Cns disorders

• CNS DISORDERS

Structure of the Nervous System

• Divided into two parts– Central nervous system (CNS)

– Peripheral nervous system (PNS)

© 2012 Pearson Education Inc.


• Composed of the brain and spinal cord– Brain has several main parts

– Cerebrum controls voluntary muscles, perception, and “thinking”

– Cerebellum controls many involuntary body movements

– Brain stem controls breathing, heart rate, blood pressure

– Spinal cord– Extends from the brain stem to the lumbar region



• Structures of the Peripheral Nervous System– Nerves transfer commands from CNS to muscles

and glands– Cranial nerves extend from brain through holes in

the cranial bones– Spinal nerves extend from spinal cord through

vertebral gaps– Three types of nerves

– 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© 2012 Pearson Education Inc.


• Cells of the Nervous System– Two basic cell types

– Neuroglia– Provide support, insulation, nutrients; phagocytize

microbes

– Neurons– Carry nerve impulses

– Nucleus lies in a region called the cell body

– Ganglion is collection of many neurons’ cell bodies

– Dendrites and axons extend from the cell body



• Portals of Infection of the Central Nervous System

– 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

– Travel in peripheral neurons to the CNS

– Infect and kill cells of the meninges, causing meningitis


Factors Important to Understanding Nervous System Pathology

1. The nervous system consists of highly specialized functional units called neurons. Damage to neurons is irreversible because neurons cannot regenerate. Injury to certain areas of the brain result in loss of function to that particular area. A loss of vision center in the occipital lobe causes blindness. Lesions of the respiratory centers in the medulla oblongata causes death.

2. The central nervous system (CNS) is protected from mechanical injury by the bones of the skull and vertebrae. If the vertebrae were detached from one another or dislocated, the spinal cord may be severed.

3. The CNS is separated from the remainder of the body by meninges and by a bloodbrain barrier. The brain is protected from harmful substances in that the blood or cerebral spinal fluid (CSF) acts as filters.Examples:Bilirubin does not enter the CNS compartment, even in the most severe forms of jaundice.Glucose concentration in the CSF is at a level that is one-half that of the blood concentration.


4. The brain and the spinal cord are surrounded by CSF.CSF separates the brain from the meninges and serves as a mechanical buffer (cushion) between the brain and bones of the skull

CSF serves as a venue to remove metabolites and waste products from the brainCSF remains constant under normal circumstances in regards to rate of production, flow and reabsorption


5. Neurons do not divide, but supporting glial cells are capable of dividing. The brain contains billions of neurons, all of which were formed during prenatal, intrauterine life.Neurons are long-lived cells. Nevertheless, every hour of our lives, we lose thousands of neurons due to natural death. Since neurons cannot divide, neurons cannot become tumors. However, support structures such as the meninges or bloodvessels are capable of proliferation and/or malignant transformationGlial cell tumors are called gliomas Meningiomas are tumors of meninges Hemangioblastomas are tumors of blood vessels


6. The CNS may be affected by diseases that involve other organs, but also by diseases that are unique to the CNS.

Examples: Atherosclerosis of the coronary arteries and aorta is often accompanied by CerebroVascular Accidents (CVA).

Uremia or hepatic encephalopathy eventually would cause a coma Prions, minute infectious particles, survive only in nerve cells (kuru, mad cow disease, Creutzfeldt-Jacob disease)


7. The symptoms of CNS diseases result from dysfunction or loss of function of neurons. Examples: Headaches are a result of brain tumors, and increased intracranial pressure from massive bleeding causes generalized paralysis, coma, and death if vital centers in the brain are compressed.

Loss of neurons in Alzheimer’s disease causes loss of memory Abnormal function of neurons in Parkinson’s disease causes rigidity of muscles. Abnormal excitation of neurons causes convulsions in epilepsy


Bacterial Diseases of the Nervous System

• Bacteria cause disease in two ways– Infect cells of the nervous system

– Meningitis– Leprosy

– Bacteria growing elsewhere release toxins that affect neurons

– Botulism– Tetanus



• Bacterial Meningitis– Signs and symptoms

– Sudden high fever and severe meningeal inflammation

– Encephalitis can result in behavioral changes, coma, and death

– Can develop rapidly



• Bacterial Meningitis– Pathogens and virulence factors

– Five species cause 90% of bacterial meningitis cases

– Neisseria meningitidis

– Streptococcus pneumoniae

– Haemophilus influenzae

– Listeria monocytogenes

– Streptococcus agalactiae


Diplococci of Neisseria meningitidis

Cells of Streptococcus pneumoniae

The pleomorphic bacili of Haemophilus influenzaePleomorphisms


• Bacterial Meningitis– Pathogenesis

– S. agalactiae acquired during birth– Listeria transmitted via contaminated food– Other species transmitted via respiratory droplets

– Epidemiology– S. pneumoniae present in throat of 75% of

humans– Not spread by casual contact– Meningococcal meningitis can become epidemic



• Bacterial Meningitis– Diagnosis, treatment, and prevention

– Diagnosis based on symptoms and culturing of bacteria from CSF

– Treated with intravenous antimicrobial drugs– Vaccines available for S. pneumoniae, H.

influenzae type b, and N. meningitidis– Individuals at risk for listeriosis should avoid high-

risk foods



• Hansen’s Disease (Leprosy)– Signs and symptoms

– Tuberculoid leprosy – nonprogressive – Lepromatous leprosy – progressive tissue

destruction

– Pathogen and virulence factors– Mycobacterium leprae is the causative agent

– Gram-positive bacillus with mycolic acid in cell wall

– Pathogenesis– M. leprae grows best in cooler regions of the body– M. leprae can live inside infected cells for years


Lepromatous leprosy


• Hansen’s Disease (Leprosy)– Epidemiology

– Transmitted by person-to-person contact or breaks in the skin

– Diagnosis, treatment, and prevention– Diagnosis based on the signs and symptoms

– Confirmed by presence of acid-fast bacilli in samples

– Treated with multiple antimicrobials– BCG vaccine provides some protection



• Botulism– Signs and symptoms

– Caused by intoxication from ingested toxin– Three forms

– Foodborne botulism– Infant botulism– Wound botulism

– Pathogen and virulence factors– Clostridium botulinum is the causative agent

– Different strains produce one of seven neurotoxins


Botulism toxin-overview


• Botulism– Epidemiology

– ~50 cases of foodborne and wound botulism per year in U.S.

– Infant botulism most common form in U.S.

– Diagnosis, treatment, and prevention– Three approaches to treatment

– Washing of intestinal tract to remove Clostridium– Administration of botulism immune globulin – Treatment with antimicrobial drugs

– Prevented by destroying endospores in contaminated food



• Tetanus– Signs and symptoms

– Lockjaw– Spasms and contractions may spread to other

muscles

– Pathogen and virulence factors– Clostridium tetani is causative agent

– Produce neurotoxin called tetanospasmin


A patient with tetanus

Tetanus toxin-overview


• Tetanus– Pathogenesis

– Can acquire through break in skin or mucous membrane

– Distance of infection from CNS determines incubation period

– Epidemiology– Mortality rate is ~50% if left untreated

– Diagnosis, treatment, and prevention– Diagnosis based on characteristic muscle contraction– Treated with passive immunotherapy, antimicrobials,

active immunization– Vaccine available against tetanus


Viral Diseases of the Nervous System

• Viruses more readily cross the blood-brain barrier

• Occur more frequently than bacterial and fungal infections

• Include meningitis, polio, rabies, and encephalitis



• Viral Meningitis– Signs and symptoms

– Similar to those of bacterial meningitis– Usually milder than those of bacterial or fungal

meningitis

– Pathogens and virulence factors– 90% of cases caused by viruses in the genus

Enterovirus

– Pathogenesis– Damage to cells in the meninges triggers

meningitis



• Viral Meningitis– Epidemiology

– More common than bacterial and fungal meningitis

– Spread via respiratory droplets and feces

– Diagnosis, treatment, and prevention– Diagnosed by characteristic signs and

symptoms in the absence of bacteria in the CSF– No specific treatment exists



• Poliomyelitis– Signs and symptoms

– Asymptomatic infections – almost 90% of cases– Minor polio – nonspecific symptoms– Nonparalytic polio – muscle spasms and back pain– Paralytic polio – produces paralysis

– Pathogen and pathogenesis– Poliovirus is the causative agent– Transmitted most often by drinking contaminated

water


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Cns disorders