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After studying this chapter, youshould be able to:

  • Name the types of touch and pressure receptors found in the skin.

  • Describe the receptors that mediate the sensations of pain and temperature.

  • Define generator potential.

  • Explain the basic elements of sensory coding.

  • Explain the differences between pain and nociception, first and second pain, acute and chronic pain, hyperalgesia, and allodynia.

  • Describe and explain visceral and referred pain.

  • Compare the pathway that mediates sensory input from touch, proprioceptive, and vibratory senses to that mediating information from nociceptors and thermoreceptors.

  • Describe processes involved in modulation of transmission in pain pathways.

  • List some drugs that have been used for relief of pain and give the rationale for their use and their clinical effectiveness.


We learn in elementary school that there are “five senses” (touch, sight, hearing, smell, and taste); but this dictum takes into account only those senses that reach our consciousness. There are many sensory receptors that relay information about the internal and external environment to the central nervous system (CNS) but do not reach consciousness. For example, the muscle spindles provide information about muscle length, and other receptors provide information about arterial blood pressure, the levels of oxygen and carbon dioxide in the blood, and the pH of the cerebrospinal fluid. The list of sensory modalities listed in Table 8–1 is overly simplified. The rods and cones, for example, respond maximally to light of different wavelengths, and three types of cones are present, one for each of the three primary colors. There are five modalities of taste: sweet, salt, sour, bitter, and umami. Sounds of different pitches are heard primarily because different groups of hair cells in the cochlea are activated maximally by sound waves of different frequencies.

TABLE 8–1Principle sensory modalities.

Sensory receptors can be thought of as transducers that convert various forms of energy in the environment into action potentials in sensory neurons. The ...

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