The Chemical Senses Flashcards
Chemoreceptor
A protein responsive to chemical stimuli - in arteries of the neck measure CO2/O2 levels in our blood
Glomerulus
A cluster of nerve endings in the olfactory bulb
Gustation
The perception of taste
Gustatory Nucleus
Region of the medulla that conveys gustatory signals
Olfaction
The perception of smell
Olfactory Blub
Region to which olfactory receptor cells project
Olfactory Cortex
Region of the cortex that perceives smell
Olfactory Epithelium
Mucus covered layer into which cilia of olfactory receptor cells protrude to facilitate odour detection
Olfactory Receptor cell
Neuronal cell responsible for odour detection
Papilla
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.
Pheromone
A chemical substance produced and released into the environment by an animal that affects the behaviour or physiology of others of its species
Population Coding
The temporal and spatial frequencies of sensory signals from multiple neurons
Primary gustatory cortex
Region of the cortex that perceives taste
Taste bud
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.
Taste receptor cell
Sensory thalamic nucleus through which gustatory signals are transmitted. Form synapses with gustatory afferent axons.
Ventral Posterior Medial Nucleus
Sensory thalamic nucleus through which gustatory signals are transmitted
How are chemical irritants detected?
Nerve endings in skin/mucous membranes warn us of chemical irritants.
What measures acidity levels in our body?
Sensory nerve endings in muscle respond to acidity- burning feeling that comes with exercise and O2 debt
What are the 5 tastes we can recognise?
Saltiness, Sourness, Sweetness, bitterness and Umami
How do we perceive flavours?
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
What organs are primarily in charge of taste?
- 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.
What are each parts of the tongue responsible for?
Tip = Sweetness
Back = Bitterness
Sides: Saltiness and Sourness
Doesn’t necessarily localise tastes, most of the tongue is able to taste all the tastes
Transduction
The process by which an environmental stimulus causes an electrical response in an sensory receptor cell. Taste are transduced via different mechanisms.
Saltiness Transduction Mechanism
• 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
Sourness Transduction Mechanism
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
Bitterness, Sweetness and Umami Transduction
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
Bitterness Transduction Mechanism
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
Sweetness Transduction Mechanism
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
Why do we not confuse bitter, sweet and umami tastes?
Taste cells express either bitter, sweet or umami receptors
• In turn, bitter, sweet and umami taste cells connect to different
gustatory axons
Umami Transduction Mechanism
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
