Figure 6 (below) shows tidal volume tracings (the peaks on the right) obtained f

Question

Figure 6 (below) shows tidal volume tracings (the peaks on the right) obtained from animals with various brain areas severed. The tracings illustrate the role each of the centres of the brain has in controlling breathing WARNING: This is a difficult exercise and you will have to think about what happens witlh each cut (in answering the questions below with reference to Fig 5 and the associated text). BOTH VAGUS BOTH VAGUS NERVES INTACTNERVES CUT FIRST CUT SC SUPERICR COLLICUL SECOND CUT INFER LICULI CENTRE 2 APNBUSTC CENTRE THIRD CUT et VRG FOURTH CUT 4. Figure 6: Tidal volume tracings with sectioning of the nervous system

Explanation / Answer

1) Severing the pneumotaxic center decreases the breathing rate and increases the depth (i.e., more inhalation)

2) The reason for this is that the pneumotaxic center's function is usually inhibitory on apneustic center which controls inhalation rate. So, function of pneumotaxic center in this case is to reduce (i.e., inhibit) the inhalation and allowing exhalation. This means increased respiratory rate.

Hence, making a cut just above apneustic center removes this inhibition leading to deeper inhalation and reduced breathing rate. This can be noticed in the diagram in parallel to 2nd cut under both vagus nerves intact compared to 1st cut which had higher respiratory rate compared to after 2nd cut.

3) Vagal nerve is another inhibitor of the apneustic center (which controls inhalation). So, cutting the vagal nerves also removes the inhibition completely on apneustic center which will lead to breathing getting stuck in inhalation phase (as apneustic center controls inhalation). This is usually characterized by long gasping inhalation and short exhalation period. This effect is clearly noticed in the diagram parallel to the 2nd cut indicating when both vagus nerves were severed.

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