The function of the recurrent laryngeal nerve : from experimental studies in the Biological Laboratory of the Johns Hopkins University / by Frank Donaldson, jr.

  • Donaldson, Frank.
Date:
1886
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Licence: Public Domain Mark

Credit: The function of the recurrent laryngeal nerve : from experimental studies in the Biological Laboratory of the Johns Hopkins University / by Frank Donaldson, jr. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    periments II. and VI.) where the animal was made thoroughly apnceic, and where for some seconds there was neither glottic nor respiratory movement, adduction resulted from stimulation. In two cases after the animal was chad, hut before death of the nerves or muscles of the larynx, stimulation produced closure of the glottis. Under all these conditions of unconsciousness and narcotism, then, was adduction pro- duced. This result followed, in these experiments, stimulation of the cut and uncut nerve; and followed chemical and mechanical, as well as electrical, stimulation. Again in Experiment II., where the separate branches of the recurrent to the individual muscles were dissected out, and stimulated equally, neither showed a tendency to more rapid de- generation than the other. My conclusions, then, from this first series of experiments are: 1st. That the constrictor muscles of the larynx do not cease to act during profound narcosis or during suspension of consciousness from any cause; or, in other words, that their action is not dependent upon volition, in the sense that they lose their power with the loss of volition. 2d. That we do not always obtain abduction of the arytenoids when consciousness is suspended. Under what conditions, then, do we get abduction of the cords upon stimulation of the recurrent nerve? Such conditions must exist, for abduction of the cord has been obtained by Hooper, who con- siders that suspension of volition is the one condition under which stimulation of the recurrent nerve brings about abduction. What the conditions are under which these abductors act was, I think, partly dis- covered in the next series of experiments. In them it was found: 1st. That the abduction obtained by Hooper was in no way reflex. 2d. That abduction is in no way dependent upon the unconsciousness of the animal. 3. That it is with weak stimuli only that abduction of the cords takes place, which movement of abduction gradually passes into one of adduc- tion as the strength of the stimulus is increased. 4th. That this result invariably followed, whether the animal was slightly, deeply, or thor- oughly narcotized; whether the animal was eupnceic or apnoeic, when the dog had his medulla destroyed, and after local death had taken place. 5th. That the rate of stimulation did not affect the general result. 6th. That after strong and constant stimulation the abductor muscles became worn out and ceased to answer to stimuli. 7th. That in apnoea the cords came nearer the middle line, the abductors receiving no stimulus in this condition from the respiratory centre. Here then, I think, we have a suggestion at least, as to the innervation of the muscles of the larynx. And again we state that volition, consciousness, or uncon- sciousness in no way affect the action of the laryngeal nerves or muscles. In our first series of experiments adduction resulted under all conditions of unconsciousness; in our second series abduction, in all conditions of consciousness or deep narcotism: we may, therefore, cast out volition as