal Desai

62. 5. MULLER’S DOCTRINE OF SPECIFIC NERVE ENERGIES.
•It is Specificity of n.fibres to transmit only one
Modality of sensation.
•It follows Labelled Line Principle.
•Collection of sensory neurons carrying the
same sensation is called Labelled Line
•Activation of the same group of nerve fibers always
produces sensations of the same modality
(no matter how the neurons are stimulated)
•Activation of nerve fibers in different sensory tracts
produces different modalities of sensations
•E.g. Action potentials travelling in Spinothalamic tract are
perceived as Pain
•E.g. Action potentials travelling in Dorsal-column Medial-
lemniscal pathway are perceived as touch or pressure.
Dr. Hetal Desai
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63. 63
How can we locate the area from where
sensation is perceived?
Depends on particular part of brain area/Map
in Somato Sensory Cortex which is activated.
Dr. Hetal Desai

64. 6. LAW OF PROJECTION.
•Stimulus location is recognized due to
point-to-point representation of body in
somatosensory cortex (SSA)
•Receptor→ sensory n. →CNS
•When any part of a sensory pathway is
stimulated,
the Conscious sensation produced
is referred to the location of receptor.
•Eg. PHANTOM LIMB: sensation is
produced in limb which is no longer
present. Dr. Hetal Desai
64

65. 7. INTENSITY DISCRIMINATION
a. BY FREQUENCY OF A.P. GENERATED IN SENSORY
n.fib.
Intensity of Applied αMagnitude of αFreq. of A.P.
Stimulus Generator pot.in n.fibres
65
Dr. Hetal Desai

66. 7. INTENSITY DISCRIMINATION
a.BY FREQUENCY OF A.P. GENERATED IN
SENSORY n.fib.
Intensity of Applied αMagnitude of αFreq. of A.P.
Stimulus Generator pot.in n.fibres
WEBER FECHNER LAW:
S αlog Ior
S = k log I + c (k & c are constants)
Dr. Hetal Desai
66

67. b. RECRUITMENT OF SENSORY
UNITS:
Strong sti. Spreads over a large area=>
Stimulates more no. of Receptors=>
more Afferent n. fibs. are activated=>
Brain interprets this as :
↑ intensity of Sensation
Greater the Intensity of Stimulus = More
the no. of Sensory units activated.
67
7. INTENSITY DISCRIMINATION
Dr. Hetal Desai

68. Greater the Intensity of Stimulus = More the no. of Sensory units
activated.
•A single afferent neuron with all its receptor endings is
called a SENSORY UNIT.
•Each sensory n. receives info. From a particular sensory
area called its Receptive field.
•Receptive fields of neighbouring neurons overlap.
•Smaller the receptive field, more precise is the encoding of
stimulus localization.
68
Dr. Hetal Desai

69. Dr. HetalDesai
69
(a) Effect of Strength of
stimulus:
Receptor potential & A.P.
frequency increases with
increasing strength of
stimulus
(b) Effect of Velocity of
stimulus:
Receptor potential & A.P.
frequency increases with
increase in rate of change
of stimulus

70. RECENT ADVANCES & Applied : -
Olfactory, Taste, and Photo Sensory Receptors in Non-
sensory Organs: "It Just Makes Sense”
•Our classic understanding of sensory receptors has been
that they are confined to the sensory organs in which they
were initially identified: olfactory receptors in the nose,
taste receptors on the tongue, and light receptors in the
retina.
•However, this idea was quickly altered after olfactory
receptors were identified in extra-olfactory tissue and cells.
•A growing body of literature describes unexpected
functions for sensory receptors in other organs, including
regulation of vascular relaxation in blood vessels by opsins
and involvement of taste receptors in the airway.
70
Dr. Hetal Desai

71. 71
•Example:-
•Bitter taste receptors in the respiratory system have
been the most studied.
•They can be found on ciliated epithelial, solitary
chemosensory, ciliated brush, and airway smooth
muscle (ASM) cells.
•When activated, TAS2Rs cause an
–increase in ciliary beat frequency (Shah et al.,
2009) and mucociliary clearance (Ortiz et al.,
2016) as well as
–release of nitric oxide from ciliated cells and
–release of antimicrobial proteins (Lee and Cohen,
2016) from solitary chemosensory cells.
Dr. Hetal Desai

72. •Within ASM cells, activation of TAS2R-
10,−14, and−31 have been shown to
cause relaxation and bronchodilation
(Deshpandeet al., 2010;An et al., 2012).
•Interestingly, bitter taste receptors mediate
relaxation but cause a seemingly
paradoxical increase in intracellular
calcium upon activation.
•Although increased calcium typically leads
to contraction, bitter taste receptor-
mediated increases in calcium cause
these cells to relax.
Dr. Hetal Desai

73. SENSATIONS
73
Dr. Hetal Desai

74. SENSATION
•The basic recognition of stimulus is
defined as sensation.
•Clinically,
•Sensation = Aesthesia (Gr. feeling)
•Absence of sensation = Anaesthesia
•Parasthesia = Abnormal sensation
•tingling or pricking / “pins & needles”;
•Caused by pressure/damage to peripheral nerves.
•Sensation of movement = Kinesthesia
Dr. Hetal Desai
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75. Types of sensation
•Sensation is classified into 3
categories:
1.Somatic sensation (Somesthesia),
2.Visceral sensation, &
3.Special sensation
Dr. Hetal Desai
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76. 1. Somatic Sensations
(Somesthesia)
•Arise from receptors present on body surface,
body wall, muscles, tendons, bones, joints,
connective tissues.
•Eg. are
1.Touch (fine, crude & pressure touch)
2.Pain (slow & fast pain)
3.Temperature (warm & cold)
4.Vibration
5.Joint movement (Proprioception)
Dr. Hetal Desai
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77. 2. Visceral Sensations
•They originate from stimulation of
receptors in viscera.
•Usually receptors are located in
walls of viscera or in connective
tissue of viscera.
•the visceral organs are present in
skull, thorax, abdomen and pelvis.
Dr. Hetal Desai
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78. 3. Special sensations
•Originate in special sense organs
•Special sensory receptors are present in
Eye, Ear, Nose, Tongue.
•Special senses include:
1.Vision
2.Audition
3.Olfaction
4.Gustation &
5.Vestibular senses.
Dr. Hetal Desai
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79. Modality
•It is the control of Quality/ Type of
sensation.
Intensity of sensation.
•Increase or decrease in intensity
of stimulus causes accentuation
or inhibition of sensation
Dr. Hetal Desai
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80. Perception
•It is Appreciation and Interpretation
of Sensation.
•It involves firstRecognition,
thenComparision (strong/weak),
Discrimination(fine/crude),&
Integration of sensations.
Dr. Hetal Desai
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81. Dimensions of Sensation
1.Modality= quality / type of sensation
2.Intensity= degree of perception of stimulus
3.Affect= emotional component of sensation
-affect is positive(evokes pleasant response) or
-negative(evokes unpleasant response).
-(sensation which does not have emotional
component is called Neutral)
4. Acuity= precision of stimulus localization.
-it varies with conc. of R. & receptive field size of
area where stimulus is applied, & size of cortical
area representing that somatic body part.(next slide)
-greater Acuity = 2-point discrimination is better
and vice-versa.
Dr. Hetal Desai
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82. 82

83. Dr. Hetal Desai
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