22.1 Structure and Function of the Nervous System

• The central nervous system (CNS) consists of the brain and the spinal cord

• The peripheral nervous system (PNS) consists of all the nerves that branch off from the brain (cranial nerves) and spinal cord (spinal nerves).

• Between the pia mater and arachnoid membranes is a space called the subarachnoid space, in which an adult has 100 to 160 ml of cerebrospinal fluid (CSF) circulating.

• These remarkable results were the first evidence of an important feature of anatomy: the blood–brain barrier.

• An inflammation of the meninges is called meningitis.

• An inflammation of the brain itself is called encephalitis.

  • If both the brain and the meninges are affected, the inflammation is  called meningoencephalitis.

22.2 Bacterial Diseases of the Nervous System

• Viral meningitis is probably much more common than bacterial meningitis but tends to be a mild disease

• Haemophilus influenzae type B, once responsible for a majority of cases, has been nearly eliminated in the United States since introduction of an effective vaccine.

• Meningococcal meningitis is caused by Neisseria meningitidis

  • The symptoms of meningococcal meningitis are mostly caused by an endotoxin that is produced very rapidly and is capable of causing death within just a few hours.

• A diagnosis of bacterial meningitis requires a sample of cerebrospinal fluid obtained by a spinal tap, or lumbar puncture

  • Bacterial meningitis is life-threatening and develops rapidly.

• In recent years, the disease listeriosis has changed from a disease of very limited importance to a major concern for the food industry and health authorities.

• The causative agent of tetanus, Clostridium tetani, is an obligately anaerobic, endospore-forming, gram-positive rod

• To minimize the production of more toxin, damaged tissue that provides growth conditions for the pathogen should be removed, a procedure called debridement and antibiotics should be administered

• Botulism, a form of food poisoning, is caused by Clostridiumbotulinum, an obligately anaerobic, endospore-forming grampositive rod found in soil and many aquatic sediments.

• Hansen’s disease is the more formal name for leprosy; it is sometimes used to avoid the dreaded name

22.3 Viral Diseases of the Nervous System

• Poliomyelitis (polio) is best known as a cause of paralysis.

• Animals with furious (classic) rabies are at first restless, then become highly excitable and snap at anything within reach.

  • Some animals suffer from paralytic (dumb or numb) rabies, in which there is only minimal excitability.

• Rabies is usually diagnosed in the laboratory by detection of the viral antigen using the direct fluorescent-antibody (DFA) test, which is nearly 100% sensitive and highly specific.

  • If the animal is positive for rabies, the person must undergo postexposure prophylaxis (PEP)—meaning a series of anti rabies vaccine and immune globulin injections.

• The original Pasteur treatment, in which the virus was attenuated by drying in the dissected spinal cords of rabies infected rabbits, has long been replaced by __human diploid cell vaccin__e (HDCV), or chick embryo–grown vaccines.

22.4 Fungal Disease of the Nervous System

• The central nervous system is seldom invaded by fungi.

• The disease cryptococcosis is caused by fungi of the genus Cryptococcus

  • The best serological diagnostic test is a latex agglutination test to detect cryptococcal antigens in serum or cerebrospinal fluid.

22.5 Protozoan Diseases of the Nervous System

• African trypanosomiasis, or sleeping sickness, is a protozoan disease that affects the nervous system.

  • The disease is caused by two subspecies of Trypanosoma brucei that infect humans: Trypanosoma brucei gambiense and T.b. rhodesiense

  • Typanosomiasis is treated with suramin and pentamidine, but these do not alter the course of the disease once the CNS is affected

• Naegleria fowleri is a protozoan (ameba) that causes a neurological disease, primary amebic meningoencephalitis (PAM)

• A similar neurological disease is granulomatous amebic encephalitis (GAE).

22.6 Nervous System Diseases Caused by Prions

• In recent years, the study of these diseases, called transmissible spongiform encephalopathies (TSE), has been one of the most interesting areas of medical microbiology.

• A typical prion disease in animals is sheep scrapie, which has been long known in Great Britain and made its first appearance in the United States in 1947.

• Humans suffer from TSE diseases similar to scrapie; Creutzfeldt-Jakob disease (CJD) is an example.

  • A TSE that is much in the news is bovine spongiform encephalopathy (BSE).

22.7 Diseases Caused by Unidentified Agents

• In August 2014 and November 2016, the CDC received increased reports of people with acute flaccid myelitis (AFM).

• Bell’s palsy occurs when a nerve that controls facial muscles is inflamed and can’t communicate with muscles.

• There is no diagnostic test for chronic fatigue syndrome (CFS).