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Sensory Systems
The difference in perception between a strong smell and a weak smell is due to
differences in the strength of the action potential sent from the receptor.
1. False. My 6th sense is
telling me that this is a
function of how fast the
information is received
by the brain.
3. False. My spidy-sense
interprets sensory
information based on how
large the action potential is.
2. False. Action potentials are
always the same strength, so
the difference must be due to
how many smell receptors
are stimulated.
4. When I smell fear,
my brain is combining
information from more
than one receptor type.
(I don’t know what I’m
talking about.)
Learning Objectives (3/9/09)
1.
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7.
Differentiate between sensation and perception
Describe the sequence of events in general receptor
function
Describe how and where integration of sensory
information occurs for perception and for simple
behavioral responses
Compare the structure and function of various receptor
types (i.e. classification of receptors)
Compare and contrast structure and function in the eye
cups of Planaria, the compound eyes of insects, and the
single-lens eyes of mollusks.
Compare the systems for hearing and equilibrium in
various animals
Describe how chemoreceptors may function in taste and
smell
Basic Function
Sequence of Events in a Biological Receptor
Stimulus
Reception
Amplification
Receptor Protein Activated
Enzyme Cascade (in some cases)
Receptor Ion Channels affected
(deplorization or hyperpolarization)
Receptor Potential (graded)
Transduction
Change in Neurotransmitter
release from Receptor Cell
Transmission
p. 1053
Integration
Modulated Impulse
Frequency in Receptor
Cell Axon to CNS
Modulated Impulse
Frequency in Second
Order Neuron to CNS
“Decoding” Sensory Information
Qualitative
• What kind of stimulus…i.e. what kind of
receptor?
• What is the destination for the resulting nerve
impulses?
Quantitative
• How “important” is the stimulus?
The population code
= number of similar neurons activated
The frequency code
= number of impulses per unit time
Receptor
Classification
All receptors are specialized to
act as transducers; transforming
one type of energy into an
electrical potential.
Pacinian corpuscle
(pressure receptor)
This means that in all receptors,
energy transduction results in
opening or closing __________.
Shown are two types of
mechanoreceptors. How are
their functions different?
Hair cell receptor
Receptor
Classification
Pain receptors (nociceptors) are
specialized sensory neurons that
may respond to a variety of
noxious stimuli.
This composite taste cell represents
an example of a chemoreceptor.
Review the variety of signal
transduction pathways employed.
Receptor Classification
Photoreceptors, like chemoreceptors often employ G-proteins to
regulate ion channels, and thus may respond to the direction of change
as well as magnitude of the stimulus.
In vertebrate photoreceptors
(rods and cones), light
triggers a receptor potential
that is hyperpolarization,
instead of the usual
depolarization.
The sensory pathway is thus
stimulated by a reduction in
the release of inhibitory
neurotransmitter.
Is this a level of integration?
Pit Vipers detect
infrared radiation
(heat).
Receptor Classification
Thermoreceptors are specialized to respond to
the physical stress of temperatures either above
or below the animal’s normal body
temperature.
It is unclear whether these receptors are more
like mechanoreceptors, or operate by some
other mechanism.
Why do you think that there are separate
hot and cold receptors?
Population Code
Integration begins at the level of the receptor, and continues
at each synapse in the sensory pathway.
Has a receptor potential led to
an action potential in the first
(primary) sensory neuron(s)?
What type of receptor has been
stimulated? How many?
In this example, how would the
two stimuli be perceived:
as one point or two points?
Is the neurotransmitter between
first order and second order
sensory neurons excitatory or
inhibitory?
Population Code (continued)
Convergence of primary sensory neurons onto a single sensory neuron
reduces sensory acuity.
How many receptors have
been stimulated? (How is
the sensation different than
in the previous figure?)
How many first order
neurons are conducting
action potentials?
How is perception changed
by this convergence?
Muscle
Stretch
Receptors:
Frequency Code
Weak stretch
causes low impulse
frequency on
neuron leaving
receptor.
Strong stretch
causes high
impulse frequency
on neuron leaving
receptor.
Membrane
potential
Time
Sensory Adaptation is one form
of Integration
Phasic receptors quickly
adapt. The frequency of
action potentials
diminishes or stops if the
stimulus is unchanging.
Tonic receptors adapt
slowly or not at all.
Most exteroreceptors
(receptors that monitor the
external environment) are
_________receptors.
Why?
Photoreceptors in Invertebrates
Explain the difference between the function of screening
pigment in this flatworm and visual pigments. Describe the
integration of information from these two receptor organs.
Image-forming Eyes
in Invertebrates
One advantage to compound
eyes is that the area of best
focus is not limited to just
one area (like in mammalian
eyes). Explain why.
The visual sensory system of
mammals has a refractory
period which is almost 7x
longer than that of animals
with compound eyes. What
does this mean in terms of
visual perception?
p. 1037
Which animal groups
possess compound eyes?
The number of ommatidia per eye varies from species to species with only
a few in ants, to 800 in fruit flies, to as many as 10,000 ommatidia in the
compound eye of the horsefly. The compound eye provides information
about patterns in the environment and is very good at detecting movement.
The world looks different to an insect because of the compound nature of
its eyes, and also because it is sensitive to different wavelengths of light
than our eyes are.
Invertebrate Single-lens Eye
How do these animals focus light
on photoreceptor cells?
What is the difference in function
between the pupil and the lens?
http://www.cas.vanderbilt.edu/bsci111b/eye/supplemental.htm
Why are there pigments in
photoreceptors?
Vertebrate Single-lens Eye
p. 1038
Equilibrium
Statocyst of an invertebrate:
Lateral line system in fish:
What are the common structures among all receptor systems for
equilibrium in animals?
The Vestibuluar Apparatus in
Mammals
What other sensory systems are important in the maintenance of balance
and the coordination of skeletal muscle contraction?
Hearing
While statocysts may be sensitive to lowfrequency sound energy, most
invertebrates live in a “silent” world. Only
crustaceans, insects, and spiders have
developed true sound-receptor organs.
Which animal groups have
a tympanic membrane
associated with their
hearing apparatus?
Compare and contrast the
function of body hairs to
the function of the tympanic
membrane.
How is reception of sound
energy similar to the
function of sensory systems
for balance?
Human Ear
p. 1034