BIOLOGY PORTION
SCIENCE OF SENSORY PERCEPTION FALL 2015
WEEK THREE READINGS: SMELL
As a reminder, you will need to answer the following questions fully and completely,
a hard copy turned in before you take a quiz. I recommend that you handwrite
your answers, and definitely make your own diagrams and drawings (versus lifting
stuff off the internet).
Your reading is a bit light this week, so you might want to get a head start on the
workshop readings which are longer and more complex. The first reading is again from
Silverthorn’s textbook and should give you a basic overview.
Human Physiology by Silverthorn Pages 341-343
1. You need to identify the basic anatomic structures involved in olfaction.
Figure 10.13 is as detailed as you need to know. Make your own diagram or
drawing showing how an odor molecule can result in the perception of odor.
See concept check problem 10 and 11 at the end of the reading.
2. T or F: The olfactory bulb connects to the thalamus
3. I want you to put together what you have learned the first two weeks and
apply it to olfaction. Think about molecules binding to receptors, signal
transduction, graded potentials, action potentials, neurotransmission,
convergence and divergence, primary sensory neurons, secondary and higher
order neurons, fields etc. Do the figure question on figure 10.13
4. What is a “descending modulatory pathway” (you may need to look this up
in other resources) and how might this relate to the psychological sensation
of smell?
5. Based on different places that the olfactory bulb connect to the brain, why
might certain smells evoke intense emotions and memories?
6. Notice some of the cellular details in figure 10.13. There are many different
cell types present near the olfactory epithelium. Some basal cells are “stem
cells”. These cells may differentiate into olfactory cells to replace ones that
die after approximately 2 months. This means that you are constantly
replacing your olfactory receptor cells, and also that there may be a great
deal of neuronal plasticity in the olfactory system. One of your workshop
readings addresses this. Also note that “cilia” and olfactory cell dendrites
are considered the same in this diagram. Unfortunately the figure does not
include glomerular structures in the olfactory bulb which are important.
Here is a better diagram.

Let me stress again, the importance of linking molecule (odorant) to
perception (or perception to molecule if you prefer). You need to draw
and/or describe in detail how a molecule can bind to an odorant receptor and
result in the perception of that molecule. The more detail, the better. The
more you use the basic concepts you learned the first few weeks, the better.
7. Along with the reading’s description of odorant receptors G proteins, here is
an animation that includes the signal transduction pathway for olfaction
(about midway through). Note that this type of signal transduction is rather
similar to how our retinal cells transduce photon signals.
http://sites.sinauer.com/neuroscience5e/animations15.01.html
a. Is the G protein active when it is bound by GDP?
b. What does adenalyl cyclase enzyme do?
c. How does sodium and calcium enter the cilia? What does that do the
graded potential of the cilia? Why does chloride efflux contribute to
this?
d. What enzyme helps deactivate the signal? Name two other
intracellular processes that help with this
8. Approximately how many active odorant receptor genes do most mammals
have?