CNS- 23 Flashcards
CNS consists of
brain and spinal cord
brain consists of:
cerebrum
cerebellum
brain stem (midbrain, pons, medulla)
cerebrum consists of:
outer layer of gray matter (cortex)
deep gray matter
white matter
cortex
replete with neurons that are employed for intellectual (cognitive) functions as well as for sensory and motor functions above the vegetative level
deep gray matter
consists of groups of neurons such as the thalamus and basal ganglia that perform functions similar to the cortex, albeit at a much more primitive level
white matter
composed primarily of the axons and their myelin sheaths.
brain axons
long processes of neurons that connect with neurons in other prts of the brain and spinal cord.
axons of spinal cord neurons
innervate skeletal muscles
*voluntary thought generated from neurons of the cerebral cortex can control skeletal muscle movement
some axons convey sensory impulses in the opposite direction- from the spinal cord to carious parts of the brain
cerebellum
situated in the posterior inferior aspect of the skull
responsible for coordination of motor functions
brainstem
a relay between brain and spinal cord and is also a control center for heart rate, respiration rate, sleep and wakefulness, integration of eye movements and other functions
meninges
cover the brain
include an outer, tough membrane called the DURA (next to the skull), and an inner lace-like membrane= PIA-ARACHNOID (lies directly over the cortex
form a continuous covering over the spinal cord too
cerebrospinal fluid
utilized for metabolic exchange, as an excretory vehicle and as a means to absorb pressure changes in the CNS
formed in the ventricles of the brain by secretion from the CHOROID PLEXUS and by filtration through the ependyma.
-flows from 3 ventricles in the anterior part of the brain, through a narrow aqueduct, to the medulla (area of brain stem). then passes out of the ventricular system and percolates between the layers of the pia-arachnoid membrane, bathing the brain and spinal cord before being absorbed back into veins.
most blood flows to the brain through:
the 2 internal carotid arteries anteriorly and the paired vertebral arteries posteriorly
carotid to bulk of cerebrum
vertebral to brain stem, cerebellum and post cerebrum (supply control centers for respiration and consciousness)
circle of willis
vessels all interconnect at the base of the brain
*so occlusion at one major artery to the brain may no necessarily result in deprivation of blood
blood-brain barrier
selective exclusion of substances- brain capillaries are constructed to function in such a manner as to prevent passage of many substances into the brain that can easily reach tissues in other organs.
important cellular constituents of the brain stem and spinal cord:
neurons
astrocytes
oligodendroglia
neurons
large cells found in gray matter that conduct nervous impulses
- efferent processes (axons) may extend for long distances in gray and white matter
- short afferent processes (dendrites) connect to other neurons through synapses
astrocytes
spider lie processes provide structural support to the CNS
regulate blood-brain barrier and tissue electrolytes
when brain is injured, astrocytes proliferate to form a glial scar composed of glial processes but lack collagen
oligodendroglia
manufacture and maintain the myelin sheath that surrounds and protects axons and dendrites
major brain diseases
CVAs/strokes- 3rd cause of death traumatic injuries infections (meningitis, encephalitis, abscess) alzheimer disease neoplasms multiple sclerosis parkinson's senile dementia
most common presenting symptoms
headache diminution or loss of motor function sensory loss seizures disturbances in intelectual or memory capabilities
neurologic exam
exam of motor and sensory systems
testing cognitive function
special tests for ability to perform coordinated movements
motor system exam
gait posture symmetry of muscle mass muscle strength coordination quality of reflexes
decreased reflux indicates:
lesion in peripheral nerve with resultant inability to either transmit the sensoryy impulse back to the spinal cord or to transmit the motor impulse out to the muscle
hyperactive reflex
represents an intact nerve but without the modifying control normally mediated by the CNS
focal vs general
focal= referable to a specific area of nervous system involvement
general=involving integrated functions of the whole brain
hemiparesis
weakness of one side of the body
focal
focal examples
hemiparesis
localized areas of sensory deprivation
abnormalities of 1 or 2 cranial nerves
localized headaches
general examples
intellectual impairment
generalized headaches
stupor
loss of consciousness (coma)
major cause of generalized s&s
increased intracranial pressure
foramen magnum
only major opening in the skull- for spinal cord
substance of the brain tends to be pushed toward this foramen as a consequence of any increased intracranial pressure
treatment of increased intracranial pressure
removal of any space occupying lesion
steroid drugs and osmotic agents may help relieve brain edema by drawing fluid back to vascular system
most important lab exam for CNS
analysis of cerebrospinal fluid usually by a needle into lumbar parachnoid space in sitting
pressure is measured as fluid is being drawn.
electroencephalogram (EEG)
evaluates electrical activity simultaneously in various areas of the brain
developmental abnormalities of the CNS divided into:
1: malformations
2: destructive brain lesions
malformations
result of deleterious forces acting upon the embryonic or fetal brain~1/2 gestation
down syndrome spina bifida meningomyelocele anencephaly hydrocephalus
spina bifida
post arches and spines of some vertebrae are absent
if severe a meningomyelocele results
meningomyelocele
defect in the spinal column through which spinal cord and meninges protrude into the skin of the back.
may result in severe paralysis of the legs
anencephaly
severe malformation- entire forebrain is missing
infants are stillborn or die soon after birth
destructive brain lesions
occur in last 1/2 of gestation or during firth 2 years of life.
most occur at time of labor - result of anoxia from prolonged/difficult labor or respiratory distress
also common from infections. especially meningitis
vary greatly in severity
most pts have motor problems , 1/3 mentally retarded
cerebral palsy maternal diet drugs radiation toxins
cerebral palsy
non-progressive condition manifested by motor retardation and sometimes mental.
inflammatory diseases
meningitis
encephalitis
rabies
myelitis
meningitis
=inflammation of the pia-arachnoid
most often caused by bacteria
usually abrupt onset
bacteria gains access to brain and spinal cord via blood.
escherichia coli and group B streptococci cause majority of newborn cases
haemophilus influenzae for small children
s&s of meningitis
fever, headache, neck rigidity, pain caused by muscle spasm from nerve irritation
neisseria meningitis
can occur in epidemics
encephalitis
=diffuse inflammation of the brain
usually caused by viral infections (mosquito borne) occur in epidemics
*west nile, st louis, equine, venezuelan
s&s of encephalitis
irritability
drowsiness
headache
no tx. pts die, fully recover or recover with neurologic deficit
rabies
the virus travels up the peripheral nerve to the brain and once infected death is practically inevitable.
s&s of rabies
pain at bite site fever malaise vomiting progressing to delirium painful laryngeal spasm when attempting to drink (hydrophobia)
myelitis
infection of the spinal cord
poliomyelitis
specific infection of the gray matter of the spinal cord
killing anterior horn motor neurons with resultant paralysis
vascular disease and trauma
CVA (1/3 die, 1/3 serious neuro deficits)
trauma
cerebrovascular accident (stroke)
=sudden neurologic deficit caused by either vascular occlusion from thrombosis or embolism, from hemorrhage to the brain, or from ruptured saccular aneurysm
- majority from emboli
- *common atherosclerotic vascular disease
artery most occluded by emboli
middle cerebral artery: largest and a direct continuation of the carotid artery
supplies the part of the cortex controlling motor function
aphasia
impaired language function
brain hemorrhage
rupture of vessels and bleeding into the brain
saccular (berry) aneurysms
occur mostly in the circle of willis where vessels branch. deficiencies in the blood vessel walls result in outpouching.
trauma
concussion contusion epidural hematoma subdural hematoma penetrating injuries
why should a pt be watched closely after trauma?
late deterioration- subdural or epidural bleed developed immediately following injury but did not affect the pt until a critical amount of blood accumulated
concussion
momentary loss of consciousness and loss of reflexes following head trauma
amnesia for the traumatic event and complete recovery
no structural damage in the brain
contusion
bruises of the surface of the brain from time of impact
“coup lesions”-contusion of same side
“contrecoup lesions”- opposite side
result in hemorrhages from small blood vessels in the brain can cause further vessel occlusion and edema- vulnerable for intracranial pressure
epidural hematoma
epidural hemorrhage occurs between dura and skull
associated with severe trauma- skull usually fractured.
bc artery is ruptured (middle meningeal) the blood accumulates rapidly and pt will die w/in hours unless hematoma is removed.
subdural hematoma
=collection of blood beneath the dura
rupture of veins on the dorsum of the brain
bc bleeding is venous- does not accumulate as rapidly as epidural so not as life threatening but bleed still needs to be removed surgically to prevent compression of brain
penetrating injuries
bullets
fractured bone splinters
herniation- spinal cord
*infection to wound
degenerative diseases
multiple sclerosis creutzfeldt-jakob disease senile dementia parkinsons hydrocephalus epilepsy
multiple sclerosis
women>men
=focal loss of myelin sheath (demyelination)- appears to render axons incapable of properly transmitting a nervous impulse.
can occur anywhere in the brain and spinal cord so varies with pt
visual impairment
unknown cause
5-25 lifespan. remission and relapse
pt becomes debilitated from muscle weakness
dx: increased immunoglobin G (IgG) protein in cerebrospinal fluid
MRI-may see lesion
creutzfeldt-jakob disease (CJD)
human prototype of a group of diseases in animals and humans that result in brain degeneration. rare
“slow virus” diseases
“mad cow”
pt becomes rapidly demented and usually die 4-6 months after dx w/ severe brain degeneration
cause of CJD
appears to be the result of transformation of a normal brain protein into an abnormal configuration allowing it to replicate.
protein PRION builds up in the brain- associated with gray matter degeneration
senile dementia
=decrease in cognitive function, memory loss
-pick at their clothes, get lose easily, often irritable
degree depends on loss of substance in the frontal lobes, the region of that brain associated with higher cognitive function
alzheimer’s disease
dementia accompanied by certain microscopic brain changes
disease of age
large number of plaques, tangles and amyloid are found in hippocampal formation in the temporal lobe- explaining loss of recent memory
parkinson’s disease
-caused by degeneration of certain portions of the extrapyramidal (involuntary) motor system, especially the substantia nigra nucleus in the midbrain
classic inclusion= LEWY BODY
tremors at rest, masklike facial expression, shuffling gait, rigidity of skeletal muscles
hydrocephalus
=”water brain”
ventricles enlarge bc of block in the flow of cerebrospinal fluid at some level.
stenosis of aqueduct btwn 4and 5th ventricles- head may enlarge
if pressure is not released brain may herniate toward foramen magnum
epilepsy
=recurrent seizures
seizures=focal or generalized disturbances of neuronal electrical activity, may manifest abnormal movements or sensations and loss of reflexes, memory or consciousness
seizures may be caused by
electrolyte imbalance, high fever, uremia
generalized brain neoplasms symptoms
headaches
vomiting
blurred vision
seizures
from intracranial pressure
astrocytomas
slower growing brain tumors from astrocytes
glioblastoma
fast growing malignant brain tumor
most common in adults
result in death w/in 1-2 years
meningioma
2nd most common brain tumor
benign neoplasm that arises from dura and slow growing
adenomas
pituitary tumors
difficult to remove
some secrete growth hormone and result in gigantism or acromegaly
medulloblastoma
arises in cerebellum in children from primitive cells that are neuronal precursors
malignant but do respond well to radiation
