3. RECEPTORS

4. Receptors
Receptors are transducers which detect the Change in the environment (stimulus)
& converts it into Propagated action Potential
( Impulse)

5. Classification of Receptors
1. On the basis of Modality of sensations Carried by Receptors
( Five Major Groups )
I. .Mechanoreceptors – ( Mechanical Change )
1. skin tactile – Free Nerve Endings, Hair end organs etc
2.Deep tissues - ( Pacinian Corpuscles )
3. Muscles / Tendons (Muscle spindles & Golgi tendons Organs
4. Hearing - ( Organ of Corti )
5. Equilibrium – ( Vestibular apparatus)
6. B.P. ( Baroreceptors )
II. Thermoreceptors - Cold & Warm Receptors
III. Nociceptors (pain) - Free Nerve Endings

6. Classification of Receptors- contd
IV. Electromagnetic Receptors (Vision)- Rods & Cones.
V. CHEMORECPTORS;
- Taste- Taste Buds
- Smell – Olfactory Epithelium.
- Arterial PO2- Aortic & Carotid Bodies
- PCO2 - Central Chemo receptors
- Osmolality - Neurons in Supraoptic Nucleus of Hypothalamus
- Blood Glucose, A.A & F.A- Receptors in Hypothalamus

7. Classification of Receptors
2. On the Basis of Distribution in the Body i.e
Somatic (Somesthetic) &
Special Senses
3. On the basis of Origin of Stimuli:
Interoceptors
Proprioceptors
Exteroceptors
4. Structural Classification
Non Encapsulated
Encapsulated
5. On the Basis of Adaptation:
Phasic ( Rapidly Adapting)- Pacinian Corpuscles
Tonic ( Slowly Adapting)- Pain (free Nerve endings)

8. Mechanoreceptors Non-encapsulated receptors Free Nerve Endings
Skin tactile sensibilities (dermis & epidermis )
Free Nerve Endings
Expanded Tip Endings Merkel’s Discs
Hair End Organs

9. 1.Mechanoreceptors Un encapsulated Free Nerve Endings
Location: Widespread especially in Epithelia & Connective Tissue
Modalities: touch, Pressure, Pain, Heat & Cold
Nerve fiber: Type C

10. 1.Mechanoreceptors Expanded Tip Endings-. Merkel’s Discs
Location: Stratum Basale of Epidermis.
Finger tips, Lips
(Mostly Hairless Skin)
Modality: Light Touch, Texture & shapes
Informs for longer time
Nerve type A-β

11. Iggo dome receptor

12. Hair End Organ Location: Entwined Around Hair Follicle
Modality: Movement of Hair
Movement of objects on the
surface of the body
Initial contact with the body
Readily adapting.
Nerve. A-β

13. EncapsulatedEndings:
Mechanoreceptors
EncapsulatedEndings:
. Meissner,s Corpuscles
. Pacanian Corpuscles
Ruffini Corpuscles
. Krause,s Corpuscles
Meissner’s
Corpuscl e
Pacinian Corpuscle

14. Encapsulated Endings:
Meissner,s Corpuscles.-
Egg shaped
Location: Dermal Papillae of finger tips, Palms, Lips, tongue, Eyelids Genitalia.(Hairless Skin only)
Modality: Light Touch & Texture &
low frequency vibration
Adapts in fraction of seconds .
Nerve A-β
Particularly sensitive to movement of objects over the surface of the skin
Meissner’s
Corpuscl e

15. Encapsulated Endings Pacanian Corpuscles- Onion shape
Location: Dermis, Joint Capsules & some Viscera
Modality- Deep Pressure, Stretch &
high frequency Vibration
Adapts – Very rapidly
Nerve A-β

16. Encapsulated Endings Ruffini Corpuscles.
Multibranched encapsulated endings
Location: Dermis, Subcutaneous Tissues &
Joint Capsules
Modality- Crude Touch & Pressure,
Stretching of Skin, Joint movement
Adapt slowly. Nerve. A-β
Hence give information about continuous state of Deformation of the tissues.

17. EncapsulatedEndings Krause,s Corpuscles
Minute cylindrical or oval bodies .
Bulboid corpuscles
Cutaneous thermoreceptors
Conjunctiva of eye
Mucous membrane of lips and tongue
Penis and clitoris

18. Mechanoreceptors Deep Tissues Sensibilities: Free Nerve Endings
Expanded Tip Endings- Merkle’s Discs
Spray endings- Ruffini’s Endings
Muscles- Muscles Spindles,
&Golgi Tendon organs.
Hearing - Organ Of Corti
Equilibrium- Vestibular Apparatus
B. Pressure - Baroreceptors

19. Transmission in Peripheral Nerve fibers
Type Aβ nerve fibers (30-70m/sec) Meissners corpuscles Iggo dome receptors Hair receptors Pacinian corpuscle Ruffinis endings.

20. Transmission in Peripheral Nerve fibers
Free nerve endings : Pain Type Aδ myelinated (5-30m/sec) Type C un myelinated fibers ( 0.5-2m/sec) All tactile receptors detect vibration although different receptors detect different frequencies.

21. Proprioception (Sense of Position)
Static Proprioception. Conscious perception of the orientation of the different parts of the body with respect to each other
Dynamic-Conscious perception of rate of movement ( Kinesthesia)

22. Multiple Receptors are involved in Proprioception.
Muscle Spindles (important)
Pacinian Corpuscles
other tactile receptors also participate

23. Tactile Receptors in the Skin
Figure 15.3a-f

24. Classification of Receptors on the basis of Capsule

25. Type of Receptor Location Stimulus Modality

26. Specific Function of Receptors

27. Doctrine of Specific Nerve Energies
The specificity of a sensory receptor for
a particular type of stimulus is called the
law of specific nerve energies.

28. Law of Projection:
Conscious perception of a sensation produced is always referred to the location of the receptor, no matter where a sensory pathway is stimulated along its course to the cortex.
Phantom limb

29. Phantom limb
Neuromas.
The ends of the nerves cut at the time of amputation often form nerve tangles called neuromas.

30. Phantom limb Cortical Plasticity.
Brains remarkable ability to reorganize itself by forming new neuronal connections based on individual experiences, life style and environment.
In brain neuronal connections and cortical maps are continuously remodeled through out life.

31. Topographical MAP
Broadman’s ares

32. Sensory Transduction
Q:How is a stimulus converted into a neural signal?
Ans:
The stimulus opens ion channels in the receptor membrane, either directly or indirectly (through a second messenger).
In most cases, channel opening results in depolarization of the membrane .(Excitation)
In a few cases, the response to the stimulus is Hyperpolarization when K+ leaves the cell
or Cl- enter the cell. ( Inhibition)

33. Sensory Transduction
Sensory transduction converts stimuli into graded potentials or Receptor potential
MECHANISM:
1. By Mechanical Deformation
2. By application of Chemical (Neurotransmitter)
3. By change of Temperature
4. By electromagnetic radiation e.g light

34. Sensory Transduction. Contd.
Receptor or Generator Potential;
When Receptor Potential rises above the threshold level ,action potential is elicited in the nerve attached to the Receptor.
Frequency of A.P > more the Receptor Potential above the threshold level

35. Sensory Representations
To create an accurate neural representation of sensory stimuli, the brain must distinguish FOUR properties of stimulus :
1) stimulus modality
2) stimulus location
3) stimulus intensity
4) stimulus duration

36. Stimulus Modality
Each receptor type is most sensitive to a particular type of stimulus (Modality).
The brain thus associates a signal coming from a specific group of receptors via specific nerve fibers with a specific modality.
This specificity of nerve fiber for transmitting only one modality of sensation is called labeled line Principal.

37. Stimulus Location
The area of the body that when stimulated leads to activity in a particular afferent neuron is called the receptive field for that neuron
When action potentials are elicited from a sensory neuron, the neuron’s receptive field codes the stimulus location.

39. Stimulus Location
Sensory receptive fields vary in size and frequently overlap.

41. Stimulus Location
Lateral inhibition enhances the contrast between the stimulus and its surrounding, facilitating its perception and localization.

43. Stimulus Location
Sensory neuronal receptive fields are orderly organized in cortical sensory areas to form
topographical maps.
The location of a stimulus is coded according to which group of neurons are activated

45. Topographical MAP
Broadman’s ares

46. Stimulus Location (Exception)
Auditory information is the exception
to the topographical localization rule.
For this sensory modality the brain uses the timing difference in receptor activation to compute the source location of sounds

47. Locating sensations from internal organs is less precise than from the skin because there are few afferent neurons in the internal organs and each has a larger receptive field.

48. Vision hearing and smell stimulus location is interpreted as arising from the site from which the stimulus originated than the place on our body where the stimulus is actually applied.

49. Stimulus Intensity
Stimulus intensity is transmitted to the brain by two mechanisms:
1) the number of receptors activated
(population coding), from low-threshold receptors to high-threshold ones.
2) the frequency of action potentials
(frequency coding), following not a linear but a power relationship. (Weber-Fechner Law)

50. Weber-Fechner- Law
During the stimulation of a receptor, if the response given by the receptor is to be doubled the strength of stimulus must be increased 100 times.

51. Stimulus Intensity
Different gradations of intensity can be transmitted to Nervous system by two Mechanisms:
1. By using more than one fiber to send action potentials - (spatial Summation)
2. By sending more & more Impulses along a single fiber (Temporal Summation)

52. Stimulus Duration
Stimulus duration can be coded by the spike train duration, but not all sensory receptors can sustain their responses.
The neural code best reflects the change in stimulation, not the steady state.

53. Adaptation of Receptors
All sensory receptors adapts partially or Completely to a constant stimulus.
Mechanism:
Readjustment- in the Receptor
Accomodation- occurs in nerve fiber itself
TYPES:
1. Slowly or Non Adapting (Tonic Receptors)
2. Rapidly adapting (Phasic Receptors, Rate Receptors)

54. Physiological Classification Of Nerve Fibers & their Functions

55. .
Convergence of inputs onto a single sensory neuron enhances that neuron’s sensitivity, but reduces its spatial resolution.