The blood-brain barrier is primarily composed of:

 A) Astrocytes

 B) Ependymal cells

 C) Microglia

 D) Endothelial cells

 Answer: D) Endothelial cells

 Rationale: The blood-brain barrier is formed by endothelial cells

that tightly regulate the passage of substances from the bloodstream

into the brain.

Which structure is responsible for the production of cerebrospinal

fluid?

 A) Arachnoid villi

 B) Choroid plexus

 C) Dura mater

 D) Pia mater

 Answer: B) Choroid plexus

 Rationale: The choroid plexus produces cerebrospinal fluid, which

cushions the brain and spinal cord.

During muscle contraction, what role does calcium ion (Ca2+) play?

 A) It breaks down ATP to release energy.

 B) It binds to troponin, changing its shape and removing the

blocking action of tropomyosin.

 C) It forms cross-bridges with myosin heads.

 D) It depolarizes muscle fibers to initiate contraction.

 Answer: B) It binds to troponin, changing its shape and removing

the blocking action of tropomyosin.

 Rationale: Calcium ions bind to troponin during muscle