Biological Systems MCAT Practice Exam

What is the primary function of microglia in the central nervous system?

1. Regulate blood flow

2. Produce and circulate cerebrospinal fluid

3. Provide immune defense

4. Generate electrical signals

The correct answer is: Provide immune defense

Microglia play a crucial role in the central nervous system as the primary immune defense cells. They are specialized macrophages that originate from yolk sac progenitors and migrate to the brain during development. Once in the brain, microglia constantly scan their environment for signs of injury or infection. When they detect harmful stimuli such as pathogens, damaged neurons, or other forms of cellular distress, they can activate and transform into a reactive state. In this reactive form, microglia perform several functions essential for maintaining homeostasis and protecting the neural environment. They can phagocytize (engulf and digest) cellular debris and pathogens, thereby contributing to the cleanup of the central nervous system. They also release signaling molecules (cytokines and chemokines) that help recruit other immune cells to the site of injury or infection, further enhancing the immune response. Their ability to respond rapidly to changes in the microenvironment makes them a fundamental component of the neuroimmune system. Therefore, the primary function of microglia is indeed to provide immune defense within the central nervous system, helping to maintain overall brain health and respond to various pathological conditions.