Infections of the Central Nervous System Quiz

See Meningitis. Option E is correct. The meninges are three membranes wrapped around the brain and spinal cord: the dura mater (tough and outermost), the arachnoid mater (a thin, web-like middle layer) and the pia mater (a delicate layer stuck closely to the brain surface). Meningitis is inflammation of the leptomeninges, which are the pia and arachnoid together. The name helps, because lepto- means thin. Between these two layers lies the subarachnoid space, which is filled with cerebrospinal fluid (CSF), so bacteria or inflammatory cells that reach it spread easily around the brain and spinal cord. That is why a lumbar puncture, which samples CSF, is the key test. Irritation of these membranes explains the classic headache, neck stiffness and photophobia, and it is why the inflamed layers are the pia and arachnoid mater. The dura mater is usually not the main site, although it can become inflamed in rarer conditions. Memory aid: lepto means thin, so the leptomeninges are the two thin layers.

• Layers: the meninges are the dura mater, the arachnoid mater and the pia mater.
• Meningitis: inflammation of the leptomeninges, which are the pia and arachnoid together.
• Spread: the subarachnoid space between these layers is filled with cerebrospinal fluid, so infection spreads easily around the brain and spinal cord.