SECTION A SUMMARY
I. Sensory processing begins with the transformation of stimulus
energy into graded potentials and then into action potentials in
nerve ﬁ bers.
II. Information carried in a sensory system may or may not lead to
a conscious awareness of the stimulus.
I. Receptors translate information from the external and internal
environments into graded potentials, which then generate
a. Receptors may be either specialized endings of afferent
neurons or separate cells at the ends of the neurons.
b. Receptors respond best to one form of stimulus energy,
but they may respond to other energy forms if the stimulus
intensity is abnormally high.
c. Regardless of how a speciﬁ c receptor is stimulated,
activation of that receptor can only lead to perception of
one type of sensation. Not all receptor activations lead,
however, to conscious sensations.
II. The transduction process in all sensory receptors involves—
either directly or indirectly—the opening or closing of ion
channels in the receptor. Ions then ﬂ ow across the membrane,
causing a receptor potential.
a. Receptor potential magnitude and action potential
frequency increase as stimulus strength increases.
b. Receptor potential magnitude varies with stimulus strength,
rate of change of stimulus application, temporal summation
of successive receptor potentials, and adaptation.
Primary Sensory Coding
I. The type of stimulus perceived is determined in part by the
type of receptor activated. All receptors of a given sensory unit
respond to the same stimulus modality.
II. Stimulus intensity is coded by the rate of ﬁ ring of individual
sensory units and by the number of sensory units activated.
III. Perception of the stimulus location depends on the size of
the receptive ﬁ eld covered by a single sensory unit and on the
overlap of nearby receptive ﬁ elds. Lateral inhibition is a means
by which ascending pathways increase sensory acuity.
IV. Stimulus duration is coded by slowly adapting receptors.
V. Information coming into the nervous system is subject to
control by both ascending and descending pathways.
Neural Pathways in Sensory Systems
I. A single afferent neuron with all its receptor endings is a
a. Afferent neurons, which usually have more than one
receptor of the same type, are the ﬁ rst neurons in sensory
b. The area of the body that, when stimulated, causes
activity in a sensory unit or other neuron in the ascending
pathway of that unit is called the receptive ﬁ eld for that
II. Neurons in the speciﬁ c ascending pathways convey information
about only a single type of stimulus to speciﬁ c primary
receiving areas of the cerebral cortex.
III. Nonspeciﬁ c ascending pathways convey information from
more than one type of sensory unit to the brainstem reticular
formation and regions of the thalamus that are not part of the
speciﬁ c ascending pathways.
Association Cortex and Perceptual Processing
I. Information from the primary sensory cortical areas is
elaborated after it is relayed to a cortical association area.
a. The primary sensory cortical area and the region of
association cortex closest to it process the information in
fairly simple ways and serve basic sensory-related functions.
b. Regions of association cortex farther from the primary
sensory areas process the sensory information in more
c. Processing in the association cortex includes input from
areas of the brain serving other sensory modalities, arousal,
attention, memory, language, and emotions.
SECTION A KEY TERMS
cortical association area
nonspeciﬁ c ascending
rapidly adapting receptor
receptive ﬁ eld
slowly adapting receptor
speciﬁ c ascending pathway
SECTION A CLINICAL TERMS
SECTION A REVIEW QUESTIONS
1. Distinguish between a sensation and a perception.
2. Deﬁ ne the term
3. Describe the general process of transduction in a receptor that is a
cell separate from the afferent neuron. Include in your description
the following terms: speciﬁ city, stimulus, receptor potential,
neurotransmitter, graded potential, and action potential.
4. List several ways in which the magnitude of a receptor
potential can vary.
5. Differentiate between the function of rapidly adapting and
slowly adapting receptors.
6. Describe the relationship between sensory information
processing in the primary cortical sensory areas and in the
cortical association areas.
7. List several ways in which sensory information can be distorted.
8. How does the nervous system distinguish between stimuli of
9. How does the nervous system code information about stimulus
10. Describe the general mechanism of lateral inhibition and
explain its importance in sensory processing.
11. Make a diagram showing how a speciﬁ c ascending pathway relays
information from peripheral receptors to the cerebral cortex.