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Sensory system


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Sensory system

  1. 1. Sensory System Dr Saadiyah RaoDepart Of Physiology DIMC 1
  2. 2. A GeneralSense… 2
  3. 3. Sensory systemClassification Receptors: Extroceptors:Which response to stimuli arising outside the body. Introceptors:Which response to stimuli arising inside the body. 3
  4. 4. Sensory Receptors:Are specialized epithelial cells or neurons thattransduce environmental signals into neuralsignals.specialized epithelial cells: E.g.?neurons: E.g.?environmental signals: E.g.? 4
  5. 5. Receptive Field:Area of coverage of a sensory receptor or sensory neuron.Sensory neurons:(Afferent)Carry messages toward the CNS fromsensory receptors all over body.Dermatome:Each spinal nerve innervates a segmental field of skin. 5
  6. 6. Sensory receptors in skin: Receptor Sensory Modality Meissner’s corpuscles Touch (rapidly adapting) Vibration Pancinian corpuscles Touch (rapidly adapting) Proprioception Pressure Vibration Merkel’s disks Touch (slowly adapting) Texture Ruffini endings Touch (slowly adapting) Pressure Krause’s corpuscles Touch Temperature? Nerve endings Cold Warmth Touch Pressure Nociceptors Pain 6
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  8. 8. Difference between Touch , Pressure & Vibration?Fast pain (felt within 0.1 sec)is also called as:SharpAcutePricking etcSlow pain (felt after 1 sec)is also called as:AchingChronicThrombing etc 8
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  10. 10. Sensory Pathway: First order neurons: Are the primary afferent neurons that receive the transduced signal & send information to CNS.Second order neurons: They are located in spinal cord or brain stem.• Receive information from primary afferent neurons in relay nucleus & transmit to thalamus.• May cross the midline. 10
  11. 11. Third order neurons: Are located in the relay nuclei of the thalamus.Forth order neurons: Are located in the appropriate sensory area of the cerebral cortex. The information received results in conscious perception of the stimulus. 11
  12. 12. Spinal cord 12
  13. 13. Posterior Column Sensory Pathway Primary afferent neurons(1st)• Posterior column Fine Touch• Vibratory Nucleus gracilis & Nucleus cuneatus• Pressure• Proprioception Medulla (ipsilateral)• Stereognosis Cross in medulla• Two point discrimination (2nd) Medial lemniscus Thalamus (cotralateral) Sensory cortex (4th) 13
  14. 14. Anterolateral (Spinothalmic) Sensory Pathway• Pain(lat) Primary afferent neurons(1st)• Temperature(lat) Posterior horn (ipsilateral)• Crude touch(ant)• Pressure(ant) (2nd) cross midline Anterolateral qud of Spinal cord Thalamus (cotralateral) (3rd) Sensory cortex (4th) 14
  15. 15. Two-point touch• Discriminationtouch can be Is minimum distance at which 2 points of perceived as separate• Measure of tactile acuity or distance between receptive fields 15