Chapter 6

THE NERVOUS SYSTEM

INTRODUCTION

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). The coordination of our central and

peripheral nervous systems allows us to move, talk, think, and respond.

INTRODUCTIONThe 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

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

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

 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.

  c) Magnetic Resonance Imaging

(MRI) Captures what is happening in the

brain physiologically before, during, and after an individual performs a task.

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.

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: 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

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.

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.

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 Injuries1-ConcussionA concussion is a closed head injury

usually characterized by loss of consciousness..

TYPES OF HEAD INJURIES

2-Epidural HematomaAn epidural hematoma is the

accumulation of blood above the dura mater.

3-Subdural HematomaA subdural hematoma is the

accumulation of blood under the dura mater, but above the arachnoid membrane.

TYPES OF HEAD INJURIES 4-Subarachnoid HemorrhageA 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 InjuryLoss of Sensation, Motor Control, and ReflexesWith 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

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.

COMPLICATIONS

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), 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

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

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

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.

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

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.