Sen recep bes


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  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Bradykinin is activated by enzymes released into ECF from damaged tissue Signals from mechanical and thermal nociceptors are transmitted via A-delta-fibers. Impulses from polymodal nociceptors are carried by C fibers.
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Baroreceptor: One of the pressure-sensitive nerve endings in the walls of the atria of the heart, the vena cava, the aortic arch and the carotid sinus. They stimulate central reflex mechanisms that allow physiological adjustment and adaptation to changes in blood pressure via vasodilatation or vascoconstriction. Further example of tonic receptors: Muscle stretch receptors, which monitor muscle length, and joint proprioceptors, which measure the degree of joint flexion. To maintain posture and balance, CNS must continuously be apprised of the degree of muscle length and joint position.
  • Sensory Receptor Physiology VMED 5171/NS6/S99/AFL
  • Modality: Each receptor type is most sensitive to a specific stimulus type.
  • Sen recep bes

    1. 2. Sensory Physiology <ul><li>Sensory system makes you aware about external and internal environments </li></ul>
    2. 3. Sensory System <ul><li>Somatic (= general) senses </li></ul><ul><li>Touch </li></ul><ul><li>Proprioception </li></ul><ul><li>Temperature </li></ul><ul><li>Nociception </li></ul><ul><li>Itch </li></ul><ul><li>Special senses </li></ul><ul><li>Vision </li></ul><ul><li>Hearing </li></ul><ul><li>Taste </li></ul><ul><li>Smell </li></ul><ul><li>Equilibrium </li></ul>Conscious vs. Unconscious
    3. 4. <ul><li>Sensation : the information processed by the brain and reaches consciousness is called sensation </li></ul><ul><li>Perception : Interpreting the meaning of sensation is called perception </li></ul><ul><li>Modality : Each type of sensation e.g; temperature, touch, pressure is called modality of sensation. </li></ul><ul><li>Labeled line principle : each type of nerve fibers transmitt only one modality of sensation </li></ul>
    4. 5. <ul><li>Receptor : Specialized structure at termination of afferent neuron, sensitive to changes. </li></ul><ul><ul><li>Receptors transform an external signal into a membrane potential </li></ul></ul><ul><li>Adequate stimulus : is that physical energy to which receptor is tuned. </li></ul><ul><li>Transduction : Receptors transform an external signal into a membrane potential </li></ul><ul><li>Transducer : Sensory receptors act as transducers. </li></ul>
    5. 6. Sensory transduction <ul><li>Receptors transform an external signal into a membrane potential </li></ul><ul><li>Two types of receptor cells: </li></ul><ul><li>- a nerve cell </li></ul><ul><li>- a specialized epithelial cell </li></ul>
    6. 7. Classes of receptors <ul><li>Exteroceptors </li></ul><ul><li>Proprioceptors </li></ul><ul><li>Interoceptors </li></ul>
    7. 8. Exteroceptors <ul><li>Detect stimuli near the outer surface of the body _ and include those from the skin _ _that respond to cold, warmth, touch, pressure and vibration. </li></ul><ul><li>May also include special receptors for hearing and vision. </li></ul>
    8. 9. Exteroceptors <ul><li>Mechanoreceptors – mechanosensitive ion channels </li></ul><ul><li>Thermoreceptors </li></ul><ul><li>Nociceptors :_ pain </li></ul><ul><li>Teloceptors - receptors of electromagnetic radiation </li></ul><ul><li>Chemoceptors (taste and smell) </li></ul>
    9. 10.
    10. 11. Mechanoreceptors <ul><li>Pacinian corpuscle – vibration </li></ul><ul><li>Meissner’s corpuscle – touch </li></ul><ul><li>Hair-follicle receptor – touch </li></ul><ul><li>Merkel’s disk – pressure </li></ul><ul><li>Tactile disk – pressure </li></ul><ul><li>Ruffini’s corpuscle – pressure </li></ul>
    11. 12. Nerve Fiber Classification <ul><li>General classification scheme : </li></ul><ul><ul><li>A fibers: Myelinated </li></ul></ul><ul><ul><ul><li>Subtypes:  some overlap in ranges  </li></ul></ul></ul><ul><ul><ul><li>Fastest conducting and largest diameter –  m/sec,  </li></ul></ul></ul><ul><ul><ul><li>“ A” often dropped: alpha motor neuron </li></ul></ul></ul><ul><ul><li>B fibers : Slower myelinated (seldom used) </li></ul></ul><ul><ul><li>C fibers : Unmyelinated </li></ul></ul><ul><ul><ul><li>Slower conducting than As and smallest diameter (0.5 m/sec, 0.5  ) </li></ul></ul></ul>
    12. 13. Proprioceptors <ul><li>Located in skeletal muscles, tendons, ligaments and joint capsules. </li></ul><ul><li>Sensitive to muscle stretch, muscle tone, position and angle of joints. </li></ul><ul><li>Provide a sense of body position – “self” receptors. </li></ul>
    13. 14. Proprioceptors <ul><li>Muscle spindle </li></ul><ul><li>Golgi tendon organ </li></ul><ul><li>Joint receptor </li></ul><ul><li>Vestibular hair cell </li></ul>
    14. 15. Interoceptors <ul><li>Detect stimuli from inside the body </li></ul><ul><li>Receptors that respond to pH, pO2, pCO2, osmolality of body fluids, distention and spasm (e.g., gut), and flow (e.g., urethra) </li></ul>
    15. 17. Nociceptors <ul><li>Free nerve endings </li></ul><ul><li>Activation by strong, noxious stimuli </li></ul><ul><li>3 categories : </li></ul><ul><ul><li>Mechanical </li></ul></ul><ul><ul><li>Thermal ( menthol and cold / capsaicin and hot ) </li></ul></ul><ul><ul><li>Chemical (includes chemicals from injured tissues) </li></ul></ul><ul><li>May activate 2 different pathways : </li></ul><ul><ul><li>Reflexive protective – integrated in spinal cord </li></ul></ul><ul><ul><li>Ascending to cortex (pain or pruritis) </li></ul></ul>
    16. 18. Pain <ul><li>C fibers mediate pruritis </li></ul><ul><ul><li>Slow pain (C) is throbbing </li></ul></ul><ul><li>Fast (A  fibers) pain is sharp </li></ul><ul><ul><li>Ascend to limbic system and hypothalamus: </li></ul></ul><ul><ul><li>Emotional Distress </li></ul></ul><ul><ul><li>Modulation </li></ul></ul><ul><li>Gate Control Theory: We can inhibit the pain response </li></ul><ul><li>Pain control </li></ul><ul><ul><li>NSAIDs (inhibit COX) </li></ul></ul><ul><ul><li>Opiates (inhibit NT release) </li></ul></ul>
    17. 19. Referred Pain <ul><li>Pain in organs is poorly localized </li></ul><ul><li>May be displaced if </li></ul><ul><li>Multiple 1° sensory neurons converge on single ascending tract </li></ul>
    18. 20. Modification of sensation <ul><li>Adaptation - property of the receptor where an initial _high rate of response_ is followed by a lower response rate with a continued stimulus. E.g. Pacinian corpuscle. </li></ul><ul><li>Centrifugal control of sensory receptors – increased or decreased sensitivity from central inputs to sensory cells - e.g., cochlear hair cells, olfactory system </li></ul><ul><li>Tonic vs. phasic receptors </li></ul><ul><ul><li>Tonic (adapts slowly) </li></ul></ul><ul><ul><li>Phasic (adapts rapidly) </li></ul></ul>
    19. 21. Tonic Receptors <ul><li>Slow or no adaptation </li></ul><ul><li>Continuous signal transmission for duration of stimulus </li></ul><ul><li>Monitoring of parameters that must be continually evaluated, e.g.: baroreceptors </li></ul><ul><li>Rapid adaptation </li></ul><ul><li>Cease firing if strength of a continuous stimulus remains constant </li></ul><ul><li>Allow body to ignore constant unimportant information, e.g.:Smell </li></ul>Phasic Receptors
    20. 22. Receptive fields in skin large if receptors are few, small if receptors are dense measured by two-point touch threshold Lateral inhibition - sensory neurons most strongly affected by a stimulus inhibit others in nearby receptive fields
    21. 23. Receptive field sizes vary by type: Meissner’s corpuscles - small Pacinian corpuscles - large
    22. 24. Two-Point Discrimination
    23. 26. Sensory Pathway <ul><li>Stimulus </li></ul><ul><li>Sensory receptor (= transducer) </li></ul><ul><li>Afferent sensory neurons </li></ul><ul><li>CNS </li></ul><ul><li>Integration, perception </li></ul>
    24. 27. CNS Distinguishes 4 Stimulus Properties <ul><li>Modality of stimulus </li></ul><ul><ul><li>Type of receptor </li></ul></ul><ul><li>Location </li></ul><ul><ul><li>lateral inhibition </li></ul></ul><ul><ul><li>population coding) </li></ul></ul><ul><li>Intensity </li></ul><ul><li>Duration </li></ul>Somatosensory cortex
    25. 28. Somatic Senses <ul><li>1 st order neurons: from receptor to spinal cord or medulla </li></ul><ul><li>2 nd order neurons : always cross over (in spinal cord or medulla)  thalamus </li></ul><ul><li>3 rd order neuron :  Thalamus   (post central gyrus) </li></ul>
    26. 29. Thank you
    27. 30. Referred Pain: Heart