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At least 991 records · Page 55Linked to original sources
PubMed2004

Critical points in the forelimb fictive locomotor cycle and motor coordination: evidence from the effects of tonic proprioceptive perturbations in the cat.

During locomotion, the limbs of one girdle must remain coordinated in different conditions. To understand the neural mechanisms underlying such coordination, tonic protraction/ retraction of one shoulder or tonic flexion/extension of one elbow was applied during fictive locomotion in high decerebrate and paralyzed cats. We studied bilateral changes in the timing and amplitude characteristics of electroneurographic (ENG) muscle nerve bursts of cleidobrachialis (ClB, elbow flexor and shoulder protractor) and the two heads of triceps (long, TriLo, elbow extensor and shoulder retractor and lateral, TriLa, elbow extensor). Perturbations induced bilateral changes in amplitude and timing of ENG bursts that were anchored on certain critical points in the cycle. These critical points could correspond to morphological characteristics within the bursts or to bilateral onsets or offsets of ENG bursts. For instance, in response to shoulder and elbow perturbations, burst changes occur in relation to a fixed point, labeled point C, occurring at about mid-extensor burst and corresponding to a simultaneous abrupt increase in TriLa amplitude and a decrease in amplitude of contralateral ClB. At a point labeled B, corresponding to about mid-flexor burst, ClB amplitude increases above control with elbow extension or starts decreasing with shoulder protraction. Although cycle reorganization is specific for each type of tonic perturbation, a common feature is that the changes in burst duration are achieved through discrete shifts between consecutive critical points. It is postulated that coordination may be based on a discrete temporal cycle structure along which critical points delimiting burst components are shifted.

Animals↗
PubMed1982

Specificity of electrical coupling among neurons innervating forelimb muscles of the adult bullfrog.

1. The specificity of electrical connections among sensory fibers and motoneurons in the bullfrog's spinal cord was studied by recording intracellularly from brachial motoneurons. Synaptic potentials evoked by stimulation of individual muscle nerves were recorded in normal and reduced-calcium solutions and after acute section of dorsal or ventral roots. 2. Homonymous motoneurons are electrically coupled. After the dorsal roots were cut to abolish sensory input, short-latency potentials were almost always evoked anti-dromically in a motoneuron by stimulation of its own muscle nerve but rarely by stimulation of nerves innervating other muscles. These potentials differed from chemically mediated synaptic potentials in this preparation; they had a shorter latency and remained after perfusion with reduced-calcium solutions. This evidence suggests that they are mediated electrically. 3. Some motoneurons that innervate functionally equivalent muscles are electrically coupled. Approximately two-thirds of the motoneurons innervating the internal or external heads of the triceps muscles received coupling potentials on stimulation of the other nerve, although never on stimulation of the heteronymous, medial, triceps nerve. 4. The monosynaptic potentials evoked by muscle sensory afferents in motoneurons often have both electrical and chemical components. The electrical component occurred with short delay and persisted in reduced-calcium solutions. The chemical component occurred 1.5-2.0 ms later, at 14 degrees C, and was abolished by reducing calcium in the bathing solution. Muscle sensory afferents make these mixed synapses on homonymous, heteronymous, and other motoneurons.

Animals↗
PubMed1994

Synaptic plasticity in the thalamo-cortical pathway as one of the neurobiological correlates of forelimb flexion conditioning: electrophysiological investigation in the cat.

1. In a previous study, using a chronic cat preparation subjected to an associative conditioning procedure, we described the plasticity of the thalamo-cortical pathway by qualitatively and quantitatively analyzing the motor responses induced by stimulating each of the relays on the cerebello-thalamo-cortical pathway. In the present study, it was proposed to analyze the effects on the synapses located between thalamic endings and cortical neurones, using a twofold behavioral and electrophysiological approach, with a view to correlating the patterns of synaptic plasticity with the changes in the motor responses recorded. 2. For this purpose, a reduced, functionally organized sensorimotor circuit, which can be taken to be a neuronal analog of associative conditioning, was studied in an awake chronic animal preparation. This circuit was defined on the basis of the sites at which conditioned (CS) and unconditioned stimuli (UCS) were applied: the CS was applied at a site on the cerebellar interpositus nucleus which activated the forepaw musculature so as to induce flexion movements and the UCS was applied to the skin of the distal part of that paw so as to induce reflex flexion movements. By repetitively activating the central nervous pathways by the associated CS and UCS according to a predefined temporal pattern, the efficiency of the thalamo-cortical pathway's contribution to the movement production was enhanced, and its capacity to convey the cerebellar inputs to neurons in the motor cortex increased. 3. The associative nature of the conditioning was tested using previously established criteria. The setting up of motor and central changes in response to the repetitive presentation of paired CS and UCS, the fact that these changes were reversible because they could be abolished by applying extinction procedures, and the consistency of their occurrence whenever the CS was applied repeatedly alone for several days to naive animals, all showed that the stimuli of both kinds (CS and UCS) had to be applied together for the plasticity of the thalamo-cortical pathway to be expressed. 4. By determining whether the waves constituting the cerebello-cortical responses were excitatory or inhibitory, the nature of the changes in the transmission of the cerebellar impulses to neurons in the motor cortex was established.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Does postbrachial deafferentation modify the cortical responses to forelimb stimulation?

Epidural evoked potential recordings were performed in four macaque monkeys on peripheral nerve stimulation, before and after spinal transection, to evaluate whether the Schiff-Sherrington phenomenon could be demonstrated in this manner. No change in evoked potentials from upper extremity stimulation was seen after mid-thoracic spinal cord transection.

Afferent Pathways↗
PubMed1993

Determination of the center of pressure of the hoofs of the forelimbs of horses standing on a flat level surface.

The pressure exerted on a flat level surface by recently trimmed, unshod hoofs of the front limbs of 23 sound, adult horses was measured using pressure-sensitive film and a specially built cassette. The horses were tranquilized and stood with one foot on the 2.9-cm-thick cassette and the other on a block of equal height. The hoofs were observed for motion during the measurement, and the developed film was examined for improper alignment of the film or slipping of the hoof. The center of pressure was located using the method of weighted proportions of Barrey. This static measurement system with a long measurement time and the number of measurements reduced the influence of variables inherent in the horses' behavior and the measuring system. The calculated point was recorded as falling medial to, lateral to or on a line bisecting the central sulcus of the frog. In the dorsal to palmar orientation the point was classified with reference to a line drawn halfway between the most dorsal and the most palmar mark on the film. Forty-six percent of the calculated centers of pressure were located in the medial heel area. Binomial analysis for large samples indicates that this was a significant variation from a random distribution. Seventy-six percent of the centers were located in or on the borders of the medial heel.

Animals↗
PubMed1991

Multivariate comparison of the forelimb between stump-tailed and rhesus macaques.

Rhesus macaques and stump-tailed macaques are sympatric in western Yunnan (China), coexisting or occupying habitats that show little difference. This paper tests hypotheses based on theoretical expectation from the differing biomechanical demands of terrestrial and arboreal quadrupedalism in stump-tailed macaques and rhesus macaques, respectively. Individuals of these two macaque taxa were markedly separated by the first two principal components and discriminant analyses based on 18 variables of the upper limb. The rhesus macaques appear to be more adapted for arboreal quadruped habits because of elongation of the clavicle and forearm, a larger humeral head and greater midshaft sagittal diameters of the radius and ulna.

Analysis of Variance↗