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14 October 2009
Chapter 7 Sensory Physiology
Aspects of a stimulus that must be encoded using
only action potentials:
What? (modality & labeled line)
Where? (location enhanced by lateral inhibition)
How long? (duration, onset/offset.. Adaptation)
How strong? (intensity)
Figure 7.01
1st order sensory neuron
1st order sensory neuron
Example: a rod or cone
of the retina
Figure 7.16
Adequate
Stimulus
& Labeled
Line
Stimulus Modality
Each type of receptor responds best to a specific stimulus called its adequate stimulus.
Figure 7.02
Figure 7.03
Figure 7.11
Examples: waistband of underwear, top of socks, earrings,
mechanoreceptors in carotid arteries for blood pressure
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Figure 7.04
Review definition of receptive field;
1st, 2nd, and 3rd order
sensory neurons each have receptive fields.
= 1st order sensory neuron
Figure 7.05
Stimulus
Intensity
Within a cell’s receptive field, stimulus intensity
is encoded by frequency of action potentials.
Figure 7.06
Stimulus
Localization
The size of receptive fields
varies dramatically in
different regions of skin (i.e.
lips, palm, fingertip, calf).
For touch discrimination, small receptive fields allow greater
accuracy in “two point discrimination” test (upcoming lab!)
Figure 7.07
Stimulus
Localization
This 1st order sensory neuron will
have a higher frequency of action
potentials if the stimulus is in the
center if its receptive field.
However, this neuron also uses
action potential frequency to
encode stimulus intensity.
Therefore, this neuron would not
be very good at encoding the
precise location at which a
stimulus was delivered.
Figure 7.08
Stimulus
Localization
& Intensity
Receptive fields of different
neurons often overlap such
that any patch of skin may
have several receptors of the
same type (modality) and
receptors of different types
(different modalities I.e. touch,
pain temperature, etc.)
Overlapping receptive fields of
touch receptors (Meissners,
Merkels) allow for more
precise localization of a
stimulus via the mechanism of
lateral inhibition (next slide.)
Figure 7.09
Lateral inhibition exaggerates the
difference in stimulus intensity
detected by adjacent neurons.
Stimulus
Localization
& Intensity
Figure 7.10
Stimulus
Localization
& Intensity
Lateral inhibition
improves stimulus
localization.