Chapter 51. Sense of Smell

Learning Objectives

axon

part of a neuron specialized to send impulses to other neurons (or to muscles or glands)

olfactory cortex

part of the brain that processes information about smell; located at the lower edges of the frontal and temporal lobes

olfaction

the sense of smell

olfactory receptor cells

specialized cells in the nose that detect chemicals floating in the air; located at the top of the nasal cavity

olfactory bulb

tube-shaped structure at the lower front of the brain that receives signals from the olfactory receptor cells

Sense of Smell

true

Photo: Close-up photo of a person smelling a flower

Aleksandr Markin/Shutterstock

Learning Objective:

Describe the sequence of events that allows a person to smell an odor.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

The figure is a side image of the head and brain. Odor molecules travel from flowers inside the nose and up the nasal cavity, a large area going from the nose to the throat. At the top of the nasal cavity the odor molecules stimulate the olfactory receptors, which connect the nasal cavity to the front of the brain.

1. How do we smell the odors around us? Many substances, especially foods, release molecules into the air. The act of breathing draws these molecules into our nostrils, where they stimulate olfactory receptor cells located high in the nasal cavity.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

The figure shows an enlarged view of the olfactory receptors at the top of the nasal cavity. There are three layers to the image. At the bottom are the olfactory receptor cells, which match to specific odor molecules. The messages from the olfactory receptors travel up through the next layer, which is bone. Then the messages travel up to the last layer to arrive in the olfactory bulb in the brain.

2. The axons from these olfactory receptor cells travel through small openings in the bone that divides the nasal cavity from the brain. They enter the olfactory bulb, where the signals from many receptor cells converge to create messages that can be carried to the olfactory cortex in the brain.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

asset/activities/smell/images/review_3-v2.svg

3. Humans have several hundred different types of olfactory receptor cells, and the brain combines the messages from these cells to detect about 10,000 different odors. There is no specific odor for “spaghetti” or any other food. Instead, each recognizable odor represents a specific profile of many olfactory cells responding simultaneously.

Review

concept_review

Review

Select the NEXT button to continue with the Review.

Photo: dog (beagle preferred) sniffing the ground or an object

iStock/Getty Images

4. Although human olfaction (sense of smell) is impressive, most animals are much more sensitive to odors. Each human olfactory receptor cell is about as good as a single cell from animals with a superior sense of smell. But, those animals have many more receptors, with a larger portion of their brains dedicated to analyzing smells.

Practice: Detecting and Identifying Odors

video

true

Practice: Detecting and Identifying Odors

Play the animation to watch the sequence of events that allow this person to smell the flower.

asset/activities/smell/video/smell.mp4

Quiz 1

dnd_test

Quiz 1

Drag each event to arrange the events in the proper sequence. After all the events have been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.

Perhaps you should go back to review the sequence of events that allows a person to smell an odor.

Receptor cells are activated

Odor molecules drawn into nose

Odor molecules bind to receptors

Signal goes to olfactory bulb

Message goes to higher brain centers

Odor molecules released by flower

Quiz 2

radio_quiz_upd

1,0,0,1,1,0

Select the NEXT button and move to the Conclusion.

Try to respond to the statements again.

Quiz 2

For each statement, select one of the buttons to indicate whether the statement is True or False. When a response has been placed for all statements, select the CHECK ANSWER button.

True

False

The sense of smell is called olfaction.

The olfactory bulb is located near the tip of the nose.

The olfactory receptor cells detect the various molecules in the air we breathe.

Conclusion

end_slide

Close-up photo of a person smelling a flower

Aleksandr Markin/Shutterstock

Congratulations!

You have completed
Sense of Smell