Injuries of nerves and their consequences - Reflex Sympathetic ...

188 INJURIES OF NERVES.
the muscle in a definite amount in order to evoke motion,
and there is reason to think that this amount must be
comparatively large to get from the muscle a useful
motor response, or, indeed, any at all. We can thus
understand that if the motor and sensory lilaments be
equally enfeebled as to transmissive capacity, the brain
may continue to receive sensory messages, while the
muscles still fail to aret nerve force enoua^h to call them
into functional activitj'. Sometliing illustrative of this
exists normally in the ulnar nerve, which may be easily
elbow so as to cause sensation, but which
irritated at the
needs much more severe stimulation in order to produce
movement in the muscles which it controls.
There may be in other cases an anatomical cause for
of one or other set of nerve fibres when
the total escape
the injury falls on a nerve trunk where its strands are
beginning to separate.
In some of the lower animals the
separation of the various nerve filaments into groups,
some merely sensori-motor, and others either motor or
sensory alone, is well marked in the parent trunk far above
the point at which they leave it to seek their points of distribution.
Now, although the eye does not reveal in
man any such distinct arrangement of this nature, the
phenomena of a large number of nerve wounds seem to
make it
probable that very soon after leaving the spine
the nerves become grouped, as it were, with intention
towards their final distribution. In no other way can
we explain some of the phenomena which arise out of
such cases ;
but even this resource does not suffice to
make clear such a case as the following, nor yet others
which I have seen, where, without obvious cause, a compound
nerve being hurt, motion was lost and sensation
merely enfeebled or preserved entire.*
* In cases of contusion or compression of nerves, the first evidence of
injury is usually some eflect upon sensory filaments, and the mechanical