Some behaviour associated with olfaction Two olfactory subsystems Main Vomeronasal
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Transcript of Some behaviour associated with olfaction Two olfactory subsystems Main Vomeronasal
Physiological and behavioural responses to odours.
• Visceral responses: Smell food--> salivation and gastric motility– Noxious smell-->gag
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.
Physiological and behavioural responses to odours.
• Infants recognize mothers by scent
• Mothers can recognize the scent her baby.
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.
Olfactory receptor (sensory) neuron
• In the olfactory epithelium
• Have cilia projecting into the nasal cavity mucus
• These cells become damaged, and turnover.
Odorant Receptors
• Homologous to a large family of G protein coupled receptors.
• G proteins interact with the carboxyl terminal
• Membrane spanning regions differ.
Odorant Receptors
• The largest known gene family
• Between 3% and 5% of all genes.
• In humans, 60% of the odorant receptors are not transcribed.
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.
Olfactory Coding
• Each olfactory sensory neuron responds to a subset of odorants.
• Threshold values vary.
• Number of ligands vary.
Olfactory Coding
• I7 receptor
• N-octanol (cut grass)
• The I7 olfactory receptors are spatially coded in the olfactory epithelium and in the olfactory bulb.
Olfactory Coding
• Temporal coding.– MAYBE information conveyed by timing.
– In insects (now also in fish) brain neurons sychronize responses. (Gilles Laurent)
Olfactory signals in the brain.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Olfactory bulb
• Glomerular subsets receive input from olfactory sensory neurons that express distinct odorant receptor molecules.
• These glomeruli seem to be selective for odors.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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.
Taste cells synapse onto primary sensory axons of:
• Cranial nerves:– VII (facial nerve branches)– IX (glossopharyngeal nerve branches)– X (vagus nerve branches)
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.
Human taste perception
• Soluble in saliva
• NaCl (electrolyte balance)
• Glutamate (amino acids)
• Sugars (glucose)
• Acids (palatability)
• Plant alkaloids (bitter, poison indicating)
Threshold concentrations
• NaCl, 2 mM
• Sucrose 10 mM
• Quinine 0.008 mM, strychnine 0.0001 mM
• Gustatory sensitivity decreases with age.
Human taste
• Response thresholds vary in different parts of the tongue.
• Taste sensations as well: fat, spicey, metallic, taste mixtures.
Sweet
• Saccharides - glucose, sucrose, fuctose, cAMP pathway
• Organic anions - saccharin
• Amino acids - aspartame, activate IP3 pathways
• People can discriminate these.
Peripheral organization
• Papillae– Fungiform– Circumvallate– Foliate QuickTime™ and a
TIFF (Uncompressed) decompressorare needed to see this picture.