Objectives:

• Discover how chemoreceptors make it possible for us to taste and smell.  

• Approach: I have selected two topics about which I have been curious to find out more. For each topic I will pose a question that extends beyond the information presented in the text. I will offer you some URLs where you can investigate additional information on each topic. You can use CUT and PASTE to bring information, including graphics, back to this web page to include in your answers in addition to the writing that you do. You do not have to do the questions in order. As is common on the web, there is always more that you can find to investigate beyond the suggestions I am providing for you.

Dr. Paul Tabor

OK, here are the questions:

1. You probably know that the senses of taste and smell work hand-in-hand.  The sense of smell (olfaction) is the most primal sense we have.  Memories of smell are the strongest memories we have.  The most recent research indicates that the processing and registering of smells in the brain may be the most complex sensory processing we have.  They appear to be recorded in the area of the brain where our earliest memories are recorded.  How do we register a smell?  From very sophisticated neuron lableling experiments in rats, it appears a smell is dissected into the molecular components and each component that can bind an olfactory receptor causes an independent signal in the brain. Here is a diagram of an olfactory receptor neuron.  Alzheimer patients suffer from loss of memory.  Do you think that the loss of recognition of smells is more rapid in Alzheimer patients than in the normal aging population?  What is it like not to be able to smell (here are some personal expressions of what it is like)?  This is called anosmia.  What causes anosmia? Can it be treated? It is of great interest to neurobiologists that only olfactory neurons and neurons of the receptor cells of taste buds can regenerate.  The NIH does support research on smell disorders.   

2. Are tastes processed  the same way?  The knowledge of how we taste at the molecular level is sparse.  Only one gene has been identified that is involved with taste.  It is known that the four types of taste that we are all familiar with are sensed differently.  The tastes of salt and sour involve ion interactions between the ionic tastant molecules of salts and acids and ion channels on cells in the taste buds.  Bitter and sweet are processed differently.  In these cases, the molecules are ligands and bind with specific receptors on cells in the taste buds.  This activates G proteins secondary messengers in cells of the taste buds.  What constitutes a taste bud?  It appears that the recording of tastes in the brain is an indirect process.  The cells of the taste bud with receptors transmit signal to the other receptor cells and only then is a signal sent to the basal cells of the taste bud.  Only then is a signal sent to the brain.  Are there taste disorders?  Are taste disorders serious?  How prevalent are these disorders?  The use of taste intensifiers may make a major impact in reducing malnourishment amongst elderly people who have diminshed senses of taste and smell.   The loss of the sense of smell and taste are losses of warning signals to the body.