NERVOUS TISSUE

 

There are two basic systems of internal communication and physiological homeostasis in the body: the endocrine system and the nervous system.

The nervous system is derived from embryonic neuroectoderm.

The human nervous system is divided anatomically into:

• Central Nervous System (CNS), consisting of the brain and spinal cord.
• Peripheral Nervous System (PNS), consisting of nerve fibers, aggregates of nerve cells and glia and ganglia.

It is estimated that the human nervous system consists of at least 10 billion neurons.

Nervous tissue consists of two groups of cell types:

• Nerve cells (Neurons)
  
  
• Neuroglia.
• Nervous tissue is responsible for carrying out all the informational signaling in our bodies.  Our brain is made of nervous tissue, and it can choose to tell our muscles (via the spinal cord and nerves) to carry out certain actions.  Our sensory systems all provide information to our brains via nervous system cells as well.
•     There are two main cell types in the nervous system:  neurons and glia (your book calls the second type neuroglia, but "glia" is fine).  Neurons are the electrically active, signaling cells of the nervous system.  Glia are the support cells, and they have many, many other functions that we will discuss when we get to the nervous system.
•     Nervous tissue receives nutrients from the blood, but not all blood borne factors can enter nervous tissue... nervous tissue lies within a protective ensheathment which creates the blood-brain barrier.  However, nervous tissue can still be considered vascularized.
•     The neurons of nervous tissue are unable to divide-- ever.   Once they die, they can thus never be replaced.  The glia are able to reproduce, but cannot take over the functions of neurons.
  
   

The CNS consists of the brain, enclosed in the skull and then lower spinal cord, located in the spinal canal. The gray matter consists mainly of the neuronal cell bodies and glial cells, while white matter is named for the myelinated nerve fibers within it.

The neuronal bodies in the white matter are grouped into core and extensions histologically organized nerve fibers pass between regions of the CNS forming fascicles or nerve cords.

    The PNS includes all existing nerve tissue outside the brain and spinal cord and consists of nerve cell bodies arranged in ganglia, nerve fibers or crosslinks plexus and nerve fiber bundles organized parallel scan nerves.

GUILLAIN-BARRE SYNDROME

Guillain-Barre syndrome is a serious disorder that occurs when the body's defense (immune) system mistakenly attacks part of the nervous system. This leads to nerve inflammation that causes muscle weakness.

Guillain-Barre syndrome is an autoimmune disorder (the body's immune system attacks itself). Exactly what triggers Guillain-Barre syndrome is unknown. The syndrome may occur at any age, but is most common in people of both sexes between ages 30 and 50.

It often follows a minor infection, such as a lung infection or gastrointestinal infection. Most of the time, signs of the original infection have disappeared before the symptoms of Guillain-Barre begin.

The swine flu vaccination in 1976 may have caused rare cases of Guillain-Barre syndrome. However, the swine flu and the regular flu vaccines used today have not resulted in more cases of the illness.

Guillain-Barre syndrome damages parts of nerves. This nerve damage causes tingling, muscle weakness, and paralysis. Guillain-Barre syndrome most often affects the nerve's covering (myelin sheath). Such damage is called demyelination, and it causes nerve signals to move more slowly. Damage to other parts of the nerve can cause the nerve to stop working altogether.

Symptoms

Symptoms of Guillain-Barre can get worse very quickly. It may take only a few hours to reach the most severe symptoms, but weakness that increases over several days is also common.

Muscle weakness or the loss of muscle function (paralysis) affects both sides of the body. In most cases, the muscle weakness starts in the legs and then spreads to the arms. This is called ascending paralysis.

Patients may notice tingling, foot or hand pain, and clumsiness. If the inflammation affects the nerves to the diaphragm and chest and there is weakness in those muscles, the person may need breathing assistance.

Typical symptoms include:

• Loss of reflexes in the arms and legs
• Low blood pressure or poor blood pressure control
• Muscle weakness or loss of muscle function (paralysis)
  • In mild cases, there may be weakness instead of paralysis
  • May begin in the arms and legs at the same time
  • May get worse over 24 to 72 hours
  • May occur in the nerves of the head only
  • May start in the arms and move downward
  • May start in the feet and legs and move up to the arms and head

Signs and tests

A history of increasing muscle weakness and paralysis may be a sign of Guillain-Barre syndrome, especially if there was a recent illness.

A medical exam may show muscle weakness and problems with involuntary (autonomic) body functions, such as blood pressure and heart rate. The examination will also show that reflexes, such as the "ankle or knee jerk," are decreased or missing.

There may be signs of decreased breathing caused by paralysis of the breathing muscles.

The following tests may be ordered:

• Cerebrospinal fluid sample ("spinal tap")
• ECG
  
• Electromyography (EMG) tests the electrical activity in muscles
• Nerve conduction velocity test
• Pulmonary function tests
  

Treatment

There is no cure for Guillain-Barre syndrome. However, many treatments are available to help reduce symptoms, treat complications, and speed up recovery.

When symptoms are severe, the patient will need to go to the hospital for treatment, which may include artificial breathing support.

In the early stages of the illness, treatments that remove or block the proteins that attack the nerve cells, called antibodies, may reduce the severity and duration of Guillain-Barre symptoms.

One method is called plasmapheresis, and it is used to remove the antibodies from the blood. The process involves taking blood from the body, usually from the arm, pumping it into a machine that removes the antibodies, and then sending it back into the body.

A second method is to block the antibodies using high-dose immunoglobulin therapy (IVIG). In this case, the immunoglobulins are added to the blood in large quantities, blocking the antibodies that cause inflammation.

Other treatments are directed at preventing complications.

• Blood thinners may be used to prevent blood clots.
• If the diaphragm is weak, breathing support or even a breathing tube and ventilator may be needed.
• Pain is treated with anti-inflammatory medicines and narcotics, if needed.
• Proper body positioning or a feeding tube may be used to prevent choking during feeding if the muscles used for swallowing are weak.

 

MULTIPLE SCLEROSIS

Multiple sclerosis (MS) is a disease in which the nerves of the central nervous system (brain and spinal cord) degenerate. Myelin, which provides a covering or insulation for nerves, improves the conduction of impulses along the nerves and also is important for maintaining the health of the nerves. In multiple sclerosis, inflammation causes the myelin to disappear. Consequently, the electrical impulses that travel along the nerves decelerate, that is, become slower. In addition, the nerves themselves are damaged. As more and more nerves are affected, a person experiences a progressive interference with functions that are controlled by the nervous system such as vision, speech, walking, writing, and memory,

The cause of multiple sclerosis is still unknown. In the last 20 years, researchers have focused on disorders of the immune system and genetics for explanations. The immune system is the body's defender and is highly organized and regulated. If triggered by an aggressor or foreign object, the immune system mounts a defensive action which identifies and attacks the invader and then withdraws. This process depends upon rapid communication among the immune cells and the production of cells that can destroy the intruder. In multiple sclerosis, researchers suspect that a foreign agent such as a virus alters the immune system so that the immune system perceives myelin as an intruder and attacks it. The attack by the immune system on the tissues that it is supposed to protect is called autoimmunity, and multiple sclerosis is believed to be a disease of autoimmunity. While some of the myelin may be repaired after the assault, some of the nerves are stripped of their myelin covering (become demyelinated). Scarring also occurs, and material is deposited into the scars and forms plaques.

There are different clinical manifestations of multiple sclerosis. During an attack, a person experiences a sudden deterioration in normal physical abilities that may range from mild to severe. This attack, sometimes referred to as an exacerbation of multiple sclerosis, typically lasts more than 24 hours and generally more than a few weeks (rarely more than four weeks).

About 65%-80% of individuals begin with relapsing-remitting (RR) MS, the most common type. In this type, they experience a series of attacks followed by complete or partial disappearance of the symptoms (remission) until another attack occurs (relapse). It may be weeks to decades between relapses.

In primary-progressive (PP) MS, there is a continuous, gradual decline in a person's physical abilities from the outset rather than relapses. About 10%-20% of individuals begin with PP-MS.

Those beginning with RR-MS can then enter a phase where relapses are rare but more disability accumulates, and are said to have secondary-progressive (SP) MS. About 50% of RR-MS individuals will develop SP-MS within 10 years. Over several decades, most RR-MS persons will experience progression to SP-MS. Progressive-Relapsing (PR) MS is a type of multiple sclerosis characterized by a steady decline in abilities accompanied by sporadic attacks. There are cases of multiple sclerosis that are mild and can be recognized only retrospectively after many years and also rare cases of extremely rapid progression of multiple sclerosis symptoms (sometimes fatal) known as malignant or fulminant (Marburg variant) multiple sclerosis.

Symptoms of multiple sclerosis may be single or multiple and may range from mild to severe in intensity and short to long in duration. Complete or partial remission from symptoms occurs early in about 70% of individuals with multiple sclerosis.

• Visual disturbances may be the first symptoms of multiple sclerosis, but they usually subside. A person may notice a patch of blurred vision, red-to-orange or red-to-gray distortions (color desaturation), or monocular visual loss (loss of vision in one eye). Visual symptoms due to optic nerve inflammation (optic neuritis) in multiple sclerosis usually are accompanied or preceded by eye pain.
• Limb weakness with or without difficulties with coordination and balance may occur early.
• Muscle spasms, fatigue, numbness, and prickling pain are common symptoms.
• There may be a loss of sensation, speech impediment (typically a problem articulating words), tremors, or dizziness

GLIOMA:

A glioma is a type of tumor that starts in the brain or spine. It is called a glioma because it arises from glial cells. The most common site of gliomas is the brain.

Symptoms of gliomas depend on which part of the central nervous system is affected. A brain glioma can cause headaches, nausea and vomiting, seizures, and cranial nerve disorders as a result of increased intracranial pressure. A glioma of the optic nerve can cause visual loss. Spinal cord gliomas can cause pain, weakness, or numbness in the extremities. Gliomas do not metastasize by the bloodstream, but they can spread via the cerebrospinal fluid and cause "drop metastases" to the spinal cord.

Gliomas cannot be cured. The prognosis for patients with high-grade gliomas is generally poor, and is especially so for older patients. Of 10,000 Americans diagnosed each year with malignant gliomas, about half are alive 1 year after diagnosis, and 25% after two years. Those with anaplastic astrocytoma survive about three years. Glioblastoma multiforme has a worse prognosis with less than 12 month survival after diagnosis.

Gliomas are classified by cell type, by grade, and by location.

By type of cell

Gliomas are named according to the specific type of cell they most closely resemble. The main types of gliomas are:

• Ependymomas — ependymal cells
• Astrocytomas — astrocytes - Glioblastoma multiforme is the most common astrocytoma.
• Oligodendrogliomas — oligodendrocytes
• Mixed gliomas, such as oligoastrocytomas, contain cells from different types of glia.

By grade

Gliomas are further categorized according to their grade, which is determined by pathologic evaluation of the tumor.

• Low-grade gliomas are well-differentiated (not anaplastic); these are benign and portend a better prognosis for the patient.
• High-grade gliomas are undifferentiated or anaplastic; these are malignant and carry a worse prognosis.

Of numerous grading systems in use, the most common is the World Health Organization (WHO) grading system for astrocytoma.

By location

Gliomas can be classified according to whether they are above or below a membrane in the brain called the tentorium. The tentorium separates the cerebrum, above, from the cerebellum, below.

• supratentorial: Above the tentorium, in the cerebrum, mostly in adults (70%). Senator Edward M. Kennedy's brain tumor, for example was supratentorial, in the parietal area in the upper part of the left side of his brain, above the ear.
• infratentorial: Below the tentorium, in the cerebellum, mostly in children (70%)

Stroke

A stroke happens when blood flow to a part of the brain stops. A stroke is sometimes called a "brain attack."

STROKE RISK FACTORS

High blood pressure is the number one risk factor for strokes. The other major risk factors are:

• Atrial fibrillation
  
• Diabetes
  
• Family history of stroke
• High cholesterol
  
• Increasing age, especially after age 55
• Race (black people are more likely to die of a stroke)

Symptoms

The symptoms of stroke depend on what part of the brain is damaged. In some cases, a person may not know that he or she has had a stroke.

Symptoms usually develop suddenly and without warning. Or, symptoms may occur on and off for the first day or two. Symptoms are usually most severe when the stroke first happens, but they may slowly get worse.

A headache may occur, especially if the stroke is caused by bleeding in the brain. The headache:

• Starts suddenly and may be severe
• Occurs when you are lying flat
• Wakes you up from sleep
• Gets worse when you change positions or when you bend, strain, or cough

Treatment

A stroke is a medical emergency. Immediate treatment can save lives and reduce disability. Call 911 or your local emergency number or seek urgent medical care at the first signs of a stroke.

It is very important for people who are having stroke symptoms to get to a hospital as quickly as possible. If the stroke is caused by a blood clot, a clot-busting drug may be given to dissolve the clot.

Most of the time, patients must reach a hospital within 3 hours after symptoms begin. Some people may be able to receive these drugs for up to 4 - 5 hours after symptoms begin.

Treatment depends on how severe the stroke was and what caused it. Most people who have a stroke need to stay in a hospital.

 

TREATMENT IN THE HOSPITAL

Clot-busting drugs (thrombolytic therapy) may be used if the stroke is caused by a blood clot. This medicine breaks up blood clots and helps bring back blood flow to the damaged area. However, not everyone can get this type of medicine.

• For these drugs to work, a person must be seen and treatment must begin within 3 hours of when the symptoms first started. A CT scan must be done to see whether the stroke is from a clot or from bleeding.
• If the stroke is caused by bleeding instead of clotting, clot-busting drugs (thrombolytics) can cause more bleeding.