The Journal of physiology
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The Journal of physiology · May 1979
Effects of nerve impulses on threshold of frog sciatic nerve fibres.
1. The firing thresholds of single myelinated fibres of frog sciatic nerves were monitored as a function of impulse activity in the fibre. The threshold was given by the number of coulombs in current pulses that excited a particular fibre half the time when delivered to the whole nerve. ⋯ The duration of the superexcitable phase interpreted as a relative change in excitability was roughly the same regardless of the level of depression. 8. The magnitude of the oscillation in threshold was give to ten times larger than the grey region (the range of stimuli for which response is probabilistic). It is concluded that at regions of low conduction safety such as axonal branches, where weak forces can influence whether an impulse will pass, such pronounced and long-lasting after-effects of firing can be expected to modulate conduction of nerve impulses.
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The Journal of physiology · May 1979
The initiation and maintenance of bradycardia in a diving mammal, the muskrat, Ondatra zibethica.
1. The cardiac and respiratory responses shown by muskrats in both unrestrained and restrained dives have been compared with responses elicited by stimulation of a number of cardio-depressant receptor inputs, in an attempt to determine which are most important in initiating and maintaining diving bradycardia. 2. In unrestrained voluntary dives heart rate fell from 310 +/- 3 to 54 +/- 3 beats min-1 in 1 to 2 sec, which was significantly below that seen in dives by restrained unanaesthetized or anaesthetized animals. 3. ⋯ Artificial ventilation of paralysed muskrats with 5% CO2 in N2 caused bradycardia when Pa, O2 reached 8.4 +/- 0.8 kPa and heart rate declined to 76 +/- 7 beats min-1 at 4 kPa. Bilateral section of the sinus nerve delayed bradycardia until Pa, O2 reached 4.5 +/- 0.5 kPa. 8. These results suggest that the cardiac response to submergence could be the expression of input from three groups of receptors, nasal, lung and carotid chemoreceptors, although it is not clear how they interact with one another to generate the cardiac responses displayed by unrestrained animals during submergence.
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The Journal of physiology · Oct 1978
Spatial summation in the receptive fields of simple cells in the cat's striate cortex.
1. We have examined the responses of simple cells in the cat's atriate cortex to visual patterns that were designed to reveal the extent to which these cells may be considered to sum light-evoked influences linearly across their receptive fields. We used one-dimensional luminance-modulated bars and grating as stimuli; their orientation was always the same as the preferred orientation of the neurone under study. ⋯ We compared simple receptive fields with their sensitivity to sinusoidal gratings of different spatial frequencies. Qualitatively, the most sensitive subregions of simple cells' receptive fields are roughly the same width as the individual bars of the gratings to which they are most sensitive. Quantitatively, their receptive field profiles measured with thin stationary lines, agree well with predicted profiles derived by Fourier synthesis of their spatial frequency tuning curves.
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The Journal of physiology · Mar 1978
The sacral parasympathetic reflex pathway regulating colonic motility and defaecation in the cat.
1. The sacral parasympathetic outflow to the large intestine of the cat was studied by monitoring simultaneously intestinal motility and the efferent firing in postganglionic fibres on the serosal surface of the mid-distal colon. 2. Increases in efferent firing were noted during the occurrence of spontaneous propulsive activity (tonic pressure waves) or segmental contractions (slow rhythmic pressure waves). ⋯ Electrophysiological measurements indicated that the sacral reflexes to the large intestine were mediated by non-myelinated afferent and preganglionic efferent fibres. The central delay for the reflex was estimated to be 45-60 msec. 7. It is concluded that the sacral parasympathetic reflexes to the large intestine are mediated via a spinal pathway and have an essential role in the initiation of propulsive activity during defaecation.