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  • Man  (4)
  • Cortico-cortical relationships  (1)
  • Ib projections  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Sensitivity of monosynaptic test reflexes to facilitation and inhibition as a function of the test reflex size: a study in man and the cat (1990)
    Springer
    Experimental brain research 81 (1990), S. 35-45 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Spinal cord ; Spinal reflexes ; Monosynaptic reflex ; Motor control ; Man ; Cat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In parallel experiments on humans and in the cat it was investigated how the sensitivity of monosynaptic test reflexes to facilitation and inhibition varies as a function of the size of the control test reflex itself. In man the monosynaptic reflex (the Hoffmann reflex) was evoked in either the soleus muscle (by stimulation of the tibial nerve) or the quadriceps muscle (by stimulation of the femoral nerve). In the decerebrate cat monosynaptic reflexes were recorded from the nerves to soleus and medial gastrocnemius muscles; they were evoked by stimulation of the proximal ends of the sectioned L7 and S1 dorsal roots. Various excitatory and inhibitory spinal reflex pathways were used for conditioning the test reflexes (e.g. monosynaptic Ia excitation, disynaptic reciprocal inhibition, cutaneous inhibition, recurrent inhibition, presynaptic inhibition of the Ia fibres mediating the test reflex). It was shown that the additional number of motoneurones recruited in a monosynaptic test reflex by a constant excitatory conditioning stimulus was very much dependent on the size of the test reflex itself. This dependency had the same characteristic pattern whatever the conditioning stimulus. With increasing size of the test reflex the number of additionally recruited motoneurones first increased, then reached a peak (or plateau) and finally decreased. A similar relation was also seen with inhibitory conditioning stimuli. The basic physiological factors responsible for these findings are discussed. Finally, the implications for the interpretation of experiments in man with the H-reflex technique are considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00230098
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  • 2
    Digitale Medien
    Digitale Medien
    Influence of remote targets on directionality of striate neurons in rabbits (1992)
    Springer
    Experimental brain research 89 (1992), S. 531-539 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Visual cortex ; Response to motion ; Direction index (DI) ; Cortico-cortical relationships ; Rabbits
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The described investigations study the influence of additional targets located well outside the classical receptive field on responses to motion of cortical cells in rabbits. Animals are anesthetized and prepared for acute single cells recordings in a conventional manner. The interactions between remote targets and central stimuli are abolished with microinjections of lidocaine hydrochloride or GABA at the site excited by remote stimuli. Results show that responses to motion of cortical cells are particularly sensitive to these manipulations. Although supplementary targets fail to influence spontaneous activity of all cells, they do influence responses to motion. Overall, the directionality indices (DI) declined. (53 to 45.) This decline may express itself either by a decrease of responses in the preferred direction or an enhancement of responses in the non-preferred direction or both. By contrast, responses to stationary stimuli are unaffected by additional targets in the visual field. Globally, cells whose directionality index was superior to 50% were significantly more affected then cells whose DI was less than 50%. This result suggests that similarly to cats, the directionality of cells in the striate cortex rests on a very fragile convergence of excitatory and inhibitory influences.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00229878
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  • 3
    Digitale Medien
    Digitale Medien
    Pattern of group I fibre projections from ankle flexor and extensor muscles in man (1981)
    Springer
    Experimental brain research 42 (1981), S. 337-350 
    Details
    ISSN: 1432-1106
    Schlagwort(e): H-reflex ; Ia projections ; Ib projections ; Man
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Variations in the H-reflex of soleus, tibialis anterior, quadriceps and short head of biceps femoris muscles were studied in normal man, preceded by a conditioning stimulus applied to either gastrocnemius medialis, the inferior branch of soleus or the common peroneal nerve. The observed variations were evoked by low threshold afferents, had a very short latency suggesting oligosynaptic linkage and disappeared during a selective ischaemic blockade of group I fibres; they were therefore regarded as due to group I fibre stimulation. Biphasic variations were observed in almost all cases: evidence is presented that the early low threshold effects, facilitatory for synergistic and inhibitory for antagonistic motoneurone pools, are due to stimulation of Ia fibres, while the subsequent opposite effects which had a slightly higher threshold are Ib in origin. Even though the pattern of projections of group I fibres from ankle flexors and extensors is qualitatively the same in normal man as in the spinal cat, large quantitative differences are observed: in normal man the effects of group I fibres from ankle flexors and extensors upon close synergistic and direct antagonistic motoneurone pools are weak, and often negligible, whereas they are extremely potent upon quadriceps motoneurones.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00237499
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  • 4
    Digitale Medien
    Digitale Medien
    Cutaneous depression of Ib reflex pathways to motoneurones in man (1981)
    Springer
    Experimental brain research 42 (1981), S. 351-361 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Cutaneous afferents ; Ib effects ; Locomotion ; Man
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Variations in the H-reflex of soleus (Sol), quadriceps (Q) and short head of biceps femoris (Bi) muscles in normal man were used to investigate the effect of volleys in low threshold cutaneous afferents from the ipsilateral limb on transmission of Ib effects from ankle and Q muscles to these different motoneurone (MN) pools. Stimulation of cutaneous afferents from the foot sole and the toes (but not from the thigh, knee or calf), which did not modify the size of the test reflexes when applied alone, strongly depressed Ib reflex pathways to MNs supplying muscles operating at the knee. The very brief central latency of this depression suggests that tactile cutaneous afferents from the foot have oligosynaptic spinal connexions with the interneurones intercalated in the Ib pathways to MNs. The same cutaneous stimuli did not at all modify Ib inhibition of Sol MNs from triceps surae. These findings are discussed with regard to the role of the different muscles in human locomotion. It is suggested that during the stance phase of heel bipedal locomotion, the cutaneous depression of Ib reflex pathways to MNs supplying muscles operating at the knee might operate in association with the strong Ia connexions from ankle to knee muscles described in the previous paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00237500
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  • 5
    Digitale Medien
    Digitale Medien
    Role of Ia afferents in the soleus motoneurones inhibition during a tibialis anterior voluntary contraction in man (1977)
    Springer
    Experimental brain research 27 (1977), S. 509-522 
    Details
    ISSN: 1432-1106
    Schlagwort(e): Man ; H-reflex ; Reciprocal Ia inhibition ; Voluntary contraction ; Gamma loop
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Variations of the soleus H-reflex were studied during voluntary isometric or anisometric contractions of the tibialis anterior in man. At the onset of isometric contractions there was a weak inhibition of the soleus H-reflex, which was not related to the force of the tibialis anterior contraction. 110 msec after the onset of the EMG activity, the inhibition became secondarily more marked and was then related to the force of the contraction. This secondary potentiation of the H-reflex inhibition is brought about by group I fibres activity, since it was markedly reduced during is-chemia of the leg. It persisted during local muscular fatigue, this indicating that Ib fibres from tibialis anterior are not involved and that, by the process of elimination, group Ia fibres must be responsible for the supplementary secondary inhibition. It is concluded that the early inhibition is only due to suprasegmental activity, whereas during the secondary part of the inhibition there is a supplementary inhibitory action brought about by Ia fibres from tibialis anterior. The secondary potentiation of the inhibition is therefore likely to be produced via the gamma loop.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00239040
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