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Biomedical subjects

U Proske

Publications and source records attributed to U Proske.

At least 145 records · Page 8Linked to original sources
PubMed1978

Further observations on back-firing in the motor nerve fibres of a muscle during twitch contractions.

1. The tension developed by a muscle in response to a single supramaximal nerve volley is often the sum of two contractions, the second resulting from re-excitation of some nerve terminals during the first contraction. Re-excitation or back-firing can be prevented if the muscle nerve is stimulated twice with the second volley arriving in the muscle at a time when muscle fibres are still refractory following the first volley (Brown & Matthews, 1960). 2. Back-firing has been studied here in the medial gastrocnemius muscle of the spinal cat and responses have been recorded, either representing the summed activity of the muscle's motor supply or discharges of single functional motor axons. 3. When stimulating at a distance from the muscle, the second of two shocks is effective in suppressing back-firing over a narrower range of stimulus intervals than when stimulating close to the muscle. 4. The amount of back-firing can be reduced by stretching the muscle. At a length corresponding to the optimum for a twitch little if any back-firing remains. 5. Measurements of threshold to electrical stimulation of single functional motor axons suggests that low threshold axons are more likely to show back-firing. In the majority of cases, most or all of the motor units in the muscle have to be active before back-firing can be observed.

Animals↗
PubMed1977

A 'late supernormal period' in the recovery of excitability following an action potential in muscle spindle and tendon organ receptors.

1. Discharge patterns have been recorded from five types of stretch receptor; frog muscle spindles, lizard tendon organs, cat soleus tendon organs and primary and secondary endings of cat soleus muscle spindles.2. The fully adapted discharge of each type of receptor is irregular, especially for frog spindles and primary endings of cat spindles as compared with the other three types (the ;regularly firing' receptors). Frog spindles and some cat spindle primary endings would maintain a discharge at very low mean rates (1/sec or less) while the remaining receptors would stop suddenly, as soon as their rate of discharge fell below a critical value characteristic for each individual ending.3. This pattern of discharge suggests that there is a peak in the excitability of ;regularly firing' receptors at a time following a preceding impulse, which corresponds to the intervals between impulses at each particular receptor's slowest rate of maintained firing, and that the excitability subsequently falls again. Primary endings of cat muscle spindles also showed some evidence of such a ;late supernormal period', but frog spindles did not.4. Direct evidence for the ;late supernormal period' was obtained from experiments in which a maintained discharge was restarted by an antidromic action potential in a receptor which had stopped firing, and to which had been applied a stretch just too small to restart the discharge.5. It is shown in an Appendix that a model receptor in which the recovery of excitability following an impulse has a hyperbolic time course, and in which Gaussian distributed noise is superimposed on the generator potential, can have a discharge pattern very closely resembling that of a frog spindle (cf. Buller, 1965).6. After addition of a late supernormal period to the model, its discharge pattern could mimic closely that of a lizard or cat tendon organ, or of a secondary ending of a cat spindle.

Action Potentials↗
PubMed1976

Properties of motor units of the frog sartorius muscle.

1. The mechanical properties of single motor units in the sartorius muscle of the frog Litoria aurea were examined during single shock and repetitive stimulation of motor axons. 2. The tetanic tension developed by motor units lay in the range 1-40% of whole muscle tension with two peaks in the distribution, in the range 5-10% and 25-30%. The large units had briefer times-to-peak for the twitch than the small units and were more readily fatigued during prolonged repetitive stimulation. 3. Histological examination of the muscle gave a count of 620 muscle fibres with a diameter range of 28-128 mum. Cholinesterase stained preparations showed that the majority of muscle fibres had several nerve terminals (mean 3, range 1-5). 4. Muscle fibres received their multiple innervation from different axons (polyneuronal) or branches of the same axon (multiterminal). The presence of polyneuronal innervation of muscle fibres was confirmed by a comparison of the tensions when each of a pair of motor units was stimulated alone and when they were stimulated together. The tension excess, or overlap, was up to 60% when expressed in terms of the tension developed by either unit alone. Motor units developing similar amounts of tension tended to show more overlap in their innervation than units with very different tensions. 5. An estimate of the amount of multiterminal innervation gave variable results but could account for up to 60% of a motor unit's tension. No correlation could be detected between the values for multiterminal innervation and any other measured parameter. However, it is argued that because of the limitations of the measurements the existence of a relationship between the extent of multiterminal or polyneuronal innervation and the mechanical properties of the motor unit cannot be excluded.

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PubMed1976

Short-range stiffness of slow fibers and twitch fibers in reptilian muscle.

The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivision of its motor nerve, fibers of each type may be stimulated separately. When, during repetitive stimulation of nerve filaments, the muscle was lengthened or shortened, the tension changes included an initial short-range stiffness, followed by a later compliance. With increasing velocities of movement, the short-range stiffness increased toward a limiting value. For slow fibers this limiting value was reached with lower velocities of movement than for the twitch fibers. Provided that the same velocity of movement was used and the movements began from similar initial isometric tensions, the slow fibers resisted the movements with a greater stiffness than the twitch fibers. It is suggested that not all of the observed differences between the two fiber types can be interpreted simply in terms of differences in rates of formation and breakdown of cross-links.

Animals↗
PubMed1975

Responses of muscle spindles in a tortoise.

Responses were recorded from muscle spindles in the extensor digitorum longus muscle of the freshwater tortoise Chelodina longicollis. Most spindles showed no resting discharge unless the muscle was stretched up to a millimetre beyond the minimum body length. The firing rate then increased by 2-5 imp./sec/mm extension. All spindles were relatively insensitive to the rate of change of muscle length. The dynamic index was small and increased in direct proportion to the rate of stretch. Stimulation of selected filaments of the nerve produced a response from the spindle that was attributed to intrafusal contraction. A comparison of the response of the spindle to muscle stretch with the response during simultaneous stretch and stimulation of a motor filament revealed two distinct types of behaviour. In the first, a dynamic effect, motor stimulation greatly increased the response of the spindle to the velocity component of stretch. Other filaments had a static action: an increase in firing of the spindle with the muscle at constant length, but little change in the response to the velocity component of stretch. Stimulation of up to 7 different filaments produced an effect on a spindle. When the motor effects for a given spindle could be clearly characterised, they were all static or all dynamic. Both static and dynamic effects on the one spindle were seen only rarely.

Action Potentials↗
PubMed1975

Responses of tendon organs in a lizard.

1. In the lizard Tiliqua the tendons of the caudo-femoralis muscle are supplied by a nerve which runs separately from the muscle nerve. 2. Recordings of afferent discharges in the tendon nerve revealed the presence in the tendon of stretch-sensitive mechanoreceptors which responded to both passive changes in limb position and to muscle contraction. 3. A preparation of the tendon and its nerve were dissected free of surrounding tissue and studied in isolation while recording the activity of single functional units. The minimum tension in the tendon necessary for a maintained response from a receptor lay in the range 5-35 g (mean 16 g) and the firing rates at these tensions were in the range 5-14 impulses/sec (mean 9 impulses/sec). 4. Receptors showed a steep increase in firing rate with increase in tension up to about 120 g. The firing rate 30 sec after the onset of a tension change did not exceed 40 impulses/sec. 5. During the tension change the receptor responded with a burst of impulses whose frequency depended on the velocity of stretch. With large, rapidly rising tension steps peak firing rates of up to 300 impulses/sec were observed. 6. Tension and length changes recorded during rapid tendon-stretches were very similar, with little sag in tension at the new length. The response of all units however continued to fall throughout the stretch. Some of the possible causes of this adaptation have been discussed.

Action Potentials↗
PubMed1975

Structure and innervation of extraocular muscles of Carassius.

The extraocular muscles of the carp Carassius contain two types of muscle fibre. Large white fibres have ribbon-shaped peripheral myofibrils and triads located at the Z line. Small red fibres, rich in mitochondria, have polygonal-shaped myofibrils and triads at the A-I junction. Silver- and cholinesterase-stained preparations show that the large fibres are innervated by axons which spiral around them and exhibit intense cholinesterase activity over long distances. Axons supplying small muscle fibres run across bundles of fibres, making one contact with each fibre. By electron microscopy the nerve endings on each fibre type appear identical, both having a smooth post-junctional muscle membrane. The differences in structure and innervation pattern of the two fibre types are discussed in relation to their possible functional roles.

Animals↗
PubMed1973

Morphological identification and intrafusal distribution of the endings of static fusimotor axons in the cat.

1. Tenuissimus muscles of the cat were prepared in which the motor innervation was reduced to a single gamma axon by cutting all the other motor axons and allowing them to degenerate during a period of 7-12 days. The function of the surviving gamma axon was then determined, and the distribution of its endings ascertained in teased, silver preparations.2. In the ten muscles successfully prepared the function of the surviving gamma axon was static and the motor innervation distributed to the spindles consisted of trail endings. The conduction velocities of the axons ranged from 33 to 48 m/sec.3. A detailed histological analysis was made of thirty spindles innervated by six of the surviving static axons.4. The six static axons distributed trail endings to both bag and chain muscle fibres in the poles of thirty spindles with about twice the frequency of supplying them to poles in which the distribution was restricted exclusively to one type of muscle fibre or the other.5. The density of trail innervation supplied to the bag fibres, in terms of the mean number of terminals per fibre, was typically from one and a half to twice that supplied to the chain fibres. On the other hand, whereas the number of bag fibres supplied with trail endings in a spindle pole was seldom more than one, the number of chain fibres innervated was usually two in a range of one to four.6. The possible effects that partial denervation might have had on the spindles are discussed, but it is concluded that they are unlikely to have affected the results.

Action Potentials↗
PubMed1973

The muscle spindles in slow and twitch skeletal muscle of the lizard.

1. Responses from stretch receptors, identified as muscle spindles, were recorded in filaments of the nerve supplying a twitch muscle, semimembranosus, and a slow muscle, semitendinosus in the lizard Tiliqua.2. While recording afferent discharges in one filament of the motor nerve, several adjacent filaments were each in turn stimulated repetitively until one was encountered which on stimulation produced a powerful increase in spindle firing. Such an effect of the motor stimulus was interpreted as resulting from intrafusal contraction. Any interference with spindle firing patterns from extrafusal contraction produced by the motor stimulation was removed by differentially blocking the contraction with the drug curare.3. Discharge patterns of spindles in response to a slow stretch of the muscle were compared with the response to the same stretch, but during repetitive stimulation of the motor nerve filament which produced an intrafusal contraction.4. At the initial length, the firing rate of spindles in the twitch muscle was greatly increased by the motor tetanus. There was little further increase in the response during and following stretch of the muscle.5. While the spindles in the slow muscle were only moderately excited by the motor tetanus at the initial length of the muscle, a large increase was recorded during the dynamic component of the stretch. At the new length, the steady-state firing continued at a rate well above that for the initial length.6. The effect of the motor tetanus on the response to stretch of muscle spindles in the slow muscle could be mimicked by adding succinyl choline (5 mug/ml.) to the perfusion solution. Spindles in the twitch muscle did not show a sustained sensitivity to the drug.7. It is suggested that while the different effects of motor stimulation on the responses to stretch of spindles in slow and twitch muscle can be explained by propositions based on the sliding filament theory of contraction, the sustained elevation, at the new length, of firing frequencies of spindles in slow muscle might require an additional explanation.

Action Potentials↗
PubMed1972

The effect of muscle length and rate of fusimotor stimulation on the frequency of discharge in primary endings from muscle spindles in the cat.

1. Responses from the primary endings of muscle spindles in the soleus muscle of the cat were recorded during repetitive fusimotor stimulation at a number of different muscle lengths.2. An increase in the rate of stimulation increased the size of both the peak and the plateau of the responses to stimulation of both static and dynamic fusimotor fibres.3. Responses, with the exception of the peak frequency of the discharge during dynamic fusimotor stimulation, increased in size on raising the muscle length up to maximum body length. The peak of the dynamic response reached its highest value at intermediate lengths.4. The effect of increasing stimulation rate and muscle length was to reduce both the latency and time to peak of fusimotor responses. The change in latency with muscle length was particularly dramatic at low stimulus rates.5. In an attempt to compare fusimotor responses with the behaviour of extrafusal muscle fibres, a model is proposed which consists of a mixture of extrafusal tension and rate of change of tension. This model could simulate the static fusimotor responses reported here.

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