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Chapter 6
THE NERVOUS SYSTEM
INTRODUCTION
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The nervous and endocrine systems are the
communicate channels of the body. The nervous
system composed of:
Central nervous system (nerve pathways of the brain
and spinal cord), and
 Peripheral nervous system, (nerves that innervate the
rest of the body).
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The coordination of our central and peripheral
nervous systems allows us to move, talk, think,
and respond.
INTRODUCTION
The Blood-Brain Barrier (tightly fused endothelial 
cells present in the brain capillaries and from cells
lining the ventricles that limit diffusion and
filtration). The blood-brain barrier protects delicate
brain cells from exposure to potentially harmful
substances. Many drugs and chemicals cannot
cross the blood-brain barrier.
Intracranial Pressure (ICP) 
ICP is determined by the volume of blood in the 
brain, the volume of CSF, and the volume of brain
tissue. Normally, ICP ranges from 5 to 15
millimeters of mercury (mmHg).
PATHOPHYSIOLOGIC CONCEPTS
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Brain Death
Brain death is irreversible loss of cerebral hemisphere,
brainstem, and cerebellum function. Consciousness is
lost, as is maintenance of respiration, cardiovascular,
and temperature control function, no sleep-wake cycle,
no pain response, and no reflexes.
The electroencephalogram (EEG) is flat, LOC.
2) Dementia
Dementia is a loss of intellectual functioning without a
loss of arousal functioning. Memory, general knowledge,
abstract thought, judgment, and interpretation of written
and oral communication may be affected.
Causes: infection, drugs, trauma, or tumors.
3) INCREASED INTRACRANIAL PRESSURE
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Intracranial pressure may increase with increases in cranial
blood, CSF, or tissue, leading to hypoxia, neuronal injury and
death.
If intracranial pressure reaches systemic mean arterial
pressure, blood flow to the brain will stop and the individual
will die.
Causes of Increased Intracranial Pressure
- Anything that significantly increases CSF production or
blocks CSF outflow .
- Any increase in tissue mass (e.g., that associated with a
growing brain tumor)
- Edema due to infection and inflammation
- Severe trauma to the head, a burst aneurysm, or a
hemorrhage in the brain,
ICP
Treatment of Intracranial Hypertension
 Effective monitoring of intracranial pressure
(ICP).
 Osmotic diuretics (mannitol) to reduce blood
volume
 Steroids to decrease inflammation
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TESTS OF NEUROLOGIC FUNCTIONING
There are several methods to measure neuronal 
and brain electrical activity and observe for
malformations, injuries, or tumors. Some of these
techniques are presented briefly.
 Electromyography(EMG)
Measures peripheral nerve function and is used to 
diagnose, describe, and monitor neuromuscular
pathology
TESTS OF NEUROLOGIC FUNCTIONING
b) Electroencephalography (EEG)
 Measures electrical activity occurring in the
brain through electrodes placed on the scalp.
This technique offers a fast, real-time picture of
brain activity.
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c) Magnetic Resonance Imaging (MRI)
 Captures what is happening in the brain
physiologically before, during, and after an
individual performs a task.
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TESTS OF NEUROLOGIC FUNCTIONING
d) Computed Tomography (CT)
 Involves computer analysis of multiple radiologic
images. In a CT scan, an x-ray beam is rotated
around the patient, and passes successively
through tissue from multiple directions
 d)Ultrasonography
 Use reflected sound to measure blood flow
velocity, which is important for assessment of
cerebral blood flow when evaluating ischemic
cerebrovascular disease. Ultrasound is used
during surgical procedures on the brain to study
the development of vascular spasm or blockage in
real time.
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CONDITIONS OF DISEASE OR INJURY
A seizure is the sudden, uncontrolled discharge
of brain neurons, which produces changes in
brain function. Seizures result when certain
cerebral neurons exist in a hyperexcitable or
easily depolarized state. Neurons of the
epileptogenic focus respond to levels of stimuli
that do not produce disorderly discharge in
other neurons.
 Seizure may be:
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 partial
seizure, (consciousness is usually not lost)
 generalized. The time of unconsciousness after any
generalized seizure is called the postictal phas
 Status epilepticus is said to occur.
CONSEQUENCES OF A SEIZURE
During a seizure, cerebral oxygen demand
increases more than 200%. If this oxygen
demand cannot be met, brain hypoxia and
brain damage may occur.
 Seizures that continue for extended periods, or
the occurrence of status epilepticus, greatly
increase the chance of brain damage.
 Social isolation and reduced employment
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CAUSES OF SEIZURE DISORDERS
 severe hypoxemia (decreased oxygen in the
blood),
 hypoglycemia (decreased glucose in the
blood),
 acidemia (increased acid in the blood),
 alkalemia (decreased acid in the blood),
 dehydration, water intoxication,
 high fever.
 Drug withdrawal, drug abuse, and toxemia
in pregnancy also may cause seizures.
EPILEPSY
Epilepsy refers to a seizure that occurs without
a reversible, metabolic cause. Epilepsy may be:
 Primary epilepsy develops spontaneously,
usually in childhood, and has a genetic
predisposition
 Secondary epilepsy occurs as a result of
hypoxemia, head injury, infection, stroke, or
central nervous system tumor. Adult-onset
epilepsy is usually caused by one of these
incidents.
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CLINICAL MANIFESTATIONS
*Partial seizures may be associated with:
- Facial movements or grimace
- Jerking beginning in one part of the body,
which may spread
- Sensory experiences of sights, smells, or
sounds
- Tingling
- An alteration in level of consciousness
*GENERALIZED SEIZURES MAY BE ASSOCIATED
WITH:
- Unconsciousness, usually accompanied by a
fall,
- Uncontrolled jerking of arms and legs
- A short period of apnea (breathing cessation)
- Salivation and frothing at the mouth
- Tongue biting
- Incontinence
- A postictal stage of stupor or coma, followed by
confusion, headache, and fatigue
*GENERALIZED SEIZURES MAY BE ASSOCIATED
WITH:
- A prodroma may occur with any seizure type. A
prodoma is a certain feeling or symptom that
may precede a seizure by hours or days.
 - An aura may occur with any seizure type. An
aura is a certain sensory sensation that
frequently or always immediately precedes a
seizure.
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DIAGNOSTIC TOOLS
-A
detailed medical history is required for an accurate
diagnosis of a seizure.
- Basic laboratory evaluation must be performed to rule out
metabolic causes or drug-induced seizures.
- Lumbar puncture is performed to rule out meningitis or
encephalitis if suspected.
- MRI is the imaging modality of choice to identify brain lesions
such as tumor, abscess, or vascular malformation as the
cause of the seizure.
- A CT scan may be used for patients with emerging neurologic
symptoms who need immediate diagnostic information.
- An EEG may allow diagnosis of the type and location of the
occurring seizure.
COMPLICATIONS
- Hypoxic brain damage and mental retardation may
follow repeated seizures.
- Depression and anxiety may develop.
 Treatment
 - The goal of seizure treatment is zero seizure
occurrence with a minimum of treatment-induced
side effects.
 - The medication selected must be appropriate for
the seizure type.
 - Resective surgery to excise the epileptogenic
focus is becoming more common
2-HEAD INJURY
Head injuries may be open (penetrating through
the dura mater) or closed (blunt trauma,
without penetration through the dura).
Types of Head Injuries
1-Concussion
A concussion is a closed head injury usually
characterized by loss of consciousness..
TYPES OF HEAD INJURIES
2-Epidural Hematoma
An epidural hematoma is the accumulation of
blood above the dura mater.
3-Subdural Hematoma
A subdural hematoma is the accumulation of
blood under the dura mater, but above the
arachnoid membrane.
TYPES OF HEAD INJURIES
4-Subarachnoid Hemorrhage
A subarachnoid hemorrhage is the accumulation of blood
under the arachnoid membrane, but above the pia mater.
Clinical Manifestations
- With a concussion, consciousness is often lost.
- Respiratory patterns may become progressively abnormal.
- Pupillary responses may be absent or progressively
deteriorate.
- Headache may occur immediately or develop with increasing
intracranial pressure.
- Vomiting may occur as a result of increased intracranial
pressure.
- Behavioral, cognitive, and physical changes in speech and
motor movements may occur immediately or develop slowly.
- Amnesia related to the event is common.
DIAGNOSTIC TOOLS
- A skull X ray may locate fractures or a developing bleed or blood clot.
- A CT scan or an MRI may pinpoint the site and extent of injury.
Treatment
- Mild and moderate concussions are usually treated with observation
and bed rest.
- Surgical ligation of a bleeding vessel and evacuation of a hematoma
may be required.
- Surgical debridement (removal of foreign material and dead cells)
may be required,
- Decompression through the drilling of holes into the brain, called burr
holes, may be required.
- Mechanical ventilation may be required.
- Antibiotics are required for open head injury to prevent infection.
Methods to decrease intracranial pressure may include the
administration of diuretics and anti-inflammatory drugs
SPINAL INJURY
The spinal cord, running through the vertebral
column, may be sliced, pulled, twisted, or
compressed. Damage to the vertebral column
or cord may occur at any level. Damage may
involve the entire cord or be restricted to one
half. Damage to the spine may result in
temporary dysfunction or permanent damage if
the cord is transected (cut).
CAUSES OF SPINAL INJURY
The most common causes of spinal injury are
automobile and motorcycle accidents, falls,
sports injuries, and wounds from guns and
knives.
Results of Spinal Injury
Loss of Sensation, Motor Control, and Reflexes
With severe spinal injury, sensation, motor
control, and reflexes at and below the level of
cord injury are lost. The loss of all reflexes is
called spinal shock.
PARALYSIS
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Paralysis is the loss of sensory and voluntary
motor function. With spinal cord transection,
paralysis is permanent. Paralysis of the upper
and lower extremities occurs with transection
of the cord at level C6 or higher and is called
quadriplegia. Paralysis of the lower half of the
body occurs with transection of the cord below
C6 and is called paraplegia. If only one half of
the cord is transected, hemiparalysis may
occur.
CLINICAL MANIFESTATIONS
- Loss of sensation, motor control, and reflexes
below the level of injury, and up to two
levels above, will occur.
 - The pulse rate is often normal, with low blood
pressure.
 Diagnostic Tools
 Physical examination coupled with CT and MRI
will document vertebral and spinal injury and
edema.
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COMPLICATIONS
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If damage and swelling around the cord is in
the cervical spine (down to approximately C5),
respirations may cease because of
compression of the phrenic nerve, which exits
between C3 and C5 and controls the movement
of the diaphragm.
TREATMENT
- Immobilization to prevent cord severing or additional 
damage
- Early surgical intervention to relieve pressure on the cord 
- Immediate (within the first hour) large-dose administration 
of steroids has been shown to reduce cord swelling and
inflammation and limit the extent of permanent damage.
- Surgical fixation of the vertebral column hastens and 
supports healing.
 - Physical therapy, including speech therapy if the lesion
interferes with speech and respiratory movements, is begun
soon after the patient's condition stabilizes
A CEREBRAL VASCULAR ACCIDENT (CVA),
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A cerebral vascular accident (CVA), often called a stroke
or a brain attack, is a brain injury related to an
obstruction in brain blood flow. There are two general
classifications of CVAs: ischemic and hemorrhagic.
Complications
A major CVA to the part of the brain controlling
respiration or cardiovascular response may lead to
death
Communication difficulties. Hypoxia of motor areas in
the brain may lead to
paresis.
Emotional changes .
TREATMENT
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In patients in whom the CVA can be identified as ischemic in
nature, thrombolytic agent, can be administered. as early as
possible (at least within the first 3 hours of the attack)
- A hemorrhagic stroke is treated with emphasis on stopping
the bleeding and preventing another occurrence. Surgery
may be required.
- All stroke patients are treated with bed rest and a reduction
of external stimuli to reduce cerebral oxygen demands.
- Measures to reduce intracranial edema and pressure may
be instituted.
- Physical, speech, and occupational therapy are often
required.
CENTRAL NERVOUS SYSTEM INFECTION
A central nervous system infection may involve the
brain tissue (encephalitis), or the meninges
(meningitis).
 1-Encephalitis
 Encephalitis is usually a viral infection of the brain.
It is often carried by a mosquito vector or related
to infection with herpes simplex 1 or
cytomegalovirus. Nerve cell degeneration is
widespread and edema and swelling are severe
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2-Meningitis
Meningitis is the most common serious infection of the
CNS. It is usually caused by bacteria or a virus, although
fungi, protozoa, and toxins are also causes.
Meningitis frequently occurs from the spread of an
infection elsewhere in the body, for example, the
sinuses, ears, or upper respiratory tract. A posterior
basilar skull fracture with a ruptured eardrum may also
cause meningitis. With bacterial meningitis, released
toxins destroy meningeal cells and stimulate immune
and inflammatory reactions. Secondary encephalitis
may occur. Even when treated, up to 40% of meningitis
cases are fatal and up to 30% of survivors have
neurological
CLINICAL MANIFESTATIONS
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Symptoms of increased intracranial pressure may develop with
meningitis and encephalitis, including headache, decreased
consciousness, and vomiting.
Papilledema (swelling of the area around the optic nerve) may occur
in severe cases. Typically, the symptoms are worse with encephalitis.
- Fever from infection is common in meningitis and encephalitis.
- Photophobia (painful response to light) from irritation of the
cranial nerves frequently accompanies meningitis and encephalitis.
- Inability to flex the chin to the chest without pain (nuchal rigidity)
occurs in meningitis and encephalitis as a result of irritation of the
spinal nerves.
- Encephalitis typically presents with dramatic signs of delirium and
a progressive decrease in consciousness. Seizures and abnormal
movements may occur.
Treatment
 - A broad spectrum antibiotic is administered after
CSF collection and is changed if necessary after
culture results.
 - An antiviral drug will be administered for
encephalitis.
 - Measures to reduce intracranial pressure will be
initiated, especially for encephalitis.
 - Some types of meningitis will require the patient
to be isolated in the hospital.
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Spina Bifida
Spina bifida is a congenital neural tube defect characterized
by a failure of the vertebral arches to close. This results in a
cyst-like protrusion of the meninges alone (meningocele) or
of the meninges and the spinal cord (myelomeningocele) out
of the vertebral column.
Causes of Spina Bifida
Although the cause of spina bifida is unknown, a genetic
predisposition may exist. Increased risk of the disorder
occurs with maternal folic acid deficiency. Folic acid
deficiency is common in women; therefore, it is strongly
recommended that all women anticipating pregnancy begin
taking folic acid vitamin supplements at least 3 months
before conception.
HYDROCEPHALUS
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Hydrocephalus is characterized by an accumulation of
CSF anywhere in the ventricles of the brain.
Effect of Hydrocephalus
Intracranial pressure increases with hydrocephalus; this
can directly injure underlying nervous tissue and
compromise cerebral blood flow and the neuronal
supply of oxygen and glucose
Treatment
- Placement of a shunt to drain CSF in utero or after
birth may be performed.
- Treatment of the underlying cause is required.