Peripheral sensory receptors.
Axons of the neuron cell bodies in the posterior root
ganglia carry information from
skin, muscles, joints, viscera, blood vessels, mesentaries,
and other connective tissues. Sensory receptors associ-
ated with these axons may consist of
, specialized endings around
in conjunction with specialized cells (e.g.,
, and specialized regions of axonal mem-
free nerve endings
(see Figs. 6-7A,B and
two types of encapsulated endings and are easier to see
using light microscopy than other receptors in the skin.
In these receptors, the axonal membrane is specialized to
change its permeability in response to mechanical pres-
sure (the regions of specialization are indicated by the
thicker blue lines
). The connective tissue capsules help to
focus mechanical force on the axonal membrane.
J. Lynch &T. Yang
Meissner corpuscle, thick skin of palm.
are encapsulated, quickly adapting
mechanoreceptors that are sensitive to light touch and
low-frequency vibration. They are important for the
sensation of discriminative touch. Meissner corpuscles
are located in the
, at the interface of the
. Only the nuclei of the capsu-
lar connective tissue cells are visible after H&E stains.
Using special stains, the corpuscle looks like a stack of
pancakes (Schwann cells, Fig. 7-8A) with one or more
axons intertwining among them. The main axons associ-
ated with Meissner corpuscles are large (6–12
heavily myelinated, hence their rapid conduction veloci-
ties. Meissner corpuscles are found in all parts of the skin
of the hand and foot, in the lips, and in a number of
other locations but are most concentrated in thick, hair-
Pacinian corpuscle, thick skin of palm.
are large, encapsulated structures that
detect very light touch and vibration. They are located
primarily in the
of the palms of the hands
and ± ngers and the soles of the feet but are also found in
other areas of skin as well as in the periostea and mes-
entery. They are much larger than Meissner corpuscles,
sometimes reaching 2 mm in length (note different mag-
cation). Pacinian corpuscles consist of a specialized
zone of axonal membrane that is exquisitely sensitive
to pressure (Fig. 7-8A) surrounded by a layered cellular
structure that consists of a
rounding the axon, an
intermediate growth zone
, and an
. Around 60 to 100 layers are formed by
very thin cells that overlap at their edges, giving the Pacin-
ian corpuscle the appearance of an onion when
This sample is from the hypodermis of the skin.