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Biomedical subjects

S Grillner

Publications and source records attributed to S Grillner.

At least 217 records · Page 12Linked to original sources
PubMed1981

Peripheral feedback mechanisms acting on the central pattern generators for locomotion in fish and cat.

The feedback mechanisms taking part in the control of locomotion in cat and fish are reviewed, particularly with regard to position- and movement-related feedback. It is shown that in both fish and cat there is a powerful position-dependent negative feedback which will act only in the position range where the muscle activity normally changes, e.g., from extensor to flexor activity. In addition, there is positive feedback in the middle of the movement range which will act in certain conditions, e.g., to promote and maintain flexor activity during the flexion of the hind limb.

Animals↗
PubMed1980

The locomotion of the low spinal cat. I. Coordination within a hindlimb.

Kittens were subjected to a complete transection of the spinal cord (Th 10--12) 1--2 weeks after birth. A few days after the operation they could perform alternating limb movements and somewhat later walking movements with their hindlimbs on a treadmill. The stepcycle of the hindlimbs could be divided into a flexion phase (F) and a first (E1), second (E2) and third (E3) extension phase. The duration of the support phase decreased markedly with treadmill velocity while the swing phase decreased to a much smaller extent. The pattern of electromyographical activity in hip, knee, ankle and toe muscles during treadmill locomotion was very similar to that of the intact cat. This related to both the timing and the general shape of locomotor bursts. The extensor muscles were thus activated well before the placement of the foot and able to produce enough force to support the body. The propulsive thrust in each step was, however, decreased and the animals showed more severe deficits particularly in their equilibrium control. It is concluded, however, that neural networks in the spinal cord (with its peripheral inflow intact but without supraspinal influences) have the capacity to generate a specific and detailed locomotor pattern.

Animals↗
PubMed1980

The locomotion of the low spinal cat. II. Interlimb coordination.

The interaction of the two hindlimbs were investigated by an analysis of the muscular activity and the movements in 14 chronic spinal kittens during treadmill locomotion (i.e. in kittens subjected to a transection of the spinal cord (Th10--12)) one or two weeks after birth). At low speed the limbs were alternating (walk or trot). At higher they were activated more simultaneous, as during gallop. The two limbs could walk at different velocities, as during walking in a circle, when the two belts of the treadmill were driven at different speeds. The duration of the support phases was mainly influenced by the speed of the belt on which the limb was walking. The limbs could still maintain a common rhythm up to a two or three fold speed difference, as the flexion or the first extension phase of the limb walking on the "fast" belt was prolonged and the flexion phase of "slow limb" was shortened. At extreme speed differences the limb on the "fast belt" performed 2, 3 and even 4 steps during one stepcycle of the "slow limb". The placement of the feet was found to maintain the most stable relationship during alternating gaits at different speed differences. It is concluded that all phases of the step cycle are modifiable and that there are several mechanisms coordinating the limbs within the spinal cord.

Animals↗
PubMed1979

On the central generation of locomotion in the low spinal cat.

A central network of neurones in the spinal cord has been shown to produce a rhythmic motor output similar to locomotion after suppression of all afferent inflow. The experiments were performed mainly in acute spinal cats (th. 12), which had received DOPA i.v. and the monoamine oxidase inhibitor Nialamide. In some preparations all dorsal roots supplying the spinal cord were transected, in others phasic afferent activity was suppressed by curarization. The activity was recorded as neurograms from nerve filaments or as electromyograms. It is concluded that: 1. alternating activity between flexors and extensors of foot, ankel, knee, and hip of one limb can still occur 2. the duration of the flexor discharges vary less with the cycle duration than the extensor discharges 3. different flexor muscles may retain individual patterns 4. the activity at different joints can be dissociated 5. there is at least one network for each limb. 6. the coordination between the two hindlimbs can be alternating as in walking or be more closely spaced as in galloping 7. alternating activity in the ankle remains even when only segments L6, L7 and S1 are intact.

Afferent Pathways↗
PubMed1978

On the initiation of the swing phase of locomotion in chronic spinal cats.

In chronic spinal cats walking with the hind legs on a treadmill, one limb can be stopped by holding the paw while the other limb continues to walk. If the held limb is slowly brought backwards at one point the limb flexes and continues walking. It was found that the hip position at which the leg lifts off during such reaction is very close to the hip angle at the initiation of swing during locomotion. Similar findings were obtained by extending only the femur. The hand-held limb tends to initiate lift-off during the midstance or the midswing of the contralateral limb step cycle. It is concluded that hip position and the contralateral step cycle phase are two important factors determining the initiation of swing in one leg.

Action Potentials↗
PubMed1978

Intra-abdominal pressure changes during natural movements in man.

The weight of the upper part of the trunk is partially transmitted to the pelvis via the vertebral column. If the muscle walls around the abdominal cavity are contracted, a high pressure can be generated within the cavity (greater than 200 mmHg). The abdominal space can them transmit part of weight to, e.g., the upper part of the body, Intra-abdominal pressure recordings have been performed during locomotion and other natural movements with intragastric pressure recordings. With each step, there is a phasic variation in pressure, with its peak coinciding with that of the peak vertical force exerted by the leg against the ground. The peak values increase progressively with the speed of walking/running up to a mean of 38 mmHg and with trough values of 16 mmHg. The phasic variations with each step is due to a phasic activation of the abdominal muscles, with an EMG activity starting 50 ms or more before foot contact. If an extra load is put on the back, the posture changes and at the highest speed of running the pressure values are significantly higher than without this additional load. After a jump down from a moderate height of 0.4 m, the average increase is 89 mmHg and can often exceed 100 mmHg. These pressure changes are large and will presumably act to unload the spine under the prevailing biomechanical conditions and, in addition, there will no doubt be an effect on the circulatory system.

Abdomen↗
PubMed1977

The adaptation of a reflex response to the ongoing phase of locomotion in fish.

The reflex response to stimulation of the tail fin has been studied in the swimming fish, by bilateral electromyographical (EMG) recordings in several segments along the body. The response varies with the phase of swimming. When the muscles on one side (segment) are active, a large response will occur on this side but no response on the contralateral side at the same level. When the other side becomes active an identical stimulus will cause an activation of this side but no response on the previously active side. When the movements were filmed a powerful mechanical effect was demonstrated with an augmentation of the ongoing movement, that would result in an instantaneous increase in speed. The stimulus causes in addition a shortening of the duration of the swimming cycle and its components. Most of the results were obtained on spinal dogfish, which also exhibits spontaneous locomotion after a spinal transection. Mainly electrical bipolar stimulation of the tail fin was used. Identical stimuli applied in different phases on an ongoing movement, thus give a reflex response that changes dramatically with the phase of the movement. This phase dependent reflex reversal is functionally meaningful; it is fast and due to spinal mechanisms.

Adaptation, Physiological↗
PubMed1977

Phasic gain control of reflexes from the dorsum of the paw during spinal locomotion.

In chronic spinal cats walking with their hindlimbs on a treadmill belt, tactile stimuli were applied to the dorsum of the paw during various phases of the step cycle. A stimulation during the swing phase evoked a flexion response with a concomitant crossed extension, whereas in stance it induced an increased ipsilateral extension. EMG-recordings show short latency reflex responses in flexors and extensors, respectively. The responses are organized such that latencies of knee muscles are shorter than those of ankle and hip muscles. The movements induced by the stimulations appear to be very meaningful during normal conditions in compensating for any unpredicted obstacle disturbing the movement of the paw during locomotion. Responses during forward flexion and during the support phase are well adapted to the ongoing locomotor activity and do not influence the interlimb coordination whereas a stimulation when the foot approaches the ground after the end of flexion disturbs the regular alternating pattern. Different possible mechanisms underlying this phase-dependent reflex reversal are discussed.

Animals↗
PubMed1976

Central generation of locomotion in the spinal dogfish.

After a transection of the spinal cord a dogfish performs continuous swimming movements with a phase lag between adjacent segments. It is shown that the intersegmental coordination remains after an extensive dorsal root transection as well as after curarization. In the former case the motor activity was recorded electromyographically in several segments along the body, in the latter case the intersegmental coordination was evaluated by recording the efferent activity in different ventral roots along the body. It was concluded that a spinal central network can account for the phase lag observed between successive segments during swimming. It was also shown that the efferent activity from parts of the spinal cord with no dorsal roots intact could be influenced by peripheral stimuli such as pressure on the pelvic fins; this result suggests that some afferent fibres reach the spinal cord via the ventral roots.

Animals↗