Page 250 - Anatomy and Physiology of Farm Animals, 8th Edition

Sense Organs / 235

called taste cells, are arranged in a group part of the tongue is conveyed by fibers
of the glossopharyngeal nerve. Somatic
with supporting cells, a cluster that consti­
VetBooks.ir tutes the taste bud (Fig. 12‐4). Taste buds sensations (heat, cold, touch, pain) from
the tongue are conveyed by branches of the
are not distributed evenly on the surface of
the tongue; they are confined to specific trigeminal and glossopharyngeal nerves.
forms of papillae (tiny projections), the Taste buds on areas other than the tongue
vallate, foliate, and fungiform papillae, (e.g., soft palate) are innervated by the
which are found on the tongue (the greatest vagus nerve.
number), soft palate, parts of the pharynx, Traditionally, four basic taste sensations
and epiglottis of the larynx. had been identified. These are sweet,
Sensory nerve fibers subserving taste salt, bitter, and sour. Individual taste
are distributed to the rostral portions of cells have membrane receptor physiology
the tongue by a branch of the facial nerve, designed to detect the chemical substances
the chorda tympani. Taste in the caudal associated with these tastes. The more
complex sensory experiences that we
(A) normally associate with taste (for example,
the flavors that we detect when we distin­
guish between an apple and a carrot) are
created primarily from stimulation of
olfactory (smell) receptors in combination
with the basic taste modalities. For them to
stimulate taste cells, chemicals must be in
solution. Dissolution of substances so
that they can be tasted is an important
function of saliva.
In addition to the four basic tastes, a fifth
taste modality with its own specific taste
cell receptor is also recognized. This taste,
experienced when the amino acid gluta­
mate is present along with sodium, imparts
(B) a savory quality to foodstuffs. Because
this taste modality was first described by
Japanese researchers, it is known by the
Japanese word for savory or delicious:
umami. It is the presence of the umami
taste receptor that explains the enhanced
flavor of foods when monosodium gluta­
mate (MSG) is added.

Olfaction

Olfaction is the sense of smell. Olfactory
sensory neurons are scattered among
Figure 12-4. Photomicrograph of lingual supporting cells throughout the olfactory
papillae. (A) 10 ×, box indicates single taste bud
on lateral aspect of papilla. (B) 40 × of several mucosa in the dorsocaudal part of the nasal
taste buds; arrow indicates opening (taste pore) cavity (Fig. 12‐5). The apex of each olfac­
into bud which allows dissolved substances to tory neuron bears a single dendrite with a
contact taste cells. Source: micrograph courtesy of tuft of several fine hair‐like projections,
Gretchen Delcambre, Colorado State University, which bear the chemical receptors for the
Fort Collins, Colorado, USA. sense of smell. An axon from each olfactory