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Section II: Sensory Systems
9. Chemical Senses: Olfaction and Gustation
Part 4 of 4

Max O. Hutchins, Ph.D.
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Neural Pathway into the Olfactory Cortex

Axons from mitral and tuft cells project caudally into the olfactory tract. Fibers diverge and synapse with neurons of the anterior olfactory nucleus (AON). Axons from the AON cross to the opposite side of the hemisphere through the anterior commissure. The majority of the axons from the olfactory bulb diverge laterally and form the lateral olfactory tract which synapse with nuclei of the olfactory cortex. These are the piriform cortex (pc), the periamygdaloid cortex, part of the amygdala, and hippocampus. There are no direct relays from the olfactory bulb into the thalamus, but a few fibers synapse with 3rd order sensory neurons in the thalamic dorsomedial nucleus which are projected to the ipsilateral cerebral hemisphere (Figure 9.11).


Figure 9.11

Projection of olfactory bulb into the olfactory cortex.

Conclusion

In conclusion, many olfactory receptors respond to more than one odorant quality just like the taste receptor cells. Coding of the primary odor depends on the intensity of the odor and on a population response within the olfactory neurons. During neural processing in the olfactory bulb, a particular discharge occurs to one odorant and a different pattern for another odorant. This sensory input must be processed before being relayed to the olfactory cortex for perception and recognition of the individual odor.

 

Test Your Knowledge

  • Question 1
  • A
  • B
  • C
  • D
  • E

Second-order sensory neurons for taste are located in the

A. Insula

B. Amygdala

C. Nucleus solitarius

D. Uncus

E. Trigeminal ganglion

Second-order sensory neurons for taste are located in the

A. Insula This answer is INCORRECT.

The insula is not the site for the 2nd order neurons but does have gustatory and autonomic areas.

B. Amygdala

C. Nucleus solitarius

D. Uncus

E. Trigeminal ganglion

Second-order sensory neurons for taste are located in the

A. Insula

B. Amygdala This answer is INCORRECT.

The amygdale is a main component of the limbic system and has areas for olfaction.

C. Nucleus solitarius

D. Uncus

E. Trigeminal ganglion

Second-order sensory neurons for taste are located in the

A. Insula

B. Amygdala

C. Nucleus solitarius This answer is CORRECT!

Afferents from the 1st order sensory neurons of the facial, glossopharyngeal and vagus nerves terminate on 2nd order neurons in the nucleus solitarius.

D. Uncus

E. Trigeminal ganglion

Second-order sensory neurons for taste are located in the

A. Insula

B. Amygdala

C. Nucleus solitarius

D. Uncus This answer is INCORRECT.

The uncus is a small gyrus near the olfactory cortex.

E. Trigeminal ganglion

Second-order sensory neurons for taste are located in the

A. Insula

B. Amygdala

C. Nucleus solitarius

D. Uncus

E. Trigeminal ganglion This answer is INCORRECT.

First-order sensory neurons for sensory input from the orofacial region are located in this large ganglion.

 

 

 

 

 

 

 

 

  • Quetion 2
  • A
  • B
  • C
  • D

All of the following statements are correct about the olfactory receptor neruons EXCEPT:

A. These specialized neurons are replaced about every 5- 8 weeks.

B. Each neuron contains receptors which are specific for a single odorant molecule.

C. The axon of each olfactory neuron synapses in only one glomerulus in the olfactory bulb.

D. Odorant molecules interact with receptors coupled to a G protein called Golf.

All of the following statements are correct about the olfactory receptor neruons EXCEPT:

A. These specialized neurons are replaced about every 5- 8 weeks. This is not the exception.

Olfactory neurons are replaced by basal cells.

B. Each neuron contains receptors which are specific for a single odorant molecule.

C. The axon of each olfactory neuron synapses in only one glomerulus in the olfactory bulb.

D. Odorant molecules interact with receptors coupled to a G protein called Golf.

All of the following statements are correct about the olfactory receptor neruons EXCEPT:

A. These specialized neurons are replaced about every 5- 8 weeks.

B. Each neuron contains receptors which are specific for a single odorant molecule. This IS the exception, and is an incorrect statement!

Olfactory receptors interact with many different odorant molecules with the generation of a neural code that permits us to discrimination between odors.

C. The axon of each olfactory neuron synapses in only one glomerulus in the olfactory bulb.

D. Odorant molecules interact with receptors coupled to a G protein called Golf.

All of the following statements are correct about the olfactory receptor neruons EXCEPT:

A. These specialized neurons are replaced about every 5- 8 weeks.

B. Each neuron contains receptors which are specific for a single odorant molecule.

C. The axon of each olfactory neuron synapses in only one glomerulus in the olfactory bulb. This is not the exception.

Axons of each olfactory neurons interact with only one glomerulus.

D. Odorant molecules interact with receptors coupled to a G protein called Golf.

All of the following statements are correct about the olfactory receptor neruons EXCEPT:

A. These specialized neurons are replaced about every 5- 8 weeks.

B. Each neuron contains receptors which are specific for a single odorant molecule.

C. The axon of each olfactory neuron synapses in only one glomerulus in the olfactory bulb.

D. Odorant molecules interact with receptors coupled to a G protein called Golf. This is not the exception.

Receptors interact with and produce a release of active G-protein which activate cAMP.

 

 

 

 

 

 

 

  • Question 3
  • A
  • B
  • C
  • D

Which of the following cells are 2nd order neurons with axons projecting into the anterior olfactory cortex?

A. Mitral cells

B. Glomerular cells

C. Periglomerular cells

D. Granule cells

Which of the following cells are 2nd order neurons with axons projecting into the anterior olfactory cortex?

A. Mitral cells This answer is CORRECT!

Mitral cells and tufted cells in the lamina of the olfactory bulb send axons into the olfactory cortex.

B. Glomerular cells

C. Periglomerular cells

D. Granule cells

Which of the following cells are 2nd order neurons with axons projecting into the anterior olfactory cortex?

A. Mitral cells

B. Glomerular cells This answer is INCORRECT.

There are no glomerular cells in the olfactory bulb, but a site where many olfactory receptor neurons converge on the mitral and tufted cells.

C. Periglomerular cells

D. Granule cells

Which of the following cells are 2nd order neurons with axons projecting into the anterior olfactory cortex?

A. Mitral cells

B. Glomerular cells

C. Periglomerular cells This answer is INCORRECT.

The periglomeurlar cells are inhibitory and by lateral inhibition control output from the glomeruli.

D. Granule cells

Which of the following cells are 2nd order neurons with axons projecting into the anterior olfactory cortex?

A. Mitral cells

B. Glomerular cells

C. Periglomerular cells

D. Granule cells This answer is INCORRECT.

The granule cells also modulate activity from the mitral cells and tufted cells.

 

 


 

 

 

 

 

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