Module B: Chemical Senses

Question 1

Sensation

Answer 1

Detection of physical stimulus

Question 2

Perception

Answer 2

Interpretation modified by experience

Question 3

Modality (type)

Answer 3

class of stimulus

Question 4

Location

Answer 4

position of stimulus in space

Question 5

Intensity

Answer 5

measure of the severity or amount of the stimulus

Question 6

Timing

Answer 6

Onset, duration and offset of stimulus

Question 7

5 major modalities

Answer 7

vision, hearing, taste, smell and touch

Question 8

4 other modalities

Answer 8

Vestibular(balance)
electrosensory
magnetic
additional somatosensory (pain, temperature, itch, proprioception)

Question 9

Transduction

Answer 9

sensory receptors transform signal into electrical energy

Question 10

Receptor potential

Answer 10

Excitation leads to electrical responce

Question 11

Receptor specificity

Answer 11

Receptors morphologically specialised for specific form of energy

Question 12

Labelled line

Answer 12

neurons from specific receptors are modality specific

Question 13

Mechanoreceptors:

Answer 13

detect mechanical deformation

Question 14

Mechanical transduction mechanism (and example)

Answer 14

mechanical stimulus acts directly on cell structures to cause receptor potential

Eg muscle spindle detecting muscle displacement or position
Eg detection of vibration by the cochlear

Question 15

Chemical transduction mechanism

Answer 15

Chemical utilise intracellular second messenger systems or sense chemical directly (eg salt on tongue)

Question 16

Photoreceptor transduction mechanism

Answer 16

Photoreceptors utilize intracellular second messenger systems

Question 17

Chemoreceptors in olfactory epithelium and photoreceptors in retins used what transduction mechanism

Answer 17

2nd messenger system

Question 18

Spatial arrangement of receptors: (x3)

Answer 18

• provides information on location of stimulus source on body or in space
• enables discrimination of size and shape of object
• enables resolution of fine detail of stimulus or environment

Question 19

What defines the resolution of the stimulus(sensation)

Answer 19

The density of receptors

Question 20

What area of the retina has a high density of receptors and a small receptor field

Answer 20

Fovea of retina

Question 21

Intensity is determined by the stimulus amplitude which is…

Answer 21

the number of neurons activated and frequency (rate) of neural impulses

Question 22

(Timing) onset, duration and offset of stimulus is coded by…

Answer 22

Frequency of the neural activity

Question 23

Sensory input from the eyes goes to the

Answer 23

Thalamus (in forebrain)

Question 24

Sensory information from the ears and skin goes to the…

Answer 24

midbrain then thalamus

Question 25

Sensory input from taste goes to...

Answer 25

the medulla oblongata then thalamus

Question 26

Sensory input from smell goes to...

Answer 26

primitive part of cortex then thalamus

Question 27

What are 5 sensory areas in the forebrain

Answer 27

- Primary visual cortex - temporal lobe - primary sensory cortex - Parietal lobe - Frontal lobe

Question 28

Pericheral sensory organs project to the cortex through...

Answer 28

polysynaptic pathways

Question 29

Diversity and adaptation: | Fish have weak ___ but many use ____ and ____

Answer 29

weak vision | use magnetic electrical fields and presure

Question 30

Diversity & adaptation: | In fish, esp Sharks, they use the _______ system, which uses ____-receptors to detect variations in ____

Answer 30

lateral line system; mechano-receptors; pressure

Question 31

Diversity & adaptation: | Insects have ____ organs on thorax or legs for localization

Answer 31

hearing

Question 32

Whats the oldest and most common sensory system that even brainless bacteria can detect and react to

Answer 32

Chemical senses

Question 33

Gustation = | Olfaction =

Answer 33

``` Gustation = taste Olfaction = smell ```

Question 34

Sensory receptors in the tongue, mouth and near the larynx go to the brain via what Cranial nerves?

Answer 34

7 (Facial) 9 (Glossopharyngeal) 10 (Vagus) And go to the Nucleus of the solitary tract (gustatory nucleus), and then ventral posterior medial nucleus of the thalamus, which then goes to the frontal taste cortex (frontal operculum) (see image in slide 4, lecture 2 of chemical senses)

Question 35

List the 3 papillae on the tongue and what are the % of them: (for image of them see slide 5, lecture 2 of chemical senses)

Answer 35

``` Circumvallate papillae (cranial nerve 9) = 50% (aka vallate papillae) Foliate papillae = 25% Fungiform papillae (cranial nerve 7) = 25% ```

Question 36

What are papillae?

Answer 36

Multicellular protuberances surrounded by invaginations in the tongue epithelium. The invaginations form a trench to concentrate tastants. Taste buds are distributed along the lateral surfaces of the papillae protuberances as well as in the trench walls.

Question 37

What is a taste bud made up of?

Answer 37

``` Taste cells (long) + basal cells (circular) +Microvilli (at one end) At apex is a taste pore and the other end has Gustatory afferent axons. ```

Question 38

What are taste cells?

Answer 38

Specilized neuroepithelial receptor cells, they cluster around the taste pore (1mm opening)

Question 39

What is the life time of a taste cell and how are they regenerated?

Answer 39

2 weeks and are regenerated from basal cells

Question 40

How many taste buds are there | How many taste receptor cells per taste bud

Answer 40

- 2000-5000 on the tongue, plate, epiglottis and esophagus | - 50-150 taste receptor cells per taste bud

Question 41

Fungiform papillae (x4)

Answer 41

- Only found on the anterior two-thirds of the tongue - High density - mushroom-like - each one has 3 tastebuds at their apical surface

Question 42

Circumvallate papillae (4)

Answer 42

- x9 circumvallate papillae - align in a V shape (chevron) - a the back of the tongue - each one has 250 taste buds

Question 43

Foliate papillae (x3)

Answer 43

- x2 foliate papillae - present on the posterolateral part of the tongue - each has 600 tastebuds

Question 44

At ___ concentrations papillae are selective to specific stiumuls At ___ concentration they are less sensitive

Answer 44

Low; high

Question 45

Activation of taste cells via a stimulus leads to _____ or _____, and then release of _____ or reduction in activity

Answer 45

depolarization or hyperpolariation | release of neurotransmitter

Question 46

Most taste (cells) receptors respond to 1 or 2 or more taste stimuli

Answer 46

more than 2

Question 47

What are the 5 different tastants? | see slide 9, lec2 of chemical sense for image

Answer 47

- sour - bitter - salty - sweet - umami (savory, meat, protein rich)

Question 48

Salt tastes include:

Answer 48

NaCl | amino acids like glutamate

Question 49

Sour tastes are associated with:

Answer 49

acidity and protons, this indicates the palatability of foods

Question 50

Bitter tastes include:

Answer 50

Plant alkaloids like atropine, quinine, stychnine, indicating foods that might be poisonous

Question 51

Describe a Taste cell/receptor

Answer 51

- Are specilized for sensory transduction - have an apical and basal domain - There are tastant-transducing channels (salt & sour) on the APICAL domain - There are G-protein-coupled receptors (for sweet, umami(aa), bitter) on the APICAL domain - Voltage regulated Na, K, Ca channels that mediate the release of neurotransmitter on the BASAL domain

Question 52

What in the APICAL domain of a taste cell/receptor

Answer 52

- There are tastant-transducing channels ie ion channels (salt & sour) on the APICAL domain - There are G-protein-coupled receptors (for sweet, umami(aa), bitter) on the APICAL domain

Question 53

What in the BASAL domain of a taste cell/receptor

Answer 53

- Voltage regulated Na, K, Ca channels that mediate the release of neurotransmitter on the BASAL domain - Endoplasmic reticulum (release Ca2+)

Question 54

Neurotransmitter from the taste receptor is released onto the terminals of...

Answer 54

peripheral sensory afferents

Question 55

ATP, GABA and ______ are neurotransmitters found in taste cells

Answer 55

Serotonin (with serotonin receptors found on the sensory afferents)

Question 56

Transduction mechanism of salt tastants:

Answer 56

Tastants can interact directly with Na+ ion channels by passing through them -Then the membrane voltage with influence Ca2+ channels on basal membrane and hense neurotransmitter release

Question 57

Transduction mechanism of sour tastants:

Answer 57

Tastants can interact directly with K+ ion channels by passing through them or by blocking K+ channels Then the membrane voltage with influence Ca2+ channels on basal membrane and hense neurotransmitter release

Question 58

Transduction mechanism of bitter, sweet and umami tastants: (x4)

Answer 58

- Tastants bind to G-protein-coupled receptor on apical membrane - This activates Phospholipase C, which increases the synthesis of IP3 (2nd messenger) - IP3 triggers the release of Ca2+ from internal storage sites - Ca2+ opens taste cell ion channels (taste specific), leading to depolarization and transmitter release

Question 59

Bitternes Receptors: | x4

Answer 59

- T2R receptors - 30 different types of T2R receptors - Each taste cell expresses many or all of the 30 bitter receptors, and each taste cell can only send 1 type of signal to its afferent nerve --> not good at telling bitter tastes apart, only know they are bad - Bitter receptors are poison receptors - Use 2nd messenger system

Question 60

Sweet receptors: | x4

Answer 60

- T1R receptors - Need 2 members of the T1R receptor family: T1R2 & T1R3, if you dont have both wont be able to detect sweetness - Use 2nd messenger system - Bitter receptor proteins and sweet receptor proteins are expressed in differnet taste cells (so can distinguish between the 2 tastes)

Question 61

Amino Acid (Umami) receptors: (x2)

Answer 61

- T1R receptors | - Need 2 members of the T1R receptor family: T1R1 & T1R3