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Biomedical subjects

J C Eccles

Publications and source records attributed to J C Eccles.

At least 37 records · Page 2Linked to original sources
PubMed1981

Physiology of motor control in man.

The physiology of motor control is considered in hierarchical terms. In that way it is possible to gain insight into the complex superimposed systems of motor control. In the execution of a voluntary movement the neural machinery is called into operation at all of the hierarchical levels: (1) the motor unit; (2) spinal reflex mechanisms; (3) brain stem mechanisms; (4) cerebellar vermis controls; cerebrocerebellar controls, (5) via the pars intermedia and (6) via the cerebellar hemispheres and also of the basal ganglia. At level 6 there is design for reverberatory loop operation within the association cortex and with the subcortical structures, which gives opportunity for preprogramming movements by motor memories. This is especially important for ballistic movements that are too fast for updating by feedback from the periphery. Reverberatory loop operation both within the neocortex and with cortico-subcortical circuits presumably is occurring during the readiness potential preceding a voluntary movement.

Animals↗
PubMed1979

Synaptic plasticity.

Synaptic plasticity is manifested by long-lasting changes in synaptic potency. Increased potency is of special importance in relation to the neural basis of memory. Even mild repetitive stimulation evokes large and prolonged potentiations of hippocampal synapses, as is revealed by electrical recording either in vivo or in vitro. More importantly there is a matching hypertrophy of the synaptic spines on the dendrites of hippocampal granule cells, as is shown by most convincing electronmicrographs. The increase is to about 40% some 2 h after a mild stimulation (900 impulses) and there was relatively little decline by 23 h. There is brief reference to the metabolic processes that could be involved in this plastic response.

Animals↗
PubMed1976

Medial reticular and perihypoglossal neurons projecting to cerebellum.

Almost 10% of neurons in the medial reticular nucleus or adjacent thereto were invaded antidromically in response to stimulation of the fastigial and interpositus nuclei. The fraction was 77/835 for the bulbar and caudal pontine levels, but 0/167 for rostral pontine levels. The mahority, 49, of the neurons projecting to the cerebellum were superficially located in the region of the perihypoglossal nucleus, but 23 were scattered through the medial reticular nucleus, being 2.5-5.0 mm below the bulbopontine dorsum. Both classes of cerebellopetal neurons had a similar range of antidromic latencies, usually from 0.8 to 2.0 ms, but some were ober 3 ms. Both classes responded to volleys from limb nerves and inputs from cutaneous mechanoreceptors, with ranges of excitatory and inhibitory latencies that were similar to those for other medial reticular neurons. It is conjectured that the axonal projection is primarily to the cerebellar cortex and that the branches to the nuclei are often slender, hence the long antidromic latencies; 31 of 59 neurons tested projected to cerebellar nuclei on both sides, often with a considerable latency differential. Rarely, there were also axonal branches projecting up the central tegmental tract. The experimental findings are in very good accord with the anatomical descriptions of Brodal and associates (4, 5, 8, 19). It is suggested that the paramedian reticular and the perihypoglossal nuclei may provide a background excitatory input to the interpositus nuclei.

Animals↗
PubMed1976

Topographic studies on medial reticular nucleus.

Several distinct classes of neurons have been identified in the medial reticular nucleus of the medulla and pons and in proximity thereto. Neurons projecting down the spinal cord comprised the principal class with two subclasses according as the neurons did or did not receive monosynaptic inputs from the fastigial nuclei of the cerebellum. Two other classes were recognized accordings as they projected to the cerebellum or rostrally to the mesencephalon. Topographic planar maps giving the location of these neurons have been constructed by exploring the nucleus with series of microelectrode tracks in parasagittal or in transverse planes. The different classes of neurons were not arranged in large discrete nuclei. In part they appeared to be randomly distributed, but many colonies of one or another class of neurons could be recognized with 3-11 neurons in zones with dimensions of a millimeter or so. Because of the limitations of sampling by microelectrode tracks at spacings of 0.5 mm, single colonies might have an actual population of 100 or more. Many of the class of neurons projecting to the cerebellum were in the region of the perihypoglossal nucleus. However, almost as many were located deep in the medial reticular nucleus. None was found at the pontine level. Reticulospinal neurons with fast axonal conduction velocities tended to be located dorsally to those with slow velocities. Correlation with the findings of Ito et al. leads to the conjecture that the neurons with fast axons are excitatory, while those with slow axons are primary inhibitory neurons. There is a brief reference to the problems raised by the admixture of the various neuronal classes, there being discrete colonies immersed in a scattered arrangement of all classes.

Animals↗
PubMed1975

The differential effect of cooling on responses of cerebellar cortex.

1. Responses of the cerebellar cortex in anaesthetized cats were evoked by mossy fibre and/or climbing fibre inputs, and the effects of graded cooling of the cerebellar cortex were investigated. Cooling was applied either globally by flooding the exposed cortex with cooled Ringer Locke, or in later experiments locally be passing cooled fluid through a silver tube in contact with the cerebellar cortex. The cortical temperature was continuously monitored by a thermistor inserted to a depth of 0.5 mm close to the recording site. 2. In the granular layer the cooling caused a large increase in the diphasic P1N1 wave generated by the afferent mossy fibre volley. The waves generated by synaptic excitation and discharge of granule cells, N2P2, were not diminished until the temperature fell towards 20 degrees C. In contrast the N3 wave of the molecular layer was largest with cooling in the range of 35 to 25 degrees C, often several times larger than at 38 to 40 degrees C. Associated with the enhanced N3 wave there was an enhanced N4 wave, which indicates an increased discharge by Purkynĕ cells. 3. Climbing fibre inputs generate a negative field potential in the molecular layer due to the powerful excitation of Purkynĕ cells. In contrast to the N3 potential this climbing fibre wave was largest at the higher temperatures 35-40 degrees C and declined progressively with cooling, being usually suppressed at moderate coolings of 31-27 degrees C. Intracellular recording revealed that the diminution was due both to the elimination of all but the first impulses of the normal burst discharge of the climbing fibre impulses and to the diminution of the synaptic excitation of a single climbing fibre impulse. 4. It is shown that the negative potentials produced in the molecular layer by combinations of mossy fibre and climbing fibre inputs can be very effectively distinguished by this differential effect of cooling. 5. The effects of cooling even to a severe level are immediately recoverable on warming. Repeated cooling has no untoward effects and there is no sign of the hysteresis reported for the cuneate nucleus. 6. There is a discussion of the factors that could cause cooling to differentiate between the actions of the mossy fibre and climbing fibre impulses on Purkynĕ cells.

Action Potentials↗
PubMed1975

Reticulospinal neurons with and without monosynaptic inputs from cerebellar nuclei.

An account is given of the responses of 557 medial reticular neurons with axons projecting down the spinal cord. All 30 experiments were on decerebrated unanesthetized cats paralyzed by Flaxedil. Recording from single neurons was by extracellular glass microelectrodes. Identification was first by location (confirmed by subsequent histology) in the medial reticular nucleus of medulla or pons, and second by antidromic activation from cord stimulation at C2 and L2 segmental levels. Axonal conduction velocities were calculated from the latency differential between L2 and C2 antidromic responses, and were usually in the range of 90-140 m/s; but about 25% were slower, ranging down to 30 m/s. Stimulation by electrodes in the ipsilateral and contralateral fastigial nuclei differentiated reticulospinal neurons into two classes according to whether they did or did not receive monosynaptic inputs, the respective populations of fully investigated neurons being 270 and 174. The fastigioreticular neurons were distinguished by a higher background frequency with mean values of 28 as against 15/s. There were also significant diffences in both the excitatory and inhibitory responses to afferent volleys from forelimb and hindlimb nerves. Comparison of the respective latency histograms showed that the responses of neurons with a fastigial input had an excess of latencies in the ranges that can be correlated with the latency histograms observed for fastigial responses. Thus, there is evidence for the effectiveness of the fastigial input and so for the pathway with monosynaptic linkage: Purkinje cells of cerebellar vermis yields fastigial neurons yields medial reticular neurons projecting down the spinal cord. Adequate stimulation of cutaneous receptors by pad taps and air-jet stimulation of hairy skin in a disppointingly small action when compared with fastigical responses. Explanations of this deficiency are suggested. Another discrpancy from the fastigial responses is that the medial reticular neurons have much wider receptive fields with little discrimination between ipsilateral and contralateral and between forelimb and hindlimb. Stimulation of the ipsilateral tegmental tract was tested on 183 reticulospinal neurons, 112 being with fastigial inputs. In about half there was a powerful monosynaptic excitation, which would identify such neurons as being on the pathway from mesencephalic and diencephalic centers to the spinal cord. There is a general discussion of transmission across successive synaptic relays, where specificity is sacrificed to integration.

Action Potentials↗