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Introduction to fainting (syncope)
Fainting, "blacking out," or syncope is the temporary
loss of consciousness followed by the return to full wakefulness. This loss of
consciousness may be accompanied by loss of muscle tone that can result in falling or slumping over.
To better understand why fainting can occur; it is helpful to explain why
somebody is awake.
The brain has multiple parts, including two hemispheres, the cerebellum, and
the brain stem. The brain
requires blood flow to provide oxygen and glucose
(sugar) to its cells to sustain life. For the body to be awake, an area known as
the reticular activating system located in the brain stem needs to be turned on,
and at least one brain hemisphere needs to be functioning. For fainting or syncope to occur,
either the reticular activating system needs to lose its blood supply, or both
hemispheres of the brain need to be deprived of blood, oxygen, or glucose. If
blood sugar levels are normal blood flow must be briefly disrupted to
the whole brain or to the reticular activating system.
Fainting is not caused by head trauma, since loss of
consciousness after a head injury is considered a concussion. However, fainting can cause injury if
the person falls and hurts themselves, or if the faint occurs while
participating in an activity like driving a car.
Fainting is differentiated from
which patients may also lose consciousness.