Olfaction and Gustation Flashcards
Sensation
- conscious/subconscious awareness of changes in internal or external environment
- components: stimulation of sensory receptor –> transduction of stimulus–> generation of nerve impulses –> integration of sensory input
Transduction
- receptors change stimuli into electrical event
- stimulus opens/closes ion channels in memrane of receptor –> usually net influx of Na to depolarize membrane
Classification of sensory receptors
General senses
- somatic = tactile, thermal, pain, proprioceptive
- visceral = info about conditions w/in internal organs
Special senses
-smell, taste, vision, hearing, equilibrium/balance
Types of sensory receptors
Free nerve endings = pain and thermoreceptors
Encapsulated nerve endings = pacinian corpuscles
Separate cells = hair cells, photoreceptors, gustatory receptor cells
Generator vs Receptor Potential
Generator Potential = produced by free nerve endings, encapsulated nerve endings, and olfactory receptors. When it reaches threshold, it triggers 1+ nerve impulses in the axon of a first-order sensory neuron
Receptor potential = triggers release of neurotransmitter –> postsynaptic potential –> AP
Classification of sensory receptors based on stimulus
mechanoreceptors = vibration + movement Thermoreceptors =temp Nociceptors = pain Photoreceptors = light Chemoreceptors = chems Osmoreceptors = osmolarity
Receptor Adaptation
Tonic receptors = respond to stimulus that requires constant monitoring –> keep making elec signal as long as stimulus persists (e.g. mechanoreceptors monitoring BP)
Phasic Receptors = respond to stimulus CHANGES–> stop signals if stimuls remains constant –> reduced sensitivity (e.g. tactile receptors)
Special sense receptor types
olfaction and gustation = chemoreceptors
Audition and equilibrium = mechanoreceptors
vision = photoreceptor
general senses vs special senses
general are simple in structure and scattered thru body
special are anatomically distinct, concentrated in specific locations in head, and involve a complex neural pathway
olfaction
- olfactory epithelium (over superior nasal concha) has 10-100 mil receptors
- olfactory receptor = bipolar neuron with cilia (olfactory hairs which respond to chem stimulation of an odorant molecule)
- supporting cells provide support and nourishment
- basal cells = stem cells which replace olfactory receptors every 60 days (RECEPTORS ARE NEURONS)
- olfactory glands in lamina propria produce mucus
physiology of olfaction
-can detect 10,000 dif odors
Odorant binds to receptor of olfactory hair –> G-prot activation –> activation of adenylate cyclase –> production of cAMP –> opening of Na channels –> inflow of Na (and Ca)–> generator potential –> nerve impulse thru olfactory nerves –> olfactory bulbs –> olfactory tract –> primary olfactory area of cerebral cortex (and limbic system)
Doesn’t go thru thalamus
Adaptation and threshold for olfation
Fast adaptation – reduced sensitivity occurs quickly
Low threshold – very small quantity required to percieve as an odor
Anatomy of Taste buds and papillae
-Taste bud = 3 types of epithelial cells (supporting cells, gustatory receptor cells, basal cells)
~50 gustatory cells/taste bud, each with gustatory hair thru taste pore
- taste buds are on papillae
- 3 kinds of papillae w/ taste buds (vallate/circumvallate, fungiform, and foliate)
structure of taste bud
- 50-100 lask shaped epithelial cells
- gustatory cells with micreovilli (hairs)
- 3 types of gustatory epithelial cells: one releases seratonin; others lack synaptic vessicles, but one releases ATP as a neurotrans
-basal epithelial cells = dynamic stem cells that divide every 7-10 days
Tongue papillae
Foliate papillae: on sides of tongue –> minimal taste buds and none in adults
Fungiform papillae: on dorsum surface of tongue – taste buds
Vircumvallate papillae: posterior ~10 – taste buds
Filiform papillae = no taste buds, but provide friction
physiology of gustation
-5 tastes: sweet, sour, salty, bitter, umami
Tastant dissolves in saliva –> plasma membrane of gustatory hair –> receptor potential –> nerve impulse via cranial nerves 7,9, and 10 –> medulla –> thalamus –> primary gustatory area of cerebral cortex
Where 5 tastes come from
Sweet = sugar, alcohol, artificial sweeteners Salt = metal ions (Na+) Sour = acids (H+) Bitter = Alkaloids (quinine, nicotine, caffeine) Umami = AAs, glutamate and aspartate
Most tastes are combos
Physiology of salty tastes
Sodium ions diffuse thru Na+ channels, resulting in depolarization
Physiology of sour taste
Hydrogen ions cause depolarization in one of these ways:
- enter cell directly thru H+ channels
- bind to gated K+ channels, closing the gate and preventing K+ from leaving cell
- Open ligand-gated channels for other positive ions
Physiology for sweet taste
Sugars bind to receptors and cause cell to depolarize using G-prot mechanism
- G-prot activates adenylate cyclace which makes cAMP
- cAMP activates kinase that phosphorylates K+ channels
- K+ channels close, resulting in depolarization
Bitter Physiology
Bitter tastants bind to receptors and cause depolarization using G-prot mechanism
- G prot activates phospholipase C, which converts phosphoinositol (PIP2) to inositol triphosphate (IP3)
- IP3 causes Ca release from intracellular stores an depolarization of cell
Umami physiology
AAs bind to receptors and cause depolarization with G-prot mechanism
- G prot activates adenylate cyclase which catylizes conversion of ATP to cAMP
- cAMP opens CA channels, depolarizing the cell
Gustatory Pathway
- sensory neurons from cranial nerve 7 or 9
- medulla (purpose of this synapse is to stimulate digestion reflexes, like salivary an gastric secretions)
- thalamus
- gustatory cortex in insula
- linked to limbic system (emotional response to tastes)
gustatory adaption/threshold
rapid adaptation
variation in threshold
- bitter = lowest = most sensitive
- sour/umami = medium
- sweet/salty = highest = least sensitive
