the chemical senses Flashcards
whats the function of the chemical senses
-Identify food sources
-Avoid noxious substances
-Find a mate or mark territories
-gustatory system (tongue tasting) and olfactory system (chemicals detected in air from smell air)
what does salty taste relate to
-relates to: vital electrolytes
-preferences: high salt content, needed for GI tract wall and reabsorption in renal system
-relevance: required for many physiological processes
what are the 5 basic tastes
-salty
-sour
-sweet
-bitter
-unami (savoury)
what does sour taste relate to
-relates to: acidity - H+ content
-preferences: avoid high acidity
-relevance: avoid rotting food, injury to GI tract
what does a sweet taste relate to
-relates to: sugars
-preferences: high sugar content
-relevance: required for energy, growth
what does a bitter taste relate to
-relates to: diverse chemical structures
-preferences: avoid bitter content
-relevance: avoid toxic substances, poisonous
what does Unami taste relate to
-relates to: amino acids e.g. glutamate
-preferences: high amino acid preference
-relevance: protein synthesis, neurotransmission etc
what does lingual papillae contain
-taste buds which are groups of taste cells
-lingual papillae are ridges in the tongue
-back of tongue= circumvallate
-side of tongue= foliate
-front of tongue= fungiform
what are taste organs
-primarily tongue, also cheeks, soft palate, pharynx, epiglottis
-2000-5000 taste buds
-100 chemoreceptive taste cells per taste bud
-Taste pore allows sensory transduction by microvilli
what does Transduction of different stimuli depen on
-depends on which membranous receptors are expressed
what do taste buds contain
-contain taste cells which respond to various stimuli
what are gustatory afferents separate from
-taste cells
-Requires neurotransmitter release across the synaptic cleft
whats the olfactory system
-Odorants as low as a few parts per trillion can be detected
-Human olfactory epithelium = 10 cm2
-2 olfactory bulbs- one beneath each cerebral hemisphere
-smelling a flower dissolves in mucus beneath olfactory epithelium
what are the olfactory receptor cells
-bipolar chemoreceptive neurons
-Odorants must dissolve in the mucus layer to reach olfactory receptor cells
-Transduction machinery is found within the cilia at the end of the dendrite
-The primary afferent neuron is the axon of the olfactory receptor cell
-The axons are thin, unmyelinated
-Olfactory receptor cells are regularly replaced
what are Odorant receptor proteins (ORs)
-Humans have ~350 odorant receptor proteins
-Olfactory receptor cells only express one type of odorant receptor
-One odorant receptor can recognise multiple odorants
-It is the unique combination of odorant receptors that recognise an odorant that allows us to distinguish a specific odor
what does transduction occur via
-Golfs
-Odorant receptor proteins (ORs) are G-protein coupled receptors.
-Every OR uses the same downstream pathway
=Golf ->
=Adenylyl cyclase ->
=cAMP ->
=Cyclic nucleotide gated ion channels ->
=Depolarisation ->
=Ca2+-gated Cl- channels ->
=Further depolarisation ->
how do Receptor potentials trigger action potentials
-Large enough receptor potential = threshold for action potential firing reached
-Intense stimulus = large receptor potential = increased action potential firing rate
what does each glomerulus of the olfactory bulb receive
-receives input from only one type of olfactory receptor
-Convergence on second order neurons
what are olfactory projections
-Second order neurons carry information from glomeruli to various regions of the brain
-Conscious smell- Olfactory cortex
-Hippocampus- Olfactory memory
-Amygdala- Emotional responses
-Reticular formation-visceral responses
-Hypothalamus- Sex & neuroendocrine
