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Pathological processes active in the nervous system include congenital defects or alterations that may be degenerative, inflammatory, toxic, traumatic, mechanical or neoplastic. Circulatory impairment or disuse will cause impaired function as well.

Cerebrovascular accidents (CVAs)
The majority of lesions affecting the motor cortex and pathways are vascular resulting in anoxic tissue damage (stroke) that is sometimes reversible dependent on the location and severity of the CVA. Frequently vascular accidents are associated with hypertension and atherosclerosis. Interruption of blood flow to the brain causes ischemia that can progress to cellular death. If the ischemia is reversible, i.e. arterial spasm, then tissue changes are temporary. Episodes of muscle weakness, sensory deficits or visual disturbances may occur.

The majority of CVAs are associated with thrombosis that obstructs blood flow and causes infarction to the area served by the vessel. Tissue served by the affected cerebral artery is destroyed. The neurologic deficits seen depend on the severity and location of the affected tissue but symptoms generally include headache, dizziness, confusion and aphasia (defect in speech).

Embolisms, most often blood clots originating in the heart, cause 8% of all CVAs. The emboli travel to the brain and lodge in the middle cerebral artery most frequently. Classic stroke symptoms of opposite side paralysis, sensory loss, aphasia, apraxia (lack of voluntary movement) and agnosia (lack of recognition) are sudden in onset. Sometimes a weakness of the tunica media in cerebral arteries (congenital or atherosclerotic) causes an enlargement of blood vessels that may subsequently rupture and hemorrhage resulting in the symptoms of stroke.

Alterations of consciousness & functional disturbances
Coma is an abnormally deep stupor occurring as a result of illness or injury. Most cases result from head trauma or circulatory accidents in the brain (stroke), infections of the brain or meninges, or due to the effects of drugs or gases.

Paralysis is the temporary or permanent loss of motor or sensory function and is a relatively common occurrence with trauma to the nervous system. A flaccid paralysis is characterized by a loss of muscle tone, loss of tendon reflexes, and muscle atrophy. Excessive muscle tone and exaggerated tendon reflexes are characteristic of spastic paralysis. There is no muscle atrophy unless there is prolonged disuse.

Epilepsy is the second most common neurologic disorder after stroke. About 1% of the US population has epilepsy and 80% of the cases can be controlled pharmacologically. This paroxysmal disorder of cerebral function is characterized by sudden, brief seizures and altered consciousness, motor activity and sensory phenomenon. Seizures are defined episodes of brain dysfunction resulting from abnormal neuronal discharge. Such seizures may be the result of microscopic brain lesions, metabolic aberrations, infections, toxic agents or trauma. In 75% of affected adults no cause is identified.

Seizures that affect the entire brain and produce a loss of consciousness, muscle contractions, and possibly incontinence are termed grand mal seizures. Those that are sudden in onset, brief (10-30 seconds) and produce a loss of muscle tone are called petite mal. Petite mal seizures occur mostly in children and may occur up to hundreds of times a day. Partial seizures are those where the electrical disturbance has minimal spread such that normal consciousness and awareness are preserved.

During an attack the person should not be restrained but care should be taken that the local environment is free of things that may cause injury. Swallowing the tongue is not a danger for the epileptic. Do not try to put something in their mouth. The person will require rest after the attack. Anticonvulsant drugs can help control seizures in a majority of cases.

Trauma to the head
Concussion is usually caused by a blow to the head that may cause transient dizziness or actually cause unconsciousness or paralysis dependent on the area and extent of the injury. The period of unconsciousness may las just a few seconds to a few hours. The patient may experience vomiting, elevated temperature, rapid pulse, restlessness or headache for 12-24 hours after the initial injury.

Bleeding into the rigid skull results in increased intracranial pressures that produces either localized or generalized effects. Hematomas carry a high mortality when acute. Bleeding into the epidural space causes increasing pressures, brain distortion and death within 24 hours without surgical intervention. Subdural hematoma is also a surgical emergency and the blood must be drained rapidly.

Spinal cord injury
Spinal cord injuries most commonly occur by trauma causing hyperextention or hyperflexion and sometimes rotation of the spinal column. The resultant damage may be transient or permanent. Spinal cord transection causes immediate and permanent loss of all voluntary movement below the level of the injury.

The degree of loss of function in spinal cord injuries depends on the level of the injury. Cervical spine injuries above the 4th vertebra may be fatal because control of the diaphragm and intercostal muscles used in respiration is lost. Such high cervical injuries result in quadriplegia. Injuries at the 5th and 6th cervical nerve retain some function of the neck, shoulder and upper arm. Additional elbow, wrist and hand function is seen in individuals with injuries at the 7th and 8th cervical level. Injuries to the thoracic and lumbar spine produce paraplegia. The lower the level of the injury the more function the person retains.

Herniation of the cartilaginous discs that cushion the articulation of the vertebral bodies is most commonly caused by trauma. The central nucleus of the disc is forced out by sudden training of the back causing pain, sensory loss, and paralysis due to pressure on the spinal nerve roots. Most of the time a herniation occurs in the lumbosacral spine between the 4th and 5th vertebrae. Cervical herniations usually occur at between the 5th and 7th cervical nerves resulting in shoulder pain that radiates down the arm and a stiff neck. Initial treatment includes pain relievers, hot packs and bed rest. If the condition does not get better, surgical intervention is warranted.

The extent and severity of neurologic symptoms resulting from CNS tumors, whether benign or not, is largely determined by the location, size and invasiveness of the tumor. Distruction and displacement of nervous tissue is damaging giving even benign tumors the capability of producing harmful effects. Compression and the lack of blood flow to normal tissue can lead to altered neural excitability and seizure activity. Mobidity and mortality are high for brain tumors. Tumors of the CNS are not rare and can occur at any age although they are more common in children and those over 50.

Generalized symptoms of CNS tumors are headache, vomiting, blurred vision, and papilledema (edema and inflammation of the optic nerve). Other symptoms depend on the location of the tumor. Frontal lobe tumors may produce speech disturbances, apathy, dementia, memory and intellect deficits, diminished judgment, depression, aphasia and apraxia. Tumors of the temporal lobe usually produce sensory aphasia while those of the occipital lobe are characterized by agnosia, paraesthesia, and dyslexia. When the occipital lobe is effected, patients may have visual disturbances, hallucinations and visual agnosia. Cerebellar tumors result in disturbances of equilibrium and coordination.

Sometimes cancer cells originating from a peripheral tumor of the lung, breast or other tissue may enter the CNS and begin to grow. This usually only happens when the metastatic cancer is well advanced. Prognosis for recovery is poor.

Infections of the CNS can arise by spread from the sinuses and middle ear, enter via penetrating wounds to the head or spread via the bloodstream from other sites in the body. Infectious agents include viruses, bacteria, fungi, protozoa, metazoa, prions and bacterial exotoxins. Viral encephalitis may be caused by various arthropod borne (mosquito, flies, ticks) viruses, sexually transmitted disease (herpes simplex) and directly transmitted viruses like rabies. Symptoms of encephalitis include headache, high fever, confusion, convulsions, restlessness progressing to stupor and coma.

Any bacteria may potentially cause meningitis but some are more prominent. Meningitis is an infection of the membranes that surround and protect the brain and spinal cord. Symptoms of such an infection include fever, headache, photophobia, dizziness, neck and back stiffness, drowsiness, stupor and coma. Prompt diagnosis and antibiotic therapy are critical. Diphtheria, tetanus and botulism toxins cause profound effects on the CNS that may be prevented by immunization. Antitoxins are available and may prevent clinical symptoms in many cases.

Fungal infections of the CNS are not very common and usually occur secondary to an infection elsewhere or immunosuppressant therapy. Protozoal infections such as malaria, toxoplasmosis, ambiasis, Chagus, sleeping sickness, and trichinosis (Nematode) can produce CNS produce neurologic symptoms that are acutely fatal or chronic deficits dependent on the causative organism.

Developmental disorders
Spina bifida is a defect of the spinal cord caused by the lack of fusion of the vertebral lamina primarily in the lumbar region. Some forms can be diagnosed in utero using amniocentesis. The degree of impairment depends on the location and degree of the defect. If there is no other neurologic deficit surgical repair is usually successful and many children reach adulthood with mobility using some supportive aids.

An increase in the amount of cerebral spinal fluid within the ventricles of the brain may be the result of developmental abnormalities, infections, injury or brain tumors. Cerebrospinal fluid is made and reabsorbed routinely. Alterations in the synthesis or removal of the fluid can cause increased volumes and therefor increased ventricular pressure. In infants this results in head swelling because the cranial sutures are still unfirm. In adults, there is no room for the brain to expand and the pressure caused headache, vomiting and visual and mental disturbances.

Cerebral palsy results from developmental defects in the brain or trauma at birth and is characterized by nonprogressive paralysis occurring on both sides of the body in a symmetrical fashion. Classic symptoms are mental retardation, seizures and motor disabilities with a diagnosis usually occurring in early childhood. The areas of the brain that are damaged determine the clinical picture.

Progressive disorders
Myasthenia gravis is a chronic disease of variable course characterized by muscular weakness without atrophy and progressive fatigue. Nerve impulses fail to initiate normal muscle contractions due to an autoimmune attack on acetylcholine receptors at the neuromuscular junctions. MG is more common in women and generally is diagnosed between the ages of 20-50. Remissions and exacerbations routinely occur. Physostigmine or neostigmine are effective treatments as they block the action of the enzyme that breaks down the neurotransmitter acetylcholine.

Guillain-Barre Syndrome is an autoimmune disorder that occurs after an infectious disease (usually viral) producing a progressive muscle weakness and paralysis. Both sensory and motor functions are effected by the breakdown of myelin surrounding peripheral nerves. Recovery is usually complete but may take several months. Indeed, most patients (85%) make a full recovery in 4-6 months. Treatments include steroids, ACTH or immunosuppression that are variably effective.

Multiple Sclerosis is a chronic slowly progressive CNS disease where demyelination causes scarring and patches in the tissue. It may be autoimmune in nature. Late signs are nystagmus, tremor, and speech disorders progressing to paraplegia, incontinence and emotional instability.

Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig’s disease) is characterized by muscular weakness and atrophy, spasticity, and hyperflexion due to degeneration of the spinal cord and medullary motor neurons. This steadily progressive disease has a greater incidence in men and usually results in death within 2-6 years although this is sometimes extended to 10+ years depending on where along the spinal cord the degenerative process began and how quickly the medulla becomes involved.

Movement disorders
Parkinson’s disease is a chronic disease characterized by fine tremors that are slow spreading, muscular weakness, slow movement and rigidity. Usually occurs between the ages of 50-80. The normally high level of the neurotransmitter dopamine is reduced in some portions of the brain in parkinsonism. The use of levodopa and dopamine agonists can alleviate many of the symptoms of Parkinson’s.

Huntington’s chorea is a dominantly inherited disease of the CNS having an onset at 30-50 years. It is characterized by progressive dementia, bizarre involuntary movements, and abnormal posture. There seems to be an imbalance in several neurotransmitters in parts of the brain. Treatment is usually aimed at blocking neurotransmission via dopamine. A commonly used drug is reserpine. It acts to deplete dopamine by preventing storage within neurons. It has some side effects, however, such as low blood pressure, depression, sedation, diarrhea, and nasal congestion. The disease is uniformly fatal usually within 10-15 years after symptoms appear.

Memory & judgment disorders
Dementia is a deteriorative mental state with the absence or reduction of intellect due to organic brain disease. There is a progressive lack of judgment, abstract thinking, decreased memory, confusion, and emotional changes. Senile dementia occurs in elderly individuals and is most often due to cerebral anoxia due to diminished blood flow. Almost 50% of the population over 85 have some degree of dementia.

Alzheimer’s disease is a presenile dementia caused by an atrophy of the frontal and occipital lobes of the brain. It occurs between the ages of 40 and 60, more often in women than men. There is a progressive, irreversible memory loss, deterioration of intellectual function, disorientation and motor dysfunction. The loss of cholinergic nerve terminals in the basal forebrain is characteristic of Alzheimer’s as are plaques having a core of amyloid protein.

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