The brain is protected by:

Correct Answer: D

Rationale: The brain is protected by multiple layers of defense, including the meninges (protective membranes), cerebrospinal fluid (a cushioning fluid), and the bony skull. The meninges consist of three layers—dura mater, arachnoid mater, and pia mater—that provide structural support and protection. Cerebrospinal fluid surrounds the brain and spinal cord, acting as a shock absorber. The skull provides a rigid barrier against physical injury. Together, these structures safeguard the brain from damage.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: D

Rationale: Dantrolene, a peripherally acting muscle relaxant, acts directly on spastic muscles and inhibits muscle contraction by preventing the release of calcium in skeletal muscles. Anticholinergic drugs or muscarinic antagonist block acetylcholine at the neuromuscular junction. Baclofen, a centrally acting muscle relaxant, relieves spasticity by interrupting nerve signals from the spinal cord. Most drugs used to treat myasthenia gravis act by preventing the destruction of acetylcholine at the neuromuscular junction.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: Semaphorins and Eph ligands act as guidance cues for growing axons. They generally function as repulsive signals, causing growth cones to turn away from inappropriate regions. This ensures precise navigation of axons to their correct targets, which is essential for establishing functional neural circuits.