The correct option is
B. Axon.
Explanation of the Correct Answer
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Understanding Neuron Structure: Neurons are specialized cells that transmit nerve impulses throughout the body. They consist of three main parts: the cell body (soma), dendrites, and axons.
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Role of the Axon: The axon is a long, slender projection that extends from the neuron cell body. Its primary function is to carry electrical impulses (action potentials) away from the cell body to other neurons, muscles, or glands. The axon can be quite long, allowing it to transmit signals over considerable distances.
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Action Potential Transmission: When a neuron is activated, an action potential is generated. This is a rapid change in electrical charge that travels along the axon. The axon is often covered by a myelin sheath, which is a fatty layer that insulates the axon and speeds up the transmission of impulses. However, the axon itself is the structure that conducts the impulse away from the cell body.
Why the Other Options are Incorrect
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A. Dendrite: Dendrites are the branched extensions of a neuron that receive signals from other neurons. They are responsible for bringing information into the neuron, not transmitting impulses away from it. Therefore, they play a crucial role in receiving signals but do not carry impulses away from the cell body.
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C. Synapse: A synapse is the junction between two neurons where communication occurs. It is not a structure that transmits impulses; rather, it is the site where neurotransmitters are released to pass signals from one neuron to another. The synapse facilitates communication but does not conduct impulses away from the neuron.
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D. Myelin sheath: The myelin sheath is a protective covering that surrounds the axon in many neurons. While it plays a critical role in speeding up the transmission of nerve impulses (by allowing the action potential to jump between nodes of Ranvier), it is not the structure that transmits the impulses itself. The myelin sheath enhances the function of the axon but does not replace its role.
Summary of Key Points
- The axon is the primary structure responsible for transmitting nerve impulses away from the neuron cell body.
- Dendrites receive signals, while synapses facilitate communication between neurons.
- The myelin sheath insulates the axon and speeds up impulse transmission but does not conduct impulses itself.
- Understanding the roles of different neuron structures is crucial for grasping how nerve impulses are transmitted in the nervous system.
Revision Summary
- The axon transmits nerve impulses away from the neuron cell body.
- Dendrites receive incoming signals from other neurons.
- Synapses are junctions for communication between neurons.
- The myelin sheath insulates axons and enhances impulse speed.