Inflammation of the meninges, or meningitis, is usually caused by bacteria that enter through the ear, nose, or throat or are carried by the blood. One of these organisms, the meningococcus (Neisseria meningitidis), is responsible for epidemics of meningitis among individuals living in close quarters. Other bacteria implicated in cases of meningitis include Haemophilus influenzae, Streptococcus pneumoniae, and Escherichia coli. A stiff neck is a common symptom. The presence of pus or lymphocytes in spinal fluid is also characteristic. Fluid is withdrawn for diagnosis by a lumbar puncture (Fig. 17-10), in which a needle is used to remove CSF from the meninges in the lumbar region of the spine. This fluid can be examined for white blood cells and bacteria in the case of meningitis, for red blood cells in the case of brain injury, or for tumor cells. The fluid also can be analyzed chemically. Normally, spinal fluid is clear, with glucose and chlorides but no protein and very few cells.
Other conditions that can cause meningitis and encephalitis (inflammation of the brain) include viral infections, tuberculosis, and syphilis. Viruses that can involve the central nervous system include the polio and rabies viruses; herpes virus; HIV (the cause of AIDS); tick- and mosquito-borne viruses, such as West Nile
Virus; and, rarely, common infections such as measles and chickenpox. Aseptic meningitis is a benign, nonbacterial form of the disease caused by a virus. Herpes zoster, the chickenpox virus, is also responsible for shingles, an infection that spreads along peripheral nerves, causing lesions and inflammation.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.