Question

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

Short answer

The correct answer is 'b': a group of neurons that are interconnected and are activated all at once.

Step-by-step solution

Defining a Nerve Net

A nerve net is a type of simple nervous system that is composed of interconnected neurons and does not have a brain or any centralized structure. The neurons in a nerve net are spread out, and most often, if one is stimulated, they all react together.

Comparing With Given Options

Now, comparing this understanding with the given options in the question, clearly option 'b': a group of neurons that are interconnected and are activated all at once corresponds best to the accepted definition of a nerve net.

Eliminating Other Options

Options 'a', 'c' and 'd' describe more complex nervous systems that are usually found in animals that have a centralized nervous system, such as humans and other vertebrates. Option 'c' describes a nerve cord, which is like a simplified version of a spinal cord, while 'd' describes a central nervous system that we commonly associate with vertebrates. Option 'a' describes bilateral neurons which is not a feature specific to nerve nets. Option 'e' can also be eliminated, since it negates all the other options, and we already have a valid answer in option 'b'.

Key concepts

Interconnected Neurons

Interconnected neurons are a fascinating element of biological systems that help organisms respond to their environment. In a nerve net, these neurons are connected in such a way that when one is activated, it often triggers the others. This forms an extensive communication network across the organism's body without a centralized structure like a brain.
Nerve nets are found in simpler organisms such as cnidarians, including jellyfish and sea anemones. These species rely on interconnected neurons to coordinate basic bodily functions, like movement and feeding responses. Think of it as a web of connections—a signal in one part can swiftly travel throughout the entire net, enabling a coordinated reaction from the organism.
The simplicity of nerve nets showcases an evolutionary step before the development of more complex nervous systems like that seen in vertebrates.

Simple Nervous System

A simple nervous system, such as a nerve net, doesn't mean inadequate. Rather, it's perfectly suited to meet the needs of the organism that has it. In simple nervous systems, there is no central processing unit, like a brain. Instead, signals are spread throughout a network of neurons that offer a form of decentralized processing. This setup is particularly advantageous for organisms that don't require complex decision-making processes.
The nerve net allows these organisms to respond to stimuli in a flexible and often rapid manner. Their neurons work together to manage routine tasks such as basic movement or sensory processing. This decentralized method of processing allows for a form of 'thinking' or reaction that isn't reliant on a central authority but is rather a collective effort. For the organisms with simple nervous systems, it is the most efficient way to survive and thrive in their environment.

Centralized Nervous System

Unlike simple nervous systems, a centralized nervous system features a distinct organizational structure that includes a brain and spinal cord. This design is capable of processing more sophisticated information and supporting complex behaviors. In vertebrates and other more evolved creatures, the centralized nervous system acts as the critical command center that interprets input from the environment and dictates responses.
In centralized systems, peripheral nerves extend from the main control hub (the brain or spinal cord) to various parts of the body. This arrangement allows for efficient communication and intricate coordination of diverse body functions, ranging from deliberate movement to emotional response. While different from the decentralized nerve net, the centralized nervous system presents an advanced step in evolution, enabling higher-order tasks and thought processes.

Bilateria

Bilateria refers to animals with bilateral symmetry, which means they have symmetric left and right sides. This group includes most higher organisms, including humans, and represents a significant evolutionary advancement over simpler life forms. With this symmetry usually comes the development of more complex structures, including a centralized nervous system.
The formation of a centralized nervous system is a key characteristic in Bilateria. The presence of bilateral symmetry often goes hand-in-hand with the development of a head region where neural structures are concentrated. This concentration of neurons, often forming a brain, enables nuanced control over diverse activities and an organism's interaction with its environment.
Overall, Bilateria's structure has allowed for complex behaviors, facilitated movement, and has helped species with bilateral symmetry to populate a wide range of niches in various ecosystems across the globe.