**Core Concept**
The central nervous system (CNS) contains a unique population of macrophages, known as microglia, which play a crucial role in maintaining immune homeostasis and responding to pathological insults within the brain and spinal cord.

**Why the Correct Answer is Right**
Microglia are resident macrophages of the CNS, derived from the yolk sac and migrating to the brain during embryonic development. They are the primary immune cells of the CNS, responsible for phagocytosing foreign substances, dead neurons, and other cellular debris. Microglia also play a key role in neuroinflammation, releasing cytokines and chemokines in response to pathogens or injury. Their unique morphology, with branching processes and a small cell body, allows them to survey the surrounding tissue and respond rapidly to changes.

**Why Each Wrong Option is Incorrect**
**Option A:** does not apply, as this option is not related to the question.
**Option B:** This option might refer to other types of immune cells, such as T cells or B cells, which are not the primary macrophages of the CNS.
**Option C:** This option might refer to astrocytes, which are a type of glial cell that provide support and nutrition to neurons, but are not macrophages.

**Clinical Pearl / High-Yield Fact**
Microglia can be activated in response to various pathological insults, including infection, trauma, and neurodegenerative diseases, leading to the release of pro-inflammatory cytokines and the exacerbation of tissue damage.

**Correct Answer: C. Microglia.**