Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

Discuss Concepts Most sensory neurons form synapses either on interneurons in the spinal cord or on motor neurons. However, in many vertebrates, certain sensory neurons in the nasal epithelium synapse directly on brain neurons that activate behavioral responses to odors. Suggest at least one reason why natural selection might favor such an arrangement.

Summary Introduction

To review:

In case of some vertebrates, nasal epithelium synapse directly with the brain neurons that activate behavioral responses to odors. Reviewing the reason for this type of development in animals favored by natural selection.


Animal brains are filled with neurons in which analysis of stimulus, that comes from all over the body takes place. Sensory neurons are associated with sensory organs such as skin, or other sensory organs. They carry impulse to the CNS (central nervous system), that is, the brain and the spinal cord. Motor neuron carries impulse or messages from the brain to the muscles hence, known as a motor neuron. Interneurons are present between these two neurons and they relay and carry electric impulses in between the central nervous system.


Stimulus perceived through sense organs like skin, eye, nose, and then the message or impulse are sent to the spinal cord via sensory neurons. sensory neurons connect with either spinal cord or interneurons via a synapse. So, electric impulse normally is sent to the spinal cord or interneuron first then is relayed to the brain if needed.

Normally nose is present just below the head so, it is easier to send the neuron directly to the brain than to send it to the spinal cord, as spinal cord presents far away from the nose. It would have been time consuming to send the impulse to the spinal cord and then to the brain. This type of neural arrangement could have decreased the survival rate of the animal,

Although, in many vertebrates, neurons of nasal epithelium directly synapse with the brain neurons instead of interneuron or spinal cord...

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