Introduction to Physiological Psychology

Transcription

1 Introduction to Physiological Psychology Psych 260 Kim Sweeney cogsci.ucsd.edu/~ksweeney/psy260.html n Vestibular System Today n Gustation and Olfaction 1

2 n Vestibular sacs: Utricle Saccule Vestibular System 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

3 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

4 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

5 Gustation Different modalities are encoded by different receptor types Somatosensation Proprioception Olfaction Gustation Audition Vision 5

6 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

7 Gustation n 4 primary tastes (sweet, sour, salty, bitter) n 5 th 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

8 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. n Most taste receptors (~90%) respond to at least 2 basic tastes Gustation salt sweet sour bitter Ogawa et al.,

9 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

10 Population coding! The neural pathways of taste 10

11 The neural pathways of taste VPM nucleus (thalamus) GUSTATORY, /(Solitary Nucleaus) Top-down processing matters n Culture n Current experience Miraclefruit Information from other sensory modalities n Past experience 11

12 Top-down processing matters Peter Menzel, photography Taste and Smell work together n Try eating a jelly bean while holding your nose! 12

13 Taste and Vision work together Brochet, 2001 Taste and Sound work together! Spence et al.,

14 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

15 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. 15

16 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

17 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

18 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

19 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

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