Structural and functional units of nervous system are neurons/nephron.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the structural and functional units of the nervous system, providing two options: neurons and nephron.

2. **Defining Neurons**: Neurons are specialized cells that transmit nerve impulses. They are the basic building blocks of the nervous system and are responsible for carrying signals throughout the body. This includes communication between the brain, spinal cord, and other parts of the body.

3. **Defining Nephrons**: Nephrons are the structural and functional units of the kidney. Their primary role is in the filtration of blood and the formation of urine, which is unrelated to the functions of the nervous system.

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