Introduction to Physiological Psychology Psych 260
Kim Sweeney [email protected] cogsci.ucsd.edu/~ksweeney/psy260.html
Today… n Vestibular System n Gustation and Olfaction
1 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.
2 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.
3 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
4 Gustation
Different modalities are encoded by different receptor types
Somatosensation
Proprioception
Olfaction
Gustation
Audition
Vision
5 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
6 Gustation n 4 primary tastes (sweet, sour, salty, bitter) n 5th is umami, meat or savory (MSG)
?
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.
7 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 salt n Most taste
receptors (~90%) sweet respond to at least 2 basic tastes… sour
bitter
Ogawa et al., 1968
8 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?
9 Population coding!
The neural pathways of taste
10 The neural pathways of taste
/(Solitary Nucleaus)
VPM nucleus (thalamus) GUSTATORY,
Top-down processing matters n Culture n Current experience – Miraclefruit – Information from other sensory modalities n Past experience
11 Top-down processing matters
Peter Menzel, photography
Taste and Smell work together n Try eating a jelly bean while holding your nose!
12 Taste and Vision work together
Brochet, 2001
Taste and Sound work together!
Spence et al., 2009
13 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!
14 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).
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.
15 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
16 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!
17 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
18 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!
19 Coming up…
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