Yngve Zotterman

The impulses produced by sensory nerve‐endings

IN Part I of the present series (1) one of us described an instrument consisting of a capillary electrometer with a 3-valve amplifier, capable of recording the action currents set up in sensory nerve fibres by appropriate stimulation of their end-organs. A preliminary analysis of the results was given, but it was pointed out that an essential step was missing. All the records were made from nerve trunks containing many afferent fibres and it was impossible to tell with certainty what was happening in each fibre, what was the frequency of the response, how it varied with the stimulus, etc. The present paper remedies this defect, for it is concerned with the impulses set up by a single end-organ and travelling in a single afferent nerve fibre. Only one type of end-organ has been investigated, but the results seem to be of such general application that it will be surprising if other types are found to behave very differently. Preparation employed. The recording instrument has already been described in detail and the only modification introduced has been the provision of a variable shunt to reduce the excursions of the electrometer, should this be necessary. The preparation employed was suggested to us by the papers ofKeith Lucas on the all-or-none response of muscle fibre. In these experiments Lucas used the m. cutaneus dorsi of the frog. He found that the nerve supplying this muscle had ten fibres only, of which one or two might be sensory. We have investigated this muscle, but so far we have been unable to detect any action currents in the nerve roots when the muscle is stretched, and we are inclined to think that all the fibres are motor. But in a footnote -Lucas mentions another muscle -the sterno-cutaneus-in which there is no doubt of the existence of sensory end-organs. The number of fibres in the nerve supplying the muscle varies from 12 to 25. There is certainly one muscle-spindle inthe muscle (it is figured in Cajals book, Textura del Sistema Nervioso, Madrid, 1899, p. 404), and as our results show there are usually three or

Touch, pain and tickling: an electro-physiological investigation on cutaneous sensory nerves.

IN 1933 Blair and Erlanger demonstrated that the recorded spike heights of axone potentials from a phalangeal nerve preparation of the frog varied as their rate of conduction. On the assumption that the intrinsic potential is independent of fibre size the recorded spike heights vary as the diameters squared. Their result offers the possibility of computing the relative rate of axone potentials recorded from sensory nerves in response to various stimuli applied to their receptors. Such a procedure was adopted in some recent investigations on the lingual nerve [Zotterman, 1936]. The present research was started in order to study the response of the thinnest afferent fibres to various stimuli applied to the skin. When records of axone potentials from the thinnest nerve fibres had been obtained attempts were made to measure their rate of conduction directly. This was possible for fibres conducting at rates down to 10 m./ sec. Slower potentials than these, however, could not be measured. Although direct measurements of the slowest rates have not yet been made, the present data concerning the larger fibres provide some fixed points for the correlation of results from different experiments.

The relation between neural and perceptual intensity: a comparative study on the neural and psychophysical response to taste stimuli

1. Recording the summated electrical response from the human chorda tympani in the middle ear provides data for a quantitative study of the relation between the neural activity and the strength of the stimulus applied to the tongue which can be compared with the relation between the subjective estimation and the stimulus strength.

The impulses produced by sensory nerve endings: Part 3. Impulses set up by Touch and Pressure

IN Part I of the present series one of us (1) described a method of recording nerve action currents by means of a capillary electrometer and a threestage amplifier, together with some preliminary observations on the impulses set up in various types of sensory nerve fibres by stimulation of their end organs. In Part II(2) we gave a more detailed analysis of the sensory impulses produced by stretching a muscle, and we were able to show that in a single nerve fibre the impulses usually recurred in a regular series with a frequency depending on the intensity of the stimulus, that the impulses (or rather their action currents) were all of the s8me intensity and that their frequency was low enough to leave the nerve fibre time for complete recovery between one impulse and the next. As these observations were made on the frog and were confined to one type of sensory ending, we were anxious to extend them to mammals and to some other form of sensation. The results given in Part I had shown that a cutaneous afferent nerve in the cat (the internal saphenous) usually exhibits a series of action currents and that these increase in number when the skin is pricked or pinched. There is, however, a considerable drawback to the use of such forms of stimulation, since their intensity is not readily measured, and to overcome this difficulty we decided to use moderate pressure as the stimulus in the present research. The end organs sensitive to pressure are not known with certainty, but they are generally supposed to be the touch corpuscles in the skin and the Pacinian and other types of corpuscle in the subcutaneous tissues. Since the latter occur singly or in small groups in the mesentery of the cat, we thought at first that the most suitable preparation would be a single Pacinian corpuscle from the mesentery with its nerve fibre isolated and connected to the electrometer. Unfortunately, we found that various technical difficulties stood in our way. In the living animal it is extremely difficult to detect the

THE NERVOUS MECHANISM OF TASTE

Electrophysiological studies of the impulse traffic in the taste nerves have in general confirmed the old conception that there are four classes of taste, namely, sweet, sour, bitter, and salty. The response of single taste fibers in amphibians as well as in mammals has revealed that the taste fibers seem, to a great extent, specific. A complication was added to this view, however, when Pfaffmann (1941) found in the cat that strong acid solutions not only stimulated specific “acid fibers,” but also “salt fibers.” The salty taste would thus be discriminated from acid taste only by the absence of impulses in the specific acid-taste fibers. A further complication in the classic psychophysical way of regarding the matter was the finding that the frog possessed taste fibers that respond to the application of pure water to the tongue (Zotterman, 1949, 1950). I originally believed that the fibers that responded specifically to water (Anderson and Zotterman, 1950) served a particular purpose in the regulation of the water intake in these animals, which live chiefly in fresh water. This finding, however, raised the old question, debated by psychologists for a half century a t least, of whether mammals, including man, are equipped with specific taste organs for water. At Stockholm University, David Katz had long maintained that this must be the case. In examinations he often put the question: “What is the taste of water?” The correct answer was: “wet.” In 1954 Liljestrand, confirming earlier investigations, found in experiments upon him5elf that the threshold value for NaCl solutions lay between 0.009 and 0.002 iV, that is, about 0.05 to 0.01 per cent NaC1. This was just between the concentrations a t which I had found that the specific water taste fibers began to respond. Liljestrand also found that Stockholm tap water (with a dry residue of 0.014 per cent) could be distinguished from distilled water (dry residue of 0.0004 per cent) with a certainty of 100 per cent. This also held after the tap water had been boiled for 5 minutes and then cooled (Liljestrand and Zotterman, 1954). In the old literature the flat taste of water was held to represent a special sapor insipidus or sapor aquosus (see Ohrwall, 1891). According to Henle, 1880, this would be characteristic of solutions containing less salt than the saliva; Henle maintained that the flat taste is to the sense of taste what black is to the sense of vision. An alternative interpretation was suggested, however, by the experiments on water taste in the frog that were quoted above. Furthermore, Skramlik (1926) reported that in humans salt solutions below 0.03 ibl taste sweet, and that saltiness appears only with concentrations above 0.03 R9. For that reason, in 1954, Liljestrand and I decided to study the effect of water upon the taste fibers of the chorda tympani in some mammals.

Wirkung von Alkohol, Aceton, Äther und Chloroform auf die Chemoceptoren des Glomus caroticum

ZusammenfassungIntracarotidale Einspritzung von Alkohol, Aceton, Äther oder Chloroform in Ringerlösung bewirkt eine Verstärkung der von den Chemoceptoren ausgelösten Aktionspotentiale des Sinusnerven. Da alle diese Substanzen in vitro einen hemmenden Einfluß auf die Cholinesterasen ausüben und Acetylcholin wahrscheinlich eine Rolle als Überträgerstoff im Glomus caroticum spielt, wurde geprüft, wie sich die erwähnte Wirkung durch verschiedene Pharmaka modifizieren läßt. Es stellte sich heraus, daß sowohl durch Atropin, D-Tubocurarin und Hexamethonium als auch durch Ammoniak die Potentiale vermindert oder ausgelöscht werden konnten. Diese Befunde sprechen für die Annahme, daß die betreffenden Narkotica durch Hemmung der Cholinesterasen eine Zunahme des chemischen Impulsverkehrs im Glomus hervorrufen.

The neural mechanism of taste.

Publisher Summary It is still not known what happens to the neural innervation of a single taste cell as it ages and moves toward the centre of the taste bud. This migration of cells raises a fundamental problem of neural organization because the pattern of chemical sensitivity varies from one cell to another. Different neurons have been found to react on different sapid stimuli. The electrical response to the application of various sapid solutions on the tongue has been studied in amphibians, birds and mammals, including the rhesus monkey as well as man. Positive response to the application of tap water was obtained from frogs, chicken and pigeons, cats, dogs, pigs, and rhesus monkeys, but not from rats and humans. Great species differences were also noticed in the response to different sapid stimuli. A study of the response of individual taste fibers in the rhesus monkey revealed that each fiber has a specific pattern of sensitivity to the various sapid substances. Certain gustatory fibres responded very specifically to one class of substances only, for example, to salt, acid, or quinine. Fibres responding to sucrose almost always responded to saccharine as well, but the sweet fibres of the dogs chorda tympani did not respond to saccharine. Extracts of Gymnema silvestris on the human tongue abolished both the sweet sensation and the nerve response to sugars and saccharine but not to quinine.