Ganong's Review of Medical Physiology, 23rd Edition

A Modality
Receptors
B Location
Receptive
field
GENERATION OF IMPULSES IN
CUTANEOUS RECEPTORS
PACINIAN CORPUSCLES
Meissner’s
corpuscle
C Intensity and time course
Neural
spike train
Stimulus
The way receptors generate action potentials in the sensory
nerves that innervate them varies with the complexity of the
sense organ. In the skin, the Pacinian corpuscle has been
studied in some detail. As noted above, the Pacinian corpuscles
are touch receptors. Because of their relatively large size
and accessibility, they can be isolated, studied with microelectrodes,
and subjected to microdissection. The myelin sheath
of the sensory nerve begins inside the corpuscle (Figure 8–2).
The first node of Ranvier is also located inside, whereas the
second is usually near the point at which the nerve fiber leaves
the corpuscle.
CHAPTER 8 Properties of Sensory Receptors 151
FIGURE 8–1 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 Meissner’s and Pacinian
corpuscles causes tingling and vibratory sensation. B) Location of a stimulus is encoded by spatial distribution of the population of receptors activated.
A receptor fires only when the skin close to its sensory terminals is touched. These receptive fields of mechanoreceptors (shown as red
areas on fingertips) differ in size and response to touch. Merkel cells and Meissner’s corpuscles provide the most precise localization as they have
the smallest receptive fields and are most sensitive to pressure applied by a small probe. C) Stimulus intensity is signaled by firing rates of individual
receptors; duration of stimulus is signaled by time course of firing. The spike trains indicate action potentials elicited by pressure from a small
probe at the center of each receptive field. Meissner’s and Pacinian corpuscles adapt rapidly, the others adapt slowly. (From Kandel ER, Schwartz JH,
Jessell TM [editors]: Principles of Neural Science, 4th ed. McGraw-Hill, 2000.)
Merkel
cells
Touch
Pacinian
corpuscle
Ruffini
endings
GENERATOR POTENTIALS
Recording electrodes can be placed on the sensory nerve as it
leaves a Pacinian corpuscle and graded pressure applied to the
corpuscle. When a small amount of pressure is applied, a nonpropagated
depolarizing potential resembling an EPSP is recorded.
This is called the generator potential or receptor
potential (Figure 8–2). As the pressure is increased, the magnitude
of the receptor potential increases. When the magnitude
of the generator potential is about 10 mV, an action
potential is generated in the sensory nerve. As the pressure is
further increased, the generator potential becomes even larger
and the sensory nerve fires repetitively.
SOURCE OF THE GENERATOR POTENTIAL
By microdissection techniques, it has been shown that removal of
the connective tissue lamellas from the unmyelinated nerve