Chapter 22, part A

1. Chapter 22, part A Microbial Diseases of the Nervous System

2. Portal of entry for CNS and PNS Difficult Portal of Entry • Skull or backbone fractures • Medical procedures • Along peripheral nerves • Blood or lymph • Blood brain barrier not everything can cross • Choramphenicol - fat soluble and small • Penicllin - poor crossing - not fat soluble

3. The Nervous System Figure 22.1

4. Microbial Diseases of the Nervous System • Bacteria can grow in the cerebrospinal fluid in the subarachnoid space of the CNS • The blood brain barrier (capillaries) prevents passage of some materials (such as antimicrobial drugs) into the CNS • Meningitis • Inflammation of meninges • Encephalitis • Inflammation of the brain

5. The Meninges and Cerebrospinal Fluid The Meninges and Cerebrospinal Fluid Skull bone Cerebrum Subarachnoid space (contains cerebrospinal fluid) Skull bone Dura mater Arachnoid mater Cranial meninges Pia mater Blood vessel Cerebrum Cerebellum Spinal cord Dura mater Spinalmeninges Arachnoid mater Pia mater Subarachnoid space of spinal cord Subarachnoid space (contains cerebrospinal fluid) Central canal

6. Bacterial Meningitis • Less common but often more serious than viral • Sudden High Fever, headache, stiff neck, fear • Non blanching rash - petechial rash • Followed by nausea and vomiting • May progress to convulsions and coma • 10% mortality • Diagnosis by Gram stain of CSF • Treated with cephalosporins • The tumbler test

7. Etiologies of Bacterial Meningitis Table 22.1

8. Figure 22.4 Spinal tap (lumbar puncture). Meningitis Spinal needle is inserted, usually between the fourth and fifth lumbar vertebrae Cerebrospinal fluid Spinal cord Fourth lumbar vertebra L4 Cauda equina L5 Sample of cerebrospinal fluid Longitudinal section of the spine Fifth lumbar vertebra

9. Haemophilus influenzae Meningitis • Occurs mostly in children (6 months to 4 years) • Gram-negative aerobic bacteria, normal throat microbiota • Capsule antigen type b • Prevented by Hib vaccine

10. Haemophilus influenzae Meningitis Figure 22.3

11. Neisseria Meningitis, Meningococcal Meningitis • N. meningitidis • Gram-negative aerobic cocci, capsule • 10% of people are healthy nasopharyngeal carriers • Especially 15 to 24 years carry 25% • Students and military • Begins as throat infection, rash • Serotype B is most common in the U.S. • Vaccine against some serotypes is available

12. Neisseria Meningitis, Meningococcal Meningitis Figure 22.4

13. Streptococcus pneumoniae Meningitis, Pneumococcal Pneumonia • Gram-positive diplococci • 70% of people are healthy nasopharyngeal carriers • Most common in children (1 month to 4 years) • Mortality: 30% in children, 80% in elderly • Prevented by vaccination

14. Nervous System: Bacterial - Tetanus • Clostridium tetani • Gram-positive, endospore-forming, obligate anaerobe • Grows in deep wounds • Tetanospasmin released from dead cells blocks relaxation pathway in muscles • Prevention by vaccination with tetanus toxoid (DTP) and booster (dT) • Treatment with tetanus immune globulin • Tetanus exotoxin is a neurotoxin that binds to inhibitory interneurons of the spinal cord and blocks their release of inhibitors. It is these inhibitors from the inhibitory interneurons that eventually allow contracted muscles to relax by stopping excitatory neurons from releasing the acetylcholine that is responsible for muscle contraction. The toxin, by blocking the release of inhibitors, keeps the involved muscles in a state of contraction and leads to spastic paralysis, a condition where opposing flexor and extensor muscles simultaneously contract.

15. Tetanus Figure 22.6