Showing papers in "The Journal of Physiology in 1979"
TL;DR: The spatial distribution of densities supports the idea that the RA and SA I units account for spatial acuity in psychophysical tests, which is known to increase in distal direction along the hand.
Abstract: 1. Single unit impulses were recorded with percutaneously inserted tungsten needle electrodes from the median nerve in conscious human subjects. 2. A sample of 334 low threshold mechanoreceptive units innervating the glabrous skin area of the hand were studied. In accordance with earlier investigations, the units were separated into four groups on the basis of their adaptation and receptive field properties: RA, PC, SA I and SA II units. 3. The locations of the receptive fields of individual units were determined and the relative unit densities within various skin regions were calculated. The over-all density was found to increase in the proximo-distal direction. There was a slight increase from the palm to the main part of the finger and an abrupt increase from the main part of the finger to the finger tip. The relative densities in these three regions were 1, 1.6, 4.2. 4. The differences in over-all density were essentially accounted for by the two types of units characterized by small and well defined receptive fields, the RA and SA I units, whereas the PC and SA II units were almost evenly distributed over the whole glabrous skin area. 5. The spatial distribution of densities supports the idea that the RA and SA I units account for spatial acuity in psychophysical tests. This capacity is known to increase in distal direction along the hand. 6. On the basis of histological data regarding the number of myelinated fibres in the median nerve, a model of the absolute unit density was proposed. It was estimated that the density of low threshold mechanoreceptive units at the finger tip is as high as 241 u./cm2, whereas in the palm it is only 58 u./cm2.
1,148 citations
TL;DR: Individual quantal responses exhibited a smooth shape very similar to that of the average quantal response, which suggests that a single photoisomerization releases many particles of transmitter and that radial diffusion of internal transmitter is not a major source of delay in the light response.
Abstract: 1 A suction electrode was used to record the membrane current of single rod outer segments in pieces of toad retina During dim illumination the membrane current showed pronounced fluctuations 2 Amplitude histograms of responses to dim flashes of fixed intensity exhibited two discrete peaks, one at 0 pA and one near 1 pA, suggesting that the response was quantized By setting a criterion amplitude level, flash responses could be classed as 'failures' (no response) or as 'successes' (at least one quantal event) 3 The variation of fraction of successes with flash intensity was consistent with the hypothesis that each quantal electrical event resulted from a single photoisomerization 4 The quantal event had a mean amplitude of about 1 pA (5% of the standing dark current) and a standard deviation of 02 pA Dispersion in the event amplitude prevented identification of histogram peaks corresponding to two or more photoisomerizations 5 Individual quantal responses exhibited a smooth shape very similar to that of the average quantal response This suggests that a single photoisomerization releases many particles of transmitter and that radial diffusion of internal transmitter is not a major source of delay in the light response 6 The 'quantum efficiency' with which an absorbed photon generated an electrical event was measured as 05 +/- 01 (SE of mean, n = 4) This is slightly lower than the quantum efficiency of photoisomerization obtained previously for rhodopsin in solution 7 At wavelengths between 420 and 700 nm the quantal event was invariant in size, although the cell's sensitivity varied over a range of 10(5) 8 The power spectrum of the fluctuations in dim steady light was predicted by assuming that a random series of quantal events occurred independently 9 In brighter light the fluctuations were faster, and the response to an incremental flash was reduced in size and duration The power spectrum could be predicted by assuming random superposition of events with the shape of the incremental flash response
836 citations
TL;DR: The velocity of shortening at zero load was studied during fused tetanic contractions and single twitches in isolated skeletal muscle fibres of Rana temporaria and the technique used for determination of the speed of unloaded shortening consisted of a series of quick releases of different amplitudes applied at a given instant during activity.
Abstract: 1. The velocity of shortening at zero load was studied during fused tetanic contractions and single twitches in isolated skeletal muscle fibres of Rana temporaria. 2. The technique used for determination of the speed of unloaded shortening consisted of a series of quick releases of different amplitudes applied at a given instant during activity. The time, delta t, needed for the fibre to take up the slack was plotted against the amplitude of release, delta L. The slope of the straight line relating delta t-delta L provided a measure of the velocity of shortening at zero load, V0. 3. V0 was compared with force-velocity data obtained at finite loads (load-clamp recordings). The predicted velocity of shortening at zero load, derived by hyperbolic extrapolation from velocities at low and intermediate loads, was not significantly different from V0. 4. The temperature dependence of isometric force and of shortening velocity was investigated between 2 and 12 degrees C in the same fibres. Q10 was 2.67 +/- 0.07 (S.E. of mean, n = 6) for V0 and 1.24 +/- 0.01 for tetanic force. 5. The velocity of unloaded shortening was determined at different sarcomere lengths in the range 1.4--3.1 microns. V0 was constant between 1.65 microns and approximately 2.7 microns. It decreased below 1.65 microns and increased above 2.7 microns. 6. The decrease in velocity at short sarcomere lengths probably reflects an increase of the passive resistance to shortening. The increase in velocity at long sarcomere lengths can be accounted for by the passive compressive force that is produced by the parallel elastic elements of the prestretched fibre. 7. V0 was determined at the peak of the twitch and during the plateau of the fused tetanus in the same fibre. Whereas the peak twitch force varied between 38 and 85% of the tetanic tension in the different fibres (mean: 71 +/- 5%, n = 8), V0 during the twitch was 99 +/- 2% of the value recorded during the tetanus. Depression of the isometric twitch amplitude to 10% of the control value by dantrolene did not cause any significant reduction of V0.
767 citations
TL;DR: A method was developed to allow the ionic currents through the modal membrane to be calibrated exactly under voltage‐clamp conditions by measuring the resistance of the internode through which the current was injected.
Abstract: 1. Voltage-clamp studies were carried out on single rabbit myelinated nerve fibres at 14 degrees C with the method of Dodge & Frankenhaeuser (1958). 2. A method was developed to allow the ionic currents through the modal membrane to be calibrated exactly under voltage-clamp conditions by measuring the resistance of the internode through which the current was injected. 3. The ionic currents in a rabbit node of Ranvier can be resolved into two components, a sodium current and a leak current. Potassium current is almost entirely absent. 4. The sodium currents in rabbit nodes were fitted by the Hodgkin-Huxley model using m2h kinetics. The kinetics of sodium currents in a rabbit node differ from that in a frog node under similar experimental conditions in two respects: (a) inactivation is faster, tau h for rabbit being 2-3 times smaller around -50 mV; (b) the P(Na) (E) curve for mammal is shifted 10-15 mV in the hyperpolarizing direction. 5. From the kinetics of sodium current, the non-propagating rabbit action potential was reconstructed at 14 degrees C. The transient inward sodium current is responsible for the fast initial depolarization phase of the action potential, while the repolarizing phase is accounted for by leak alone. The computed shape of the action potential was in good agreement with the experimentally obtained action potential. 6. At 14 degrees C, frog and rabbit nodes with similar diameters have similar measured gNa values.
534 citations
TL;DR: Out Outer segments of individual rods in the retina of the toad were drawn into a glass pipette to record the membrane current, indicating that adapting light modifies the kinetics and gain of the transduction mechanism within the outer segment.
Abstract: 1. Outer segments of individual rods in the retina of the toad, Bufo marinus, were drawn into a glass pipette to record the membrane current. 2. Light flashes evoked transient outward currents. The peak response amplitude was related to flash intensity by a Michaelis equation with half-saturating intensity about 1 photon mum-2. 3. The saturating response amplitude ranged up to 27 pA and corresponded closely to complete suppression of the steady inward current present in darkness. 4. For a given cell the saturating response amplitude varied linearly with the length of outer segment within the pipette. This is consistent with a uniform density of light-sensitive channels and negligible gradient of membrane potential along the outer segment. 5. Responses to bright flashes never showed the relaxation from an initial peak seen previously in intracellular voltage recordings, suggesting that the conductance change responsible for the relaxation does not occur in the outer segment. 6. Responses to local illumination of only the recorded outer segment were very similar to those obtained with diffuse light at the same intensity, indicating that peripheral rods made little contribution to the responses. 7. The spectral sensitivity of 'red' rods was consistent with a retinal1-based pigment with lambda max = 498 +/- 2 nm. 8. The kinetics of the response were consistent with four stages of delay affecting action of the internal transmitter. Responses were faster at the basal end of the outer segment than at the distal tip. 9. Background light reduced the sensitivity to a superposed dim test flash and shortened the time course of the response, indicating that adapting light modifies the kinetics and gain of the transduction mechanism within the outer segment. 10. Responses to dim lights exhibited pronounced fluctuations which are attributed in the succeeding paper (Baylor, Lamb & Yau, 1979) to the quantal nature of light.
532 citations
TL;DR: Stimulation was effective in adrenalectomized rats, in dexamethasone‐primed animals, and in rats pre‐treated with exogenous progesterone, and thus, adrenal prodesterone release is not required for the v.m.n.n.'s facilitation of lordosis.
Abstract: 1. Effects of electrical stimulation of hypothalamic ventromedial nucleus (v.m.n.) on the lordosis reflex of female rats were examined in ovariectomized and oestrogen-primed animals with chronically implanted electrodes. 2. Lordosis triggered either by manual cutaneous stimulation or by male mounting, was facilitated by electrical stimulation of the v.m.n. 3 A gradual increase in lordosis performance followed a relatively long period of stimulation; never less than 15 min and usually about 1 hr of stimulation was necessary for maximum facilitation. Following the termination of stimulation, the performance returned gradually to the control level during a 5--8 hr period. 4. The optimal frequency of stimulation was between 10 and 30 Hz. Threshold for effective facilitation was, on the average, 12.5 microA. 5. Stimulation tended to induce larger facilitation when applied to the lateral side of v.m.n. 6. Pre-treatment with oestrogen was necessary to obtain facilitation by v.m.n. stimulation. The threshold dosage of oestrogen was 2.5 microgram per animal. 7. Stimulation was effective in adrenalectomized rats, in dexamethasone-primed animals, and in rats pre-treated with exogenous progesterone. Thus, adrenal prodesterone release is not required for the v.m.n. facilitation of lordosis. 8. Medial preoptic stimulation with the same parameters suppressed the lordosis reflex. 9. The v.m.n. participates in the control of lordosis by a facilitatory output. The delay before facilitation implies that the v.m.n. is not in the direct reflex-arc for the execution of lordosis. Rather, a summation or interaction process with an unusually long time course is involved.
389 citations
TL;DR: The acetylcholine‐sensitive ionic channels at the neuromuscular junction were studied in voltage‐clamped single muscle fibres from a monolayer preparation of the cutaneous pectoris muscle from Rana pipiens to argue that ion interactions must occur at e.p.c. channels because ion flux independence is the only asumption in the derivation of the Takeuchi approach.
Abstract: 1. The acetylcholine-sensitive ionic channels at the neuromuscular junction were studied in voltage-clamped single muscle fibres from a monolayer preparation of the cutaneous pectoris muscle from Rana pipiens. The experimental observations were of three types: (a) reversal potential as a function of external Na and Ca concentrations, (b) the single channel conductance (gamma) from noise analysis as a function of these same concentrations, and (c) gamma as a function of membrane potential. 2. The reversal potential in normal Na Ringer was -3.8 +/- 0.5 mV (+/- S.E. of mean, n = 22) and decreased approximately linearly as the logarithm of the outside Na activity as this activity decreased to 10% of normal. 3. The single channel conductance in normal Na Ringer was 27.5 +/- 0.7 pS (n = 28) and reached a limiting value close to 10 pS as Na was replaced with sucrose. 4. Increasing [Ca]o from 2 to 10 mM made the reversal potential more positive and decreased the single channel conductance. Mg caused similar effects. 5. Various theories that have been used to describe the mechanism of ion permeation through e.p.c. channels were tested. Constant field theory (eqns. (3), (4) and (5)), a modified Takeuchi approach (eqn. (6)), and a single barrier theory (eqns. (8), (9) and (10)) could not account for all of the experimental observations. 6. In particular, constant field theory, with no surface charge density, could account for the following: (a) the reversal potential measurements for solutions containing 2 mM-Ca (with PK/PNa = 1.2 and PCa/PNa = 1.02), (b) the single channel conductance values for solutions containing 2 mM-Ca and Na concentrations down to 20% of normal, (c) that gamma has little voltage dependence. 7. However, constant field theory, with no assumed surface charge density, could not account for the following: (a) the reversal potential observed for Ringer containing 80 mM-Ca, (b) the gamma values observed for very low Na concentrations, (c) the observation that increasing Ca from 2 to 10 mM in a solution containing 75% normal Na results in a decrease in gamma. 8. From the failure of the Takeuchi approach (eqn. (6)), it is argued that ion interactions must occur at e.p.c. channels because ion flux independence is the only asumption in the derivation of eqn. (6) without experimental verification. 9. The ion interactions at e.p.c. channels probably include both surface charge effects and competition for a binding site.
366 citations
TL;DR: The data suggest that type IIAB may represent a transitional state between type IIA and IIB, and that significant changes in subtypes take place during the endurance training in the type II group.
Abstract: Seven young females were subjected to 24 weeks of intensive endurance training. Adaptive changes in myofibrillary ATP-ase activity, capillary supply and mitochondrial content were investigated with light- and electron microscopy in needle biopsies from the quadriceps femoris. 1. The average value for the maximal oxygen uptake increased from 45.7 to 57.2 (ml . kg-1 min-1) (25.2%, P less than 0.005). 2. The average number of capillaries per muscle fibre increased from 1.39 to 1.79 (28.8%, P less than 0.005). Since no significant change in fibre area was found, this suggests that a considerable number of new capillaries have been formed during the training period. 3. An increased capillary supply of all fibre types was found, being greatest for type I and smallest for type IIB. 4. The relative amount of type I fibres before and after the training period was 57.9 and 56.5% respectively (n.s.), for type IIA fibres 26.4 and 31.5% (P less than 0.005), for type IIB fibres 9.2 and 3.4% (P less than 0.005) and for type IIC fibres 0.4 and 2.2% (P less than 0.005). Thus, in the type II group, significant changes in subtypes take place during the endurance training. The data suggest that type IIAB may represent a transitional state between type IIA and IIB. 5. Correlation of capillary supply, myofibrillar ATP-ase activity and mitochondrial content (determined semiquantitatively of individual muscle fibres indicators that the capillary supply to a given fibre is more closely related to its mitochondrial content than to the fibre type as determined on the basis of myofibrillar ATP-ase activity.
360 citations
TL;DR: Afferent activity of 111 single units from the glabrous skin area was recorded percutaneously in the median nerve of human subjects, using tungsten electrodes, with possible implications for kinaesthesia and motor control.
Abstract: 1. Afferent activity of 111 single units from the glabrous skin area was recorded percutaneously in the median nerve of human subjects, using tungsten electrodes. 2. The majority of the units (103) were classified as low-threshold mechano-sensitive units belonging to one of the four categories previously described: rapidly adapting with small receptive fields (RA), rapidly adapting with large receptive fields (PC, presumed Pacinian corpuscle units), slowly adapting with small fields (SA I), and slowly adapting with large fields (SA II). The size of the responses (in number of impulses) to indentation and stretching of the skin was compared with that of the responses elicited during voluntary isotonic finger movements, which avoided trivial excitation of the units by direct touch. 3. All four types of units, and 77% of the single units, were activated by isotonic movements. The decreasing order of responsiveness was PC, SA II, SA I, RA. 4. Almost all responsive units were excited during the dynamic phase of ramp and smooth oscillatory movements. Static responses, on the other hand, occurred only with 50% of the slowly adapting units, corresponding to a third of the total sample (SA II, 81%; SA I, 17%. 5. For all four types of units the dynamic responses to movements were of similar size as the responses to localized skin indentation with a von Frey hair at five times threshold. 6. The results are discussed with regard to the possible implications for kinaesthesia and motor control.
359 citations
TL;DR: Isolated rat neural lobes were incubated in vitro and electrically stimulated to release vasopressin and there was a reasonably good correlation between results obtained with this assay and those obtained by bioassay with the rat blood pressure method.
Abstract: 1. Isolated rat neural lobes were incubated in vitro and electrically stimulated to release vasopressin. The released vasopressin was assayed using a radioimmunoassay and there was a reasonably good correlation (r = 0.81) between results obtained with this assay and those obtained by bioassay with the rat blood pressure method.
2. Regular stimulation at frequencies of 5, 10 and 20 Hz released progressively more vasopressin and the release could be blocked by addition of tetrodotoxin to the incubation medium.
3. Stimulation with pulse patterns derived from tape recordings of phasically firing units in the supraoptic nucleus of dehydrated rats released more vasopressin than the same number of pulses regularly spaced in time. In the range 2-8 pulses/sec vasopressin release was related to the pulse frequency within the bursts (r = 0.90) and the number of short (< 100 msec) interpulse intervals (r = 0.92). Vasopressin released per pulse increased over the frequency range 3-6 pulses/sec, but above 6 pulses/sec vasopressin release per pulse tended to diminish.
4. We conclude that phasic firing of vasopressin neurosecretory cells may enhance vasopressin release in vivo and that an important factor in determining release is the number of short interspike intervals.
346 citations
TL;DR: The effect of electrolytic lesions of the ventromedial nucleus of the hypothalamus on the lordosis reflex has been investigated on ovariectomized female rats and lesion size in the lateral, but not medial portion was significantly correlated with lordosis deficit.
Abstract: 1. The effect of electrolytic lesions of the ventromedial nucleus of the hypothalamus (v.m.n.) on the lordosis reflex has been investigated on ovariectomized female rats. Lesions were made through chronically implanted platinum-iridium electrodes. 2. V.m.n. lesions did not disrupt lordosis immediately, but induced a gradual decline in the reflex. Lordosis performance reached it minimum no less than 12 hr after the lesion, and typically after 36--60 hr. 3. The magnitude of the lordosis deficit was related to the amount of v.m.n. damage. Destruction of other hypothalamic regions was without appreciable relation to the deficit. Within v.m.n., lesion size in the lateral, but not medial portion was significantly correlated with lordosis deficit. 4. Because of the slow time courses of v.m.n. lesions and stimulation (Pfaff & Sakuma, 1978) effects, it is postulated that the v.m.n. is not part of the direct reflex-arc for lordosis. Rather, neurones in v.m.n. are likely to exert a tonic hormone-dependent bias on brain stem reflex paths for this behaviour.
TL;DR: It is suggested that for complex cells the inhibitory input enhances the orientation tuning of an excitatory input that is already broadly orientation tuned, and this type of lateral interaction between columns may serve to enhance the contrast in the orientation domain for the cortical representation of a specific stimulus orientation.
Abstract: 1 These experiments have investigated the contribution made by GABA-mediated inhibitory processes to the orientation tuning of complex cells in the cat's striate cortex The GABA antagonist bicuculline has been ionophoretically applied to individual complex cells and the modifications produced in their orientation tuning documented 2 In terms of the type of change produced in orientation tuning by the application of bicuculline, it seems that there are two categories of complex cells 3 In one of these categories the orientation selectivity was eliminated during bicuculline application The excitatory input to these cells would therefore appear to be non-orientation specific Their orientation selectivity is presumably generated by a GABA-mediated inhibitory input 4 In the other category of complex cells, although the orientation selectivity was decreased during bicuculline application, the cells retained a preference for a range of orientations that was generally centred around the original optimal orientation It is suggested that for these cells the inhibitory input enhances the orientation tuning of an excitatory input that is already broadly orientation tuned 5 Comparison of normal orientation tuning curves with those observed during the application of bicuculline provides a basis for estimating the orientation tuning of the GABA-mediated inhibitory input In all cases, it is clear that at normal resting discharge levels, orientations either side of the optimal, and not those centred on the optimal, generate the most powerful inhibitory input 6 These results would seem to be best explained by inhibitory interconnexions between cortical columns sensitive to different orientations This type of lateral interaction between columns may serve to enhance the contrast in the orientation domain for the cortical representation of a specific stimulus orientation 7 Increasing the resting discharge level of a complex cell, without blocking the action of GABA appeared to increase the gain of the inhibitory mechanisms acting on the cell The normal excitatory responses to optimal or near optimal orientations were greatly reduced, or replaced by inhibitory responses, and non-optimal orientations produced only inhibitory responses These inhibitory effects were blocked on the context of other observations in the literature It is tentatively suggested that the interneurones providing the inhibitory drive to complex cells receive an input from recurrent collaterals of the recipient complex cells Their other inputs would derive from neighbouring colums and from the afferent input to the parent column The inputs from neighbouring columns would mediate the lateral inhibitory interactions in the orientation domain, and the recurrent collateral feed-back the decreased responsiveness at high resting discharge levels
TL;DR: Circumstantial evidence led to the conclusion that detection was dependent on one impulse in one or a few rapidly adapting units under optimal conditons in the region of low psychophysical thresholds, whereas it seemed unlikely that activity in Pacinian corpuscle units was crucial.
Abstract: 1. Psychophysical thresholds were determined at 162 points in the glabrous skin area of the human hand when slowly rising, triangular indentations of controlled amplitudes were delivered with a small probe. The method of constant stimuli was used with either the two alternative forced choice or the yes-no procedure. It was found that the distribution of the psychophysical thresholds varied with the skin region. Thresholds from the volar aspect of the fingers and the peripheral parts of the palm were low and their distribution was unimodal with a median of 11.2 micrometers. In contrast, there was an over-representation of high thresholds when observations from the centre of the palm, the lateral aspects of the fingers and the regions of the creases were pooled, and the distribution was slightly bimodal with a median of 36.0 micrometers. 2. Nerve impulses were recorded from single fibres in the median nerve of human subjects with percutaneously inserted tungsten needle electrodes. The thresholds of 128 mechanosensitive afferent units in the glabrous skin area of the hand were determined when stimuli were delivered to partly the same points as stimulated for the assessment of the psychophysical thresholds. Of the four types of units present in this area the Pacinian corpuscle (PC) and rapidly adapting (RA) units had the lowest thresholds with medians of 9.2 and 13.8 micrometers, followed by the slowly adapting type I and slowly adapting type II units with medians of 56.5 and 33.1 micrometers. There was no indication of a difference between thresholds of units located in different skin areas. 3. In the region of low psychophysical thresholds there was good agreement between the thresholds of the rapidly adapting and Pacinian corpuscle units and the psychophysical thresholds, particularly at the lower ends of the samples. In the skin regions of high thresholds, on the other hand, practically all psychophysical thresholds were higher than the thresholds of the most sensitive afferent units. Moreover, simultaneous recording of nerve impulses during a detection task indicated that subjects did not detect stimuli strong enough to elicit several impulses in afferent units in this region. 4. Circumstantial evidence led to the conclusion that detection was dependent on one impulse in one or a few rapidly adapting units under optimal conditons in the region of low psychophysical thresholds, whereas it seemed unlikely that activity in Pacinian corpuscle units was crucial. 5. The findings are consistent with the interpretation that human subjects are able to detect an input consisting of a single impulse in a single rapidly adapting unit.
TL;DR: The mode of action of ACh antagonists on the parasympathetic neurones of the submandibular ganglion of the rat was studied by means of a two‐micro‐electrode voltage‐clamp technique, and a ‘sequential’ scheme in which tubocurarine, hexameth onium and decamethonium act mainly by blocking the channels opened by the cholinergic agonists was interpreted.
Abstract: The mode of action of ACh antagonists on the parasympathetic neurones of the submandibular ganglion of the rat was studied by means of a two-micro-electrode voltage-clamp technique. The currents produced by various agonists (carbachol, ACh, suberylcholine) were studied in steady state and after voltage steps, before and after perfusion of various antagonists. 2. For three antagonists (tubocurarine, hexamethonium, decamethonium) the blocking action increases with hyperpolarization. For three other antagonists (surugatoxin, trimetaphan, mecamylamine) the effects observed at low concentrations appear to be independent of membrane potential, although in some cases voltage dependence of the block was observed for mecamylamine. 3. The blocks the 'open' channel-reception complex. The block produced by tubocurarine, hexamethonium and decamethonium increases with the agonist concentration, an observation which supports a 'sequential' scheme in which the antagonist blocks the 'open' channel-receptor complex. The block produced by trimetaphan and mecamylamine decreases slightly with increased agonist concentration, which in turn suggests that these two compounds are competitive antagonists, preventing binding of the agonists to the closed channel-receptor complex. 4. In the cases where the block is voltage dependent, voltage jumps trigger slow relaxations which are not present in control conditions. In the case of tubocurarine and hexamethonium, the relaxation following a hyperpolarizing voltage jump corresponds to a decrease in conductance. In the case of decamethonium, the slow relaxation is in the opposite direction. 5. The slow relaxations observed with tubocurarine and hexamethonium are speeded by an increase of the antagonist concentration; the slow relaxations observed with decamethonium are slowed by an increase of the decamethonium concentration. 6. The steady-state observations and the relaxations can be interpreted in terms of a scheme in which tubocurarine, hexamethonium and decamethonium act mainly by blocking the channels opened by the cholinergic agonists. 7. The two types of slow relaxation are those predicted if tubocurarine and hexamethonium dissociate slowly from the channel, and decamethonium rapidly. 8. An additional effect of tubocurarine is described, which consists of a potentiation of the rising phase of the response to an ionophoretic pulse. Possible mechanisms of this effect are discussed.
TL;DR: Receptive field centre sizes of brisk‐sustained (X) and brisk‐transient (Y) ganglion cells of the cat retina were assessed by three different methods: small spot mapping, area threshold method and spatial resolution.
Abstract: 1. Receptive field centre sizes of brisk-sustained (X) and brisk-transient (Y) ganglion cells of the cat retina were assessed by three different methods: small spot mapping, area threshold method and spatial resolution. 2. Centre sizes of brisk-sustained (X) cells increased from 20' in the central area to about 70' at an eccentricity of 4.5 mm, centre sizes of brisk-transient (Y) cells from 50' in the central area to about 140' at 5 mm eccentricity. 3. The scatter of centre sizes at one retinal location was measured by recording as many ganglion cells as possible in one cat in a small field of retina. The centre sizes of the individual classes were homogeneous and exhibited only a small amount of scatter. 4. The coverage of the retina by the different ganglion cell classes was assessed from their density and their receptive field centre area. At every retinal location the receptive field centres of seven to twenty brisk-sustained (X) cells and of three to six brisk-transient (Y) cells were found to overlap. Sluggish concentric and non-concentric cells taken together have a coverage factor of about 60.
TL;DR: Observation of internal movement during the raised tension after a lengthening contradicts theories involving ‘locked on’ bridges and an explanation for the extra tension in terms of non‐uniformity of sarcomeres is proposed.
Abstract: 1. The stability of sarcomere lengths along single frog twitch fibres was examined, during lengthening and shortening, using a spot follower appparatus to monitor or control the length of a central segment. 2. During active shortening from sarcomere lengths beyond 2.2 micrometer the end sarcomeres shortened dramatically, while much of the fibre did not shorten at all. It is proposed that this is the cause of the tension failing to recover, after the shortening ceased, to the value of isometric tension at the shorter length. 3. During active lenghtening from sarcomere lengths beyond 2.2 micrometer, non-uniformity of stretch was seen, with the middle stretching more than the ends. Some maintained extra tension after stretch above that appropriate to the longer length was found, as were consistent changes in internal movement, and in the shape of the tension record during relaxation. 4. Measurements of stiffness during and after a lengthening suggest that no increased activation is involved. Observation of internal movement during the raised tension after a lengthening contradicts theories involving 'locked on' bridges. 5. From these and other observations, an explanation for the extra tension in terms of non-uniformity of sarcomeres is proposed. The explanation is in accord with that previously suggested for the creep phase of tension rise seen at these lengths.
TL;DR: The results do not support the view that sarcomere length dependent variation in the amount of calcium which is released during tetanic stimulation is a major determinant of the form of the length‐tension relation in living muscle fibres at Sarcomere lengths less than about 2.0 microns.
Abstract: 1. Single twitch fibres were isolated from anterior tibial muscles of the frog, Rana pipiens. The relationship between sarcomere length and steady tetanic tension at 5 degrees C was obtained from these living fibres in the range of sarcomere lengths between about 2.2 and 1.3 microns . These fibres were then either mechanically or chemically skinned. 2. Segments were cut from the skinned fibres and mounted in an experimental chamber using a technique designed to minimize segment compliance at the points of attachment. A piece approximately 1 mm in length remained exposed to the bathing solution. 3. The segments were photographed through a light microscope at magnifications of about 460 or 110 X during activation and relaxation, so that the sarcomere lengths could be determined from a part or the whole of the segment. Activations were done with solutions of pCa either 5.49 or 6.09 and at a temperature of 5 degrees C. Fibre segments which developed striation pattern irregularities during contraction were rejected. 4. The sarcomere length-tension relation obtained from these segments in the sarcomere length range 1.3-2.2 microns was similar to that obtained from the same fibres while still living. The results were similar at the two values of pCa used. 5. These results do not support the view that sarcomere length dependent variation in the amount of calcium which is released during tetanic stimulation is a major determinant of the form of the length-tension relation in living muscle fibres at sarcomere lengths less than about 2.0 microns.
TL;DR: It is likely that facilitations of the cerebellar nuclear cells result at least in part from reductions in the tonic inhibitory input from the P cells, which are likely to coincide with equally variable periods of facilitation previously seen in neurones of nucleus interpositus.
Abstract: 1. Glass-insulated tungsten micro-electrodes were used to record from single neurones in the intermediate zone of the cerebellar cortex of cats in a state of quiet wakefulness. 2. Two hundred and seventy Purkinje (P) cells were recorded extracellularly, 95% of which displayed an irregular tonic discharge at rates between 19 and 95/s (over-all mean 44/s), including complex spikes (c.s.) which occurred at 1.0--2.5/s )over-all mean 1.5/s). The remaining cells discharged c.s. at the usual rate but only one or two simple spikes (s.s.) per minute. C.s. of spike plus wavelet and of multi-spiked type were present in approximately equal numbers of cells. 3. Presumed climbing fibre-e.p.s.p.s were recorded from fifty-six P cells and occurred both singly and in groups of two to six e.p.s.p.s at an intra-group frequency of about 500/s. The cells giving rise to the c.f.s therefore discharge propagated impulses both singly and in short bursts as previously reported for anesthetized animals. A single e.p.s.p. can give rise to more than one spike in the multi-spiked type of c.s., and probably to a complete c.s. event. 4. Following spontaneous c.s. the interval to the next s.s. varied from 8 to 600 ms. There was an inverse correlation between duration of the post-c.s. interval and the rate at which s.s. were discharged in the preceding 100 ms. The duration exceeded the mean s.s. interval provided s.s. rate was less than 40--50/s, and the post-c.s. interval would then constitute a real interruption of s.s. discharge. 5. When the superficial radial (s.r.) nerves were stimulated with single shocks too weak to produce a behavioural response changes in discharge pattern were detected in eighty-eight of 151 P cells tested. The initial responses were almost always excitatory and consisted in seventy-two cells of a c.s., in eleven of a c.s. preceded by a brief increase in s.s. and in two cases of a s.s. discharge alone. The spino-olivo-cerebellar paths responsible for the c.s. showed transmission characteristics similar to those reported for animals anaesthetized with barbiturates. 6. C.s. were readily evoked by tapping or squeezing the forepaws. 7. Excitatory responses to nerve stimulation were usually followed by a depression of the tonic s.s. discharge. Its duration ranged widely in different cells (from 10 to 500 ms) and it would coincide with equally variable periods of facilitation previously seen in neurones of nucleus interpositus. It is therefore likely that such facilitations of the cerebellar nuclear cells result at least in part from reductions in the tonic inhibitory input from the P cells. 8. Thirty-six units were classes as 'probable cortical interneurones'. They discharged more regularly, at rates between 9 and 28/s. Twenty such units (56%) responded to s.r. stimulation with a brief excitation not usually followed by any pronounced depression.
TL;DR: AVP plasma levels correlated negatively with fever magnitude following premature birth induced by dexamethasone, and the amounts of AVP in perfusates from the septal region correlated positively with changes in body temperature.
Abstract: 1. The antipyretic effect of arginine vasopressin (AVP) introduced into the brain by push-pull perfusion was investigated in the sheep. 2. Control perfusions with sucrose solutions had no effect on fevers induced by a bacterial endotoxin. Sucrose solutions containing AVP (4.0 microgram/ml.) perfused at 40 microliter./min had significant antipyretic activity, reducing the two peaks of the fever but had no effect on resting body temperature. 3. Loci in which AVP induced antipyresis were limited to the septal region about 2-3 mm anterior to the anterior commissure. 4. The amounts of AVP in perfusates from the septal region correlated negatively with changes in body temperature. 5. AVP administered I.V. did not lower fever. 6. AVP plasma levels correlated negatively with fever magnitude following premature birth induced by dexamethasone.
TL;DR: The vomeronasal organ can be adequately stimulated by activation of the pumping mechanism in the presence of odour, and the time course of neuronal response in the accessory olfactory bulb is more rapid than predicted and cannot be ruled out as a possible sensory pathway in many odour related behaviours.
Abstract: Previous workers had identified the vomeronasal organ, on anatomical evidence, as an accessory olfactory organ, present in most terrestrial vertebrates. Lesion experiments had demonstrated its importance in sexual behaviour in the hamster. Howevever, the sequestered position of the vomeronasal receptor epithelium within the organ raised questions concerning the access of olfactory stimuli. Using electrophysiological and pharmacological methods we have now demonstrated the following. 1. A pumping mechanism exists, powered by vasomotor movements, which can suck stimulus substances into the vonmeronasal organ. 2. A mechanism also exists for the active expulsion of the contents of the vomeronasal organ. 3. These mechanisms are activated by fibres running in the nasopalatine nerve. 4. The suction mechanism is controlled by sympathetic, probably adrenergic, fibres from the superior cervical sympathetic ganglion. Control of the expulsion mechanism has not been definitely established but does not appear to be sympathetic. 5. The vomeronasal organ can be adequately stimulated by activation of the pumping mechanism in the presence of odour. 6. Odour responses of single units in the accessory olfactory bulb have been recorded for the first time. 7. The time course of neuronal response in the accessory olfactory bulb is more rapid than predicted by many authors. The response is sufficiently fast that the vomeronasal system cannot be ruled out as a possible sensory pathway in many odour related behaviours. Possible modes of action of the pumping mechanism in awake animals are discussed.
TL;DR: The mechanism that fits them best appears to be a combination of competitive block (or block of shut channels), with a strongly voltage‐dependent block of open ion channels by tubocurarine.
Abstract: 1. The action of tubocurarine on voltage-clamped frog muscle end-plates has been re-examined by means (a) equilibrium dose-ratio measurements, (b) current fluctuation measurements and (c) voltage-jump relaxation measurements. 2. The equilibrium measurements can be interpreted as implying that tubocurarine has (a) a competitive blocking action, with a dissociation constant of 0.34 microM, which is not dependent on membrane potential, and (b) an additional voltage-dependent blocking action. 3. In the presence of tubocurarine two kinetic components can be seen. The faster one is similar to, but rather faster than, the normal ion channel closing rate. The other is much slower (1--3 sec), and, in relaxation experiments it is in the opposite direction to the fast relaxation. 4. A number of alternative explanations for the results are discussed. The mechanism that fits them best appears to be a combination of competitive block (or block of shut channels), with a strongly voltage-dependent block of open ion channels by tubocurarine. Estimates of the rate constants for channel blocking (and their voltage dependence) are derived. From these estimates the dissociation constant for the binding of tubocurarine to open channels appears to be roughly 0.12 microM at --70 mV and 0.02 microM at --12 mV. 5. Several potential sources of error in the experiments, and in their interpretation, are discussed. The most serious of these are problems associated with diffusion in the small volume of the synaptic cleft, viz. (a) changes in cleft concentration consequent on changes in binding, and (b) ionophoretic flux of antagonist and agonist into the synaptic cleft.
TL;DR: While naloxone did not antagonize the effects of the dorsal raphe stimulation towards locus coeruleus activity, these effects were absent in rats pretreated with a serotonin synthesis inhibitor, PCPA or with 5,7‐DHT which destroys serotonin‐containing terminals, and were reduced by the serotonin antagonist methysergide.
Abstract: The connexions between the dorsal raphe nucleus and the nucleus locus coeruleus were studied in urethane anaesthetized rats. 1. Cells in the locus coeruleus gave an excitatory response to a noxious stimulus, e.g. leg pinch. 2. This excitatory response was blocked by either a parenteral or an ionophoretic injection of morphine and recovered after an injection of naloxone. 3. Electrical stimulation in the region of the dorsal raphe blocked excitatory locus coeruleus responses to noxious stimuli. 4. While naloxone did not antagonize the effects of the dorsal raphe stimulation towards locus coeruleus activity, these effects were absent in rats pretreated with a serotonin synthesis inhibitor, PCPA or with 5,7-DHT which destroys serotonin-containing terminals, and were reduced by the serotonin antagonist methysergide. 5. A serotonin-containing inhibitory pathway between the dorsal raphe and the locus coeruleus is proposed to account for these results.
TL;DR: This study evaluated the contribution of carotid and cardiopulmonary baroreceptors to reflex splanchnic and forearm vascular adjustments during venous pooling in man and suggested simultaneous application of neck suction would minimize the contribution.
Abstract: 1. This study evaluated the contribution of carotid and cardiopulmonary baroreceptors to reflex splanchnic and forearm vascular adjustments during venous pooling in man. We compared (a) responses to lower body suction which produces venous pooling with (b) responses to lower body suction plus simultaneous application of neck suction. The rationale was that simultaneous application of neck suction, which stretches carotid baroreceptors, would minimize the contribution of carotid baroreceptors to circulatory adjustments produced by lower body suction.
2. Lower body suction at 40 mmHg decreased central venous pressure and arterial pulse pressure and increased forearm vascular resistance (plethysmography), splanchnic vascular resistance (indocyanine green dye clearance), and heart rate. Simultaneous application of neck suction prevented the tachycardia and most of the splanchnic vasoconstriction during lower body suction, but did not significantly attenuate the forearm vasoconstriction.
3. The major findings in this study are first, that the splanchnic vasoconstrictor response during venous pooling is mediated primarily through carotid baroreceptors, and secondly, that carotid and cardiopulmonary baroreceptors produce strikingly contrasting and non-uniform regional vascular responses during venous pooling. Cardiopulmonary baroreceptors exert the predominant influence on forearm vascular resistance, but appear to have only a minor influence on splanchnic vascular resistance. Carotid baroreceptors produce most of the splanchnic vasoconstriction during venous pooling. but have a minor role in the forearm vasoconstriction.
TL;DR: Single, isolated, rod photoreceptors obtained by enzymatic dissociation of the tiger salamander retina retained the morphological features of rods of the intact retina and could be maintained in culture for several days.
Abstract: 1. Single, isolated, rod photoreceptors were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. These solitary cells retained the morphological features of rods of the intact retina and could be maintained in culture for several days. Solitary cells were penetrated with one or two micropipettes and their electrophysiology was studied by the voltage-clamp technique. 2. Intracellular recording with two micropipettes demonstrated that the inner segment of a solitary rod was effectively isopotential with the outer segment. 3. The time course of the voltage response to a flash resembled that of responses observed in rods in the intact retina. At low light intensities the response reached a peak in approximately 0.7 sec and then slowly declined. At high light intensities the time to peak response decreased and an initial transient arose as the response, after reaching the peak, quickly decreased to a less polarized plateau. 4. The normal voltage response could be compared with the current observed during a voltage clamp. At low light intensities the time course of the current response resembled the time course of the voltage response. When light intensity was increased the time course of the current response differed from the voltage response in that the time to peak amplitude remained relatively constant and an initial transient did not occur. It was possible to predict the current response produced by any intensity of light by using (i) an empirical equation which reproduced the time course of a dim response and (ii) the Michaelis-Menten equation. 5. The time course of the voltage-clamp current produced by a flash was the same at different values of maintained voltage. 6. The maximum amplitude of the voltage-clamp current produced by a flash or step of light was a non-linear function of membrane potential. It was relatively constant within the physiological range, decreased as the membrane potential was moved toward 0 mV, reversed polarity between 0 and 10 mV, and rapidly increased in magnitude as membrane potential was made more positive. Although this current was voltage dependent, no time dependence was evident (recording resolution greater than or equal to 5 msec). 7. Voltage-clamp experiments demonstrated an inward current which slowly developed after a hyperpolarizing voltage step. The effect of this voltage and time dependent current was to reduce, after a delay, the polarization initiated by light.
TL;DR: The orientation tuning, spatial‐frequency tuning and responsiveness of cells to a plaid pattern were found to be predictable from the pattern's two‐dimensional Fourier spectrum, and both simple and complex striate cortex cells can be characterized as two-dimensional spatial‐ frequencies filters.
Abstract: 1. Cells in visual cortex have been alternately considered as bar and edge detectors, or as spatial-frequency filters responding to the two-dimensional Fourier component of patterns. 2. The responses to gratings and to checkerboards allow one to test these alternate models: the Fourier components of a checkerboard pattern do not occur at the same orientation as the edges, nor do the checkerboard spatial frequencies correspond to the check widths. 3. Knowing the orientation tuning of a cell for gratings, one can precisely predict its orientation tuning to checkerboards from the orientation of the fundamental Fourier components of the patterns, not from the orientation of their edges. This was found for both square and rectangular checkerboards, and held for both simple and complex cortical cells. 4. Knowing the spatial tuning of a cell for sine-wave gratings, one can precisely predict its spatial tuning to square and rectangular checkerboards from the spatial frequencies of the fundamental Fourier components of the patterns, not from the widths of their checks. 5. When presented with checkerboards in which not the fundamental but the upper harmonics were within its spatial bandpass, a cell's orientation tuning was found to be predictable from the (quite different) orientation of the higher Fourier harmonic components, but not from the orientation of the edges. 6. Knowing a cell's contrast sensitivity for gratings, one can predict the cell's contrast sensitivity for checkerboards much more accurately from the amplitudes of the two-dimensional Fourier components of the patterns than from the contrasts of the patterns. 7. The orientation tuning, spatial-frequency tuning and responsiveness of cells to a plaid pattern were also found to be predictable from the pattern's two-dimensional Fourier spectrum. 8. Both simple and complex striate cortex cells can thus be characterized as two-dimensional spatial-frequency filters. Since different cells responsive to the same region in the visual field are tuned to different spatial frequencies and orientations, the ensemble of such cells would fairly precisely encode the two-dimensional Fourier spectrum of a patch of visual space.
TL;DR: The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b Muscle fibres in stronger contractions.
Abstract: 1. The properties of fifty-seven motor units in human medial gastrocnemius have been studied using controlled intramuscular microstimulation, glycogen depletion and muscle biopsy. 2. Motor units could be divided into three classes on the basis of their mechanical properties. Type S units were slow, small and fatigue resistant. Type FR units were fast, intermediate in size, and fatigue resistant. Type FF units were fast, large and fatigable. 3. Glycogen depletion of a number of type S and FF units revealed them to be composed of type 1 and type 2b muscle fibres respectively. 4. The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b muscle fibres in stronger contractions.
TL;DR: It was concluded that cone sensitivity during any state of light‐adaptation is determined by two mechanisms; response compression resulting from the instantaneous non‐linearity between 'internal transmitter' concentration and membrane potential and a more active 'cellular adaptation' mechanism which is manifest as a shift in the intensity‐response curve.
Abstract: 1. The photoresponses of light- and dark-adapted red and green cone photoreceptors were recorded intracellularly in the retina of the turtle, Pseduemys scripta elegans. Background illumination produced similar effects on both types of cones. 2. In response to the onset of a prolonged, steady background illumination the cone initially hyperpolarized to a peak which then sagged back to a steady-state polarization that was typically about one half the initial peak amplitude. This sag was observed for all backgrounds studied (dim as well as bright). 3. A resensitization was observed concomitantly with this sag; both the maximum increment and decrement responses grew in amplitude as light-adaptation proceeded. After about 2--3 min of background illumination, the amplitudes of these responses stabilized. 4. The dark-adapted cone produced graded responses to test pulses over a range of intensities spanning about 3.5 log units. The amplitudes of these responses were well fit by the relationship V = I.Vm/(I + sigma). 5. After 2--3 min of background illumination, 500 msec test pulses either brighter or dimmer than the background intensity were substituted for the background. The light-adapted intensity-response curves constructed from this data were similar to the dark-adapted curve but were shifted horizontally and slightly vertically, so that they still spanned about 3.5 log units of intensity. Thus, in the light-adapted cone, graded responses were elicited by a range of bright test pulses which would have produced saturated responses when delivered to the dark-adapted cone. 6. The 'off response' observed at the offset of the background became faster as the background intensity was increased. It also became faster with time following the onset of any particular background intensity. 7. It was concluded that cone sensitivity during any state of light-adaptation is determined by two mechanisms; response compression resulting from the instantaneous non-linearity between 'internal transmitter' concentration and membrane potential and a more active 'cellular adaptation' mechanism which is manifest as a shift in the intensity-response curve. In the steady-state condition of light-adaptation, most of the sensitivity changes are a result of the cellular adaptation mechanism. 8. Photopigment bleaching caused by the backgrounds, negative feed-back from horizontal cells and voltage dependent mechanisms in the cones could not account for this cellular adaptation. These effects of background illumination were interpreted in terms of the 'internal transmitter' hypothesis of phototransduction.
TL;DR: Inhibitory post‐synaptic potentials evoked by adequate stimulation of group Ia muscle spindle afferents of homonymous and synergistic muscles and by selective electrical stimulation of tendon organAfferents were analysed in motoneurones of triceps surae and plantaris to conclude that inhibition of motoneURones may be evoked from Ia Muscle spindle Afferents from homonym and synergic muscles as well as from Ib tendon organ afferentS.
Abstract: 1. Inhibitory post-synaptic potentials evoked by adequate stimulation of group Ia muscle spindle afferents of homonymous and synergistic muscles and by selective electrical stimulation of tendon organ afferents were analysed in motoneurones of triceps surae and plantaris. 2. Selective activation of Ia afferents was verified to occur with brief stretches of triceps surae and plantaris 35 micrometer or less in amplitude with an initial muscle tension of 5 N; stretches of 30--35 micrometer were estimated to activate 80--90% of Ia afferents in these muscles. Under the same conditions the lowest thresholds for group Ib tendon organ afferents were about 40 micrometer. 3. Stretches less than or equal to 30 micrometer evoked i.p.s.p.s in 80% of triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s wef triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s were 10 micrometer or less. However, such low thresholds for stretch-evoked i.p.s.p.s, lower than the thresholds for activation of Ib afferents, were found mainly in spinalized, unanaesthetized (after decerebration) or lightly anaesthetized animals. The latencies of these i.p.s.p.s indicated disynaptic and trisynaptic coupling between Ia afferents and motoneurones. The i.p.s.p.s were evoked (i) from the homonymous and synergistic muscles stretched together, (ii) from the homonymous muscles alone and (iii) from the synergistic muscles alone. 4. Control experiments showed that i.p.s.p.s could be evoked by stretches sub-threshold for discharging motoneurones, thus showing that those i.p.s.p.s were not mediated by Renshaw cells. The stretch-evoked i.p.s.p.s disappeared after sectioning the nerves from the corresponding muscles, further excluding their mediation by afferents other than group Ia afferents from thf stretched muscle. 5. In order to selectively activate tendon organ afferents, thresholds for excitation of Ia afferents by electrical stimuli were increased to a level above the threshold for Ib afferents by prolonged muscle vibration (Coppin, Jack & MacLennan, 1970). I.p.s.p.s evoked by stimuli near threshold for Ib afferents appeared with latencies indicating disynaptic coupling. Later (trisynaptic) components of Ib i.p.s.p.s required somewhat stronger stimuli. 6. Amplitudes of Ia i.p.s.p.s evoked by muscle stretches activating about 80% of muscle spindle afferents were compared with amplitudes of Ib i.p.s.p.s due to less than 50% of tendon organ afferents of the same muscles. The Ia i.p.s.p.s were much smaller (16--35%) than the Ib i.p.s.p.s. The amplitudes of such Ia and Ib i.p.s.p.s constituted about 10 and 25--66%, respectively, of the maximal i.p.s.p.s evoked by electrical stimulation of all group I afferents. 7. We conclude that inhibition of motoneurones may be evoked from Ia muscle spindle afferents from homonymous and synergistic muscles as well as from Ib tendon organ afferents...
TL;DR: It is concluded that the individual components of a ballistic movement are relatively fixed in duration and the amount of e.m. activity is altered within this time interval to produce the different forces required for fast movements of different amplitude.
Abstract: 1. In response to an auditory stimulus normal subjects made ballistic flexion movements of the top joint of the thumb against a lever attached to the spindle of a low-inertia electric motor. 2. Electromyographic (e.m.g.) activity was recorded from pairs of fine wire electrodes inserted into flexor pollicis longus and extensor pollicis longus, respectively the sole flexor and extensor of the joint. 3. Movements of 5 degrees, 10 degrees and 20 degrees were made from initial angles of 10 degrees, 20 degrees and 30 degrees flexion against torques of 0.04, 0.08 and 0.16 Nm. 4. The e.m.g. activity initiating such movements was characterized by a ‘triphasic’ pattern of sequential bursts of activity in the agonist (flexor pollicis longus), then in the antagonist (extensor pollicis longus), and then in the agonist again. 5. The duration of the first agonist and first antagonist bursts ranged from about 50 to 90 ms and there was no significant change of burst length in the different mechanical conditions. 6. In movements of differing angular distance, the rectified and integrated e.m.g. activity of the first agonist burst could be correlated with the distance moved. The rectified and integrated e.m.g. activity of the first antagonist burst could not be correlated with the distance moved. 7. Responses of the muscles to perturbations either before or during the ballistic movements were studied. Current in the motor could be altered so to extend the thumb ('stretch'), to allow it to accelerate ('release'), or to prevent further movement ('halt'). 8. Suitably timed stretch increased the e.m.g. activity of the first agonist burst while release decreased it. 9. There was a small response of the agonist to stretch or halt timed to act during the interval between the first two agonist bursts; the major response was an augmentation of the second agonist burst. 10. Stretch, timed to act between the first two agonist bursts which released the antagonist, diminished the activity of the first antagonist burst while halt virtually eradicated it in all but one subject. Release, at this time, which stretched the antagonist, increased the activity of the first antagonist burst. 11. It is concluded that the individual components of a ballistic movement are relatively fixed in duration and the amount of e.m.g. activity is altered within this time interval to produce the different forces required for fast movements of different amplitude. 12. Both agonist and antagonist muscles remain under some feed-back control during the entire course of a ballistic movement, but the amount of influence of fedd-back depends on the supraspinal command signal and the changes in the spindle during the course of the movement.
TL;DR: A selective cerebral cooling due to venous blood returning from facial skin via the ophthalmic vein to the cavernous sinus, where a cooling of arterial blood ascending to the brain can take place, is suggested.
Abstract: 1. The technique of perceptual rating of thermal stimuli was used, in eight human subjects immersed in warm water, in order to appreciate whether they were hypo-, normo- or hyperthermic. Oesophageal, tympanic and forehead skin temperatures were recorded, as also was the temperature of the skin above the angularis oculi vein. Once the subjects gave clearly hyperthermic ratings, one arm was exposed to a 6 m/s wind. After 5--10 min the arm was re-immersed and the face was fanned. 2. Fanning of the arm resulted in lowering of body core temperature. However ratings of thermal stimuli remained hyperthermic. 3. Face fanning decreased forehead skin, angularis oculi vein and tympanic temperatures. Hyperthermic ratings were replaced by normothermic ratings, although oesophageal temperature continued to rise. 4. The upper limit of oesophageal temperature for normothermic ratings was 37.o6 +/- 0.09 degrees C during the control period without fanning. This temperature rose to 37.91 +/- 0.09 degrees C during facial ventilation. 5. These results suggest a selective cerebral cooling due to venous blood returning from facial skin via the ophthalmic vein to the cavernous sinus, where a cooling of arterial blood ascending to the brain can take place.