After studying this chapter, you should be able to:
Describe the cutaneous receptors that mediate the sensations of touch, pressure, pain, and temperature.
Explain the four attributes of a stimulus to sensory receptors.
Explain acute and chronic pain, hyperalgesia, and allodynia.
Describe 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.
Identify drugs used for relief of pain, their mechanism of action, and the rationale for their use.
Sensory receptors are transducers that change a particular form of energy in the environment into electrical signals, which are then relayed to the central nervous system (CNS) which can then interpret the information received. Table 8–1 is a list of different types of receptors in the skin, muscles, and specialized organs like the eye and ear and the specific energy (stimulus) to which they respond. The emphasis in this chapter is on the characteristics of cutaneous mechanoreceptors, thermoreceptors, and nociceptors; the way they generate impulses in afferent neurons; and the central pathways that mediate or modulate information from these receptors. Subsequent chapters cover sensory receptors in the eye, ear, tongue and nose, and skeletal muscles and joints.
Table Graphic Jump Location TABLE 8–1Principle sensory modalities. ||Download (.pdf) TABLE 8–1 Principle sensory modalities.
|Sensory Receptor ||Receptor Class ||Modality ||Stimulus |
|Meissner corpuscles ||Cutaneous mechanoreceptor ||Touch ||Tap, flutter 5–40 Hz |
|Hair follicle receptors ||Cutaneous mechanoreceptor ||Touch ||Motion |
|Pacinian corpuscles ||Cutaneous mechanoreceptor ||Touch ||Deep pressure, vibration 60–300 Hz |
|Merkel cells ||Cutaneous mechanoreceptor ||Touch ||Touch, pressure |
|Ruffini corpuscles ||Cutaneous mechanoreceptor ||Touch ||Sustained pressure |
|Muscle spindles ||Mechanoreceptor ||Proprioception ||Stretch |
|Golgi tendon organ ||Mechanoreceptor ||Proprioception ||Tension |
|Cold and warmth receptors ||Thermoreceptor ||Temperature ||Thermal |
|Chemical, thermal, and mechanical nociceptors (or polymodal) ||Chemoreceptor, thermoreceptor, and mechanoreceptor ||Pain ||Chemical, thermal, and mechanical |
|Rods, cones ||Photoreceptor ||Vision ||Light |
|Hair cells (cochlea) ||Mechanoreceptor ||Hearing ||Sound |
|Hair cells (semicircular canals) ||Mechanoreceptor ||Balance ||Angular acceleration |
|Hair cells (otolith organs) ||Mechanoreceptor ||Balance ||Linear acceleration, gravity |
|Olfactory sensory neuron ||Chemoreceptor ||Smell ||Chemical |
|Taste buds ||Chemoreceptor ||Taste ||Chemical |
TOUCH, PRESSURE, PAIN, & TEMPERATURE RECEPTORS
Touch and pressure are sensed by four types of mechanoreceptors that are specialized dendritic endings of Aα and Aβ afferent nerve fibers (Figure 8–1). Meissner corpuscles respond to changes in texture and slow vibrations; Merkel cells respond to sustained pressure and touch; Ruffini corpuscles respond to sustained pressure; and Pacinian corpuscles respond to deep pressure and fast vibration.
Sensory systems encode four elementary attributes of stimuli: modality, location (receptive field), intensity, and duration (timing). (A) The human hand has four types of mechanoreceptors; their combined activation produces the sensation of contact with an object. Selective activation of Merkel cells and Ruffini endings causes sensation of steady pressure; selective activation of ...