Tactile Receptors. There are at least six entirely dif ferent types of tactile receptors, but many
more similar to these also exist. Some were shown in Figure 46-1 of
the previous chapter; their special characteristics are the following.
Transmission of Tactile Signals in Peripheral Nerve Fibers. Almost all sp ecialized
sensory receptors,such as Meissner‘s corpuscles, Iggo dome receptors, hair receptors, pacinian
corpuscles, and Ruffini‘s endings,transmit their signals in type A
nerve fibers that have transmission
velocities ranging from 30 to 70 m/sec. Conversely, free nerve ending tactile receptors transmit signals
mainly by way of the small type A
myelinated fibers that conduct at velocities of only 5 to 30 m/sec.
Some tactile free nerve endings transmit by way of type C unmyelinated fibers at velocities from a
fraction of a meter up to 2 m/sec; these send signals into the spinal cord and lower brain stem,
probably subserving mainly the sensation of tickle.
