Some behaviour associated with olfaction Two olfactory subsystems Main Vomeronasal

1. Some behaviour associated with olfaction • Two olfactory subsystems • Main • Vomeronasal

2. Olfaction

5. Physiological and behavioural responses to odours. • Visceral responses: Smell food--> salivation and gastric motility • Noxious smell-->gag

6. Physiological and behavioural responses to odours. • Reproductive and endocrine functions • Women housed together synchronize menstral cycles • Smelling gauze pads from underarms of women also synchronizes menstral cycles.

7. Physiological and behavioural responses to odours. • Infants recognize mothers by scent • Mothers can recognize the scent her baby.

8. Pheromones Species specific odorants. Some pheromones stimulate the vomeronasal organ VNO--> accessory olfactory bulb-->hypothalamus. (Found in 8% of human adults), VNO receptors are pseudogenes in humans.

9. Olfactory receptor (sensory) neuron • In the olfactory epithelium • Have cilia projecting into the nasal cavity mucus • These cells become damaged, and turnover.

11. Transduction

13. Odorant Receptors • Homologous to a large family of G protein coupled receptors. • G proteins interact with the carboxyl terminal • Membrane spanning regions differ.

14. Odorant Receptors • The largest known gene family • Between 3% and 5% of all genes. • In humans, 60% of the odorant receptors are not transcribed.

15. Odorant Receptors • Have been expressed in olfactory sensory neurons with reporter proteins. • Each olfactory sensory neuron expresses only one or at most a few odorant receptor genes. • Different odors must activate a subset of olfactory sensory neurons.

17. Olfactory Coding • Each olfactory sensory neuron responds to a subset of odorants. • Threshold values vary. • Number of ligands vary.

18. Olfactory Coding • I7 receptor • N-octanol (cut grass) • The I7 olfactory receptors are spatially coded in the olfactory epithelium and in the olfactory bulb.

19. Olfactory Coding • Temporal coding. • MAYBE information conveyed by timing. • In insects (now also in fish) brain neurons sychronize responses. (Gilles Laurent)

20. Olfactory signals in the brain.

22. Olfactory bulb • Glomerular subsets receive input from olfactory sensory neurons that express distinct odorant receptor molecules. • These glomeruli seem to be selective for odors.

24. Mitral cell projections • Mitral cell axons form the lateral olfactory tract. • Projects to accessory olfactory nuclei, olfactory tubercule, entorhinal cortex, amygdala, pyriform cortex. • Pyriform cortex axons project to thalamus, hippothalamus, hippocampus, amygdala.

25. Taste System • Taste cells • Taste buds • Peripheral cells, a number of central pathways.

26. Taste cells synapse onto primary sensory axons of: • Cranial nerves: • VII (facial nerve branches) • IX (glossopharyngeal nerve branches) • X (vagus nerve branches)

27. Projections of taste neurons • Cranial nerves VII, IX and X project to the solitary nucleus of the brainstem (gustatory nucleus) • Topography of the cranial nerve input to the gustatory nucleus. • Integration of visceral and gustatory input.

29. Projections from the gustatory nucleus • Thalamus--> cortex • Hypothalamus (homeostasis), amygdala

30. Human taste perception • Soluble in saliva • NaCl (electrolyte balance) • Glutamate (amino acids) • Sugars (glucose) • Acids (palatability) • Plant alkaloids (bitter, poison indicating)

31. Threshold concentrations • NaCl, 2 mM • Sucrose 10 mM • Quinine 0.008 mM, strychnine 0.0001 mM • Gustatory sensitivity decreases with age.

32. Human taste • Response thresholds vary in different parts of the tongue. • Taste sensations as well: fat, spicey, metallic, taste mixtures.

33. Sweet • Saccharides - glucose, sucrose, fuctose, cAMP pathway • Organic anions - saccharin • Amino acids - aspartame, activate IP3 pathways • People can discriminate these.

34. Peripheral organization • Papillae • Fungiform • Circumvallate • Foliate

38. Taste bud • Taste pore • Taste cells