A superficial substrate on the ventral surface of the medulla oblongata influencing respiration
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As has been demonstrated earlier by Loeschckeet al. (1970) stimulation of two separate areas on the ventral medullary surface caused increase in tidal volume, respiratory frequency and arterial pressure, the latter not without exception.
In the more caudal area medial of the hypoglossal roots the response to electrical stimulation was strongest at the surface or not more than 0.2 mm below the surface. The response decreased with increasing distance from the surface until at a depth of 0.6–0.8 mm no or only a minimal response was observed. In 2 to 3 mm depth either a second rise in the rhythmic ventilatory response or a maintained forced inspiration was evoked, while stimulation at still deeper location was followed by a decrease of the tidal volume or by respiratory arrest in expiratory position.
In the more rostral area, the response pattern in the more superficial layer was similar but less marked.
It is suggested that one type of substrates responding to stimulation is confined to two thin layers at the ventral surface of the medulla oblongata and that these structures are involved in the drive of ventilation and of vasomotor tone. Their location is similar to the location of chemosentitivity as described by Schläfkeet al. (1970) and it seems possible that they play a role either in the origin or the transmission of chemosensitive impulses.
Other substrates showing respiratory responses of the inspiratory or expiratory type are located deeper in the medulla oblongata and well demarcated from the described superficial substrates. They include the respiratory centres.
Key wordsChemosensitive Areas Control of Respiration Medulla oblongata Cat
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