nor at gwis2.circ.gwu.edu (Ronald Petrarca) wrote:
> I understand that a concussion is a severe blow to the head
>resulting in a temporary change in consciousness. What exactly happens
>when one suffers a concussion? What is the difference between a
>concussion and an ordinary knock on the head? Also, is there a threshold
>below which the brain is completely shielded from mechanical disturbance?
>In other words, how well do the skull and cerebrospinal fluid protect the
>brain?
There are to types of injuries to consider.
1) By physical chock. This will cause (depending on strength and direction)
synaptic connection to break up. Neurons are connected together by a maze of
dendrites and axons and that only gives them a certain distance in which they
can move relative to each other. The ideal thing would be if neurons had the
same weight as the cerebrospinal fluid but unfortunately they are a bit heavier.
So a great chock can cause movements so great that some synoptical connections
break up. This is not a "real" damage because everything is still operational
but the gap between dendrite terminal and axon has become to great for normal
communication to occur.
1a) Only a part of the connections are broken. Luck you! If connections it the
neighborhood will fire then the same thing the broken connections did represent
is relearned and the same connection will be reestablished. In practice this
will mean that you will regain lost memories by trying to think about them. The
more you think about them the more will come back.
1b) The distance (gap) is to great to bring the dendrite terminal physical back
to the neuron so you will not regain that memory but the neuron can still be
used to learn new stuff so it is not really so bad. (May sound sadistic but you
are losing memory all the time and there is not real danger in it). 1b always
occurs together with 1a. It just depends how much percentage goes to 1a and 1b
what the result will be.
2) The chock is that great that blood vessels rupture. Poor you! The blood
will flow out of the vessel and build up a region where there is only blood and
no neurons. As the region becomes greater there is a greater pressure and
deformation of the brain tissue causing more 1a and 1b to occur while the region
expands. The region will stop expanding when a certain pressure is reached.
This pressure in itself can also prohibit neurons from operating normally and
even cause them to die. Mostly the region where a blood vessel will rupture is
at the opposite side from where the blow (impact place and direction) did occur.
This is because due to the form of the skull (sphere) a shock wave in the fluid
will reach the highest pressure at the point where the fluid has not
way/path/place to go to. Just imagine that the width of the chock wave gets
smaller and smaller when the end of internal of a sphere is reached so that the
intensity per square centimeter becomes larger and larger. If the chock is
really great then there will also be change for blood vessel rupture at the side
of the impact. Then it gets really serious (permanent damage).
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