Shared Flashcard Set


Olfaction and Taste
VCU PHIS 501 September 16, 2010

Additional Physiology Flashcards




Taste Buds

-located mostly on the surface of the tongue, but also on the palate and the back of the throat

-Barrel shaped structures containing up to 50 cells or so, just below the surface

-Taste pore: small opening in the epithelial layer where the chemicals react with the surface of the taste receptor cells (microcilia to increase SA)

-Three basic cell types: basal cells (continuously divide and make new cells), supporting cells, and receptor cells

-Nerve fibers come from outside the tongue

Fungiform Papillae

-present on the anterior two-thirds of tongue

-covered with salivia

-mushroom shaped bulge with 3-5 taste buds on top

-these are the red spots seen on tonque (due to blood supply)

-responsible for sweet/salty tastes

-innervated by facial nerve VII- branches of chorda tympani

-Damage to the tympanic membrane may effect chorda tympani and result in ipsilateral taste loss on the anterior two-thirds of the tongue

Filiform Papillae

-leaf shaped

-most abundant papillae on surface of tongue

-no tastebuds- determines texture and temperature of food

-innervated by the trigeminal nerve

Foliate papillae

-present in the side of the tongue

-taste buds are in folds on the side of the papillae

-gland secretes material that covers the taste pore

-Innervated by the glosopharyngeal nerve

-Responsible for sour tastes

Circumvallate papillae

-present on the base/back of tongue

-largest papillae

-surrounded by circular trench which is where the taste buds are present (app 250 buds per circumvallate papillae)

-few in number, but responsible for half the human tastes

-responsible for bitter taste

-innervated by the glossopharyngeal nerve


Discuss how the taste system is coordinated with the motor system

1)  The tip of the tongue is used to bring nutrients into the body and detects "good" tastes

2)  The back and sides of the tongue detect sour/bitter substances that may be harmful and the back of the tongue propels it out

3)  The vagus nerve innervates deep in the throat and the eppiglottis.  It trigers the gag reflex and regurgitation.

Discuss the taste pathway

Chemical interacts with receptor cell which releases neurotransmitter to the first order neuron outside of the tongue.  The information goes to the solitary nucleus and then to the thalamus.  From there, information can go to the limbic and basal forebrain or the neocortex.


Primitive functions such as taste and smell are linked to the limbic system and basal forebrain.

Basic tastes mechanisms

Salt: Na goes through channel which depolarizes cell and makes the receptor potential


Sour: channels are sensitive to H, when H comes in it clogs K channels causing more K to stay in the cell and therefore depolarizes the cell


Sweet/Umame:  g-protein coupled receptor, second messenger is increased levels of IP3 which increases Ca causing depolarization

Across-fiber pattern codes
When your cells receive a stimulus, regardless of intensity, the response goes up and down but the overall pattern across the fibers remains the same.
Taste Disorders

Quantitative disorders are usually due to problems centrally.  These are hyperguesia, aguesia, and hypoguesia.


Qualitative disorders are usually due to problems in the periphery.  These are cacoguesia and paraguesia (everything tastes different, maybe metallic).

Location of olfaction receptors

Olfaction receptors are located in the superior turbinate, part of the medial turbinate, and the dorsal part of the nasal cavity. 


The olfaction receptors are actually nerve fibers and they pass directly through holes in the skull to the olfactory bulb.


There are other nerves located in the nasal cavity.  The trigeminal nerve picks up noxious or cooling vapors, but is NOT olfaction.

Olfactory Epithelium

Consists of basal cells, supporting calls, and receptor cells.  The basal cells continuously divide through out the lifespan to replace the cells, including the receptor cells which are NEURONS. 


The receptor cells have cilia with transduction molecules/g-proteins that interact with the odors and cause a depolarization on the cell.  These axons are the smallest axons in the body (group IV C cells).


The supporting cells regulate the mucous.


Olfactory epithelium looks different than respiratory epithelium.  Respiratory epithelium is wave-like.  Olfactory epithelium is yellow and is less organized, like a plate of spaghetti.


Olfactory bulb

Olfactory nerves go through the cribiform plate to the olfactory bulb.  Due to locations these nerves are easily damaged.


Sensory input comes in and stimulates a mitral cell.  Mitral cell axons form the olfactory tract which is the olfactory bulb's primary output.



Explain how lateral inhibition works in the olfactory system

Mitral cells have dendrodendritic synapses with granular cells.  The dendrodentritic synapses are recipricol because the mitral cell excites the granular cell, but the granular cell turns around and inhibits the mitral cell.


Periglomerular cells provide lateral inhibition for neighboring glomerulus, at the outermost glomerular level

Outline the olfactory pathway
Information comes in through the receptors and goes to the olfactory bulb.  Information then goes to the prepyriformand perianyodaloid and then to the thalamus.  Information will go from the thalamus to the neocortex as well as the limbic system and basal forebrain.
Smell Disorders

Quantitative: hyposmia, anosmia, and hyperosmia


Qualitative: cacosmia (trigeminal nerve is taking over) and parosmia (sensing a smell that is not there)


Can be caused by head injury/trauma, upper respiratory infections, tumors, exposure to chemicals, etc...

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