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Sensation > smell > Flashcards

smell Flashcards

1
Q

Olfaction

A

The sense of smell

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2
Q

Gustation

A

The sense of taste

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3
Q

Olfactory cleft

A

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

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4
Q

Olfactory epithelium

A

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

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5
Q

Odor

A

A general smell sensation of a particular quality

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6
Q

Odorant

A

Any specific aromatic chemical

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7
Q

Odors (Olfactory sensations)

A
  • Chemical compounds
  • But not every chemical is an odorant
  • In order to be smelled, molecule must be volatile,
    small, and hydrophobic
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8
Q

The human olfactory apparatus

A

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

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9
Q

Olfactory epithelium: The “retina” of the nose

A

Three types of cells:

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

Basal cells: Precursor cells to olfactory sensory
neurons

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10
Q

Olfactory sensory neurons (OSNs)

A

The main cell type in the olfactory epithelium

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

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11
Q

Cilia:

A

Hairlike structures on the dendrites of OSNs.

Contain receptor sites for odorant molecules.

first structures involved in olfactory signal
transduction

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12
Q

Olfactory receptor (OR)

A

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

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13
Q

Cribriform plate

A

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
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14
Q

Anosmia

A

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
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15
Q

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

A

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

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16
Q

Olfactory nerves

A

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

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17
Q

Olfactory bulb

A

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)
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18
Q

Mitral cells

A

The main projective output neurons in the
olfactory bulbs

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19
Q

Tufted cells

A

A secondary class of output neurons in the
olfactory bulbs

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20
Q

Glomeruli

A

Spherical conglomerates containing the
incoming axons of the OSNs

  • Each OSN converges on two glomeruli (one
    medial, one lateral)
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21
Q

Primary olfactory cortex

A

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

22
Q

Amygdala–hippocampal complex

A

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

23
Q

Entorhinal cortex

A

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

Also receives direct projections
from olfactory regions

24
Q

Limbic system

A

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

25
Q

why Olfaction is unique ?

A

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

26
Q

Subtle differences between sensation and perception:

A
  • Sensation occurs when scent is neurally registered
  • Perception occurs when becoming aware of
    Sensations
27
Q

Buck and Axel (1991)

A

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
28
Q

The feel of scent

A
  • 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
29
Q

Shape-pattern theory (correct )

A

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

30
Q

Vibration theory (incorrect)

A

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

31
Q

Specific anosmia

A

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

32
Q

Study of stereoisomers

A
  • 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
33
Q

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

A

We can detect the pattern of activity across various
receptor types

Intensity of odorant also changes which receptors
will be activated

34
Q

How do we process the components in an odorant
mixture?

A

§ 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

35
Q

Odor imagery

A
  • 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

36
Q

Olfactory detection thresholds

A

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

37
Q

Staircase method

A

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

38
Q

Triangle test

A

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

39
Q

Tip-of-the-nose phenomenon

A

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

40
Q

Sense of smell and language: Disconnected, possibly
because

A
  • 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
41
Q

Receptor adaptation

A

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

42
Q

Cross-adaptation

A

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

43
Q

Cognitive habituation

A

(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

44
Q

Three mechanisms involved:

A
  • 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
45
Q

Odor hedonics

A

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

46
Q

Two caveats for theory that odor hedonics are mostly
learned

A
  • 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
47
Q

Neuroanatomical and evolutionary connections between
odor and emotion

A

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

48
Q

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

A

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

49
Q

Vomeronasal organ (VNO)

A

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
50
Q

Pheromone

A

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
51
Q

Releaser pheromone
and Primer pheromone

A

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

Sensation (7 decks)

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