Transcript Taste Sensation

Taste Sensation
‫بسم هللا الرحمن الرحيم‬
‫ش ْيءٍ فَأ َ ْخ َر ْجنَا‬
‫ات ُك ِل َ‬
‫اء َما ًء فَأ َ ْخ َر ْجنَا ِب ِه نَبَ َ‬
‫• َو ُه َو الَّ ِذي أَنزَ َل ِم ْن ال َّ‬
‫س َم ِ‬
‫َضرا ً نُ ْخ ِر ُج ِم ْنهُ َحبا ً ُمت َ َرا ِكبا ً َو ِم ْن النَّ ْخ ِل ِم ْن َ‬
‫ط ْل ِع َها قِ ْن َوان دَانِيَة‬
‫ِم ْنهُ خ ِ‬
‫شا ِب ٍه ان ُ‬
‫ب َو َّ‬
‫َو َجنَّا ٍ‬
‫الر َّمانَ ُم ْشت َ ِبها ً َو َ‬
‫ظ ُروا‬
‫غي َْر ُمت َ َ‬
‫ت ِم ْن أ َ ْعنَا ٍ‬
‫الز ْيتُونَ َو ُّ‬
‫ِإلَى ث َ َم ِر ِه ِإذَا أَثْ َم َر َويَ ْن ِع ِه ِإ َّن ِفي ذَ ِل ُك ْم آليَا ٍ‬
‫ت ِلقَ ْو ٍم يُؤْ ِمنُونَ‬
‫ض ِق َ‬
‫ب َوزَ ْرع َون َِخيل‬
‫طع ُمت َ َجا ِو َرات َو َجنَّات ِم ْن أ َ ْعنَا ٍ‬
‫• َو ِفي األ َ ْر ِ‬
‫ص ْن َوان َو َ‬
‫ض‬
‫ان يُ ْسقَى ِب َماءٍ َو ِ‬
‫علَى بَ ْع ٍ‬
‫ض ُل بَ ْع َ‬
‫ض َها َ‬
‫اح ٍد َونُفَ ِ‬
‫غي ُْر ِ‬
‫ِ‬
‫ص ْن َو ٍ‬
‫فِي األ ُ ُك ِل ِإ َّن فِي ذَ ِل َك آليَا ٍ‬
‫ت ِلقَ ْو ٍم يَ ْع ِقلُونَ‬
Introduction
• Taste is the ability to respond to dissolved
molecules and ions.
• The sense of taste is also called Gustation.
• The substance which stimulate taste is called
Tastants
• Tongue is the sense organ that detects taste and the
sensory structure that detects taste stimuli are
Taste Buds.
Tongue Anatomy (Taste Related )
• The tongue is covered with 4 types of projections
called papillae
Sharp or Filiform papillae : no taste buds
Fungifiorm papillae : rounded with taste buds
Circumvallate papillae : large papillae with taste buds
 Foliate papillae
Vallate (Circumvallate) Papillae
• About 12 very large circular Vallate papillae form
an inverted V-shaped row at the back of the
tongue.
• Each of these papillae contains approximately
100-300 taste buds.
Vallate Papillae
Fungiform Papillae
• The Fungiform (mushroom like) papillae are
mushroom shaped elevations scattered over the
entire surface of the tongue.
• They contain about 5 taste buds each.
Fungiform or Foliate Papillae
Filiform Papillae
• Filiform papillae cover the entire surface of the
tongue.
• They are pointed, threadlike structures that
contain tactile receptors but no taste buds.
• They increase friction between the tongue and
the food, making it easier for the tongue to move
food into the oral cavity.
Filiform Papillae
Foliate Papillae
• The foliate (leaflike) papillae are located in small
trenches on the lateral margins of the tongue,
but most of their taste buds degenerate in early
childhood.
Taste Buds
• More than 10,000 or so taste buds are found on
the tongue, also located on Soft palate, Cheeks,
throat and lips!
• Taste buds are found in papillae of the tongue
mucosa. A single taste bud contains 50-100 taste
cells representing all 5 taste sensations
Cont…
• Each taste receptor (chemoreceptor) cell is
connected, through a synapse, to a sensory neuron
leading back to the brain.
• Each taste bud is made up of many (between50-150)
receptor cells. Receptor cells live for only 1 to 2
weeks and then are replaced by new receptor cells
• Each receptor in a taste bud responds best to one of
the basic tastes. A receptor can respond to the other
tastes, but it responds strongest to a particular taste.
Taste Buds
Primary sensation of taste
• The identities of the specific chemical that excite
different taste receptors are not all known. Even
so psychological and neurological studies have
identified at least 13 possible chemical receptors
in the taste cell.
• For the practical analysis of taste these receptors
have been grouped into five general categories
called primary sensations of taste.
• They are Sour, Salty, Sweet, Bitter and Umami
Cont…
 Sweet
Sugars, saccharin, alcohol, and some amino acids are plentiful near
the tip of the tongue.
 Salt
Metal ions are abundant in the tip and upper portion of the tongue.
 Sour
Hydrogen ions occur along the lateral edges of the tongue.
 Bitter
Alkaloids such as quinine and nicotine are at the back of the tongue.
 Umami
Elicited by the amino acid glutamate ( Protein )
Taste Pathway
• The stimulus energy of taste is converted into a
nerve impulse by:
Na+ influx in salty tastes
H+ in sour tastes (by directly entering the cell, by
opening cation channels, or by blockade of K+
channels)
Gustducin in sweet and bitter tastes
Taste Pathway
• Cranial Nerves VII , IX and CN X carry impulses
from taste buds to the solitary nucleus of the
medulla. These impulses then travel to the
thalamus, and from there fibers branch to the
Gustatory cortex (taste) Hypothalamus and
limbic system (appreciation of taste)
Experiment
 Objective
• To test the ability to identify familiar taste with
eye closed
 Equipment
• Solution of 5% sucrose, 1% acetic acid, 5% NaCl
and 0.5% quinine sulphat.
How to prepare the solutions
• sweet solution
Mix 2 teaspoons (~ 8 gr) of sugar in 1 glass (~250 ml) of water.
• Salt Solution
Mix 3 teaspoons (~15 gr) of salt in 1 glass (~250 ml) of water.
• Sour Solution
It usually takes 5-10 teaspoons of lemon juice per glass to get the
solution to have the same “taste intensity” as your salt solution
• Bitter solution
Mix 2 teaspoons (~114 mgr caffeine) of instant coffee in 1 glass
(~250 ml) of water
Procedure
• To test the sense of taste use strong solution of
sugar (for sweet), common salt (for salt), weak
solution of citric acid (for sour), and quinine (for
bitter). Four vials of solutions are placed on the
table with labels. Dry the tongue with paper
towel and apply the different solutions with
applicator stick/glass rod to the tip, sides and
back of the tongue as following
Cont…
• Inform the volunteer that you will be testing different
tastes and asking him/her to rate where the taste feels
stronger.
• Ask the volunteer to rinse his/her mouth with a sip of
water, occlude both his/her nostrils and stick his/her
tongue out.
• Dip a clean cotton swap into the first solution and place
it on the tip of the volunteer’s tongue.
Cont…
• Soak the cotton swab well to get a big drop and
allow a few seconds for the tastant to reach the
taste buds.
• Dip the cotton swab into the same solution again
and touch the left side.
• Repeat for the right side and the back of the tongue,
each time dipping the cotton swab in the solution
again.
• Ask the volunteer to rate the strength of each taste
(on a scale from 1-4, four being the strongest of all)
• Repeat for all solutions
Cont…
• The patient is asked to keep the tongue
protruded while applying one solution at a time.
After each taste mouth must be rinsed.
• The different taste is written on the paper
Taste adaptation
Complete adaptation of a taste can occur in 1-5
minutes if continuous stimulation.
Taste Aversion
• The taste projections to the hypothalamus and limbic
system account for the strong association between
taste and emotions.
• Sweet foods evoke reactions of pleasure, while bitter
foods can evoke reactions of disgust
Do you know ?
Why do the elders like to take in food
with strong flavour?
It’s too salty!
Because ….
• When you were a baby, you had taste buds, not only
on your tongue, but on the sides and roof of your
mouth. This means you were very sensitive to
different foods.
• As you grew, the taste buds began to disappear from
the sides and roof of your mouth, leaving taste buds
mostly on your tongue.
• As you get older, your taste buds will become even
less sensitive, so you will be more likely to eat foods
that you thought were too strong as a child.
Remember
 Spicy’ is not a taste. It is the sensation
of pain in the tongue resulting from
the destruction of taste buds by the
‘hot’ food like chilly.
It is spicy!
Also Note
 Taste is influence by olfactory sensation and nasal
congestion affect your taste.
 Tongue can detect other stimuli rather than taste
like temperature and Texture.
 In general, girls have more taste buds than boys.
Flavor is a complex mixture of sensory input
composed of taste (Gustation), smell (olfaction) and
the tactile sensation of food as it is being munched.
 The receptors for alkaloids evolved to be the most
sensitive in order to allow humans to detect plant
poisons before they are eaten.
Taste Disorders
 Ageusia (complete loss of taste)
 Dysgeusia (persistent abnormal taste)
What causes taste disorders?
 Upper respiratory and middle ear infections
 Radiation therapy for cancers of the head and neck
 Exposure to certain chemicals, such as insecticides
and some medications, including some common
antibiotics and antihistamines
 Head injury
 Some surgeries to the ear, nose, and throat (e.g.,
third molar—wisdom tooth—extraction and middle
ear surgery)
 Poor oral hygiene and dental problems