Chapter 17: Diseases of the Nervous System

Nervous System Overview

• Two main parts: Central Nervous System (CNS) & Peripheral Nervous System (PNS)
  • CNS: Brain & spinal cord
  • PNS: Nerves extending from the CNS to limbs and other body regions

Defenses of the Nervous System

• Physical Protection: Bone encasement
  • Brain and spinal cord are protected by bones
  • Cerebrospinal fluid (CSF): Provides cushion inside the skull and spine
• Pathogen Protection: Blood-Brain Barrier (BBB)
  • Separates blood vessels and brain, preventing most pathogens from entering
  • Also hinders entry of some helpful substances (e.g., antibiotics)
• Meninges: Protective layers around CNS (dura mater, arachnoid mater, pia mater)
  • Cranial meninges: Around the brain
  • Spinal meninges: Around the spinal cord
• Immunologically Privileged: Different immune response compared to other body parts
  • Reduced typical immune reactions like heat and swelling

Nervous System Infections

• Sources of Infection
  • Skull or spinal fractures
  • Medical procedures
  • Peripheral nerves
  • Blood and lymph tissues
• Sterile Environment: No normal biota; presence of microbes usually indicates disease
• Hiding Viruses: Certain viruses can reside latently (e.g., herpes simplex virus)

Meningitis

• Definition: Inflammation of the meninges
• Types: Bacterial, Viral, Fungal, Neonatal
• Common Symptoms: Fever, headache, stiff neck, nausea, vomiting, photophobia
• Bacterial Meningitis
  • Common Bacteria: Meningococcus, pneumococcus, Haemophilus, Listeria
• Meningococcal Meningitis: Nyseria meningitidis
  • Symptoms include sudden throat infection, pink rashes
  • Carriers: 10% are healthy carriers
  • Vaccine: MCV4
• Pneumococcal Meningitis: Streptococcus pneumoniae
  • Common in children and elderly
  • High mortality rate
  • Vaccine available
• Haemophilus Meningitis: Haemophilus influenzae
  • Severe before vaccines; now rare
• Listeria Meningitis: Listeria monocytogenes
  • Common from contaminated food
  • Severe in immunocompromised individuals
• Fungal Meningitis
  • Cryptococcus neoformans: Found in bird droppings, affects immunocompromised
  • Valley Fever: Caused by Coccidio species
• Viral (Aseptic) Meningitis
  • Mostly affects children
  • Usually mild; resolves within 2 weeks
• Neonatal Meningitis
  • Causes: Streptococcus agalactiae, E. coli, Chronobacter

Specific Diseases

• Zika Virus
  • Transmitted via mosquito bites, vertical transmission, sexual contact
  • Severe for fetuses (microcephaly)
  • No vaccine available
• Polio
  • Poliovirus
  • Highly effective vaccine available
  • Causes paralysis by attacking motor neurons
• Meningoencephalitis
  • Caused by amoebas: Naegleria fowleri and Acanthamoeba
  • Rapidly fatal
• Encephalitis
  • Acute Encephalitis: Caused by arboviruses, herpes simplex, JC virus
  • Subacute Encephalitis: Caused by toxoplasma, measles virus, prions
• Rabies
  • Rhabdovirus; zoonotic disease
  • Transmitted via animal bites/scratches
  • Two types: Furious and Paralytic
  • Vaccine and post-exposure treatment available
• Tetanus
  • Clostridium tetani
  • Causes muscle contraction (lockjaw)
  • Vaccine available, TIG treatment
• Botulism
  • Clostridium botulinum
  • Causes muscle paralysis
  • Associated with inadequate food preservation
  • Anti-toxin available, used as botox in modified form