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Lecture 20

ANP 1106 Lecture Notes - Lecture 20: Nociceptor, Epiglottis, Mastoid Antrum


Department
Anatomy and Physiology
Course Code
ANP 1106
Professor
Frank Feiner
Lecture
20

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Anatomy Lecture 20
Wednesday March 26, 2014
Special Senses:
- Smell and Taste
- Hearing and Balance
The Chemical Senses: Smell and Taste
Definition and Role:
A receptor sensitive to various chemicals in solution
- Smell Receptors – excited by airborne chemicals dissolved in fluids (odourants)
coating the nasal membrane
- Taste Receptors – Excited by food chemicals dissolved in saliva
- Warns us if material near or in our mouths should be savoured or avoided
- Smell/taste complimentary – respond to different classes of chemicals
Olfactory Epithelium and the Sense of Smell
Location of Olfactory Receptors
- Organ of smell: olfactory epithelium (5cm2) in roof of nasal cavity
- Olfactory receptors detects odourants in inhaled air en route to lungs via the
trachea
- Epiglottis keeps air out of the esophagus and stomach and food out of the lungs
Structure of Olfactory Epithelium
Covers nasal concha on either side of nasal septum
Millions of receptor cells: bipolar
Olfactory receptor cells
- Surrounded by supporting cells (yellow-brown pigment)
- Olfactory stem cells regenerate (impermanent: 30-60 day life, rare.)
- Dendrites with olfactory cilia: increase reception, nonmotile, covered by mucous
(traps odourants)
- Axons form filaments – pass through cribiform plate, synapse with olfactory
bulbs => olfactory tract => olfactory nerve (CN I)
Specificity and sensitivity of olfactory receptors
- Although humans can distinguish between approx. 10000 odours, there are only
approx. 400 different olfactory receptors (proteins) – one per receptor cell
- Each receptor senses more than 1 odour/each odourant binds to more than 1
receptor
- Receptors exquisitely sensitive: a few molecules to activate them
- ‘Smell may be pain/temperature: eg. Ammonia, chili peppers, menthol. Via
afferents of the trigeminal nerve (CN V)
Olfactory Transduction
- Proceeds via a second messenger process

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- Uses cAMP – cyclic adenosine monophosphate
- cf Visual transduction
- Differences: Visual: cGMP – cyclic guanine monophosphate. Ion channel opening
(smell) vs. closing (visual)
Physiology of Smell
Olfactory Transduction (continued)
Olfactory adaptation
- Na+ influx leads to action potential (ultimately smell)
- Ca2+ influx decreases response to a sustained stimulus
- Why/how a sewage plane worker can enjoy lunch!
The Olfactory Pathway
Reaches frontal lobes and limbic system
- Olfactor sensory nerve axons synapse with mitral cells, activate glomeruli
- Impulses from olfactory bulb via olfactory tracts via CN I to piriform lobe
olfactory cortex. Then 2 routes: Frontal lobes – identify/interpret. Limbic system
(eg hypothalamus, amygdala): emotional response
- Danger: fight/flight
- Foods: salivate
- Stench: gag
Activation of glomeruli
- As noted above (slide 7), each receptor senses more than 1 odour and each
odourant binds to more than one receptor
- Also, each glomerulus represents a signle aspect of an adour/each odour activates
unique set of glomeruli (eg a perfume may activate hundreds)
- Mitral cells in olfactory bulb refine/amplify/relay signal
- Amacrine granule cells in olfactory bulb (not shown in figure 15.20) release
neurotransmitter GABA
- Inihibit mitral cells – only highly excitatory olfactory impulses transmitted to CN
I
Taste Buds and the Sense of Taste
Location and Structure of Taste Buds
- These (10000) sensory organs are mainly on tongue
- A few on soft palate, cheeks, pharynx, epiglottis
- In peglike projections: papillae (3 kinds, see (a))
- Numerous taste buds in one papillus
- 50-100 epithelial cells (gustatory and basal) in one taste bud
Gustatory Epithelial Cells
- Receptor cells for taste – the taste cells
- Long microvilli (gustatory hairs) from cell tips through taste pore to surface of
epithelium
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