2. Learning objectives
Draw and explain the location and function of gustatory
receptors
Draw and explain taste pathway
Describe how different types of tastes are perceived by an
individual
Mention the factors influencing taste sensation
Biefly describe the terms ageusia, hypoguesia & dysguesia
4. Taste
Taste drives appetite and protects us from poisons.
We like the taste of sugar because we have an absolute
requirement for carbohydrates (sugars etc.).
We get cravings for salt because we must have sodium
chloride.
Bitter and sour cause aversive, avoidance reactions
because most poisons are bitter .
5. Taste
We have a need for protein--amino acids
- the building blocks for proteins
The "new" taste quality umami - which is the meaty,
savoury taste drives our appetite for amino acids.
(This taste has been known to the Japanese for a long time -
but has only recently been recognized by the West.)
7. Taste bud
sense organ for taste is
the taste bud which
contains the receptor
cells
taste buds are present
on the palate, pharynx
and papillae of tongue
8. Taste buds
Ovoid bodies measuring 50–70 µm
Made up of supporting cells, basal cells
and 5 -18 receptor cells called gustatory
receptors
Receptor cell has a number of
microvilli projecting into the taste pore
& has a life cycle of few days
Unmyelinated nerve endings innervates
at the base of the receptor cells
9. Papillae
Taste papillae can be seen on the tongue as little red
dots, or raised bumps, particularly at the front of the
tongue.
Fungiform: tip of the tongue
Vallate: arranged in a ‘v’ on the back of the
tongue
Filliform: cover the dorsum of tongue, do not
contain taste buds
Foliate: lateral border of tongue
13. Taste pathway
Sensory nerve fibres from taste buds travel by
three different nerves
– from ant 2/3 of tongue via chorda tympani branch
of facial nerve
– from post 1/3 of tongue via glossopharyngeal nerve
– from pharynx, epiglottis & palate via vagus
14.
15.
16. Taste buds
Taste fibres in VII, IX & X
nerves( I Order Neuron)
Tractus solitarius
(in medulla)
Nucleus tractus solitarius
(II order N.)
? Cross over
Joins medial leminiscus
VPM nucleus of thalamus
(III order N.)
Brodman’s area 43
17. BASIC TASTE SENSATIONS
PRODUCED BY MECHANISM OF
STIMULATION
SENSITIVE
PART OF
TONGUE
SWEET Sugars, glycols & aldehydes. ↑ cyclic AMP→ ↓K+
conductance
Tip
BITTER Alkaloids ↑ IP3→ ↑Ca++ release Posterior
SOUR H+ ions Blocking K+ channels Postero
lateral ½
SALT
UMAMI
Anions of ionised salts
Monosodium glutamate
↑ Na+ ion permeability
Stimulates glutamate
Receptor mGluR4
Antero
lateral ½
_
18. Threshold & Adaptation
Order of increasing threshold
– bitter has lowest threshold, then sour
followed by sweet & salt equally
Taste receptors show adaptation by
elevating the threshold level
20. Gustation and Olfaction
Have you ever wondered why food loses its flavor
when you have a cold?
It's not your taste buds' fault. Blame your stuffed-up
nose.
Seventy to seventy-five percent of what we perceive
as taste actually comes from our sense of smell.
Taste buds allow us to perceive only bitter, salty,
sweet, sour and savoury flavors.
It's the odor molecules from food that give us most of
our taste sensation.
22. Importance of olfaction
In food & sex motivated behaviour olfaction plays
an important role in sub human species & a minor
role in humans.
Thus olfactory impulses are projected both to
– Neocortex
perception & discrimination of odours
– Limbic system
Emotional (Amygdala) , motivational,
behavioral & physiological effects of odours
23. After effects
Some substances alter the taste of other
substances
A plant protein miraculin when applied to
tongue makes acid taste sweet
Betel nut & amla make water taste
sweeter
24. Disorders
Ageusia: Loss of taste sensation
Hypogeusia : Taste sensation is less
Dysgeusia : Disturbed taste sense
Taste blindness :
Phenyl thio carbamide (PTC) tastes
sour to 70% of population but tasteless
to other 30%
