Receptor by Pandian M, Tutor, Dept of Physiology, DYPMCKOP, MH. This PPT for MBBS and tutorial topic

Introduction
SENSORY RECEPTORS
Structurally 3 types of receptors
Transducers
CLASSIFICATION OF RECEPTORS
A. Depending on the source of stimulus�(Sherrington’s classification)
B. Depending upon type of stimulus
C. Clinical or anatomical classification of receptors
Production of receptor potential
Properties of receptors
Properties of receptor potential

1. Receptor Pandian M Dept of physiology dypmckop

2. SLO Introduction SENSORY RECEPTORS Structurally 3 types of receptors Transducers CLASSIFICATION OF RECEPTORS A. Depending on the source of stimulus (Sherrington’s classification ) B. Depending upon type of stimulus C. Clinical or anatomical classification of receptors Production of receptor potential Properties of receptors Properties of receptor potential

3. Introduction Receptors are the biological transducers which convert various forms of energy into action potential in nerve fibers

4. SENSORY RECEPTORS Definition: - Specialized nerve endings or specialized cells - More sensitive to specific type of stimulus -Are able to convert stimulus energy into electrical energy which is called as RECEPTOR POTENTIAL - Can generate A.P. in the nerve connected

5. Structurally 3 types of receptors Bare nerve endings - nerve endings that terminate in periphery as bare unmyelinated endings. Capsulated nerve endings - In the form of specialized capsulated structures i.e. Connective tissue lamellae Sense organs – Specialized cells located at the end of afferent nerve.

6. Transducers Receptors function like a transducer. Transducer is a device, which converts one form of energy into another. So, receptors are often defined as the Biological transducers, which convert (transducer) Various forms of energy (stimuli) in the environment into Action potentials in nerve fiber.

7. The stimulus arriving at the given sensory receptor may be in the form of: Mechanical force causing depression of the skin, which Stimulates mechanoreceptors, Light or electromagnetic wave, which stimulates photoreceptors of the retina, Chemical , e.g. A molecule of NaCl on the tongue which stimulates chemoreceptors, Cold or warm temperature stimulating thermoreceptors and Sound energy stimulating auditory receptors, and so on and so forth.

8. CLASSIFICATION OF RECEPTORS

9. Classifications Depending upon source of stimulus II. Depending upon type of stimulus III. Clinical or anatomical classification of receptors

10. A. Depending on the source of stimulus (Sherrington’s classification) 1. Exteroceptors , 2. Enteroceptors , 3 . Telereceptors ,

11. Exteroceptors , i.e. The receptors which receive stimuli from immediate surrounding outside the body, e.g. Cutaneous receptors for pain, touch and temperature. 2. Enteroceptors , i.e. The receptors which receive stimuli from within the body, e.g. Chemoreceptors, baroreceptors, Proprioceptors, osmoreceptors and glucoreceptors 3. Telereceptors , i.e. The receptors that receive stimuli from the distance, e.g. Visual receptors, cochlear receptors and olfactory receptors.

12. II. Depending upon type of stimulus Mechanoreceptors- special sense, muscle, skin, visceral, vascular Thermoreceptors - skin, hypothal . Chemoreceptors- olfactory, gustatory., Nociceptors Electromagnetic receptors - retina

13. 1. Mechanoreceptors, i.e. Those receptors which respond to mechanical stimuli. These include: ( i ) cutaneous receptors (in epidermis and dermis) for Cutaneous tactile sensibility. (ii) cutaneous receptors for deep tissue sensibility. (iii) muscle and joint receptors (iv) hair cells, e.G. Hair cells in organ of corti (cochlear) or Auditory receptors, and hair cells in vestibular apparatus or vestibuloreceptors for equilibrium. (v) baroreceptors of carotid sinus and aortic arch for Detecting level of arterial blood pressure.

14. 2. Thermoreceptors , which detect environmental temperature, e.g. Cold receptors and warm receptors. 3. Photoreceptors or electromagnetic receptors , i.e. rods and cones of the retina, which respond to light stimuli .

15. 4. Chemoreceptors , which detect change in the chemical composition of the environment in which they are located, e.g. Taste receptors , Olfactory receptors, Osmoreceptors in supraoptic nuclei of hypothalamus, Aortic and carotid bodies receptors, which detect level of arterial pO2, pCO2 and pH, Glucoreceptors , Chemoreceptors on the surface of medulla for detecting level of blood pCO2 and Chemoreceptors in hypothalamus detecting levels of blood glucose, fatty acids and amino acids.

16. 5. Nociceptors, i.e. The receptors which respond to Extremes of mechanical, thermal and chemical stimuli Producing pain.

17. C. Clinical or anatomical classification of receptors 1. Superficial receptors, i.e. Those present in skin and mucous membrane. 2. Deep receptors, i.e. Those present in muscles, tendons, joints and subcutaneous tissue. 3. Visceral receptors, which are present in the visceral organs.

18. Production of receptor potential When a stimulus excites the receptor, it changes the potential across the membrane of the receptors. This change in the potential is called receptor or generator potential.

19. Application of stimulus to receptors Changes in permeability of membrane Graded depolarization / hyperpolarization Generator or receptor potentials Local currents - electrotonic A.P. at the first node of Ranvier Mechanism of receptor function

20. Properties of receptors Produces Generator potential ( not A.P.) Specificity Graded response Perception and discrimination of intensity Muller’s law of specific nerve energy Law of projection Adaptation Spatial and temporal summation

21. Expt. To demonstrate mechanism Structure Diagram Response AP GP Intact AP GP Removal of capsule ” Block at first node No A.P. GP Cutting of nerve No AP & GP

22. When a mild pressure is applied on the corpuscle, a mild Non-propagated depolarizing potential, called the generator or receptor potential, can be recorded. When the pressure is increased in steps, the magnitude of receptor potential is increased (Fig -B). The depolarized segment of the unmyelinated nerve Ending produces electrotonic depolarization (current Sink action) in the first node of ranvier . When the magnitude of receptor potential is sufficient (Above 10 mv), an action potential is generated in first Node of ranvier , which is propagated in the nerve fibre (Fig. b). If still greater pressure is applied on the receptor, the frequency of discharge is proportionately increased.

23. 1. SPECIFICITY OF RESPONSE – MÜLLER LAW Specificity of response or müller law refers to the response given by a particular type of receptor to a Specific sensation. For example, pain receptors give response only to pain sensation. Similarly, temperature receptors give response only to temperature sensation . ( Ruffini’s receptors) In addition, each type of sensation depends upon the Part of the brain in which its fibers terminate. Specificity of response is also called müller’s doctrine of specific nerve energies.

24. Adaptation : when a receptor is continuously stimulated with the same strength of stimulus, after some time the receptor stop sending impulse through the afferent nerve . This property called adaptation . Depending upon this property the receptor has 2 types 1 . Phasic receptors – which adapt rapidly touch and pressure receptors 2 . Tonic receptors - which adapt slowly pain and temp recep .

25. On off Adaptation : decline in responsiveness on prolonged stimulation a. fast adapting – phasic – e.g. tactile receptors, olfactory receptors On off Stim. Stim. b. slow adapting – Tonic – e.g. proprioceptive receptors c. non adapting -

26. Intensity discrimination : Intensity discrimination is basis on logarithmic 10 fold increase in strength of stimulus doubles the intensity of sensation.

27. Law of projection : Sensation is localized at the site where receptor is located even when the stimulus is applied at any point on the sensory pathway.

28. Spatial and temporal summation Summation of stimuli applied simultaneously on the receptor or of stimuli applied repeatedly at the same site. stim. 1(small) Stim.2(large) Repeated stim. Stim.1 Stim.2 Stim.1+2 Temporal summation Spatial summation Recording graded response

29. Comparison between Generator potential Localized Magnitude decreases with time and space Graded response Lasts for 1-2 msec. No refractory period Summation possible Action potential Propogated Magnitude remains same All or none phenomenon Lasts for 0.1-0.2 msec . Refractory period present No summation

30. Functions of input to CNS Control of output :- for homeostasis Motor activity Visceral Stimulation of RAS Understanding the world Storage in memory Impact on emotions

31. Properties of receptor potential The receptor potential is not action potential. It is similar to excitatory post-synaptic potential in synapse, end plate Potential in a neuromuscular junction and electrotonic potential in a nerve fibre . The important properties of receptor potential are: Graded response. Receptor potential is a graded response, .i.e. Its amplitude increases with increasing velocity of stimulus application, and increasing strength of stimulus. Thus, Unlike action potential it does not obey all or none law.

32. 2. Summation, i.e. Receptor potential from two stimuli can be added if the second stimulus arrives before the receptor Potential developed due to first stimulus is over. Thus, receptor potential unlike action potential (which cannot be added) can be added together. 3.Refractory period is not there in the development of receptor potential while the action potential has a refractory period of 1 ms.

33. 4. Local response, i.E. Receptor potential cannot be Propagated. 5.Duration of receptor potential is greater (approximately 5–10 ms ) than action potential (approximately 1–2 ms ).

34. References Text book of Medical Physiology Guyton & Hall Human Physiology Vander Text book of Medical Physiology Indukurana & Sembulingam Net source

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