Download 14-Taste & Smell

Taste
Taste buds are the
sense organs of taste.
Each taste bud contains
a number of taste cells
which which are the
taste receptors
(gustatory receptors)
‫مستقبالت الذوق‬
They are specialized to
detect things that are
sweet ‫ حلو‬, sour ‫ حامض‬,
salty ‫ مالح‬or bitter ‫ مر‬.
Apical end
Each receptor has
microvilli on its apical
end which protrude at
the taste pore
Taste buds are present
in  (1) the walls of
Fungiform and Vallate
papilae of the tongue
( papillae are ridges and
Basal
valleys in the tongue )
end
& (2) in the mucosa of palate ,
pharynx and epiglottis .
The Basic Taste Modalities
(1) Sweet ( tested by sucrose )
and is located mainly at the tip
of the tongue .
(2) Sour ( tested by acids , e.g.,
acetic acid ) and is located
mainly along the edges of the
tongue .
(3) Bitter ( tested by quinine )
and is located mainly at the back
of the tongue .
(4) Salt ( tested by Na Cl ) and
located mainly on the dorsum
anteriorly .
However , considerable overlap
occurs .
The Taste Pathway
Electrical impulses in the sensory fibers 
(1) from the anterior 2/3 rds of tongue  are carried
by chorda tympani branch of the Facial nerve
(2) From the posterior 1/3 rd of tongue  travel via
the
Glossopharyngeal nerve
(3) and From palate ,pharynx and epiglottis  are
carried
in the Vagus nerve .
These fibers synapse in nucleus of the solitary tract (NST,
Nucleus Tractus Solitarius ) in the Medulla .
From there , second-order neurns give rise to axons
that cross the midline and join the Medial Lemniscus
to end with fibers of touch , pain and temperature in
the Ventrobasal Complex of the Thalamus .
From the thalamus third-order neurons arise and
project to the postcentral gyrus along with the other sensations
( touch and pressure ) from the mouth ) .
This cortical taste area is located at the foot of the
postcentral gyrus
Smell
Olfactory ( taste ) receptor
neurons are specialised .
ciliated, nerve cells.
They are not present all
over the nasal mucosa , but
present only in a small ,
5 cm2 , yellowish-pigmented
part of it called olfactory
epithelium ( or olfactory
mucous membrane )
This olfactory epithelium is
located at the roof of the
nasal cavity near the
septum .
Sniffing , by creating
currents of air going up ,
helps in smelling odorant
The cilia of the Olfactory
receptor cells project
into the mucus
surrounding the olfactory
epithelium .
Unlike the ear hair-cell
receptors, the olfactory
receptors are themselves
sensory neurons.
The olfactory receptors
send their axons up 
through small ( foramina )
openings in the cribriform
plate ‫ الصحن المثقّب‬of the
ethmoid bone  to enter
the cranial cavity
and then synapse on
ilarge Mitral cells in the
olfactory bulb
( which is present on the
inferior surface of the
frontal lobe ).
The area where several
axon terminals synapse
on the dendrites of an
individual mitral cell is
calle Glomerulus
The smell pathway has no
relay in the thalamus .
From there fibers go to
the olfactory cortex in the
Piriform area .