Select the related word from the given alternatives.
Kidney : Nephron :: Central Nervous System : ?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Neurons
The pair is an organ (or system) and its structural and functional unit. The nephron is the unit of the kidney: each kidney has about a million nephrons, and each filters blood and forms urine.
In the same way, the neuron (nerve cell) is the structural and functional unit of the nervous system: the central nervous system is built of neurons, which carry messages as nerve impulses.
Why the other options are incorrect
Option (1) Spinal Cord — Incorrect. It is one of the two parts of the central nervous system, itself made of neurons.
Option (2) Cerebrum — Incorrect. It is the largest part of the brain, an organ part, not the basic unit.
Option (3) Brain — Incorrect. It is the other part of the central nervous system, an organ made of millions of neurons.