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  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Cns 3

    1. 1. Sensory Receptors Perceptions of the world are created by the brain (CNS) from info derived from the sensory receptors (neurons or epithelial cells) of the PNS. Receptors transduce (change) different forms of sensation into nerve impulses.
    2. 2. <ul><li>Specialized cell or cell process that monitors specific conditions </li></ul>Sensory receptor
    3. 3. Sensory Receptors <ul><li>Structures specialized to respond to stimuli </li></ul><ul><li>Activation of sensory receptors results in depolarizations that trigger impulses to the CNS </li></ul><ul><li>The realization of these stimuli, sensation and perception, occur in the brain </li></ul>
    4. 4. Peripheral Sensory Receptors <ul><li>Two main categories of sensory receptors </li></ul><ul><ul><li>Special nerve endings of sensory neurons </li></ul></ul><ul><ul><ul><li>Monitor general sensory information </li></ul></ul></ul><ul><ul><li>Independent receptor cells – specialized epithelial cells or small neurons </li></ul></ul><ul><ul><ul><li>Monitor most types of special sensory information </li></ul></ul></ul>
    5. 5. Sensory Receptors
    6. 6. <ul><li>General senses </li></ul><ul><ul><li>Pain </li></ul></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>Physical distortion </li></ul></ul><ul><ul><li>Chemical detection </li></ul></ul><ul><ul><ul><li>Receptors for general senses scattered throughout the body </li></ul></ul></ul><ul><li>Special senses </li></ul><ul><ul><li>Located in specific sense organs </li></ul></ul><ul><ul><li>Structurally complex </li></ul></ul>Senses
    7. 7. Sensory Receptors <ul><li>Sensory receptors also classified according to: </li></ul><ul><ul><li>Location </li></ul></ul><ul><ul><li>Type of stimulus detected </li></ul></ul><ul><ul><li>Structure </li></ul></ul>
    8. 8. Receptor Class by Location: Exteroceptors <ul><li>Respond to stimuli arising outside the body </li></ul><ul><li>Found near the body surface </li></ul><ul><li>Sensitive to touch, pressure, pain, and temperature </li></ul><ul><li>Include the special sense organs </li></ul>
    9. 9. Receptor Class by Location: Interoceptors <ul><li>Respond to stimuli arising within the body </li></ul><ul><li>Found in internal viscera and blood vessels </li></ul><ul><li>Sensitive to chemical changes, stretch, and temperature changes </li></ul>
    10. 10. Receptor Class by Location: Proprioceptors <ul><li>Respond to degree of stretch of the organs they occupy </li></ul><ul><li>Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles </li></ul><ul><li>Constantly “advise” the brain of one’s movements </li></ul>
    11. 11. Receptor Classification by Stimulus Type <ul><li>Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch </li></ul><ul><li>Thermoreceptors – sensitive to changes in temperature </li></ul><ul><li>Photoreceptors – respond to light energy (e.g., retina) </li></ul><ul><li>Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry) </li></ul><ul><li>Nociceptors – sensitive to pain-causing stimuli </li></ul>
    12. 12. Classification by Structure <ul><li>Widely distributed </li></ul><ul><ul><li>Nerve endings of sensory neurons monitor: </li></ul></ul><ul><ul><ul><li>Touch, pressure, vibration, stretch </li></ul></ul></ul><ul><ul><ul><li>Pain, temperature, proprioception </li></ul></ul></ul><ul><li>Divided into two groups </li></ul><ul><li>I Simple receptors </li></ul><ul><li>Free nerve endings </li></ul><ul><li>Encapsulated nerve endings </li></ul><ul><li>II Complex receptors are special sense organs </li></ul>
    13. 13. Simple Receptors: Free Nerve Endings <ul><li>Abundant in epithelia and underlying connective tissue </li></ul><ul><li>Respond to pain and temperature </li></ul><ul><li>Monitor affective senses </li></ul><ul><li>Two specialized types of free nerve endings </li></ul><ul><ul><li>Merkel discs – lie in the epidermis </li></ul></ul><ul><ul><ul><li>Slowly adapting receptors for light touch </li></ul></ul></ul><ul><ul><li>Hair follicle receptors – wrap around hair follicles </li></ul></ul><ul><ul><ul><li>Rapidly adapting receptors </li></ul></ul></ul>
    14. 14. Unencapsulated Nerve Endings
    15. 15. Simple Receptors: Encapsulated <ul><li>Meissner’s corpuscles (tactile corpuscles) </li></ul><ul><li>Pacinian corpuscles (lamellated corpuscles) </li></ul><ul><li>Muscle spindles, Golgi tendon organs, and Ruffini’s corpuscles </li></ul><ul><li>Joint kinesthetic receptors </li></ul>
    16. 16. Simple Receptors: Encapsulated Table 13.1.2
    17. 17. Simple Receptors: Encapsulated Table 13.1.3
    18. 18. Simple Receptors: Encapsulated Table 13.1.4
    19. 19. From Sensation to Perception <ul><li>Survival depends upon sensation and perception </li></ul><ul><li>Sensation is the awareness of changes in the internal and external environment </li></ul><ul><li>Perception is the conscious interpretation of those stimuli </li></ul>
    20. 20. Transduction of Sensory signal to Nerve Impulses <ul><li>Regardless of the type of stimulus, the effect on all receptors is the same: a change in the electrical potential of the receptor: the receptor potential . </li></ul><ul><li>Heat, cold, electromagnetic radiation, mechanical deformation, O 2 content of the blood – all produce a change in electrical potential in the appropriate receptor type. </li></ul><ul><li>Depolarization </li></ul>
    21. 21. Receptor potential or Generator Potentials <ul><li>In response to stimulus, sensory nerve endings produce a local graded change in membrane potential. </li></ul><ul><li>Potential changes are called receptor or generator potential. </li></ul><ul><ul><li>Analogous to EPSPs. </li></ul></ul>
    22. 22. a a Deformation of the nerve ending results in opening of Na+ channels. Pressure Pacinian Corpuscle If depolarization above Threshold = AP
    23. 23. Properties of Receptors <ul><li>1. Specificity of response or Law of adequate stimulus </li></ul><ul><li>The receptors respond maximally only when an appropriate specific stimulus is applied. It responds to lowest threshold of stimulus. </li></ul>
    24. 24. Properties of Receptors <ul><li>2. Adequate stimulus </li></ul><ul><li>3. Muller’s Doctrine of specific nerve energies </li></ul><ul><li>Sensation characteristic of each sensory neuron is that produced by its normal or adequate stimulus. </li></ul><ul><li>Adequate stimulus: </li></ul><ul><ul><li>Requires least amount of energy to activate a receptor. </li></ul></ul><ul><li>Regardless of how a sensory neuron is stimulated, only one sensory modality will be perceived. </li></ul><ul><ul><li>Allows brain to perceive the stimulus accurately under normal conditions. </li></ul></ul>
    25. 25. Properties of Receptors <ul><li>4. Law of projection </li></ul><ul><li>Phantom limb: A person whose limb is amputated often complains of pain in the limb which is not present. </li></ul><ul><li>5. Adaptation </li></ul><ul><li>When a stimulus of constant strength is applied to the receptor, the frequency of action potential in its sensory nerves decreases over a period of time. </li></ul>
    26. 26. Response <ul><li>Phasic response: </li></ul><ul><ul><li>Generator potential increases with increased stimulus, then as stimulus continues, generator potential size diminishes. </li></ul></ul><ul><li>Tonic response: </li></ul><ul><ul><li>Generator potential proportional to intensity of stimulus. </li></ul></ul>
    27. 27. Sensory Adaptation <ul><li>Tonic receptors: </li></ul><ul><ul><li>Produce constant rate of firing as long as stimulus is applied. </li></ul></ul><ul><ul><ul><li>Pain. </li></ul></ul></ul><ul><li>Phasic receptors: </li></ul><ul><ul><li>Burst of activity but quickly reduce firing rate (adapt) if stimulus maintained. </li></ul></ul><ul><ul><li>Sensory adaptation: </li></ul></ul><ul><ul><ul><li>Cease to pay attention to constant stimuli. </li></ul></ul></ul>
    28. 28. Properties of Receptors <ul><li>6.Localization: This is due to stimulation of specific receptors present in the area. It is achieved by lateral inhibition </li></ul>
    29. 29. Sensory Modality Lateral inhibition
    30. 30. Properties <ul><li>7. Law of intensiity discrimation </li></ul><ul><li>Receptor potential amplitude and action potential frequency are proportional to stimulus intensity </li></ul><ul><li>Weber – Fechner law: The magnitude of sensation is proportional to the log of intensity of the stimulus. </li></ul><ul><li>Power function: </li></ul><ul><li>Sensation felt = KS n </li></ul>