Chronic Pain (cont.)
The nervous systems
The central nervous system (CNS) refers to the brain and
spinal cord together. The peripheral nervous system refers to the cervical,
thoracic, lumbar, and sacral nerve trunks leading away from the spine to the
limbs. Messages related to function (such as movement) or dysfunction (such as
pain) travel from the brain to the spinal cord and from there to other regions
in the body and back to the brain again. The autonomic nervous system controls
involuntary functions in the body, like perspiration, blood pressure, heart
rate, or heart beat. It is divided into the sympathetic and parasympathetic
nervous systems. The sympathetic and parasympathetic nervous systems have links
to important organs and systems in the body; for example, the sympathetic
nervous system controls the heart, blood vessels, and respiratory system, while
the parasympathetic nervous system controls our ability to sleep, eat, and
digest food.
The peripheral nervous system also includes 12 pairs of
cranial nerves located on the underside of the brain. Most relay messages of a
sensory nature. They include the olfactory (I), optic (II), oculomotor (III), trochlear (IV),
trigeminal (V), abducens (VI), facial (VII), vestibulocochlear (VIII),
glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII) nerves.
Neuralgia, as in trigeminal neuralgia, is a term that refers to pain that arises
from abnormal activity of a nerve trunk or its branches. The type and severity
of pain associated with neuralgia vary widely.
Phantom pain: how does the brain feel?
Sometimes, when a limb is removed
during an amputation, an individual will continue to have an internal sense of
the lost limb. This phenomenon is known as phantom limb and accounts describing
it date back to the 1800s. Similarly, many amputees are frequently aware of
severe pain in the absent limb. Their pain is real and is often accompanied by
other health problems, such as depression.
What causes this phenomenon? Scientists believe that following amputation,
nerve cells "rewire" themselves and continue to receive messages,
resulting in a remapping of the brain's circuitry. The brain's ability to
restructure itself, to change and adapt following injury, is called plasticity.
Our understanding of phantom pain has improved tremendously in recent years.
Investigators previously believed that brain cells affected by amputation simply
died off. They attributed sensations of pain at the site of the amputation to
irritation of nerves located near the limb stump. Now, using imaging techniques
such as positron emission tomography (PET) and magnetic resonance imaging (MRI),
scientists can actually visualize increased activity in the brain's cortex when
an individual feels phantom pain. When study participants move the stump of an
amputated limb, neurons in the brain remain dynamic and excitable. Surprisingly,
the brain's cells can be stimulated by other body parts, often those located
closest to the missing limb.
Treatments for phantom pain may include analgesics, anticonvulsants, and
other types of drugs; nerve blocks; electrical stimulation; psychological
counseling, biofeedback, hypnosis, and acupuncture; and, in rare instances,
surgery.
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