Question

In earthworm, neurons are (a) sensory only (b) motor only (c) associated only (d) all of these.

Short answer

In earthworms, neurons include sensory, motor, and associative types, so the correct answer is (d) all of these.

Step-by-step solution

Understanding Neuron Functions

Neurons in any organism, including earthworms, can serve one or more basic functions: sensory for sensing the environment, motor for activating muscles and glands, and associative (interneurons) for connecting neurons within the central nervous system.

Identifying Earthworm Neuron Types

In an earthworm, neurons are not specialized into only one of these types. Instead, they have a combination of sensory, motor, and associative neurons to function effectively.

Choosing the Correct Option

Based on the functions of neurons present in earthworms, the correct option is that they contain all of these neuron types: sensory, motor, and associative.

Key concepts

Sensory Neurons

Sensory neurons play a critical role in how organisms, including earthworms, interact with their environment. These neurons are like messengers, carrying information from the sensory receptors, such as the skin, eyes, ears, and nose, to the central nervous system.

For instance, if an earthworm comes into contact with a harmful substance, it is the sensory neurons that pick up this signal and send it to the brain. The brain then processes this information, allowing the earthworm to react accordingly. Without sensory neurons, organisms would lack a fundamental connection to their surroundings, which could mean the difference between survival and peril.

Motor Neurons

Motor neurons are the counterparts to sensory neurons; they take the baton in the relay of nerve impulses, carrying instructions from the central nervous system back out to the muscles and glands. Just as a pianist's fingers respond to messages sent from the brain to play a chord, an earthworm's muscles contract to move its body in response to signals from motor neurons.

These neurons are indispensable for voluntary movements, such as an earthworm burrowing into the soil, as well as involuntary actions like the beating of a heart. Essentially, motor neurons are the executors that translate the brain's commands into physical action, enabling movement and interaction.

Associative Neurons

Associative neurons, or interneurons, are the complex highways of the nervous system, connecting sensory and motor neurons within the brain and spinal cord. By forming networks, they facilitate communication between neurons, which is vital for processing information and executing coordinated responses.

Picture an earthworm encountering moisture in the soil. Associative neurons help integrate the sensory signal of moisture with an appropriate motor response, like moving towards the source. These neurons are the unsung heroes behind complex behaviors and reflex actions, integrating multiple streams of information to direct a comprehensive response.

Neuron Functions in Organisms

The neurons in organisms, including humble earthworms, are not mere cellular structures; they are dynamic and multifunctional elements that confer survival advantages. They are involved in the reception of sensory data, the processing of this information, and the issuance of motor outputs to orchestrate a symphony of actions and reactions.

It is the interplay of sensory, motor, and associative neurons that allows not just earthworms, but all organisms, to process complex information from the environment, make decisions, and learn from experiences. Whether it's responding to predators or finding food, neuron functions are integral to the daily life and evolutionary success of organisms.