Sensory Receptors Physiology- A detailed review

A detailed slides on sensory receptors and their properties

1. Sensory System: Classification of Sensory R eceptors and Properties Dr. Dinesh Veera MBBS (AIMST), MSC Medical Physiology(AIMST)

2. Learning Outcomes: 1. Classify sensory receptors with suitable example. 2. Explain the mechanism of sensory receptors

3. Lecture Overview Important Terminologies Sensory system introduction Sensory receptors classification Somatosensory system overview Receptor potential Receptor Properties Summary

4. Sensation : the conscious or subconscious awareness of changes in the external or internal environment. Perception: the conscious awareness and interpretation of sensations and is primarily a function of the cerebral cortex. Stimulus : any detectable change in the environment (internal or external) of an organism which is capable of activating a receptor Sensory receptors : cells or regions of cells that respond to specific stimuli and perform sensory transduction. Sensory transduction : the process by which a stimulus of any form is transformed into electrical response.

5. Sensory system

6. Human sensory system The human sensory system consists of the following sub-systems: Visual system Gustatory system Olfactory system Auditory system Vestibular system Somatosensory system Special Sensation General Sensation

7. Sensory receptor A sensory receptor is a specialized structure that responds to a stimulus in the internal or external environment of an organism. In response to stimuli, the sensory receptor initiates sensory transduction by creating graded potentials or action potentials in the same cell or in an adjacent one. Structures that are specialized to respond to the changes in the environment Sensory receptors in periphery detects the stimuli Sensation and interpretation takes place in the brain

8. Classification by location

9. *Classification by type of stimulus

10. Structural Classification

11. Somatosensation

12. Sensory Receptors

13. Receptor potentials : An initial response of a receptor cell to a stimulus, consisting of a change in voltage across the receptor membrane proportional to the stimulus strength. The intensity of the receptor potential determines the frequency of action potentials traveling to the nervous system.

14. Receptor potential ● In response to stimulus, sensory nerve endings produce a local graded change in membrane potential. Potential changes are called receptor potentials. Analogous to EPSPs. ●

15. Mechanisms of Receptor Potentials. By mechanical deformation Stretches the receptor membrane Opens ion channels By application of a chemical Opens ion channels By change of the temperature of the membrane Alters the permeability of the membrane By the effects of electromagnetic radiation, such as light Allows ions to move Basic cause of the change in membrane potential is a change in membrane permeability of the receptor

16. Pacinian Corpuscle Central nerve fiber extending through its core. Surrounding – multiple concentric capsule layers Compression anywhere on the outside of the corpuscle will Elongate, Indent or Deform the central fiber

17. Central fiber of the pacinian corpuscle The tip of the central fiber - unmyelinated The fiber - Myelinated Deformed by compression Sodium influx - a local circuit of current flow A ction potentials transmitted

18.  Sensory unit : a single afferent neuron with all its receptor endings.  Receptive field : the area of the body that when stimulated leads to activity in a particular afferent neurons.

19. Sequence of Events in a Receptor Stimulus Receptor Protein Activated Enzyme Cascade (in some cases) Receptor Ion Channels opened (or closed) Receptor Current Reception Transduction Transmission Receptor Potential Action Potential

20. 4 steps in sensation Reception A pplication of stimulus Must be adequate and specific for the particular sensory neuron Transduction: The process by which an environmental stimulus becomes encoded as a sequence of nerve impulses in an afferent nerve fiber is called sensory transduction I nduction of an action potential Stimulation of sensor receptors induces graded potentials in sensory neurons Receptor potentials– If strong enough depolarization, AP results ↑ stimulus strength above threshold → ↑ AP firing rate

21. Conduction -R elay of information through a sensory pathway to specific region of CNS Usually three neurons in sensory pathway 1st order neuron– from stimulation point to CNS 2nd order neuron– e.g., from entry into CNS to thalamus 3rd order neuron – e.g., from thalamus to perception site at cerebral cortex Perception Detection of environmental change by the higher centres in brain

22. Properties of receptors Adequate Stimulus Specificity Graded response Law of projection Adaptation Spatial and temporal summation

23. “Laws of Specific Sense Energies.” Muller (1835) proposed “each nerve fiber is activated primarily by a certain type of stimulus and each makes specific connections to structures in the central nervous system whose activity gives rise to specific sensations”. Adequate stimulus : The receptors respond maximally only when an adequate stimulus is applied. It responds to lowest threshold of stimulus. Properties of sensory

24. Adaptation: When a stimulus of constant strength is applied continuously to a receptor, frequency of the action potentials in its sensory nerve declines. Phasic/ Rapidly adapting (pacinian corpuscles) Tonic/Slowly adapting (nociceptors, baroreceptors)

25. Law of projection Each receptor (or group of the same receptor) is connected through a separate pathway to a certain point in the cerebral cortex. Stimulation of this point in the cerebral cortex (or any where in the pathway) projects the sensation to the location of the receptor. PHANTOM LIMB SENSATION

26. Homework Differences between Receptor potential vs Action Potential What is temporal and spatial summation? Draw a table listing the sensory receptors found in skin and their functions along with basic characteristics Properties of Receptor Potential

27. SUMMARY Sensation vs Stimulus vs Sensory Receptors General vs Special Sensation Classification of sensory receptors- functional , locational and structural The 4 main steps in sensation perception - Reception, Transduction, Conduction, Perception Receptor potential and its significance Sensory receptor properties

28. Clinical Significance Peripheral Neuropathy- Diabetic Neuropathy Sensory i mpairment in cases of Cerebrovascular Accident (CVA)

29. References Linda S. Costanzo - Physiology 7th edition Guyton & Hall Medical Physiology 14th edition

30. Disclaimer The texts, tables, figures and images contained in this course presentation are not my own, they can be found on: References supplied The Web

31. Thank you