Thus in ordinary breathing the
movements are increased on the paralysed side, especially in the upper part
of the chest, while in voluntary breathing they are increased on the sound
side. Hughlings Jackson suggested the following theory to explain these
facts: "_Ordinary breathing_ is an automatic act governed by the
respiratory centre in the medulla. The respiratory centre is double, each
side being controlled or inhibited by higher centres on the opposite side
of the brain. Voluntary costal breathing, such as is employed in singing,
is of cerebral origin, and controlled by centres on the opposite side of
the brain, the impulses being sent down to the respective centres for the
associated movements of the muscles of articulation, phonation, and
breathing, in the same way as they are sent to the centres for the
movements of the arm or leg. With voluntary breathing the respiratory
centre in the medulla has nothing to do. It is in fact out of gear or
inhibited for the time being, so that the impulses from the brain pass by
or evade it. There are thus two sets of respiratory nerve fibres passing
from the brain--the one inhibiting or controlling to the opposite half of
the respiratory centre in the medulla; the other direct, evading the
respiratory centre and running the same course to the spinal centres for
the respiratory movements as the ordinary motor fibres do to the centres
for other movements.
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