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Anatomical Substrates of Somatic Sensation

Anatomical Substrates of Somatic Sensation. John H. Martin, Ph.D. Center for Neurobiology & Behavior Columbia University CPS. The 2 principal somatic sensory systems: Dorsal column-medial lemniscal system Anterolateral system. Dorsal Column-Medial Lemniscal System.

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Anatomical Substrates of Somatic Sensation

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  1. Anatomical Substrates ofSomatic Sensation John H. Martin, Ph.D. Center for Neurobiology & Behavior Columbia University CPS

  2. The 2 principal somatic sensory systems: Dorsal column-medial lemniscal system Anterolateral system

  3. Dorsal Column-Medial Lemniscal System •Mediates mechanical sensations -touch, limb position sense, vibration sense •Well established; clinical & experimental

  4. Anterolateral System •Mediates protective sensations -Pain -Temperature (cold & warmth) -Itch •Not as definitively established as is the DC-ML system for touch Why? •Pain w/o tissue trauma •Trauma w/o pain •Cultural; pathological

  5. Perspective: • Peripheral somatic sensory receptors are sensitive to different stimulus qualities • Mechanical • Thermal (warm, cold) • Noxious (mechanical, thermal, polymodal) • Different receptor classes provide input to different somatic sensory pathways • Differential thalamic and cortical localization

  6. 3. Thalamus: Ventral posterior nucleus 2. Dorsal column nuclei Medial lemniscus Peripheral nerve 1. Mechanoreceptor Dorsal root ganglion 1° somatic sensory cortex Dorsal column-medial lemniscal system: Mechanical sensations Dorsal column

  7. 1° somatic sensory cortex Cingulate cortex 3. Thalamus: Ventral posterior… Insular cortex & Medial dorsal nuclei. Peripheral axon 1. NociceptorThermoreceptorItch/histamine Dorsal root ganglion Dorsal horn Anterolateral system: Pain, Thermal, Itch 2. Anterolateral system: •Spinothalamic tract •Spinoreticular tract •Spinomesencephalic tract

  8. Mechanoreceptors are encapsulated Merkel’s receptor Meissner’s corpuscle Pacinian corpuscle

  9. Nociceptors, thermoreceptors, & itch receptors are bare nerve endings Bare nerve ending Merkel’s receptor Meissner’s corpuscle Pacinian corpuscle

  10. Dorsal root ganglion neuron PNS CNS Receptive Conductive - 1° afferent fiber Output Integrative

  11. Key Characteristics of DRG Neurons • Peripheral receptive field • Spatial area within which stimulationactivates the sensory neuron

  12. Receptive field

  13. CNS Neurons have Receptive Fields

  14. Slow adaptation • Rapid adaptation Off On Key Characteristics of DRG Neurons • Peripheral receptive field • Spatial area within which stimulationactivates the sensory neuron • Response to constant stimulation

  15. Meissner's Merkel Pacinian Ruffini Rapidly adapting Slowly adapting Mechano-receptorreceptivefields

  16. Rapidly adapting Slowly adapting Mechano-receptorreceptivefields Meissner's Merkel Pacinian Ruffini

  17. Nociceptors, thermoreceptors, & itch receptors are bare nerve endings Bare nerve ending Merkel’s receptor Meissner’s corpuscle Pacinian corpuscle

  18. High force; NOT NOXIOUS; NO RESPONSE Low force; NOXIOUS; RESPONSE Nociceptorsrespond tonoxiousstimuli Bluntprobe Pin Serratedforceps Low force; VERY NOXIOUS; LARGE RESPONSE

  19. Unmyelinated Small myelinated Large myelinated Peripheral nervecrosssection

  20. Fiber Histogram: Sensory axon innervating the skin IV (C) III (A-d) II (A-b)

  21. Protective Mechanoreceptors Fiber Histogram: Sensory axon innervating a muscle IV (C) I (A-) III (A-d) II (A-b)

  22. SC SensoryDorsalroot MotorVentralroot Spinal nerve

  23. Dermatomes Area of skin innervatedby all sensory fibersw/in single dorsal root

  24. Dermatome facts: Pain dermatomesoverlap < touch Dermatomal boundariesvary Dermatomesoverlap Skin Peripheral nerve Dorsal root Ventral root

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