Final answer:
The brain is protected against trauma and infection by bones, meninges, cerebrospinal fluid, and the blood-brain barrier, all of which form a multi-layered defense system that filters substances entering the central nervous system and prevents microbial invasion.
Step-by-step explanation:
Defenses of the Brain Against Trauma and Infection
The brain's defenses against trauma and infection consist of multiple protective layers. Physically, the brain and spinal cord are safeguarded by the cranium and vertebral bones.
They are enveloped by meninges, a trio of membranes comprising the thick, durable dura mater, the weblike arachnoid mater, and the delicate pia mater which adheres to the brain's contours. Between the meninges lies cerebrospinal fluid, offering additional cushioning.
Chemically, these vital organs are defended by the blood-brain barrier, a membrane selectively permitting substances like water, oxygen, and glucose to pass while blocking many harmful agents. This barrier comprises endothelial cells, maintaining a strictly controlled environment essential for neural function.
However, certain pathogens with specialized virulence factors can breach this barrier, causing conditions like meningitis or encephalitis, necessitating prompt medical attention.
In summary, these robust defenses significantly reduce the risk of injury and infection, safeguarding the central nervous system's delicate structures and ensuring its proper functioning.