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INTRODUCTION

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And there I stood, a man grown, shaking in the sunshine with that old boyish emotion brought back to me by an odour! … Often and often have I known this strange rekindling of dead fires. And I have thought how, if our senses were really perfect, we might lose nothing out of our lives: neither sights, nor sounds, nor emotions… .

—Ray Stannard Baker (1870–1946)

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I. THE SENSES

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A. Sensation and subjectivity

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The possibility for sensation begins when a chemical or physical change stimulates the receptor endings of sensory neurons and alters the flow of impulses in the sensory pathways. The impulses in the sensory pathways then lead to an experience that we call a sensation, such as pain, touch, or sight. Nothing is more real to the patient (Pt) than the experience of the sensation, such as pain, nor less real to the observer. Although the Pt can judge the degrees of a sensation, even on scale of 0 to 10 for pain, no one else can verify the sensation or measure it objectively in grams, centimeters, or seconds, the classic units of the physics. Nevertheless, by carefully eliciting the Pt's history, the examiner (Ex) can recognize and diagnose various sensory syndromes, such as migraine or nerve root compression, with about the same degree of certainty as motor syndromes.

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B. Classification of sensation

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  1. Aristotle recognized five primary senses:

    1. Sight

    2. Sound

    3. Smell

    4. Taste

    5. Touch

  2. Tradition also recognizes special and general senses. The special senses are sight, sound, taste, smell, and equilibrium/verticality. The general sensations are the rest. Sensation also can be classified as somatic or visceral.

  3. Charles Sherrington (1857–1952) classified sensation as exteroception, proprioception, and interoception, depending on the origin of the stimulus and the location of the receptor tips of the axons (Sherrington, 1906).

    1. Exteroceptor axonal tips are located near the external body surfaces. They respond to stimuli that impinge on the body's external surfaces. These stimuli produce sight, sound, smell, taste, and superficial cutaneous sensation. Superficial skin sensations include:

      1. Touch

      2. Superficial pain

      3. Temperature

      4. Itching, tickling, and wetness

    2. Proprioceptor axonal tips are located beneath body surfaces. They respond to stimuli that originate from receptors deep in the dermis, in muscles, tendons, ligaments, and the vestibular labyrinth. In large part, they record the actions of the body on itself and orientation to the pull of gravity. (See page 404 for a fuller definition of proprioception.) Proprioceptive sensations include:

      1. Position

      2. Movement

      3. Vibration

      4. Pressure, weight, or tension

      5. Deep pain (sometimes included in proprioception)

      6. Equilibrium and verticality (via vestibular pathways and dorsal columns)

    3. Interoceptor axonal tips located in the viscera and vessels respond to stimuli that act on the internal surfaces of the viscera or originate in the visceral walls:

      1. Visceral and vascular pain

      2. Sense of fullness or distention of the viscera

  4. Obviously the various sensory classifications overlap and are inconsistent. To obviate memorizing sensory classifications, ...

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