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Psych 260

Kim Sweeney ksweeney@cogsci.ucsd.edu

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…