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Chapter 18

Chapter 18. General Sensation. Classification of Receptors. By origin of the stimuli Exteroceptors Senses stimuli external to the body Found close to the body surface Touch, cutaneous pain, vision, hearing, smell,etc Interoceptors (visceroceptors)

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Chapter 18

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  1. Chapter 18 General Sensation

  2. Classification of Receptors • By origin of the stimuli • Exteroceptors • Senses stimuli external to the body • Found close to the body surface • Touch, cutaneous pain, vision, hearing, smell,etc • Interoceptors (visceroceptors) • Reacts to stimuli arising form within the body • Visceral pain, nausea, stretch, pressure

  3. Classification of Receptors • Proprioceptors • Sense the position and movements of the body • Located in muscles, tendons and joints

  4. Classification of Receptors • According to the type of stimuli • Thermoreceptors • Mechanoreceptors • Physical deformation:vibration, touch, pressure, stretch, tension • Also hearing, balance • Located in skin, viscera, joints

  5. Classification of Receptors • Chemoreceptors • Odor, taste • Nociceptors • Tissue damage:trauma, ischemia • Photoreceptors • Respond to light • Only in the eyes

  6. The general sensory receptors • Unencapsulated nerve endings • Free nerve endings • Thermoreceptors:cold and warm receptors • Nociceptors • Most abundant in epithelia and connective tissues

  7. The general sensory receptors • Tactile (Merkel) discs • Light touch • Sense texture, shapes, edges • Merkel discs:merkel cell+nerve ending • Located in the stratum basale of the epidermis • Hair receptors (peritrichial endings) • Sense hair movement • Quick adaptation

  8. The general sensory receptors • Encapsulated nerve endings • Tactile corpuscle (Meissner) • Located in the dermal papilla in sensitive hairless areas • Light touch and texture • Krause end bulbs • Similar to tactile • Located in mucous membranes

  9. The general sensory receptors • Pacinian corpuscles • Deep pressure, stretch, tickle, vibration • Deep in the dermis and mainly found in the hands, genital, feet, breast, and some visceras • Ruffini corpuscles • Deep pressure, stretching of the skin, joint movements • Located in the dermis, subcutaneous, ligaments, tendons and joint capsules

  10. Proprioceptors • Muscle spindles • Monitor skeletal muscle length • Trigger stretch reflexes • Golgi tendon • Monitors the degree of tension of a tendon

  11. Sensory receptors

  12. Receptor physiology • Receptors are transducers • transform the stimuli into afferent nerve impulse • Stimulus is identified by the area of the brain’s sensory cortex • Four cutaneous sensations recognized • Tactile, heat, cold and pain • They cluster in certain areas • Punctuate distribution

  13. Tests for general senses • Relative density and location of receptors test • Temperature test • Touch test • Two-point discrimination test • Tactile localization test

  14. Tests for general senses • Adaptation test • For touch • For temperature • Negative afterimage • Referred pain • Pain is perceived in one area but the painful stimulus comes from another area • Angina pectoris, heart burn, phantom limb pain

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