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MD4001 Week 7 > 3. Special senses: Taste and smell > Flashcards

3. Special senses: Taste and smell Flashcards

1
Q

Where are taste buds found?

A

Taste buds found on our tongue, palate, tonsilar pillars, epiglottis and a few on the proximal oesophagus.

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2
Q

What is the distribution of taste buds in the mouth?

A

Over 3 types of papillae of the tongue:

  1. Circumvallate
  2. Fungiform
  3. Foliate
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3
Q

Describe the distribution of taste buds in the mouth:

  1. Circumvallate
  2. Fungiform
  3. Foliate
A

They a distributed differentially over three types of papillae of the tongue, these are:
1. Circumvallate (located at the posterior of the tongue in a V shape), large numbers
of taste buds are found on the walls of these papillae
2. Fungiform (found at the anterior surface of the tongue), a moderate number of
taste buds are found here, and
3. Foliate (located in the folds on the lateral margins of the tongue), a moderate number are found

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4
Q

Structure of a taste bud?

A

Taste pore and microvilli projecting from it
Taste cell and support cells
Synpases –> Sensory neurones

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5
Q

What chemicals do taste buds detect?

A 
Via 13 receptors:
2 potassium
2 sodium
1 chloride
1 adenosine 1 inosine
2 sweet
2 bitter
1 glutamate 1 H+

Receptor depolarise taste cells either via ionotropic or metabotropic pathways

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6
Q

What are the 5 categories of taste buds?

A
  1. Sour
  2. Salty
  3. Sweet
  4. Bitter
  5. Umami
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7
Q

What chemical cause stimulation of the “sour” category of taste buds?

A

H+ ions

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8
Q

What chemical cause stimulation of the “salty” category of taste buds?

A

Mainly Na+ ions

Also K+ ions

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9
Q

What chemical cause stimulation of the “sweet” category of taste buds?

A

SUGAR and a wide variety of other chemicals like:

  • Glycols
  • Alcohols
  • Ketones
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10
Q

What chemical cause stimulation of the “bitter” category of taste buds?

A

Same as sweet but also ALKALOIDS found in toxic plants.

Note sweet=
SUGAR and a wide variety of other chemicals like:
-Glycols
-Alcohols
-Ketones
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11
Q

What chemical cause stimulation of the “umami” category of taste buds?

A

L glutamate, found in meats and aged cheese

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12
Q

How does taste threshold vary and why

A

Salty taste from NaCl - 0.01M (Low)
Sweet taste from sucrose- 0.01M (Low)
Sour taste for H ions- 0.0009M (Mid)
Bitter taste from quinine- 0.000008M (High)

Because bitter tastes are generally indicative of a more dangerous substance, sensitivity needs to be high

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13
Q

What is the neuronal pathway for taste?

A 
Via
CN VII= Ant 2/3 tongue and soft palate
CN IX- Post 1/3 tongue 
CN X- Vallucula 
--> Solitary nucleus
--> VPM of thalamus 
--> Cortical areas of taste

Remember that gustation has a limbic component via the thalamus , and can activate brainstem nuclei for salivation, or vomiting

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14
Q

What is the cortical area of taste?

A

Most inf portion of the post-central gyrus extending into the insula

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15
Q

The two main sensory inputs to recognition of a foodstuff are..

A

Olfaction and gustation

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16
Q

What makes up the olfaction system?

A

Olfactory epithelium

Receptor cells (bipolar neurons)

Axons that project through the base of the skull to the olfactory bulb

Neuronal tract to multiple olfactory destinations in the brain

17
Q

Stages of odorant receptor activation?

A
  1. An odorant molecule binds to the receptor of the primary olfactory neurone
  2. The activated receptor activates a G protein, which stimulates adenylyl cyclase to convert ATP to cAMP
  3. cAMP activates a cation channel, making it permeable to Na+ and Ca2+
18
Q

Result of odorant receptor activation?

A

Activation of the receptors cause the cells to depolarise as generator potentials.

Sufficient depolarisation leads to action potentials, and the frequency of AP generation is proportional to the Log concentration of the odorant

19
Q

Process of odour detection?

A
  1. The lower end of the bipolar neurons extends into a layer of mucus secreted from the Bowman gland in the olfactory epithelium, forming and olfactory knob.
  2. From this develops olfactory cilia which detect the odorants in the nasal cavity
  3. The bipolar neurons continually develop and replace each other over time
20
Q

Journey from mouth/nose to the olfactory bulb

A

High in the nasal cavity is the 2.5cm squared area of olfactory epithelium

The odorant detectors are bipolar neurons originally derived from the CNS but now only connected by central processes

These central processes project up through the cribriform plate into the olfactory bulb of CN I from the olfactory epithelium

21
Q

Olfactory bulb to Cortex:

  1. Olfactory information is transferred from the bipolar cells to ________ of mitral cells found in the neuropil of the glomeruli in the bulb
  2. There is a massive convergence at this point which helps ensure _______
  3. Also synapsing in the glomeruli are Tufted cells which are thought to provide a form of ‘_______ inhibition’ for signal enhancement
  4. Within the bulb, it is generally thought that specific glomeruli respond to particular odorants in a dose dependent manner.
A

Olfactory bulb to Cortex

  1. Olfactory information is transferred from the bipolar cells to dendrites of mitral cells found in the neuropil of the glomeruli in the bulb
  2. There is a massive convergence at this point which helps ensure sensitivity
  3. Also synapsing in the glomeruli are Tufted cells which are thought to provide a form of ‘lateral inhibition’ for signal enhancement
  4. Within the bulb, it is generally thought that specific glomeruli respond to particular odorants in a dose dependent manner.
22
Q

What are the mechanisms of lateral inhibition in olfaction?

A
  1. Synapsing in the glomeruli are TUFTED CELLS which are thought to provide a form of ‘lateral inhibition’
  2. There is a second layer of lateral inhibition where GRANULE CELLS cells in the bulb make dendritic connections between mitral cells.
23
Q

Odours are grouped into the following categories (these are not primary odours, but formed of a spectrum of odours in specific proportions), name the 7 groups?

A
  1. Camphoraceous 2. Musky
  2. Floral
  3. Pepperminty
  4. Ethereal 6. Pungent 7. Putrid
24
Q

Odour selectivity:
There are over 300 genes in humans for different odorant receptors, and it seems that each bipolar neuron expresses _____ of these genes per neuron.
The implication is that there are a large number of chemicals that can be detected by the olfactory epithelium, which is complicated by each receptor potentially responding to a number of odorants.
Each smell we recognise is certainly a pattern of ______ receptor cells and glomeruli ______ responding in a proportional way to the odorants.

A

Odour selectivity
There are over 300 genes in humans for different odorant receptors, and it seems that each bipolar neuron expresses one of these genes per neuron.
The implication is that there are a large number of chemicals that can be detected by the olfactory epithelium, which is complicated by each receptor potentially responding to a number of odorants.
Each smell we recognise is certainly a pattern of activated receptor cells and glomeruli circuitry responding in a proportional way to the odorants.

25
Q

What are the neuronal projections from the olfactory bulb?

A

—-> Paleocortex: entorhinal cortex, olfactory tubercle, pifiform cortex

—> Amygdala + limbic system

–> Brainstem

–> Neocortex: Orbitofrontal cortex via mediodorsal nucleus of thalamus. Thought to be involved with the conscious discernment of odour and so can be under conscious control for salience

26
Q

What are the 4 pathways for olfaction?

A
  1. LATERAL OLFACTORY PATHWAY
    Feeds into piriform cortex and pre-piriform cortex in the temporal lonbe
  2. MEDIAL OLFACTORY PATHWAY
    Feeds into limbic system and encodes emotional aspects of olfaction and memory
  3. Involves in likes and dislikes for taste + visceral reactions via brainstem. Not via the thalamus
  4. To the orbitofrontal cortex via thalamus. Thought to be involved with the conscious discernment of odour and so can be under conscious control for salience
27
Q

What is anosmia?

A

Loss of smell sense

28
Q

Examples of nasal/sinus disease?

A
  • Colds
  • Polyps
  • Other blockages
29
Q

What is parosmia?

Cause

A

A distorted often unpleasant sense of smell caused by damage to the lining at the top of the nose

Cause: Upper respiratory viral infections

30
Q

Consequence to olfaction by head trauma?

A
  • leading to damage to frontal lobe processing
  • Leading to damage to ascending nerves at cribriform plate
  • Permanent compression of the nasal passages
31
Q

Problems with the sense of smell - Anosmia?

A 
Nasal / sinus disease (25%) 
Parosmia (20%) 
Congenital anosmia (1%)
Alzheimer's preceding (2-5%)
Idiopathic anosmia (25%)
Head Trauma (15%)

MD4001 Week 7 (8 decks)

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