lecture 3: Chemoreception

Chemoreceptors: contact

* taste or gustation
* dissolved chemicals at relatively high concentrations

chemoreceptors: distance

* smell or olfaction
* airborne/dissolved chemicals at relatively low concentrations

features of chemoreception

* different cell types and locations
* different transduction mechanisms
* different neural pathways

Olfactory epithelium

organ of smell in roof of nasal cavity

Olfactory sensory neurons

bipolar neurons with thin apical dendrite with several olfactory cilia

where are G protein-coupled receptors found?

on cilia

Low threshold

* high sensitivity
* low odorant concentration needed

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Olfactory adaptation

* occurs rapidly
* inrinsic and extrinsic mechanisms

Mitral cells

receive input from many olfactory cells with similar characteristics

pathway to frontal lobe

smells are interpreted and identified

pathway to limbic system

emotional response to odors

taste buds

* sensory receptor organ for taste
* within papillae of the tongue

Gustation consists of:

* gustatory receptor cells
* epithelial origin
* Microvilli
* basal cells

3 cranial nerves involved in Gustatory pathway

1. facial (VII) nerve
2. glossopharyngeal (IX) nerve
3. Vagus (X) nerve

pathways to limbic system and hypothalamus

emotional response such as taste aversion

pathway to thalamus and gustatory cortex in insula of cerebrum

conscious perception of taste

facial taste system

* high sensitivity
* uses glossophyrangeal and vagus crainal nerves to vagal lobe of medulla

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extra oral system

* less sensitive
* facial nerve to facial lobe of medulla

features of chemorecepton:

* they have different cell types and location
* different transduction mechanisms
* different neural pathways

salty

Na+ channel

sweet, bitter, umami

G protein-coupled receptors

sour

proton (H+) channel

Pathway of Gustatory transduction:

1. receptor is activated
2. receptor potential
3. intracellular Ca+ increases
4. NT releases
5. NT act on sensory neuron
6. triggers action potential

pathway of olfactory transduction

1. the odorant activates G protein-coupled receptor
2. intracellular cAMP increases
3. opens Na+ and Ca+ channels
4. depolarization
5. triggers an action potential

how are odorants removed from a receptor?

by detoxification, just like the enzymes found in the liver