The Chemical Senses

Question 1

Chemoreceptor

Answer 1

A protein responsive to chemical stimuli - in arteries of the neck measure CO2/O2 levels in our blood

Question 2

Glomerulus

Answer 2

A cluster of nerve endings in the olfactory bulb

Question 3

Gustation

Answer 3

The perception of taste

Question 4

Gustatory Nucleus

Answer 4

Region of the medulla that conveys gustatory signals

Question 5

Olfaction

Answer 5

The perception of smell

Question 6

Olfactory Blub

Answer 6

Region to which olfactory receptor cells project

Question 7

Olfactory Cortex

Answer 7

Region of the cortex that perceives smell

Question 8

Olfactory Epithelium

Answer 8

Mucus covered layer into which cilia of olfactory receptor cells protrude to facilitate odour detection

Question 9

Olfactory Receptor cell

Answer 9

Neuronal cell responsible for odour detection

Question 10

Papilla

Answer 10

A small rounded protuberance on the tongue.

Papillae:

• Ridge-shaped (foliate)
• Pimple-shaped (Valiate)
• Mushroom-shaped (fungiform)

Each one contains taste buds, ranging from 1 taste bud to 100s of taste buds.

A taste pore is the chemically sensitive end of a taste receptor cell, in which chemicals dissolved in saliva can interact directly with the taste cells.

Question 11

Pheromone

Answer 11

A chemical substance produced and released into the environment by an animal that affects the behaviour or physiology of others of its species

Question 12

Population Coding

Answer 12

The temporal and spatial frequencies of sensory signals from multiple neurons

Question 13

Primary gustatory cortex

Answer 13

Region of the cortex that perceives taste

Question 14

Taste bud

Answer 14

A cluster of taste receptor cells. The taste buds contain taste receptor cells, ranging from 50-150. The taste buds are surrounded by basal cells (precursors of taste buds) and gustatory afferent axons.

Question 15

Taste receptor cell

Answer 15

Sensory thalamic nucleus through which gustatory signals are transmitted. Form synapses with gustatory afferent axons.

Question 16

Ventral Posterior Medial Nucleus

Answer 16

Sensory thalamic nucleus through which gustatory signals are transmitted

Question 17

How are chemical irritants detected?

Answer 17

Nerve endings in skin/mucous membranes warn us of chemical irritants.

Question 18

What measures acidity levels in our body?

Answer 18

Sensory nerve endings in muscle respond to acidity- burning feeling that comes with exercise and O2 debt

Question 19

What are the 5 tastes we can recognise?

Answer 19

Saltiness, Sourness, Sweetness, bitterness and Umami

Question 20

How do we perceive flavours?

Answer 20

Each food type activates a different combination of each of the 5 tastes. This makes each food type unique.

Not just this:

• Touch: texture and temperature
• Smell

Therefore brain combines taste, touch and smell

Question 21

What organs are primarily in charge of taste?

Answer 21

• Taste is a primary function of the taste.
• Palate: Roof of mouth, separating oral and nasal cavities- taste buds present in palate
• Epiglottis: Leaf shaped cartilage covering laryngeal inlet- taste buds present in epiglottis
• Pharynx and Nasal Cavity: Odours can pass, via the pharynx, to the nasal cavity to be detected by olfactory receptors.

Question 22

What are each parts of the tongue responsible for?

Answer 22

Tip = Sweetness
Back = Bitterness
Sides: Saltiness and Sourness
Doesn’t necessarily localise tastes, most of the tongue is able to taste all the tastes

Question 23

Transduction

Answer 23

The process by which an environmental stimulus causes an electrical response in an sensory receptor cell. Taste are transduced via different mechanisms.

Question 24

Saltiness Transduction Mechanism

Answer 24

• Na+ passes through Na+ selective channels, down its concentration
gradient
• This depolarises the taste cell, activating voltage-gated Ca2+ channels
(VGCCs)
• Vesicular release of neurotransmitter is elicited, and gustatory
afferents activated

Special Na+ selective channel (amiloride sensitive) used to detect
low concentrations of salt – insensitive to voltage and generally
stays open

Question 25

Sourness Transduction Mechanism

Answer 25

H+ may affective sensitive taste receptors in several ways – although
these processes are not well understood
• Vesicular release of neurotransmitter is elicited, and gustatory
afferents activated
• However, it is likely that H+ can pass through proton channels and bind
to and block K+ selective channels
• This leads to depolarisation of the taste cell, activating VGSC and
VGCCs

Question 26

Bitterness, Sweetness and Umami Transduction

Answer 26

GPCR mechanisms via T1 and T2 taste receptors.
T1Rs and T2Rs are G-protein coupled receptors (GPCRs)
and are Gq coupled – evidence suggests that they form dimers
I. Bitter substances are detected by approximately 25
T2Rs
II. Sweet substances are detected by one receptor –
T1R2 and T1R3 proteins
III. Umami substances are detected by one receptor –
T1R1 and T1R3 proteins

Question 27

Bitterness Transduction Mechanism

Answer 27

Bitter tastants binds to T2R, which is coupled to the G-
protein Gq
• This stimulates the enzyme phospholipase C (PLC), leading
to the production of inositol triphosphate (IP3)
IP3 intracellularly activates a special type of Na+ ion
channel and releases Ca2+ from intracellular storage sites
• Both these actions depolarise the taste cell – release of ATP is
elicited, and gustatory afferents are activated

Question 28

Sweetness Transduction Mechanism

Answer 28

Sweet tastants binds to dimer receptor formed from T1R2 and
T1R3, which is coupled to the G-protein Gq

The same signal transduction mechanism as bitterness occurs

Question 29

Why do we not confuse bitter, sweet and umami tastes?

Answer 29

Taste cells express either bitter, sweet or umami receptors
• In turn, bitter, sweet and umami taste cells connect to different
gustatory axons

Question 30

Umami Transduction Mechanism

Answer 30

Umami tastants bind to dimer receptor formed from T1R1and
T1R3, which is coupled to the G-protein Gq
The same signal transduction mechanism as bitterness and sweetness
occurs
Shares T1R3 protein with sweetness – T1R subunit determines
specificity to umami