Copyright ©Mark Nelson, 2002. All rights reserved.
Chapter 9: Properties of Sensory Systems
What you need to know
(exam questions will be a drawn from this subset of material)
What is the "law of specific nerve energies"? (p. 210-211)
The idea that each sensory
nerve carries information about one particular subjective sensation.
Does the "law of specific nerve energies" arise because each sensory nerve
only responsds to one type of stimulus energy? (p.
No. Sensory nerves
usually respond best to one particular form of stimulus energy, but other
stimuli can also evoke a response.
For example, "seeing stars" after being hit in the eye.
What does sensory nerve activity give rise to one particular subjective
sensation? (p. 211)
The subjective sensation
is related to the specific part of the brain that processes the sensory activity..
Different sense organs send their messages to different
parts of the brain, which determines how the message is interpretted.
What is synesthesia? (p. 211)
A neurological condition
in which specific stimuli give rise to more than one type of subjective sensation
(tasting shapes, seeing sounds, hearing colors, etc.)
What names are used to categorize sensory receptors based on the type of
energy to which they are most sensitive? (p. 212-213)
chemo-, electro-, hygro-,
magneto-, mechano-, noci-, photo-, thermo- RECEPTORS (See Table 9-1)
What's the difference between a sense organ and a sensory receptor?
A sense organ refers the
the entire sensory apparatus (eye, ear, etc.),
whereas a sensory receptor refers to an individual cell.
A sense organ typically contains multiple sensory receptors
as well as a variety of accessory structures.
What is sensory filtering? (p. 213)
the term used to describe
the role of sense organs in limiting and shaping physical stimuli
What is sensory transduction? (p. 213-214)
the process by which
an external physical stimulus is converted into a change in membrane potential
of a sensory receptor
What is a receptor potential? (p. 213-214)
the change in membrane potential
of a sensory receptor in response to a physical stimulus
Do sensory receptors generate action potentials ? (p.
some classes of receptor can generate
APs (e.g. certain mechanoreceptors), whereas other do not (e.g. photoreceptors)
What is a generator potential? (p. 214)
it is sometimes used
to refer to the receptor potential that arises in those classes of receptors
that are capable of generating APs
What is sensory coding? (p. 215-217)
the mapping of attributes
of a physical stimulus (intensity, duration, frequency, etc.) into neural
What is a common way that sensory receptors are thought to encode stimulus
strength? (p. 217)
in the amplitude of
the receptor potential (non-spiking receptors) or the frequency of action
potentials (spiking receptors)
What is sensory adaptation? (p. 218-220)
the decline in response
of a receptor over time to a constant stimulus
What do the terms tonic, phasic, and phasi-tonic refer to?
-tonic receptors show little
or no adaptation to a constant stimulus; they encode information about stimulus
level (e.g. position)
-phasic receptors adapt rapidly to a constant stimulus;
they encode information about changes in a stimulus (e.g. velocity, acceleration)
- phasi-tonic receptors show characteristics of both phasic
and tonic receptors.
Sketch a representative (receptor potential / generator potential
/ spike train) for a (phasic / tonic / phasi-tonic)
in response to constant-amplitude step stimulus? (p. 219)
-see Fig. 9-9; note that
9-9A is labelled as "tonic" in the figure caption, but it is actually "phasi-tonic"
What is the receptive field of a sensory neuron? (p. 221)
the region(s) of the
sensory receptor surface that, when stimuluated, cause a change in (membrane
potential / spike activity) of that neuron
What is contrast enhancement? (p. 222)
an increased responsiveness
of sensory neurons to changes in intensity across a receptor surface,
What is lateral inhibition? (p. 223)
a mechanism for contrast
enhancement, based on inhibition of neighboring neurons in a sensory array
What is the relationship between sensory adaptation and lateral
inhibition? (p. XX)
-sensory adaptation is a mechanism
for enhancing the coding of changes in stimulus intensity across
-lateral inhibition is a mechanism for enhancing the coding of changes in stimulus intensity
What is range fractionation? (p. 226-227)
the use of multiple
receptor cells to cover a broad range of stimuli,
in which each cell is sensitive to only a small fraction
of the total range
What are the functional advantages of range fractionation? (p. 227)
it increases the resolution
and sensitivity of the sense organ and in some cases reduces ambiguity;
these benefits come at the cost
of needing more sensory receptors to cover the range
What is topographic organization? (p. 227-228)
mapping of a sensory surface onto a particular region of the CNS;
points maintain their neighbor relationships in
a topographic mapping; but the distances may be distorted
What are the specific terms used for topographic organization in the (visual
/ auditory / somatosensory) systems? (p. 228)
retinotopic (visual), tonotopic
(auditory), somatotopic (somatosensory)
What is columnar organization? (p. 229-230)
a pattern of functional
organization often found in association with topographic maps in the vertebrate
in which columns of neurons perpendicular
to the coritcal surface process information about the same stimulus attribute