Module 7.3 Chemical Senses- Gustation

CHEMICAL CODING
Most evolutionary scientists believe that the first sensory system of the earliest animal was a chemical sensitivity.  Before the neocortex (Forebrain) evolved, there were areas of the midbrain and hindbrain devoted solely to sensing.  Information on the Cranial Nerves are listed in a chart of the book on pg 92, table 4.4; The cranial nerves are illustrated on pg 85 (unit 5.7) of the coloring book.

What are the functions associated with the following cranial nerves (CN):
CN I.
CN II.; III, IV AND VI
CN V. AND VII
CN VIII
CN IX AND XII
CN X AND XI

STIMULUS
 Organic substances containing chemicals that are perceived as sweet-sucrose, sour-HCL, bitter-quinine, salty-NaCl and umami or meaty-MSG.  A combinaion of activity in five kinds of receptors (along with smell) give the perception of the taste of the food.

Taste buds are contained in papillae Taste receptors have excitable membranes and release neurotrnsmitters to excite other cells. Taste receptors are regenerated and replaced every 10-14 days, which is why food may taste more intense after an illness or after an extended fast.  Taste receptors are located inside of tastebuds which are located in the papillae of the tongue.

TRANSDUCTION
When a substance tastes salty for instance, it means that a salitness receptor has detected the presence of sodium. Sodium ions cross into the membrane and produces an action potential.  Sweetness, bitterness and umami receptors resemble the action of metabotropic receptors and therefore activate G-protein molecules and second messengers within the cell.

TRANSMISSION
Although each receptor detects one kind of taste, several receptors create a particular firing pattern that is perceived as a single taste experience. Information from the receptors in the anterior 2/3 of the tongue synpase with the Chorda Tympani nerve and information from the posterior tongue and the throat travel along branches of the Cranial Nervs IX and X.  What are the names of Cranial Nerves IX and X?

 Taste nerves project to the nucleus of the solitary track (NTS) in the medulla. From the NTS, the information branches out to the pons, the lateral thalamus, the amygdala and the ventral posterior thalamus (VPN), finally terminating into areas of the cerebral cortex. The somatosensory cortex is where touch or food texture is detected on the tongue and the insula or primary taste cortex is where taste is perceived..  Innervation is ipsilateral in this sensory modality. 

SENSATION, PERCEPTION AND COGNITION
  The sensation of taste can be affected by culture and familiarity but also by genes and hormones. Give examples from the textbook on how genetic differences affect taste. Also how do hormones affect taste preferences, according to the text?


 
 PUT IT ALL TOGETHER
For the final exam, you should know the answer to the questions in red above.  Also you should be able to associate the following terms within the correct cell of the class schema.

 NaCl
Nucleus of the Solitary Tract
papillae 
Primary gustatory cortex
saliva
taste buds
taste receptors
teeth
tongue 
unami
Vagus Nerve
VEntral Posterior nucleus