Chapter 14 - Smell Flashcards
Chemical senses and Differences with other systems
Olfactory system - detect airborne chemicals, perceptual quality = smell
Gustatory system - detect chemicals dissolved in saliva, perceptual quality = taste
Differes from other senses because it evokes strong emotional feelings
Function of chemical senses
Differentiate between toxicity - bitter (poison)
Danger system – gasses/fire
Communication/Territorial/fermones (attract mates) - airborne signals to communicate
Alter moods – aroma therapy, indulged eating
Odorants senesed
Odarants - volatile chemicals
Orthonasal olfaction - occurs when we sniff odarant molecules through our nostrils
Retronasal olfaction - when we inhale odorant molecules in our mouth
- travel up back of mouth into upper nasal cavity
- happens when eating, it may go through the other pathway
Olfactory epithelium
Region of tissue at the top of nasal cavity
When air enters, it bumps into tubulins that make them more puffed up (turbulent)
Mucus layer lining olfactory epithelium
Bipolar neurons with cilia has receptors that bind the odorants
Other cells include basal cells
Olfactory sensoroy neurons (OSN) regeneration
- Dying osn are replaced by new sensory neurons
- requires a population of basal cell stem cells
- OSN not protected by a barrier - new cells can be borned in adults
Olfactory sensory neurons repsond to odorants
-odor receptors are G-protein coupled receptors which oderants bind to external surface
- odor receptors are connected at the cilia
Olfactory transduction
- olfactory specific AC 111 enzymem only in cilia, G-protein is specific to olfactory neurons
- odarants binds to GPCR on OSN cilia
- GPCR activates G-protein seperates from Gbeta y
- G alpha activates adenylyl cyclase
- AC 111 makes cAMP
- cAMP binds to an open cyclic nucleotide gated channel - permits NA and
Ca entry
Neural coding of olfactory signals
The way identitiy, concentration, pleasurable/aversive values of oderant molecules are represented in a pattern of APs relayed to the brain from the OSN
Labeled line coding - different OSN and their associated sensory fibres are responsible for transmitting highly specific info
Cross fibre coding - differnt qualitites of sensory modality are disntinguished by the patten of nerve discharges across a large population of fibres
OR and gene family
- each OSN expresses only one type of OR
- each OR is sensitive to a subset of stimuli
Early olfactory processing n the olfactory bulb
- olfactory signals converge in glomeruli collections of sensory nerve endings and the dendrites postsyanptic cells
- each osn projects to only one glomerulus but each one recieves axons from multiple OSNs
Unmyelnated axons from OSNs congretage into bundles pierce cribriform plate and arrive at olfactory bulb
- form olfactory nerve
- olfactation is ipsilateral - info from right nostril goes to right bulb
ALL OSN expressing a type of converge on the same glomerulus pair provides the anatomical basis of the olfactory sensory map
Cells in the olfactory bulb
Excitatory glutamatergic synapses onto:
Juxtaglomerular cells - encircle glomeruli act as excitaory and inhibtory interneurons
Mitral cells and tufted cells - serve as relay centers, axons combine to form the olfactory tract which sends info to the piriform cortex
Granule cells - deepest layer in bulb, extensive network of inhibitory neuorns, integrate input from earlier layers to promote specific oderant identification
Higher olfactory processing
Primary olfactory cortex
- at the junction of frontal and temporal lobes
-comprises the piriform cortex
- responds to many odurs
- relay happens in anterior olfactory nucleus
Sensory Pathways of Olfactory Processing
Secondary Olfactory Cortex (in Oribtiofrontal cortex) - responsible for perception and discrimination - taste and smell integrate = flavour
Limbic System
Amygdala - emotional processing facets of olfactory experience
Hippocampus - mediate memory related to olfactory
