Book cover for Biology

Biology

Sylvia S. Mader, Michael Windelspecht

ISBN #9780078024269

12th Edition

687 Questions

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153,501 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter explores the evolution of the nervous system from simple, diffused networks in primitive organisms like hydra, through the development of cephalization and paired nerve cords in annelids, to the sophisticated, specialized neural structures found in vertebrates. Key evolutionary trends such as centralization of neural tissue and increased specialization underpin the development of complex behaviors and an active lifestyle, providing a clear framework for understanding the division between the central and peripheral nervous systems.

Learning Objectives

1

Explain the evolutionary progression of nervous systems from simple organisms to vertebrates.

2

Identify and describe key trends such as cephalization, paired nerve cords, and neural specialization.

3

Differentiate between the central and peripheral nervous systems and their roles in complex behaviors.

4

Analyze comparative studies of nervous tissue complexity across different animal groups.

Key Concepts

CONCEPT

DEFINITION

Cephalization

The evolutionary trend of forming a centralized nerve center (brain) in the head region, leading to more specialized neural functions.

Diffuse Nerve Net

A simple, spread-out network of neurons, as seen in organisms like hydra, that allows for basic responses and coordination.

Central Nervous System (CNS)

The part of the nervous system that includes the brain and spinal cord, responsible for processing and integrating information.

Peripheral Nervous System (PNS)

The network of nerves that lie outside the central nervous system, connecting the CNS to limbs and organs, important for transmitting signals to and from the brain.

Neural Specialization

The process by which neurons and neural structures become more specialized in their functions, allowing for complex behaviors and advanced adaptations.

Example Problems

Example 1

Which type of animal has a nerve net? a. cnidarians b. planarians c. sponges d. All of these are correct

Example 2

The most intelligent invertebrates are probably the a. annelids. b. arthropods. c. cephalopods. d. None of these can be regarded as intelligent.

Example 3

The part of the brain that is seen only in mammals is the a. cerebellum. b. cerebrum. c. neocortex. d. olfactory bulb.

Example 4

Which of these correctly describes the distribution of ions on either side of an axon when it is not conducting a nerve impulse? a. more sodium ions ($\mathrm{Na}^{+}$) outside and fewer potassium ions ($\mathrm{K}^{+}$) inside b. $\mathrm{K}^{+}$ outside and $\mathrm{Na}^{+}$ inside c. charged proteins outside; $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ inside d. charged proteins inside e. Both a and d are correct

Example 5

When the action potential begins, sodium gates open, allowing $\mathrm{Na}^{+}$ to cross the membrane. Now the polarity changes to a. negative outside and positive inside. b. positive outside and negative inside. c. There is no difference in charge between outside and inside. d. None of these are correct.
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Step-by-Step Explanations

QUESTION

How did nervous systems evolve from simple to complex structures across different organisms?

STEP-BY-STEP ANSWER:

Step 1: Identify primitive nervous systems such as the diffuse nerve net in hydra, where neurons are distributed throughout the body.
Step 2: Observe the trend of cephalization, where neural tissue becomes concentrated in the head region to facilitate more advanced sensory processing.
Step 3: Recognize the development of paired nerve cords in organisms like annelids (earthworms), representing an early form of segmentation and centralized control.
Step 4: Understand that increasing neural specialization allowed for more complex behaviors and active lifestyles, ultimately leading to the development of sophisticated systems in vertebrates.
Final Answer: Nervous systems evolved from a simple diffuse network in primitive animals to highly centralized and specialized systems through trends like cephalization, paired nerve cords, and neural specialization.

Evolution of the Nervous System

QUESTION

What are the primary differences between the central nervous system and the peripheral nervous system?

STEP-BY-STEP ANSWER:

Step 1: Recognize that the CNS is composed of the brain and spinal cord, serving as the central processing unit for the body.
Step 2: Understand that the PNS includes all the nerves that extend from the CNS to the rest of the body, transferring signals to and from the brain.
Step 3: Consider the functional specialization in vertebrates, where the CNS handles integration of sensory data and decision-making, while the PNS manages the execution of these commands on the periphery.
Final Answer: The CNS is the brain and spinal cord that process information centrally, whereas the PNS is a network of nerves that connects the CNS with the rest of the body to coordinate actions and responses.

Differentiating CNS and PNS

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Common Mistakes

  • Assuming that all organisms have a centralized nervous system similar to vertebrates.
  • Confusing the roles of the CNS and PNS, leading to misunderstanding of their functions.
  • Overlooking the gradual nature of neural evolution and the significance of intermediate forms like paired nerve cords in annelids.
  • Believing that neural specialization is exclusive to advanced organisms, rather than recognizing its incremental development over evolutionary time.