BIOL 251—Anatomy & Physiology I
Chapter 13—The Peripheral Nervous System and Reflex Activity
PART 1: SENSORY RECEPTORS AND SENSATION
I. Sensory Receptors (pp. 485–488; Fig. 13.1; Table 13.1)
A. Sensory receptors are specialized to respond to changes in their environment called
stimuli (p. 485; Fig. 13.1).
B. Receptors may be classified according to the type of stimulus, and include
mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors
C. Receptors may be classified according to their location, or location of stimulus, and
include exteroceptors, interoceptors, and proprioceptors (p. 486).
D. Receptors may be classified according to structural complexity, and may be simple or
complex (p. 486).
Simple receptors are general senses, and may be unencapsulated or encapsulated
dendritic endings (pp. 486–488; Table 13.1).
Unencapsulated dendritic endings are free, or naked, nerve endings, and detect
temperature, pain, itch, or light touch.
Encapsulated dendritic endings consist of a dendrite enclosed in a connective
tissue capsule and detect discriminatory touch, initial, continuous, and deep
pressure, and stretch of muscles, tendons, and joint capsules.
II. Sensory Integration: From Sensation to Perception (pp. 488–491; Fig. 13.2)
A. The somatosensory system, the part of the sensory system serving the body wall and
limbs, involves the receptor level, the circuit level, and the perceptual level (pp. 488–
491; Fig. 13.2).
Processing at the receptor level involves a stimulus that must excite a receptor in
order for sensation to occur.
Processing at the circuit level is involved with delivery of impulses to the
appropriate region of the cerebral cortex for stimulus localization and perception.