Regulation and Integration of the Body
Classiﬁcation by Stimulus Type
Tese categories are easy to remember because the name usu-
ally indicates the stimulus that activates the receptor.
respond to mechanical force such as
touch, pressure (including blood pressure), vibration, and
respond to temperature changes.
, such as those of the retina of the eye, re-
spond to light.
respond to chemicals in solution (mol-
ecules smelled or tasted, or changes in blood or interstitial
harm) respond to po-
tentially damaging stimuli that result in pain. For example,
searing heat, extreme cold, excessive pressure, and inﬂam-
matory chemicals are all interpreted as painful. Tese signals
stimulate subtypes of thermoreceptors, mechanoreceptors,
Classiﬁcation by Location
Receptors can be grouped into three receptor classes according
to either their location or the location of the activating stimulus:
exteroceptors, interoceptors, and proprioceptors.
torz) are sensitive to stimuli
arising outside the body (
outside), so most extero-
ceptors are near or at the body surface. Tey include touch,
pressure, pain, and temperature receptors in the skin and
most receptors of the special senses (vision, hearing, equilib-
rium, taste, smell).
torz), also called
respond to stimuli within the body (
as from the internal viscera and blood vessels. Interoceptors
monitor a variety of stimuli, including chemical changes,
peripheral nervous system (PNS)
links from and to the world outside our bodies. Ghostly white
nerves thread through virtually every part of the body, enabling
the CNS to receive information and carry out its decisions.
Te PNS includes all neural structures outside the brain and
spinal cord, that is, the
, and eﬀerent
diagrams its basic components.
In the ﬁrst portion of this chapter we deal with the func-
tional anatomy of each PNS element. Ten we consider the
components of reﬂex arcs and some important somatic reﬂexes,
played out almost entirely in PNS structures, that help maintain
Classify general sensory receptors by structure, stimulus
detected, and body location.
are specialized to respond to changes in
their environment, which are called
. ±ypically, activa-
tion of a sensory receptor by an adequate stimulus results in
graded potentials that in turn trigger nerve impulses along the
aﬀerent PNS ﬁbers coursing to the CNS.
of the stimulus) and
(interpretation of the meaning
of the stimulus) occur in the brain. But we are getting ahead of
For now, let’s just examine how sensory receptors are classi-
ﬁed. Basically, there are three ways to classify sensory receptors:
(1) by the type of stimulus they detect; (2) by their body loca-
tion; and (3) by their structural complexity.
Central nervous system (CNS)
Peripheral nervous system (PNS)
Motor (efferent) division
Place of the PNS in the structural organization of the nervous system.