After studying this chapter, you should be able to:
Describe the location, type, and function of receptors that mediate the sensations of touch, temperature, and pain.
Describe the steps involved in sensory transduction and action potential generation in cutaneous mechanoreceptors and nociceptors.
Explain the basic elements of sensory coding including modality, location, intensity, and duration and how these properties relate to receptor specificity, receptive field, receptor sensitivity, and receptor adaptation.
Explain the differences between pain and nociception, first and second pain, acute and chronic pain, and hyperalgesia and allodynia.
Describe and explain the basis for 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 the deficits caused by lesions of ascending sensory pathways that mediate touch, pain, and temperature.
Describe processes involved in modulation of transmission in pain pathways.
Identify drugs used for relief of pain and give the rationale for their use and their clinical effectiveness.
Table 8–1 provides a list of the principle sensory modalities. Sensory receptors convert specific forms of energy into action potentials in sensory neurons. Cutaneous mechanoreceptors mediate responses to touch and pressure. Proprioceptors in muscles, tendons, and joints relay information about muscle length and tension. Thermoreceptors detect the sensations of warmth and cold. Nociceptors respond to potentially harmful stimuli such as pain, extreme heat, and extreme cold. Chemoreceptors are stimulated by a change in the chemical composition of the local environment. These include receptors for taste and smell as well as visceral receptors that are sensitive to changes in the plasma level of O2, pH, and osmolality. Photoreceptors in the rods and cones in the retina respond to light.
TABLE 8–1Principle sensory modalities. ||Download (.pdf) TABLE 8–1 Principle sensory modalities.
|Sensory System ||Modality ||Stimulus ||Receptor Class ||Receptor Cell Type |
|Somatosensory ||Touch ||Tap, flutter 5–40 Hz ||Cutaneous mechanoreceptor ||Meissner corpuscle |
|Somatosensory ||Touch ||Motion ||Cutaneous mechanoreceptor ||Hair follicle receptor |
|Somatosensory ||Touch ||Vibration 60–500 Hz; deep pressure ||Cutaneous mechanoreceptor ||Pacinian corpuscle |
|Somatosensory ||Touch ||Touch, sustained pressure ||Cutaneous mechanoreceptor ||Merkel cell |
|Somatosensory ||Touch ||Skin stretch, vibration ||Cutaneous mechanoreceptor ||Ruffini corpuscle |
|Somatosensory ||Proprioception ||Stretch ||Mechanoreceptor ||Muscle spindle |
|Somatosensory ||Proprioception ||Tension ||Mechanoreceptor ||Golgi tendon organ |
|Somatosensory ||Temperature ||Thermal ||Thermoreceptor ||Cold and warm receptors |
|Somatosensory ||Pain ||Chemical, thermal, and mechanical ||Chemoreceptor, thermoreceptor, and mechanoreceptor ||Polymodal receptors or chemical, thermal, and mechanical nociceptors |
|Somatosensory ||Itch ||Chemical ||Chemoreceptor ||Chemical nociceptor |
|Visual ||Vision ||Light ||Photoreceptor ||Rods, cones |
|Auditory ||Hearing ||Sound ||Mechanoreceptor ||Hair cells (cochlea) |
|Vestibular ||Balance ||Angular acceleration ||Mechanoreceptor ||Hair cells (semicircular canals) |
|Vestibular ||Balance ||Linear acceleration, gravity ||Mechanoreceptor ||Hair cells (otolith organs) |
|Olfactory ||Smell ||Chemical ||Chemoreceptor ||Olfactory sensory neuron |
|Gustatory ||Taste ||Chemical ||Chemoreceptor ||Taste buds |
This chapter describes primarily the characteristics of cutaneous receptors that mediate the sensory modalities of touch, pain, and temperature; the way they generate impulses in afferent ...