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Chapter 15

PSYB51H3 Chapter Notes - Chapter 15: Ion, Central Nervous System, Sodium Chloride


Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier
Chapter
15

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PSYB51: Sensation & Perception
Chapter 15: Taste
April 11. 3017
Wei Luo
Taste Versus Flavour
According to the early Greeks, when perceiving the sensations from food and beverages in the mouth were Tastes
o However, the molecules we taste are dissolved in our saliva and it stimulates the taste receptors on our taste
buds
o When we chew and swallow foods, other
molecules are released into the air inside of our mouth
and forced up behind the palate into the nasal cavity,
where they make contact to the olfactory epithelium and
stimulate our olfactory receptors (Figure 15.1)
The brain then blends these Retronasal Olfactory
Sensations together with out taste sensations into
Flavours
TASTE Sensation evoked by solutions in the mouth that contact receptors on the tongue and the roof of the mouth that then
connect to axons in cranial nerve VII, IX, and X
RETRONASAL OLFACTORY SENSATION The sensation of an odor that is perceived when chewing and swallowing
force an odorant in the mouth up behind the palate into the nose. Such odor sensations are perceived as originating from the
mouth, even though the actual contact of odorant and receptor occurs at the olfactory mucosa
FLAVOUR The combination of tur taste and retronasal olfaction
It is easy to prevent the airflow that carries odorants through the retronasal passages such as holding your noses while
eating
Localizing Flavour Sensations
Because you only taste and feel the food in your mouth (Chewing breznot in your nose, your brain concludes that the
sensations must in your entire mouth
o Spicy wood can activate pain receptors all the way through the retronasal passage which proves the rule that
when we eat these, we experience the sensations coming from our noses as well our mouths
Consider a situation where you are a normal olfaction but damaged taste
o You reported that you can smell lasagna but when you ate it, it had no flavour
o A similar effect was produced in a laboratory using a small amount of lidocaine and a large amount of
blueberry yogurt
It has shown that the patient had their left Chorda Tympani mixed with the lidocaine while they tasted
the yogurt
In this situation, they reported that blueberry sensation which is due to the retronasal olfaction
seemed to come only from the right side of the mouth
Therefore, the intensity of the blueberry sensation was reduced and this intensity was reduced
further when both nerves were blocked
Dana Small revealed characteristics of retronasal olfaction: the brain process odors differently, depending on whether
they come from the mouth or through the nostrils
Anatomy & Physiology o the Gustatory System
Chewing breaks down food substances into molecules, which are dissolved in saliva
o The saliva-borne food molecules flow into a taste pore that leads to the Taste Buds which is provided by the
Papillae that is located on the edges of the tongue in a rough oval (Figure 15.2)
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TASTE BUDS A globular cluster of cells that has
the function of creating neural signals conveyed to the
brain by the taste nerves. Some of the cells in a taste
bud have specialized sites on their apical projections
that interact with taste stimuli. Some of the cells form
synapses with taste nerve fibers
PAPILLIA Any of multiple structures that give the
tongue its bumpy appearance. From smallest to
largest, the papilla types that contain taste buds are
fungiform, foliate and circumvallate; filiform papillae,
which do not contain taste buds
Taste buds contain multiple Taste Receptor Cells, each of which responds to a limited number of molecule types
o When it comes in contact with one its preferred molecules, the taste receptor cells produce action potentials
that send information along one of the cranial nerves to the brain
TASTE RECEPTOR CELLS A cell within the taste bud that contains sites on its apical projection that can interact with
taste stimuli. These sites fall into two major categories: those interacting with charged particles (e.g. sodium and hydrogen
ions), and those interacting with specific chemical structures
Papillae
Papillae gives the tongue its bumpy appearance and it comes in four major varieties: Filiform, Fungiform, Foliate and
Circumvallate
o The last three of these contain taste buds:
1. Filiform Papillae the one without any taste function, located on the anterior portion of the tongue
that comes in different shapes in different species
2. Fungiform Papillae tiny buttons located on the anterior part; they are easy to see if they are colour
stained
There are about six taste buds buried in the surface of each fungiform papilla
If we stained the tongue, we will see a large
amount of variation (Figure 15.3)
3. Foliate Papillae Sides of the tongue at the
point where the tongue is attached; looks like a
series of folds and that taste buds are buried in the
folds
3. Circumvallate Papillae are large, circular
structures forming an inverted V on the rear of
the tongue
They look like tiny islands surrounded by
moats
The taste buds are buried in the sides of the
moats
Taste buds are also on the roof our mouth where the hard and soft palates meet
Taste Buds & Taste Receptor Cells
Taste neurons are pseudouipolar: a single process exits the cell body and then splits into peripheral and central limbs
o The peripheral axons makeup the nerves that project into the tongue
Each taste bud is a clustered of long and wide cells
o The tips of some of the cells end are known as Microvilli that contains taste substances
MICROVILLI Slender projections of the cell membrane on the tips of some taste buds cells that extend into the taste pore
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