·
Two types of impact occur
on skull and the sound wave elicited by the impact. The first at the site where
the force is applied, the second where the advancing segments of the
accelerated brain are brought suddenly to rest by the forces that resist its
forward motion.
·
Counter coup lesions of
the brain were once thought to be caused by the brain moving within the skull
in a straight line with the force of the blow striking against its opposite
side. But, experiments on mechanics of head injuries have demonstrated these lesions
are chiefly due to local distortions of the skull and the sudden rotation of
the head as result of a blow, which arouse shear strains or slide produced by
the pulling apart of the constituent particles of the brain.
·
Shear strains occur and pull
apart the constituent particles of the brain. These are produced in all parts
of the brain, but to a large extent at the base of the frontal lobe and the tip
of the temporal lobe, as the skull gets a good grip on the brain in this region
due to the projecting ridge of the sphenoid bone. Hence, severe and extensive
injuries occur in this region with a blow on the occiput.
·
On the other hand,
countercoup injuries which are caused by rotation will not occur if the head is
so well fixed that it cannot rotate at all when it receives a blow. Cerebral
contusions and tears have been reported in autopsy as a result of trauma.
(Ref: Modi’s Medical Jurisprudence,
25th Edition)
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