Module B: Chemical Senses Flashcards
Sensation
Detection of physical stimulus
Perception
Interpretation modified by experience
Modality (type)
class of stimulus
Location
position of stimulus in space
Intensity
measure of the severity or amount of the stimulus
Timing
Onset, duration and offset of stimulus
5 major modalities
vision, hearing, taste, smell and touch
4 other modalities
Vestibular(balance)
electrosensory
magnetic
additional somatosensory (pain, temperature, itch, proprioception)
Transduction
sensory receptors transform signal into electrical energy
Receptor potential
Excitation leads to electrical responce
Receptor specificity
Receptors morphologically specialised for specific form of energy
Labelled line
neurons from specific receptors are modality specific
Mechanoreceptors:
detect mechanical deformation
Mechanical transduction mechanism (and example)
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
Chemical transduction mechanism
Chemical utilise intracellular second messenger systems or sense chemical directly (eg salt on tongue)
Photoreceptor transduction mechanism
Photoreceptors utilize intracellular second messenger systems
Chemoreceptors in olfactory epithelium and photoreceptors in retins used what transduction mechanism
2nd messenger system
Spatial arrangement of receptors: (x3)
- 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
What defines the resolution of the stimulus(sensation)
The density of receptors
What area of the retina has a high density of receptors and a small receptor field
Fovea of retina
Intensity is determined by the stimulus amplitude which is…
the number of neurons activated and frequency (rate) of neural impulses
(Timing) onset, duration and offset of stimulus is coded by…
Frequency of the neural activity
Sensory input from the eyes goes to the
Thalamus (in forebrain)
Sensory information from the ears and skin goes to the…
midbrain then thalamus
Sensory input from taste goes to…
the medulla oblongata then thalamus
Sensory input from smell goes to…
primitive part of cortex then thalamus
What are 5 sensory areas in the forebrain
- Primary visual cortex
- temporal lobe
- primary sensory cortex
- Parietal lobe
- Frontal lobe
Pericheral sensory organs project to the cortex through…
polysynaptic pathways
Diversity and adaptation:
Fish have weak ___ but many use ____ and ____
weak vision
use magnetic electrical fields and presure
Diversity & adaptation:
In fish, esp Sharks, they use the _______ system, which uses ____-receptors to detect variations in ____
lateral line system; mechano-receptors; pressure
Diversity & adaptation:
Insects have ____ organs on thorax or legs for localization
hearing
Whats the oldest and most common sensory system that even brainless bacteria can detect and react to
Chemical senses
Gustation =
Olfaction =
Gustation = taste Olfaction = smell
Sensory receptors in the tongue, mouth and near the larynx go to the brain via what Cranial nerves?
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)
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)
Circumvallate papillae (cranial nerve 9) = 50% (aka vallate papillae) Foliate papillae = 25% Fungiform papillae (cranial nerve 7) = 25%
What are papillae?
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.
What is a taste bud made up of?
Taste cells (long) + basal cells (circular) +Microvilli (at one end) At apex is a taste pore and the other end has Gustatory afferent axons.
What are taste cells?
Specilized neuroepithelial receptor cells, they cluster around the taste pore (1mm opening)
What is the life time of a taste cell and how are they regenerated?
2 weeks and are regenerated from basal cells
How many taste buds are there
How many taste receptor cells per taste bud
- 2000-5000 on the tongue, plate, epiglottis and esophagus
- 50-150 taste receptor cells per taste bud
Fungiform papillae (x4)
- Only found on the anterior two-thirds of the tongue
- High density
- mushroom-like
- each one has 3 tastebuds at their apical surface
Circumvallate papillae (4)
- x9 circumvallate papillae
- align in a V shape (chevron)
- a the back of the tongue
- each one has 250 taste buds
Foliate papillae (x3)
- x2 foliate papillae
- present on the posterolateral part of the tongue
- each has 600 tastebuds
At ___ concentrations papillae are selective to specific stiumuls
At ___ concentration they are less sensitive
Low; high
Activation of taste cells via a stimulus leads to _____ or _____, and then release of _____ or reduction in activity
depolarization or hyperpolariation
release of neurotransmitter
Most taste (cells) receptors respond to 1 or 2 or more taste stimuli
more than 2
What are the 5 different tastants?
see slide 9, lec2 of chemical sense for image
- sour
- bitter
- salty
- sweet
- umami (savory, meat, protein rich)
Salt tastes include:
NaCl
amino acids like glutamate
Sour tastes are associated with:
acidity and protons, this indicates the palatability of foods
Bitter tastes include:
Plant alkaloids like atropine, quinine, stychnine, indicating foods that might be poisonous
Describe a Taste cell/receptor
- 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
What in the APICAL domain of a taste cell/receptor
- 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
What in the BASAL domain of a taste cell/receptor
- Voltage regulated Na, K, Ca channels that mediate the release of neurotransmitter on the BASAL domain
- Endoplasmic reticulum (release Ca2+)
Neurotransmitter from the taste receptor is released onto the terminals of…
peripheral sensory afferents
ATP, GABA and ______ are neurotransmitters found in taste cells
Serotonin (with serotonin receptors found on the sensory afferents)
Transduction mechanism of salt tastants:
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
Transduction mechanism of sour tastants:
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
Transduction mechanism of bitter, sweet and umami tastants: (x4)
- 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
Bitternes Receptors:
x4
- 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
Sweet receptors:
x4
- 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)
Amino Acid (Umami) receptors: (x2)
- T1R receptors
- Need 2 members of the T1R receptor family: T1R1 & T1R3
