Central nervous system (CNS) and Peripheral nervous system (PNS)
What is the CNS composed of?
the brain and spinal cord
What are the main parts of the brain and what do they control?
Cerebrum controls voluntary muscles, perception, and "thinking" Cerebellum controls many involuntary body movements Brain stem controls breathing, heart rate, blood presure
location of spinal cord
extends from the brain stem to the lumbar region
What is the peripheral nervous system composed of?
nerves that transfer commands from CNS to muscles and glands
What are the structures of the PNS where are they located?
Cranial nerves extend from the brain through holes in the cranial bones Spinal nerves extend from the spinal cord gaps between the vertebae
what are the 3 types of nerves and their function?
Sensory nerves - carry signals toward the CNS Motor nerves - carry signals away from the CNS Mixed nerves - carry signals toward and away from the CNS
What are the defenses that protect the nervous system?
Brain encased with the bony skull Spinal cord is protected by vertebrae Brain and spinal cord are further protected by the meninges CSF circulates around the brain and spinal cord between the layers of meninges
--CSF adds protection because it absorbs some of the shock of an injury CNS is protected against chemical injury by the blood-brain barrier
What are the portals of infection of the CNS
CNS is an axenic environment - it has no normal microbiota Pathogens may access the CNS several ways -Breaks in the bones and meninges -Medical procedures -Traveling in peripheral neurons to the CNS
Portals of infection cont
-Carried by blood or lymph & breach blood-brain barrier -Circulation of cerebrospinal fluid
How many species of bacteria can cause meningitis?
over 50 species, some of which are opportunists
What species cause 90% of bacterial meningitis cases?
What is the gram stain morphology of Streptococcus pneumoniae
Gram-positive coccus; usually in pairs (pneumococcus)
How many different strains are known to infect humans
Pathogen and Virulence Factors
Normal flora of throat that opportunistically colonize lungs, sinuses, and middle ear
How does it move?
via bacteremia, during sinusitis or otitis media, or following head or neck surgery or trauma or trauma to meninges
Why is the capsule the essential determinant of virulence during invasion?
Interferes with phagocytosis
What does IgA protease destroy?
What does Pneumolysin interfere with?
The action of lysosomes
what in cell wall binds to receptors in cells lungs, meninges, and blood vessel walls?
Phosphorylcholine it stimulates target cells to endocytose them they are hidden inside body cells.
What is the Gram stain morphology of Neisseria meingitidis
How many antigenic strains are there and which ones cause the most cases of human disease worldwide?
13 A, B, C, and W135
What is Neisseria meningitidis known as?
Pathogen and Virulence Factors
Fimbriae Polysaccharide capsule that resists lytic enzymes of the body's phagocytes Lipooligosachharide (LOS; cell wall antigen) Avirulent strains lack fimbriae, capsule, & lipooligosaccharide
What are Lipooligosaccharide composed of?
Lipid A & sugars --released from outer membrane into extracellular spaces and triggers fever, vasofilation, inflammation, shock, and disseminated intravascular coagulation (DIC)
Pathogenesis - how are we infected?
Humans inhale organisms in respiratory droplets from infected individuals (droplet transmission) who may be asymptomatic (carriers)
Where is N. meningitidis a common member of the normal flora and of what percent of healthy people?
N. meningitidisis a common member of the normal flora in the upper respiratory tracts of up to 40% of healthy people -Chronic irritation or damage to pharyngeal & respiratory mucosa may be a predisposing factor for invasive disease
How does bacteria spread to meninges?
From infections of the lungs, sinuses, or inner ear via the blood
Bacteria capsules provide some protection from what?
Where is glucose metabolized?
Bacterial Meningitis signs and symptoms
May present as transient bacteremic illness with fever & malaise --symptoms resolve spontaneously in 1-2 days Acute cases characterized by increased number of WBC in CSF sudden high fever, and intense meningeal inflammation --swelling retards normal flow of CSF and causes pressure to build up
signs and symptoms cont
Inflamed cranial meninges - sever headache, nausea, vomiting, pain, loss of brain functions leading to drowsiness, confusion, fretfulness or irritability Inflamed spinal meninges put pressure surrounding nerves & muscles -Stiffness in neck -Affects sensory input & motor control
Signs and Symptoms cont
Infection of the brain (encephalitis) can result in deafness, blindness, behavioral changes, coma, and death Signs & symptoms develop swiftly -Meningococcal meningitis can kill within 6 hours
signs and symptoms cont
increase in WBC in CSF (milky white in color) Petechiae present in 30-60% of cases of meningococcal meningitis
where is steptococcus pneumoniae present
Present in mouths and throats of 75% of humans
When is the risk of meningitis increased?
When organism present in bloodstream (children and elderly)
What is the mortatlity rate compared to that of meningitis caused by other organisms?
up to 20 times it is primarily a disease of children
what is the reservoir of Neisseria meningitidis
When are carriage rates highest
in older children and young adults
N. meningitidis is the only type of bacteria meningitis that becomes epidemic..where?
Military personnel in barracks Students living in dormitories (up to 23 times more prevalent than general population)
What is the mortality rate?
~100% if untreated but <10% if treated appropriately
How many cases were there in 2009?
872 cases (114 cases in California)
How is bacterial meningitis diagnosed?
basis of symptoms and on culturing bacteria from CSF following spinal tap Serological tests can demonstrate presence of antibodies
Potentially fatal and should always be viewed as a medical emergency Prompt treatment reduces mortality to <15%
Streptococcus pneumoniae prevention
Pneumococcal polysaccharide vacine (PPV) -23 valent formulation that represents 85-90% of strains that cause invasive disease -T-independent antigens that do not produce secondary response and may not be long lasting
Heptavalent formulation conjugated to nontoxic mutant diphtheria toxin (carrier protein CRM197) T dependent B cell response - memory
Neisseria meningitidis prevention
Meningococcal polysaccharide vaccine (MPSV4) -Strains A, C, Y, and W135 -Only humoral immunity -Licensed for use in people greater than or equal to 2 years of age
Meningococcal conjugate vaccine (MCV4) -Strains A, C, Y, and W135 -Polysaccharides conjugated to diphtheria toxoid -Humoral and cell-mediated immunity -Licensed for use in people 2-55 years of age
how effective are these vaccine?
about 90% those who have close or prolonged contact with patient should receive prophylactic antibiotics
Viral Disease of the Nervous System
-Viruses more readily cross the blood-brain barrier -Viral infections of the nervous system occur more frequently than bacterial and fungal infections
What genus causes 90% of cases?
Enterovirus -Polioviruses, coxackieviruses, echoviruses, & other enteroviruses Very small, nonenveloped, RNA viruses
How is Viral Meningitis spread
Often spread from person to person via fecal contamination of food, water, or hands Virus replicates in respiratory or gastrointestinal mucosa & kills target cells Gains access to bloodstream (primary viremia)
Virus spreads to liver, spleen, & lymph nodes Secondary viremia occurs --thought to be responsible for seeding the CNS Cells in meninges killed
What is the incubation period?
3-7 days and patients recover completely after another 7-10 days
What are the signs and symptoms?
often similar to those of bacterial meningitis fever, stiff neck, severe headache, drowsiness, confusion, nausea, and vomiting --"Worst headache of my life" Rash, sore throat, and colds can also occur
Viral Meningitis - Epidemiology
Non-polio enteroviruses are very common in humans -Second only to rhinoviruses as most common viral infectious agent in humans
What is the estimated number of symptomatic infections a year in the United States
10-15 million or more -everyone is at risk for infection but most who become infected have no disease -25,000-50,000 hospitalizations each ear
Contagious from onset of signs & symptoms for up to 10 days
where is it found?
Respiratory secretions and feces of infected patients
who is at the greatest risk?
Neonates are at greatest risk with most significant risk of morbidity and mortality
What are the possible risk factors associated?
exposure to someone with recent viral infection, children in daycare facility, or having a supressed immune system
How is it diagnosed?
Characteristic signs & symptoms of meningitis without presence of bacteria in CSF Blood test also available
How is it treated?
no specific treatment bed rest, plenty of fluids, and medication to relieve fever and headache
How is it prevented?
hard to prevent Frequent hand washing, avoidance of crowded swimming pools, and refraining from touching mouth, nose, or eyes with contaminated hands
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