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Psych 260
Kim Sweeney [email protected]
cogsci.ucsd.edu/~ksweeney/psy260.html
Introduction to Physiological Psychology
Today…
n Vestibular System n Gustation and Olfaction
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Vestibular System
n Vestibular sacs: – Utricle – Saccule
n Semicircular
canals – ampullae
Vestibular Sacs n The “floor” of the utricle and “wall” of the
saccule contain hair cells. n The cilia of are covered by a gelatinous
mass which contains small crystals (otoconia). n Shifts in gravity or rapid head movements
cause the mass to shift, simulating the cells.
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Semicircular Canals
n Horizontal: rotation of the head around a vertical axis. (e.g. turning)
n Anterior: rotation of the head in sagittal plane. (e.g. nodding)
n Posterior: rotation of the head in frontal plane. (e.g. cartwheel)
Semicircular Canals n Each one ‘codes for’ a particular plane. n Hair cells are clustered within the
ampulla, and project into the gelatinous cupula.
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Semicircular Canals n All hair cells within an ampulla are
oriented to the same direction n As endolymph moves, cupula deflects,
bending the cilia.
The Vestibular Pathway
n Eighth cranial nerve contains both cochlear and vestibular nerve.
n Projections are to – Vestibular nucleus >
§ > ventral posterior nucleus of the thalamus § > Brainstem (medulla and pons)
n Vestibulo-Ocular Reflex
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Gustation
Different modalities are encoded by different receptor types
Somatosensation
Proprioception
Olfaction
Gustation
Audition
Vision
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Gustation
n Taste receptors are scattered around surface of the tongue in clusters (taste buds) – NB- this means high convergence at very lowest level!
Taste buds and papillae
n Average person has ~5,000 taste buds, but exceptional individuals may have 500… or 20,000! (supertasters)
n An individual taste receptor w/in a taste bud lives ~2 weeks
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Gustation
n 4 primary tastes (sweet, sour, salty, bitter) n 5th is umami, meat or savory (MSG)
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Gustation
n Transduction of taste is similar to the chemical transmission that takes place at synapses.
n The tasted molecule binds with the receptor and produces changes in membrane permeability that cause receptor potentials.
n Different substances bind with different types of receptors, producing different taste sensations.
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Receptors
n Two different receptors are responsible for detection of sweet tastes.
n Bitterness is detected by members of a family of about thirty different receptors.
n The existence of so many different bitterness receptors suggests that although different bitter compounds share a common taste quality, they are detected by different means.
Gustation
n Most taste receptors (~90%) respond to at least 2 basic tastes…
Ogawa et al., 1968
salt
sweet
sour
bitter
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Gustation
n If a given receptor does not respond exclusively to one kind of taste…
n A given gustatory axon doesn’t either.
Sucrose Salt Sour Bitter
Gustation
n We respond to many tastes that can not be created by combining primaries … – So how do we distinguish between chocolate and
banana… and cilantro?
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Population coding!
The neural pathways of taste
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The neural pathways of taste
VPM nucleus (thalamus)
/(Solitary Nucleaus)
GUSTATORY,
Top-down processing matters
n Culture n Current experience
– Miraclefruit – Information from other sensory modalities
n Past experience
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Top-down processing matters
Peter Menzel, photography
Taste and Smell work together
n Try eating a jelly bean while holding your nose!
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Taste and Vision work together
Brochet, 2001
Taste and Sound work together!
Spence et al., 2009
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What could possibly go wrong?
n Ageusia – inability to taste – Rare, because multiple pathways carrying taste
information… but can occur after stroke or tumor damage to VPM thalamus or gustatory cortex
The Chemical Senses: Smell and Taste
n Gustation (taste) – Responds to chemicals in the mouth
n Olfaction (smell) – Detects airborne chemicals
n Food acts on both systems to produce flavor!
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Olfaction- Broadly Speaking
n Odorants enter through the nose, hit olfactory receptors, which have axons that enter the olfactory bulbs.
n From the olfactory bulb, the olfactory tract projects to many, many brain areas, including amygdala and piriform cortex (MT).
The human olfactory system
Remember: Olfaction is the only one of our senses to have direct access to the brain, without going through the thalamus first! But… it makes it to the thalamus eventually.
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Olfaction n Receptors are embedded in the
olfactory mucosa of the nose – ~40,000,000 receptors in humans, – ~2,000,000,000 in a German Shephard!
Olfactory receptor cells n Like auditory receptor cells, they
terminate in cilia
n Transduction occurs when an odorant binds to the cilia
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n 6- Olfactory receptor cells n 5- Glomeruli n 4- Olfactory mucosa n 3- Cribriform plate n 2- (mitral cells) n 1- Olfactory Bulb
n Glomeruli each contain many axons (~2,000!) from olfactory receptors… but any given glomerulus receives input from only one kind of receptor!
Another way of looking at it n There is high convergence:
– Many receptor neurons converge onto few glomeruli (~150:1)
– Many glomeruli converge onto a single neuron of the olfactory tract (~25:1)
n This convergence increases the sensitivity of the olfactory signal sent to the brain!
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Olfaction
n In humans there are (only!) several hundred different olfactory receptors
n How can a (relatively) small amount of receptors lead to such a vast array of smells? – A particular odorant binds to more than one
receptor, thus different odorants produce different patterns of activity in different glomeruli
The human olfactory system
Vomeronasal organ
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Pheromones
n Chemicals that influence that behavior of conspecifics (members of the same species)
n Evidence of human pheromones – Changes in olfactory sensitivity across and
menstrual cycle – Synchronization of menstrual cycles – Sex identification by smell (especially by
women… and healthy mixes preferred) – Men can identify menstrual stage by smell
What can possibly go wrong?
n Anosmia- the inability to perceive smells – A strong blow to the head can sever those axons that
pass through the cribriform plate! – Old age is also often accompanied by a decreased
ability to smell
n Olfactory agnosia- inability to identify smells
n Olfactory hallucinations n … among other things!
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Coming up…