smell

Question 1

Olfaction

Answer 1

The sense of smell

Question 2

Gustation

Answer 2

The sense of taste

Question 3

Olfactory cleft

Answer 3

A narrow space at the back of the
nose into which air flows, where the main olfactory
epithelium is located

Question 4

Olfactory epithelium

Answer 4

A secretory mucosa in the
human nose whose primary function is to detect
odorants in the inspired ai

Question 5

Odor

Answer 5

A general smell sensation of a particular quality

Question 6

Odorant

Answer 6

Any specific aromatic chemical

Question 7

Odors (Olfactory sensations)

Answer 7

• Chemical compounds
• But not every chemical is an odorant
• In order to be smelled, molecule must be volatile,
  small, and hydrophobic

Question 8

The human olfactory apparatus

Answer 8

Unlike other senses, smell is tacked onto an organ
with another purpose—the nose

Primary purpose: To filter, warm, and humidify
air we breathe

Nose contains small ridges, olfactory cleft, and
olfactory epithelium

Question 9

Olfactory epithelium: The “retina” of the nose

Answer 9

Three types of cells:

Supporting cells: Provides metabolic and
physical support for the olfactory sensory
neurons

Basal cells: Precursor cells to olfactory sensory
neurons

Question 10

Olfactory sensory neurons (OSNs)

Answer 10

The main cell type in the olfactory epithelium

OSNs are small neurons located beneath a
watery mucous layer in the epithelium

Question 11

Cilia:

Answer 11

Hairlike structures on the dendrites of OSNs.

Contain receptor sites for odorant molecules.

first structures involved in olfactory signal
transduction

Question 12

Olfactory receptor (OR)

Answer 12

The region on the cilia of OSNs
where odorant molecules bind

Takes seven or eight odor molecules binding to a
receptor to initiate an action potential

Question 13

Cribriform plate

Answer 13

A bony structure riddled with tiny holes,
at the level of the eyebrows, that separates the nose
from the brain

• Axons from OSNs pass through the tiny holes to
  enter the brain

Question 14

Anosmia

Answer 14

The total inability to smell, most often
resulting from sinus illness or head trauma

• A hard blow to the front of the head can cause the
  cribriform plate to be jarred back or fractured,
  slicing off the fragile olfactory neurons
• Anosmia causes a profound loss of taste as well
  as smell

Question 15

how are Olfactory receptor cells different from all other
sensory receptor cells ?

Answer 15

They are not mediated by any
protective barrier and make direct contact with the
brain

• Contrast with visual receptors that are protected by
  cornea, hearing receptors protected by eardrum,
  taste buds are buried in papillae
• Therefore, many drugs can be inhaled
• OSN axons are among the thinnest and slowest in
  the body

§ Takes longer to perceive odors compared to
other senses

Question 16

Olfactory nerves

Answer 16

The first pair of cranial nerves. The
axons of the OSNs bundle together after passing
through the cribriform plate to form the olfactory nerve

Question 17

Olfactory bulb

Answer 17

The blueberry-sized extension of the
brain just above the nose, where olfactory information
is first processed

• There are two olfactory bulbs, one in each brain
  hemisphere, corresponding to the left and right
  nostrils. Connections are ipsilateral (same side of
  body)

Question 18

Mitral cells

Answer 18

The main projective output neurons in the
olfactory bulbs

Question 19

Tufted cells

Answer 19

A secondary class of output neurons in the
olfactory bulbs

Question 20

Glomeruli

Answer 20

Spherical conglomerates containing the
incoming axons of the OSNs

• Each OSN converges on two glomeruli (one
  medial, one lateral)

Question 21

Primary olfactory cortex

Answer 21

The neural area where
olfactory information is first processed, which includes
the amygdala–hippocampal complex and the
entorhinal cortex

Question 22

Amygdala–hippocampal complex

Answer 22

conjoined regions of the amygdala and hippocampus, which are
key structures in the limbic system.

important for the unique emotional and associative
properties of olfactory cognition

Question 23

Entorhinal cortex

Answer 23

A phylogenetically old cortical region
that provides the major sensory association input into
the hippocampus.

Also receives direct projections
from olfactory regions

Question 24

Limbic system

Answer 24

The encompassing group of neural
structures that includes the olfactory cortex, the
amygdala, the hippocampus, the piriform cortex, and
the entorhinal cortex

Question 25

why Olfaction is unique ?

Answer 25

Olfaction is unique among the senses for its direct and intimate connection to the limbic system Olfaction’s unique connection to the limbic system explains why scents tend to have such strong emotion Associations

Question 26

Subtle differences between sensation and perception:

Answer 26

* Sensation occurs when scent is neurally registered * Perception occurs when becoming aware of Sensations

Question 27

Buck and Axel (1991)

Answer 27

showed that genome contains about 1000 different olfactory receptor genes; each codes for a single type of OR * All mammals have pretty much the same set of 1000 genes. However, some genes are nonfunctional pseudogenes § Dogs and mice: About 20% are pseudogenes § Humans: Between 60% and 70% are pseudogenes

Question 28

The feel of scent

Answer 28

* Odorants can stimulate somatosensory system through polymodal nociceptors (touch, pain, temperature receptors) * These sensations are mediated by the trigeminal nerve (cranial nerve V) * Often, it is impossible to distinguish between sensations traveling up cranial nerve I from olfactory receptors and those traveling up cranial nerve V from somatosensory receptors

Question 29

Shape-pattern theory (correct )

Answer 29

The current dominant theory. Contends that different scents—as a function of odorant-shape that fit together like a puzzle

Question 30

Vibration theory (incorrect)

Answer 30

Proposes that every perceived smell has a different vibrational frequency, and that molecules that produce the same vibrational frequencies will smell the same

Question 31

Specific anosmia

Answer 31

The inability to smell one specific compound amid otherwise normal smell perception

Question 32

Study of stereoisomers

Answer 32

* Molecules that are mirror-image rotations of one another; although they contain the same atoms, they can smell completely different * Vibration theory also cannot explain this Phenomenon

Question 33

How can we detect so many different scents if our genes only code for about 1000 olfactory receptors?

Answer 33

We can detect the pattern of activity across various receptor types Intensity of odorant also changes which receptors will be activated

Question 34

How do we process the components in an odorant mixture?

Answer 34

§ Analyses: Example from auditory mixtures. High note and low note can be played together but we can detect each individual note § Synthesis: Example from color mixtures. Mixing red and green lights results in yellow light, but we cannot separately perceive the red and green in the yellow

Question 35

Odor imagery

Answer 35

* Humans have little or no ability to conjure odor “images” § We do not think in smell very well § We do not imagine smells very well—dreams with olfactory sensations are very rare

Question 36

Olfactory detection thresholds

Answer 36

Women: Generally lower thresholds than men, especially during ovulatory period of menstrual cycles, but their sensitivity is not heightened during pregnancy

Question 37

Staircase method

Answer 37

Method for determining the concentration of a stimulus required for detection at a threshold level Stimulus is presented in increasing concentrations until detection is indicated § Then, concentration is decreased until detection ceases § Ascending and descending sequence is repeated several times and concentrations at which reversals occur are averaged to determine threshold detection level

Question 38

Triangle test

Answer 38

Participant is given three odors to smell, two of which are the same and one is different § Participant must identify the odd odor § The order of the three odors is varied and tested several times to increase accuracy

Question 39

Tip-of-the-nose phenomenon

Answer 39

The inability name an odorant, even though it is very familiar

Question 40

Sense of smell and language: Disconnected, possibly because

Answer 40

* Olfactory information is not integrated in thalamus prior to processing in cortex * Majority of olfactory processing occurs in right side of brain while language processing occurs in left side of brain

Question 41

Receptor adaptation

Answer 41

The biochemical phenomenon that occurs after continuous exposure to an odorant, whereby the receptors stop responding to the odorant and detection Ceases

Question 42

Cross-adaptation

Answer 42

The reduction in detection of an odorant following exposure to another odorant

Question 43

Cognitive habituation

Answer 43

(Nose blindness)The psychological process by which, after long-term exposure to an odorant, one is no longer able to detect that odorant or has very diminished detection ability

Question 44

Three mechanisms involved:

Answer 44

* Olfactory receptors internalized into cell bodies during odor adaptation may be hindered after continuous exposure, take longer to recycle * Odorant molecules may be absorbed into bloodstream, causing adaptation to continue * Cognitive-emotional factors

Question 45

Odor hedonics

Answer 45

The liking dimension of odor perception, typically measured with scales pertaining to an odorant’s perceived pleasantness, familiarity, and intensity

Question 46

Two caveats for theory that odor hedonics are mostly learned

Answer 46

* Trigeminally irritating odors may elicit pain responses, and all humans have an innate drive to avoid pain * There is potential variability in receptor genes and pseudogenes that are expressed across Individuals

Question 47

Neuroanatomical and evolutionary connections between odor and emotion

Answer 47

Orbitofrontal cortex: Olfaction is processed here § Also the cortical area for assigning affective value (i.e., hedonic judgment)

Question 48

Animals that rely on smell for survival: Olfactory system has two subdivisions:

Answer 48

Main olfactory bulb (MOB): The structure that we have been referring to as the “olfactory bulb,” but for animals that have two olfactory bulbs we use this term § Accessory olfactory bulb (AOB): A smaller neural structure located behind the MOB that receives input from the vomeronasal organ

Question 49

Vomeronasal organ (VNO)

Answer 49

A chemical sensing organ at the base of the nasal cavity with a curved tubular shape * Evolved to detect chemicals that cannot be processed by the olfactory epithelium, such as large and/or aqueous molecules—the types of molecules that constitute pheromones

Question 50

Pheromone

Answer 50

A chemical emitted by one member of a species that triggers a physiological or behavioral response in another member of the same species * Pheromones are signals for chemical communication and do not need to have any smell

Question 51

Releaser pheromone and Primer pheromone

Answer 51

Releaser pheromone: Triggers an immediate behavioral response among conspecifics Primer pheromone: Triggers a physiological (often hormonal) change among conspecifics * This effect usually involves prolonged pheromone Exposure