405
CHAPTER ELEVEN
Nervous System II
Unlike a “conventional” TBI in which shrap-
nel penetrates the brain and surgery is obviously
warranted, blast-related brain injury may not ini-
tially produce symptoms. A soldier who the day
before could easily have run F
ve miles and chat
with friends may suddenly be unable to move or
speak or may become blind or deaf. Yet others
may have no initial e±
ects, while the soft tissue
of the brain has sustained severe damage. Blast-
related brain injury is also on the rise in combat
because of improved ability to treat other types of
injuries, enabling soldiers to survive who in wars
past would have perished. Effects are lasting—
studies on veterans of the Vietnam War indicate
cognitive decline years after the injury.
The exact mechanism of severe blast-related
brain injury is not well understood, nor do mili-
tary physicians have a precise deF
nition for it or
means of assessment. The presentation overlaps
A
traumatic brain injury (TBI) is deF
ned by
what it is not: it is not a birth defect or
degenerative, but instead happens from
mechanical force. In the United States, more than
5 million people have such injuries.
TBI may result from a fall, accident, attack,
or sports-related injury. It is on the rise in combat
situations, where the cause and pattern of damage
is so distinct that it has been designated “blast-
related brain injury.” The damage results from a
change in atmospheric pressure, violent release
of energy (sound, heat, pressure, or electromag-
netic waves), and sometimes exposure to a neuro-
toxin released from the blast. Rocket-propelled
grenades, improvised incendiary devices, and
landmines create the situations that cause the
injury. The brain is initially jolted forward at a force
exceeding 1,600 feet per second, and then is hit by
a second wave as air in the brain rushes forward.
that of mild TBI, which also occurs in combat
situations. Mild TBI, also known as a concussion,
produces loss of consciousness or altered men-
tal status. Its e±
ects are more psychological than
neurological; blast-related brain injury is the
opposite.
Mild TBI does not appear to cause lasting
damage. Symptoms include disturbed sleep, ring-
ing in the ears, memory lapse, balance problems,
irritability, and sensitivity to light and sounds.
These physical symptoms are more severe if the
person also su±
ers from depression or post-trau-
matic stress disorder (PTSD). Mild TBI may
cause
PTSD: the injury generates a shearing force as the
brain hits the skull that impairs the prefrontal cor-
tex’s control of the amygdala. With an overactive
amygdala, the person cannot let go of the psy-
chological trauma—the essence of PTSD.
11.4
CLINICAL APPLICATION
Traumatic Brain Injury
rior to the thalamic nuclei and forms the lower walls and fl oor
of the third ventricle (see reference plates 9 and 13).
Other parts of the diencephalon include (1) the
optic
tracts
and the
optic chiasma,
formed by the optic nerve
F bers crossing over; (2) the
infundibulum,
a conical process
surrounds the third ventricle and is largely composed of gray
matter. In the diencephalon, a dense mass called the
thala-
mus
(thal
ah-mus) bulges into the third ventricle from each
side. Another region of the diencephalon that includes many
nuclei is the
hypothalamus
(hi
po-thal
ah-mus). It lies infe-
Longitudinal
fissure
Thalamus
Hypothalamus
Brainstem
Right cerebral
hemisphere
Basal
nuclei
Caudate
nucleus
Putamen
Globus
pallidus
Cerebellum
Spinal cord
FIGURE 11.19
A coronal section of the left cerebral hemisphere reveals some of the basal nuclei.
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