Physiological tremor in human jaw-muscle system.

Small, quasi-rhythmical tremor of the jaw occurs at rest and during voluntary movements. In peripheral limbs, tremor consists of a component due to mechanical resonance properties of the system, and a neurogenic component mediated by a central pacemaker or neural loops. The present study attempted to determine if these components were present in jaw tremor measured with a position transducer held lightly between the incisors. When weights were suspended from the mandible, the tremor frequency was unaltered; sharp taps delivered to the jaw did not elicit any kind of damped oscillations of the system. These findings indicated the absence of mechanical resonance in the system. No correlation of the tremor signal with the electrocardiogram was found. However, a strong correlation was found between the rectified electromyographic signals recorded over the masseter muscles and the tremor signal, where the electromyographic signal preceded jaw movement by 20-30 msec. Frequency-domain analysis also showed positive peaks in a majority of coherence functions between electromyographic and tremor signals. These results suggested a strong neurogenic component of the tremor.

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels.

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

Turns and averaging as static and dynamic measures of masseter EMG activity.

Surface EMG records from human masseter muscles were analyzed at various fractions of the maximum voluntary contraction (MVC). Frequencies of turns, or reversals of signal direction, and integrated or average rectified values were compared as quantitative measures of this type of data. Averaged signals were useful for within-study comparisons or for revealing dynamic changes in EMG during excitation or inhibition. However, averaged values depend strongly on signal amplitude (and thus on electrode characteristics and muscle size), and are not easily transferable between studies. Turns frequencies increased with contraction up to 75% MVC, and were less dependent on signal amplitude than were averages. Turns frequencies may thus be useful for quantitative comparisons between studies or between different muscles.

Lithium block of outward current channels in Helix neurons.

Outward currents were studied in isolated, perfused ganglion cells from Helix aspersa. Treatment with external solutions containing 40 mM LiCl slowed and reduced the delayed outward currents after about 15 min. The leak currents were reduced by external application of Li. Electrophoretic injection of LiCl increased the leak currents and reduced the net outward currents. From fits of a model with a rapid second-order current component and a slower first-order component, the effect of Li was to reduce the asymptotic current for the first component and double the activation time constant for the second component. This was equivalent to increasing the probability of entering the blocked state in a kinetic model of the K-channels. The slowness of the block suggested that Li might act through a chemical intermediate.

Calcium dependence of A-currents in perfused Aplysia neurons.

Transient outward currents were studied in neurons in the visceral ganglion of Aplysia californica, using intracellular perfusion and voltage-clamp techniques. The early outward currents in response to depolarizations from holding potentials near -90 mV were activated in the range -60 to -20 mV, below the threshold for the delayed outward current. Resting inactivation of the early outward currents was removed by prehyperpolarizations in the range -130 to -70 mV. A-currents produced in this manner were blocked by external application of CoCl2 and augmented by increasing external Ca-concentration. They were also blocked by treatment with 4-aminopyridine. The currents were reduced by treatment with verapamil hydrochloride, further suggesting a role for calcium in the current-generating mechanism. A model with a fourth-power activation process and first-power inactivation process could fit the early outward currents reasonably well. The effect of application of Ca-free, cobalt-containing solution was modeled as a decrease in peak conductance and an increase in the time constants of activation and inactivation.

Altered invertebrate nerve function after chronic exposure to low concentrations of alcohol.

Previous studies of direct alcohol toxicity on nerve tissue have been carried out using acute, extremely high doses of alcohol. Chronic administration of 20 mM ethanol to the mollusc Aplysia californica was achieved by adding ethanol to surrounding seawater. Although the animals appeared healthy, isolated ganglion cells from treated animals had significantly decreased mean action potential amplitudes and prolonged mean action potential durations compared to controls. These findings suggest that chronic exposure to a low concentration of ethanol comparable to that producing drunkeness in humans may have a direct toxic effect on invertebrate nerve tissue.

Depressant action of lithium at the crayfish neuromuscular junction: pre- and postsynaptic effects.

1. The effects of replacement of external sodium ions with lithium have been studied at the excitatory neuromuscular junction of the crayfish. 2. Intracellularly recorded excitatory junctional potentials fall 45% in amplitude in the first 10 min after lithium substitution, and fail irreversibly in 48--120 min. 3. The quantal content of extracellularly recorded excitatory junctional potentials declines 25--70% within the first 10 min of Li+ exposure. During the next 40--120 min the nerve terminal potentials and quantal release at individual synapses fail simultaneously and irreversibly. 4. The mean amplitude of the spontaneous miniature excitatory junctional potentials (m.e.j.p.s) is reduced 13% by Li+ substitution, but recovers upon restoration of sodium. The mean frequency of m.e.j.p.s rises steadily during Li+ exposure, and continues to increase after reintroduction of Na+. 5. The postsynaptic response to iontophoretically applied L-glutamate falls 35--40% in 10 min, but never falls below 45% of the control level. The effect on the glutamate response is completely reversible with sodium restoration. 6. The effective resistance of the postsynpatic cells is unaffected or only increased slightly by lithium substitution. 7. Thus, the primary mechanism of transmission block by lithium appears to be decreased transmitter release and inexcitability of presynaptic terminals, probably as a result of intracellular accumulation of lithium.

Measurement of electrogenic-pump current in Aplysia neurones with constant-current and constant-voltage techniques.

1. The responses of the abdominal and pleural giant cells to warming and cooling were studied using constant-current and constant-voltage techniques. 2. The potential change upon warming from about 7 degrees C to 22 degrees C was reversed by application of maintained inward current. The reversal potential was -77 +/- 12 mV. 3. The membrane conductance increased with warming, but was not affected by pump-blocking agents. 4. The electrogenic-pump current was found to be about 16 nA for a model in which the pump acted across the membrane ionic conductance. This model could explain the reversal of the warming response with hyperpolarization. 5. In voltage-clamped cells, the response to warming was converted from an outward to an inward current by hyperpolarization. The reversal potential for the current response 31 +/- 7 mV more negative than resting, or about --80 mV. 6. The pump currents measured under voltage-clamp conditions were the same as those calculated for the hyperpolarizing responses in unclamped cells.

[The topography and cytoarchitectonic of the diencephalon of the cow (Bos taurus var. domesticus L.). II. The internal structure of the diencephalon of the cow (Bos taurus var. domesticus L.) (author's transl)]. / Die Topographie und Zytoarchitektonik des Diencephalon vom weiblichen Rind (Bos taurus var. domesticus L.) II. Die innere Struktur des Diencephalon vom weiblichen Rind (Bos taurus var. domesticus L.).

The five parts of the diencephalon of the cow are distinctly separated by fibrous tractuses or plates. The three main tractuses (Fornix, Tractus mamillo-thalamicus and Fasciculus retroflexus) are very strongly developed. Regarding the essential fibrous structures and the cytoarchitectonic features 62 nuclei can be differentiated in either half of the diencephalon, of which the thalamus contains 28 and the hypothalamus 23 nuclei. Epithalamus, Metathalamus and Subthalamus possess 2 big nuclei on each side. The findings are briefly compared with the data on the diencephalic structures of cow, sheep goat, pig and dromedar given in literature.

[The topography and cytoarchitectonic of the diencephalon of the cow (Bos taurus var. domesticus L.) I. The topography of the diencephalon of the cow. (Bos taurus var. domesticus L.) (author's transl)]. / Die Topographie und Zytoarchitektonik des Diencephalon vom weiblichen Rind (Bos taurus var. domesticus L.) I. Zur Topographie des Diencephalon vom weiblichen Rind (Bos taurus var. domesticus L.).

The study contains a comprehensive review of the literature on the brain of the cattle, followed by notes on form and location of the brain in the skull of the cow and of the diencephalon. In addition we point to some possibilities for locating the brain by stereotaxic manipulations. Several structural particularities are discussed, where to a limited extent references to structures of the brains of other domestic artiodactyla are made.

[Topography and cytoarchitecture of the diencephalon in the female comestic cattle (Bos taurus var. dom.)]. / Topographisch-zytoarchitektonische Untersuchungen am Dienzephalon des weiblichen Hausrindes (Bos taurus var. dom.)

Ten brains of cows were, immediately after slaughter, embedded in celloidin, sliced, and stained to visualise neurocytes and nerve fibres, with the view to elucidating the structures of bovine diencephalon. Macroscopically, the diencephalon of cow is characterised by a comparatively strong epithalamic part, large laterally supported Corpora geniculata lateralis, pronounced ventricular bulgings, almost complete fusion of thalami with Massa intermedia, and very large pituitary gland. The five compartments of bovine interbrain are strongly developed and clearly delimitated by fibrous strings and platelets. By due consideration of the major fibre structures and cyto-architectonic characteristics, 62 nuclei may be differentiated in either half of the diencephalon, with 28 being situated in the thalamus and 23 in the hypothalamus. Two nuclear regions each were recordable from the epithalamus, metathalamus, and subthalamus.

Cyclic variation of potassium conductance in a burst-generating neurone in Aplysia.

1. The hyperpolarization between bursts in the R 15 cell of Aplysia is accompanied by an increase in membrane slope conductance.2. The post-burst hyperpolarization can be observed with ouabain, lithium, or potassium-free solution if artificial inward current is applied. The hyperpolarization can be observed with dinitrophenol or cooling to 10 degrees C, with no injected current. Thus, the hyperpolarization apparently is not due to the cyclic activity of an electrogenic pump.3. A reversal potential for the post-burst hyperpolarization can be demonstrated by passage of inward current during the inter-burst period. The reversal of direction of the potential depends on recent occurrence of a burst.4. The reversal potential varies with external potassium concentration, but not with chloride or sodium.5. The post-burst hyperpolarization is not blocked by external tetraethylammonium at a concentration which greatly prolongs the action potentials.6. During the onset of spike blockage by, and recovery from, calcium-free+tetrodotoxin saline, the bursts of action potentials appear to be driven by endogenous waves of membrane potential.7. The hyperpolarizing phase of the waves in calcium-free+tetrodotoxin medium is accompanied by an increased slope conductance.8. A reversal potential can be demonstrated for the hyperpolarization following a wave in calcium-free+tetrodotoxin medium by applying inward current during the interwave period.9. The waves in calcium-free+tetrodotoxin medium are blocked by ouabain but can be reinstated by artificial hyperpolarization.10. The post-burst hyperpolarization and the post-wave hyperpolarization appear to result from a periodic increase in membrane conductance, primarily to potassium ions.

Post-stimulus hyperpolarization and slow potassium conductance increase in Aplysia giant neurone.

1. Intracellular records from Aplysia giant (R2) cell somata showed long lasting 4-10 mV hyperpolarizations after passage of outward current through a second intracellular electrode.2. An increase in membrane slope conductance occurred simultaneously with the post-stimulus hyperpolarization (PSH).3. Both the PSH and conductance-increase varied strongly with stimulus amplitude and duration.4. Both the PSH and the conductance increase occurred in Ca-free medium containing tetrodotoxin, when action-potential production was completely blocked.5. The PSH persisted in the presence of ouabain or DNP, with cooling, with removal of external K(+), and in media where all the Na(+) was replaced with Li(+), suggesting that it was not due to the activity of an electrogenic pump.6. A reversal potential for the PSH was demonstrated by application of maintained inward current following the end of an outward-directed stimulus.7. The PSH reversal potential varied with [K](o), but not with [Cl](o) or [Na](o), suggesting that the PSH was mainly due to an increase in K conductance.8. The PSH and the conductance increase were reduced strongly when all the Na(+) was replaced with Tris, and only slightly when Na(+) was replaced with sucrose.