The sense of taste allows animals to discriminate between healthful and harmful substances through taste buds located primarily on the tongue. Taste sensations in humans are categorized as salty, sweet, bitter, or sour. The sense of smell, or olfaction, is detected by olfactory receptors located in the nasal cavity. Animals with a well-developed sense of smell are called macrosmatic, while those with a lesser sense of smell are microsmatic. Pheromones allow animals to communicate chemically through scent glands and play roles in behaviors like territory marking and recognizing individuals.

1. TASTE
• The sense of taste is referred to as gustation.
• The function of taste in animals seems to be one
of discrimination; they seem to be able to
discriminate between those substances that are
healthful and harmful.
• Also, foods might be sought that contain
nutrients that are lacking in the diet

2. Taste Reception
• The receptor organ for the sense of taste is the
taste bud.
• Most of the taste buds are located on the
tongue in association with the various papillae
and some are found on the palate, pharynx, and
larynx.
• A collection of taste buds and their locations
relative to a vallate papillus.
• A taste bud contains gustatory cells and
supporting cells

3. • The gustatory cells are the receptors for taste
sensations.
• A tiny hair arises from each and extends into the
pit of the taste bud.
• The pit communicates with the oral cavity by way
of a pore.
• Any substance to be tasted must get into solution
and enter the pore of a taste bud.
• .

4. • The generated impulse is transmitted to the brain
by branches of cranial nerves VII and IX (anterior
two-thirds and posterior third of the tongue,
respectively).
• The afferent ends of these cranial nerve branches
originate at the deep ends of taste buds and are
in intimate contact with the gustatory cells..
• Their watery secretion is conveyed to the
moatlike furrow that surrounds the papillae by
excretory ducts, and the substances to be tasted
are dissolved in it.

5. Taste Sensations
• Taste sensations in humans are classified
according to verbal reports as being salty, sweet,
bitter, or sour.
• Each taste sensation probably results from some
combination of these basic tastes.
• Much of the current opinion about taste
sensations that can be perceived by animals is
based on casual observations.

6. • A common method used to evaluate the sense of
taste in animals is the preference test.
• Accordingly, responses are divided into pleasant,
unpleasant, and indifferent.
• There is considerable individual variation within
species.
• A substance considered to be pleasant by one
dog might be regarded as unpleasant or
indifferent by others.
• Similarly, variability of taste exists among pigs in
the same litter for the same substances.

7. Temperature and Taste
• In humans the temperature of a beverage or
food markedly affects its taste.
• The effect of water temperature and its
acceptance has been studied in domestic fowl.
• Acceptability of water decreases as its
temperature increases above the ambient
temperature.
• Water for domestic fowl that is placed in sunlight
soon becomes warmer than the ambient
temperature and is rejected.

8. • Chickens will suffer from acute thirst rather
than drink water that is 5ºC above their body
temperature (41ºC), but chickens readily
accept water down to the level of freezing.
• Recognition of these preferences is important
for maximum productivity and health in
poultry production.

9. Depraved Appetite
• A depraved appetite is recognized in animals
when they are seen eating dirt, wood, and other
materials not usually considered to be foodstuffs
(this is different from similar habits that can
develop in some animals).
• The depraved condition is termed pica.
• Its exact cause is difficult to determine, but it
could be related to certain dietary deficiencies.

10. SMELL
• As development progressed from the simplest
animal forms, nerve cell bodies migrated
centrally so that only the nerve fibers remained
in a peripheral position.
• Because nerve cell bodies are not regenerated,
this central location provided for greater
protection from destruction.
• If the neuron extensions are injured,
regeneration can occur to some extent.

11. • Central migration did not occur for the nerve cell
bodies of cranial nerve I (olfactory), however,
and they are found in the mucous membrane of
the nasal cavity.
• They are located in what is known as the
olfactory region.
• The size of the olfactory region is directly related
to the degree of development of the sense of
smell, and its size varies among species.

12. • The individual olfactory receptor of the dog is
probably no more sensitive than that of the
human, but their larger olfactory region allows
dogs to detect odorous substances at
concentrations 1 : 1,000 of that detectable by
humans.
• The sensation of smell is known as olfaction.
• Animals with a greatly developed sense of smell
(most domestic animals) are macrosmatic.

13. • A relatively lesser-developed sense of smell is
known as microsmatic; humans, monkeys, and
some aquatic mammals belong to this group.
Animals with no sense of smell (e.g., many
aquatic mammals) are anosmatic.
• Macrosmatic animals can become microsmatic
or anosmatic, and microsmatic animals can
become anosmatic because of disease loss of
cells or temporary impairment.
• The peripheral location of the olfactory nerve cell
bodies renders them more susceptible to
destruction from inflammatory disease.
• Sensitivity to smell probably decreases with time.

14. Olfactory Region Structure
• A microscopic view of a section taken from the
olfactory region is shown in Figure 5-4.
• Each olfactory receptor cell has a cell body and
a nerve fiber extending from each of its ends,
one a dendrite and the other an axon (see Fig. 5-
4).
• The dendritic process of the olfactory cell
extends to the outside of the olfactory region.

15. • The sustentacular cells seem to provide major
support to the dendritic processes and allow for
the olfactory cell bodies to be shielded from the
nasal cavity.
• At this location there might be several hairlike
structures (olfactory cilia) extending into the
nasal cavity from the olfactory vesicles
(expanded part of a dendrite).
• Usually they are covered with a thin secretion
from the glands of Bowman (subepithelial
glands).

16. • The ducts of these glands lead through the
epithelium to the surface.
• Their secretion constantly freshens the thin layer
of fluid that continuously bathes the olfactory
hairs on the surface of the olfactory region.
• Sniffing allows for the backand- forth movement
of air and provides a greater chance for the
substance to be smelled to go into solution.
• This becomes the stimulus for the impulse to be
transmitted to the brain.

17. • The axons of the olfactory cells join with others
and proceed with them as fibers and branches of
the olfactory nerves.
• Basal cells divide and differentiate into either
sustentacular cells or olfactory cells (replacement
of a nerve cell).
• This is a safeguard against loss of smell that might
otherwise occur as a result of nasal mucosal
disease.

18. Odor Perception
• Considering the great number of smell
possibilities, it is unlikely that a specific type of
olfactory cell exists for each smell.
• It is more probable that basic smells combine to
provide the sensation for a particular odor.
• Only one odor can be perceived at any one time.
• Some room deodorants are effective because
they can stimulate olfactory cells more than the
offensive odor.

19. • The offender is not eliminated; it is only masked.
• The olfactory cells become adapted to odors so
that they do not persist for a particular
individual.
• This is why the smell of fresh baked bread is so
apparent when someone enters a bakery,
whereas the baker might not even smell it
anymore.

20. Pheromones
Animals use odors to communicate with each
other.
Black-tailed deer and Rocky Mountain mule deer
have been found to use the tarsal glands on the
insides of their hind legs as transmitters of odors
to identify species as friendly or alien to their
own kind.
• The scent is deposited on the skin and hair by
the tarsal glands, and communication is
established by sniffing other members of their
group approximately once each hour.

21. • A chemical secreted by one animal that
influences the behavior of other animals is
known as a pheromone.
• The first chemical analysis of a mammalian
pheromone was accomplished using the deer
tarsal gland substance.
• Some animals have scent glands in the spaces
between their hoof pads.
• Rabbits have a scent gland on the chest and
around the anal opening.

22. • Cats have glands on the forehead and mark people
or objects by rubbing their heads on them.
• Pheromones provide for a chemical language among
animals for certain purposes, such as marking trails
or boundaries, recognizing individuals from the
same herd or nest, marking the location of food
sources, and emitting alarms.