Chapter 42, Problem 1TY

A nerve net consists of

1. a. bilateral neurons that extend from the head of the animal to the tail.
2. b. a group of neurons that are interconnected and are activated all at once.
3. c. a single nerve cord with ganglia in each body segment.
4. d. a central nervous system with peripheral nerves associated with different body structures.
5. e. none of the above.

Summary Introduction

Introduction: Nervous system is a system in the body that helps in the transfer of information from one part to another. Most of the animals constitute a well-defined nervous system. The body parts communicate with each other and with the external environment through the nervous system. Humans have the most complex nervous system.

Answer to Problem 1TY

Correct answer: A nerve net is composed of a group of neurons that are interconnected. All these interconnected neurons are activated at once. Hence, the correct answer is option b.

Explanation of Solution

Reason for correct answer:

Different organisms have different types of nervous system. Some of the organisms contain a complex nervous system such as in humans. However, few organisms have the simplest form of a nervous system that is the nerve net. It is observed in radially symmetrical species, such as jellyfish and hydras. The nerve net is composed of many interconnected neurons. This system has a unique feature that is the activation of one neuron initiates the activation of the rest of the neurons. This indicates that all the neurons present in the nerve net are activated together at once.

Option b. is given as “a group of neurons that are interconnected and are activated all at once”.

A group of interconnected and activated neurons forms a nerve net. All the neurons present in a nerve net are all activated together. Hence, the correct answer is option b.

Reasons for incorrect answer:

Option a. is given as, “bilateral neurons that extend from the head of the animal to the tail”.

The nerve net is observed only in the radially symmetrical species. It is not present in bilateral organisms. This indicates that the nerve net is not composed of bilateral neurons. It contains the directly interconnected neurons. Hence, option a. is incorrect.

Option c. is given as, “a single nerve cord with ganglia in each body segment”.

The nerve net does not contain any nerve cord or ganglia. The nerve net is composed of interconnected neurons only. Hence, option c. is incorrect.

Option d. is given as, “a central nervous system with peripheral nerves associated with different body structures”.

The nervous system that contains a central nervous system is not observed in the nerve net. The nerve net rather contains simple and directly interconnected neurons. Hence, option d. is incorrect.

Option e. is given as, “none of the above”.

All the options are not true about nerve net except option b. Nerve net is defined correctly in option b. Hence, option e. is incorrect.

Hence, the options a., c., d., and e. are incorrect.

Conclusion

Therefore, a nerve net is a collection of interconnected and activated neurons. All the neurons present in a nerve net are activated together at once.