Nervous System Disorders Flashcards
Pathological responses from CNS features
Protection by bony enclosures Metabolic requirements Absence of central lymphatics Cirrculation of CSF Distinctive pattern of wound healing?
Ways that neurons differ from one another
function
distribution of connections
Use of neurotransmitters
Metabolic requirements
Selective vulnerability
A group of functionally related neurons may be damaged as a result of specific injury
exposure to limited hypoglycemia and hypoxia
Cause greatest damage to portions of teh hippocampus, pyramidal cells of the cortex, purkunje cells of the cerebellum and the basal ganglia
hippocampus is affected most extensibly in
Alzheimer’s disease
______ are most susceptible to the effects of mercury
cerebellar granular neurons
_______ selectively infects and destroys anterior horn cells
Poliomyelitis
Reactions of neurons to injury
Acute neuronal injury (red neurons)
Axonal reaction
atrophy and degeneration of nerve cells in chronic progressive degenerative diseases
Intraneuronal deposits may appear with certain neurodegenerative disorders
Acute Neuronal Injury
Contributing causes include ischemia, overwhelming infections, toxicity, and others that lead to neuronal death
Alterations characterized by loss of Nissl, increased angularity, and nuclear pyknosis appear after 12-24
hours of irreversible injury
Fragmentation occurs
Pyknosis
Irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis. It is followed by karyorrhexis, or fragmentation of the nucleus.
Axonal reaction
Reactions in the cell bod that accompany axonal regenration
Associated with synthesis of proteins and sprouting of axons
Causes: Axon trauma, hypoxia, conditions that prevent a cell from maintaining its axon
Perikaryon swells and rounds up and nissl substance disappears from the central portions of the cell body and nucleus moves to the periphery
Wallerian degenration of distal axon
Atrophy and degeneration of nerve cells in
chronic progressive degenerative diseases and aging
Reduction in size, lipofuscin deposits, neuronal death and necrosis
Progressive loss of neurons results in loss of functionally associated neurons and gliosis (though singular loss does not produce this effect)
Transynaptic degenration occurs in
Communicating neurons (ex. visual pathways)
Neurofibrillary tangles
composed of twisted cytoskeletal filaments (stainable with silver)
Contains ubiquitin which tags abnormal proteins for removal
Alzheimer’s disease, postencephalitic parkinsonism, parkinson’s dementia, boxer’s dementia
Lewy bodies
pink staining spheroids made largely of ubiquitin typical of idiopathic Parkinson’s (loss of substantia nigra) and lewy body dementia (affects cortex)
Inclusion bodies (virus particles)
Appear in infected cells in polio and viral encephelitis
in rabies these structures are known as Negri bodies
Lipofuscins
(wear and tear pigment)
Accumulate in neurons under the of old age and chronic hypoxia
Metabolic storage diseases
Contribute to accumulated intraneuronal deposits of complex lipids
Degenration of neuronal elements contribute to a cherry red spot in the fovea
Myelin loss only leads to neuronal degeneration if the loss is _____
Extensive or prolonged
The most sensitive glial elements
Oligodendrocites
Most resilient glial element
Astrocytes
Survive all but the most prolonged and severe hypoxia
Astrocytes and neuronal injury
Participate in repair and produce glial scars (other types of scars are less common in the CNS)
With a penetrating injury the astrocytic scars may cause distortion of the cortex and lead to seizures
Prolonged mild ischemia may cause necrosis of astrocytes
Microglia and neuronal injury
Mesodermal cells functioning as phagocytes of the CNS, numbers may increase in response to injury and infection of components of the CNS
Oligodendrocytes
Wrap myelin around several neurons
Most vulnerable to injury and swell when stressed
Multiple sclerosis and other disease that affect myelination affect oligodendrocytes
replaced by astrocytic scars
Increased intracranial pressure can occur due to
Space occupying lesions
Swelling and edema
Hydrocephaly
Edema and swelling of the CNS
Vascular (Vasogenic)
Associated with increased vascular permeability
Most common cause of brain edema
Cellular (cytotoxic)
Increased cell water indicates injury
Hydrocephalus
Volume of CSF is increased causing the ventricles to dilate
Can be caused by:
If this follows brain atrophy then then CSF does not increase and this condition is known as hydrocephaly ex vacuo
An imbalance of the production and the drainage of CSF
Vascular tears and hemorrhage
Trauma
Infection of the CNS
Obstructive (non-communicating) hydrocephalus
CSF does not reach the subarachnoid space because it’s path is blocked internally.
results from: congeinital causes, tumors, scarring in the ventricular system, obstruction at the foramina of magdenie or luschka
Communicating hydrocephalus
CSF enters the subarachnoid space but the circulation or absorption is interrupted
Causes: scars of the arachnoid granulations (following inflammation or hemorrhage) and/or in the meninges. Thrombi, neoplasms, and other obstructions of cerebral (dural) cenous sinuses and associated veins
Severe CHF leads to venous congestion and pooling
Sites of narrowing that are vulnerable for obstruction
Aqueduct of Silvius
Foramina of Magendie and Luschka
Subarachnoid space between the forebrain and midbrain
Manifestation of hydrocephaly
Early features of increased intercranial pressure include headache, mental dullness, nausea, and vomiting
Papilledema
Herniation
Hydrocephaly herniation
Rigid skull and dural reflections force the brain to be squeezed through the openings and around the partitions like putty when it is displaced or undergoes swelling or expansion
Common examples include cingulate (subfalcine), uncal (trans-tentorial), and tonsillar (cerebellar, “coning”) herniation
Tonsillar herniation may lead to compression of the medulla at the foramen magnum and is a common mechanism of death in brain swelling
Trauma leading to hydrocephaly
Penetrating and crushing injuries: Distortion of cranial vault and vertebral column
Brain trauma with no damage to cranium (Contusion, laceration, concussion, shearing forces from rotation, contrecoup injury {damage to part of the brain opposite the side of impact])
Cord trauma: displacement or distortion of vertebral elements damage cord. Vertebral dislocations.
Meningitis
Infection of meninges and CSF
Systemic signs of infection in addition to stiff neck, headaches, photophobia, rash and fevers
leads to scarring and obstruction of the CSF
Bacterial meningitis
Pyogenic
characterized by pus in the meninges
Acute in course with a high risk for death
Causes of bacterial meningitis
Neissaria (Meningococcus) - most common epidemic form
E Coli., H. Influenza, strep. pneumonia and oppurtunistic infections in the immune compromised
CSF findings of bacterial meningitis
Increased turbidity, increased polymorphonuclear leukocytes, and bacteria
Elevated protein and reduced glucose
Meningococcal septicemia
Gives rise to purpurric lesions, high fever, and potentially shock
Consequence of severe infection and skin and organ hemmorhage and mucousal bleeding are common
Types of meningitis
Bacterial
Acute lymphatic (Vral, "aseptic") More common with milder clinical effects, increased lymphocytes in CSF, milder inflammation
Chronic
insidious origin
Causes include TB, fungi, and brucellosis
Viral encephalitis
Most common
general features include an increased number of iniltrates of lymphocytes and macrophages called “inclusion bodies” in infected cells and glial cell reactions
Delayed symptoms is common
Herpes encephalitis, post measeles, congenital malformation (if the mother has rubella), postencephalitic parkinson’s after influenza
Selectivity of encephalitis
Tropism
May choose a specific are or type of cell
may also be diffuse
Viral encephalitis causes
Arbor viruses from insect and animal hosts
Chuldhood infectiosn such as measles
Herpes Simplex I and II
Polio, rabies
HIV (60% of AIDS patients have symptoms leading to viral encephalitis)
Slow virus diseases
Infectiosn characterized by long periods of latency
Subacute Sclerosing Panencephalitis: Associated with infection of measles virus and is fatal in 2-3 years
Hallmarks of prion diseases of encephalopathies
Proteinaceous transmittable agents - NO DNA
Affect nerve tissue in humans and animals
Hallmarks:
Vacuolization (hole formation) of brain tissue and accumulation of prion proteins
Prion protein
Membrane glycoprotein that becomes changed by misfolding
Acquired through sporadic or inheireted mutations or infected animal tissue, iatrogenic effects (surgery, etc.), exposure to infected humans
Creutzfeldt-Jacob disease (encephalopathy)
Human-human transmission from breathing and certain medical procedures
Scrapie in sheep and mad cow disease
Concern for transmission to humans that eat or handle infected meats
Leads to variant CJD
Abscesses
Focal infection that is usually bacterial
During acute stage local destruction and swelling may cause symptoms
CSF findings are variable
Repair is associated with vascularized collagenous tissue and cortical adhesions may occur
Granulomas
From tuberculosis
Focal nodular infections consisting of macrophages, giant cells, etc.
Causes local destruction and expansion
Pott’s disease
Causes a collapse of vertebral bodies that makes a gibbous deformity in the spinal cord
Sources of CNS infections
Extension from middle ear and sinus infections
Hematogenous disemmination
Direct invasion - trauma, congenital defects, iatrogenic
Extension along peripheral nerves (rabies, encephelitis)
Stroke (cerebral vascular accident)
Focal loss of neurological function of vascular origin which lasts more than 24 hours
spontaneous in onset due to underlying CV disease
3rd leading cause of death
40-50% of death following the first month
defecits persist in 60%
Transient Ischemic Attacks
Spontaneous focal reversible neurological disturbance slasting less than 24 hours and results from disruption of blood supply
Most caused by emboli
Risk for stroke is 5% per year
Causes of stroke
Focal ischemic infarcts
- thrombi
- emboli
Types of stroke
Hemorrhagic - bleeding
Ischemic - obstruction
Focal ischemic stroke
75-90% of strokes
Atherosclerosis is most common underlying factor (emboli)
inflammatory arthretitis
Arterial spasms
Dissecting aneurysms
3-5 minutes before damage
F-A-S-T
Face droopin
Assymetrical movement
Slurred speech
Time call 911
TO RECOGNIZE STROKE
Ischemic encephalopathy
Cause of stroke
Generally caused by ischemia of the entire brain. Hypotension can contribute to this
Effects change from reversible confusion to infarction
May also be limited to watershed regions of the brain and spinal cord
Morphology of infarction
6-12 hours: discoloration and softening, petechiae may appear in the margin of teh affected area
2-3 Days: Cerebral tissue becomes soft and begins to break up. edema is common and may cause a herniation and exacerbates neurological symptoms but it gets better
Several months: Residual cavity surrounded by astrocytes or a collapsed scar
Spontaneous hemorrhage types
Intracerebral
subarachnoid
Intracerebral hemorrhage
peak at 60 years
Rupture of small intraparenchymal arteries
Effects: dissection of nerve tissue, mass effects, and disruption of blood supply
blood may reach the subarachnoid space or ventricles
Arises suddenly and progresses slowly
CNS effects of hypertension
Accounts for 50% of brain hemorrhage
arteriole sclerosis with occlusion of small lesions known as lacunar infarcts
Rupture of small penetrating arteries may give rise to slit hemorrhages
Multi-infarct dementia: characterized by accumulated effects of repeated brain infarcts due hypertensive arteriosclerotic disease
Exertion may contribute to onset
Subarachnoid hemorrhage
Rupture of congenital berry aneurysms is most common (other causes include other types of aneurysms, clotting defects, traumatic injury, etc.)
Onset: sudden with signs of meningeal
irritation (e.g. severe headaches)
CSF findings
• 1-24 hours: blood “stained”
• >24 hours: xanthochromia (yellow discoloration of CSF)
