Psych 115 Final Exam Questions and
Complete Solutions
Mechanical senses ✅transduce mechanical energy into nerve impulses
ex) somatosensation, vestibular, hearing
Chemical senses ✅transduce energy from chemical reactions into nerve impulses
ex) nociception, taste, olfaction
to evaluate the qualities
of substances we ingest into our bodies, namely, the food we eat (or
drink) and the air we breathe
Photosensors ✅transduce electromagnetic energy into nerve impulses
ex) vision
Taste ✅The sense of taste arises from sensory receptors on the tongue called taste
buds that directly contact the food and drink we ingest in our mouths
Olfaction (sense of smell) ✅arises from sensory receptors in the nasal cavity that
detect aerosolized molecules in the air that we breathe into our lungs
As we breath in and out, aerosolized molecules are drawn into the nasal cavity
olfactory epithelium ✅sensory organ for smell;
The air passes across the olfactory epithelium,
Odor molecules bind to receptors on the hair-like cilia which extend from the olfactory
epithelium, and are in fact the "dendrites" of bipolar olfactory sensory neurons
Orthonasal olfaction ✅is the sensing of odor molecules from the outside air; this
occurs during inspiratory breathing
Retronasal olfaction ✅is the sensing of odor molecules from the mouth; this occurs
during expiratory breathing
Olfactory chemotransduction ✅is mediated by g-protein receptors in the cilia of
olfactory sensory neurons
These g-protein receptors are embedded in the membrane of the olfactory neuron cilia
There are about _____ unique olfactory receptor genes, which is __% of all our genes!
But only about ___ of these genes are functional in humans. ✅1000; 3; 400
,Each gene codes for a unique receptor, and each receptor binds a variety of different
odor molecules (also most odor molecules bind to more than one receptor)
All of the known olfactory receptors are _________
receptors ✅g-protein coupled
Olfactory Sensory Neurons ✅The olfactory epithelium is coated with olfactory sensory
neurons
• Humans have about 40 million olfactory sensory neurons, some dog breeds have as
many as 220 million
• Each olfactory sensory neuron expresses exactly ONE type of olfactory receptor
• Olfactory sensory neurons that express the same receptors tend to cluster near on
another in the olfactory epithelium, as shown below for 4 receptor genes in the mouse
Olfactory Neurons send their axons to the glomeruli of the olfactory bulb, where they
synapse on ✅mitral cells
Unlike most neurons, __________ receptors can be regenerated throughout life; they
are replaced by new cells when they die ✅both taste and olfactory
Replacement cells are generated by stem cells in the taste buds (for taste cells) and
olfactory epithelium (for olfactory cells) that divide to create new sensory neurons
✅Since each olfactory receptor cell must send its axons to a specific glomerulus, the
axon of a new cell needs guidance to reach its target
This guidance is partly provided by chemical
signals from olfactory ensheathing cells (OECs),
which promote axon growth, and are similar to
Schwann cells because they ensheath olfactory
neuron axons (but do not myelinate them)
OECs can be transplanted into the spinal cord
where they can promote regrowth of damaged
spinal axons! This is a promising new therapeutic
approach for spinal cord injury
Odor Coding ✅Every identifiable odor is composed from
unique combinations of atoms and molecules
This unique chemical composition activates a
unique pattern of olfactory sensory neurons,
and thus a unique pattern of glomeruli
In the example shown at left, a specific odor
activates just two of the glomeruli,
generating a pattern of brain activity that is a
,unique neural signature for that odor
• Brain structures that receive olfactory inputs
can identify patterns of glomeruli activation
to recognize a vast number of different odors
• its estimated that humans, despite their limited
olfactory senses, can discriminate over 1
trillion odors!
Sparse versus distributed coding ✅Neural populations can represent information using
a sparse or distributed coding scheme
Sparse code ✅each item of information (for example, an odor) is represented by
activating (or inactivating) a small percentage of neurons in the population
• Advantages: Easy to read and decode (if you know which cell is firing, you know the
odor)
• Disadvantages: Low capacity (can only represent as many items as there are neurons)
Distributed code ✅each item of information is represented by activating (or
inactivating) a larger percentage of neurons in the population (for a maximally sparse
representation, each item would activate about half of the neurons, but which neurons
are activated would differ for every item)
• Advantages: High capacity (there are a huge number of possible patterns, so many
items can be encoded)
• Disadvantages: Difficult to read and decode
Population coding of odor identity ✅• The images below show dark shading in regions
of the mouse olfactory bulb that are activated by a specific odor
• Notice that the two odors activate different patterns of glomeruli
• This indicate a distributed code that allows the animal to discriminate between the two
odors
Olfactory Pathways ✅1st order olfactory sensory neurons (olfactory receptors) project
to 2nd order mitral cells in
olfactory bulb
2nd order mitral cells relay information from olfactory bulb to 3rd order targets in several
brain areas:
• Prepyriform cortex (PC) is the primary olfactory cortex, which performs odor
discrimination (notice that olfactory signals do not pass through the thalamus to get to
prepiriform cortex!)
• Amygdala is involved in attaching "motivational valence" to odors (pleasant, noxious,
etc.)
• Hypothalamus regulates homeostasis & drives hormonal responses to certain odors
(e.g., pheromones)
, Projections from 3rd order neurons relay olfactory signals to the medial dorsal thalamus
which relays odor information to other areas of cortex, including:
• Insular cortex, which integrates olfaction, taste, and somatosensation to encode
flavors
• Orbitofrontal cortex, which allows odors to influence decisions and behavior
• Entorhinal cortex and hippocampus, which help to weave odors into our episodic
memories of past experiences
Many vertebrates have a _______ system to
detect pheromones—odor signals secreted by
other animals. ✅vomeronasal; Receptor cells for this system are found in a
vomeronasal organ (VNO) near the olfactory epithelium; Evidence suggests that
humans do not have a functional vomeronasal organ.
When a ______ (defined as any substance that can be tasted) touches the tongue, it is
dissolved into the saliva and oozes into the grooves surrounding tiny bumps on the
tongue called _________ ✅tastant; papillae
Each papilla is lined with one or
more _________, which are
hollow sacs with walls made out
of taste receptor cells ✅taste buds
Tastants dissolved in saliva flow
into the taste bud sac through a
hole called the taste pore ✅
Each taste receptor cell extends
hair-like cilia into the taste bud
sac, and each cilium's membrane
expresses one of five types of
taste receptor: ✅- Salty
- Sweet
- Bitter
- Sour
- Umami
The five basic tastes ✅Salty taste cells are specialized for detecting
sodium, and to a lesser extent other salts
• Sour taste cells are specialized for detecting
acids
• Sweet taste cells are specialized for
detecting sugars
• Bitter taste cells are specialized for detecting
noxious ad potentially toxic substances
