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Biomedical subjects

R A Westerman

Publications and source records attributed to R A Westerman.

At least 55 records · Page 3Linked to original sources
PubMed1977

Ia afferent activity during a variety of voluntary movements in the cat.

1. Implanted dorsal root electrodes were used to record discharge trains of single spindle primary afferents (Ia's) of the cat's hind limb during different types of movement.2. The length of the ipsilateral ankle extensors was continuously monitored by an implanted length gauge. Length changes occurring during active stepping were subsequently passively reproduced during brief anaesthesia.3. A comparison of the Ia responses in active and simulated step cycles revealed that moderate fusimotor drive to ankle extensor spindles probably occurred mainly, if not exclusively, during the E(1), E(2) and E(3) phases of active stepping.4. A temporal advance in the Ia response to passive stretching in the F-phase was attributed to the after-effects of fusimotor activity in the extension phases.5. Light thrust applied to the animal's back evoked a potent fusimotor response. This load compensation effect may provide an explanation for the apparently higher degree of alpha-gamma co-activation seen in the mesencephalic locomotor preparation.6. Ankle extensor Ia discharge decreased during falls, despite an increase in extensor e.m.g. This is seen as a clear example of independent alpha and gamma control.7. Placing reactions during walking were consistent with the notion that cutaneous inputs dominate over proprioceptive inputs in these movements.8. alpha and Ia discharge during paw-shaking showed many of the characteristics of that in decerebrate and spastic clonus. The present results suggest that movements resembling clonus may be part of the animal's normal repertoire.9. Isometric co-contraction of agonists and antagonists was found to involve alpha-gamma co-activation.10. Hamstring Ia discharge behaviour during stepping further highlighted the increases in firing rate which normally occur during passive muscle stretching in ;pre-programmed' movements.

Action Potentials↗
PubMed1977

Reflexes in cat ankle muscles after landing from falls.

1. Electrical activity and length of ankle muscles were recorded by telemetry during free fall and landing in cats. 2. After foot contact, there was a delay in onset of stretch of ankle extensors of between 8 and 11 ms. High-speed cinematography showed the delay to be associated with rapid initial dorsiflexion of the toes. 3. Electromyograms (e.m.g.) from lateral gastrocnemius increased in amplitude prior to landing. An early depression of lateral gastrocnemius e.m.g. commenced at 8 ms after foot contact, and was followed by a large peak of activity commencing some 8 ms after the first increase in lateral gastrocnemius length. 4. Local anaesthesia of the plantar cushion did not alter this pattern of response. 5. The early inhibition of lateral gastrocnemius was attributed to the action on lateral gastrocnemius motoneurones of non-cutaneous afferents responding to the initial toe dorsiflexion. Additional autogenetic inhibition may also have contributed. 6. The subsequent peak of e.m.g. was at a latenty consistent with a rapid stretch reflex, and occurred soon enough for the resulting active tension to contribute significantly to the extensor force during body deceleration.

Animals↗
PubMed1976

Discharges of single hindlimb afferents in the freely moving cat.

1. Implanted semimicroelectrodes were used to record single afferent fiber discharges from L7 dorsal roots during unrestrained walking in the conscious cat. 2. A series of tests were used to identify an afferent during a short period of anesthesia following each recording session. The majority of afferents were from muscle spindle primary endings in hindlimb muscles. 3. Ankle extensor spindle primaries generally showed their highest firing rates during that phase of stepping in which they were passively stretched. During active muscle contraction there was evidence of fusimotor drive, although this was not usually sufficient to entirely overcome the unloading effect of rapid muscle shortening. The variability of firing rate from cycle to cycle was considerably greater for the phase of active muscle contraction. The EMG response to brisk stretches of the ankle extensor muscle indicated a rapid (disynaptic or trisynaptic) reflex arc in the conscious animal. 4. Knee flexor spindle primaries showed similarly higher firing rates during passive muscle stretching in the step cycle. The shorter periods of presumed alpha-gamma coactivation corresponded to the much more phasic role of these muscles in stepping. 5. Tendon organs in the physiological extensors of the toes were mainly active during stance, although some discharges were usually seen during the swing phase. It is suggested that previous experiments on mesencephalic preparations may have led to an exaggerated view of the degree of alpha-gamma coactivation during normal stepping movements.

Action Potentials↗
PubMed1974

The properties of motor units in a fast and a slow twitch muscle during post-natal development in the kitten.

1. Motor units were functionally isolated from a fast and a slow twitch muscle of kittens: flexor digitorum longus (FDL) and soleus. Both muscles were examined in two groups: one aged about 2 weeks and the other 6 weeks.2. A clear division into alpha and gamma axons could be made. The mean conduction velocity of alpha axons from FDL was higher than that of soleus axons at both ages.3. Tetanic tensions were expressed as a percentage of whole muscle tension. The distributions of motor unit tensions were symmetrical in soleus muscles but were skewed towards large values in FDL. In both types of muscle the scatter of motor unit tensions was greater at 2 weeks than at 6, the mean percentage tension also fell with age.4. The motor unit twitch times to peak were symmetrically distributed in soleus but skewed towards large values in FDL. The variance was less than in adults.5. Motor unit axonal conduction velocity was related to tetanic tension and twitch speed. The relationship between twitch time to peak and the ratio of twitch to tetanic tension varied with age but was not seen so clearly.

Action Potentials↗
PubMed1973

Polyneuronal innervation of kitten skeletal muscle.

1. Isometric contractions of kitten soleus and flexor hallucis longus (FHL) muscles have been examined for evidence of polyneuronal innervation. The sum of tetanic tensions of two almost equal divisions of the ventral roots was greater than the tetanic tension elicited by stimulating both the divisions simultaneously. The difference was large in kittens aged about 3 days, was less at 2 weeks and was small or absent at 6 weeks.2. A tetanus elicited from one division of the ventral root potentiated a twitch elicited from the other root division. The time course of this potentiation was similar to that of post-tetanic potentiation induced from the same root from which the twitch was elicited.3. It is concluded that polyneuronal innervation exists in the kitten limb muscles.4. The observed degree of tension excess was less if the divisions of the root were not equal. The observations were compatible with a model which assumed a random distribution of nerve axons to the muscle fibres.

Animals↗
PubMed1973

Isometric contractions of motor units in a fast twitch muscle of the cat.

1. Isosmetric contractions of cat flexor digitorum longus whole muscles and of functionally isolated motor units have been measured under conditions similar to those used by Buller & Lewis (1965a).2. Motor unit twitch time to peak was inversely related to axonal conduction velocity. The logarithm of tetanic tension was directly related to conduction velocity. These relationships suggest that each motoneurone has an influence on the muscle fibres which it innervates.3. The ratio of twitch to tetanic tension was directly related to the time to peak of the motor unit. This fact might be explained by variation between motor units of the duration of ;active state'.4. The muscle length at which tension was maximal varied between motor units and the optima were found over the range of muscle lengths which could occur in the body. Slow motor units had longer optimal lengths.5. The sample of motor units was considered to be unbiased because the distribution of axon conduction velocities was compatible with reported motor fibre diameter spectra of the muscle nerve. The mean motor unit tetanic tension gave a reasonable estimate of the number of alpha-motor axons in the muscle nerve. Twitch tensions gave a value that was 40% higher.6. Motor unit and whole muscle data were in good agreement for length-tetanus tension curves, for times to peak and for twitch-tetanus ratios at long muscle lengths.

Action Potentials↗