What is a long-loop reflex?

What is a retentive- wave physiological reaction?A rapid offer of a voluntarily contracting musclemanbuilderman evokes electromyographic (EMG) repartees at various latencies, as described by press, K. McCloskey, D. (1985). Response rotational response time measures the season delay amidst a perturbation and response, the response is typically great in a demoralise than a jolt as plunge by Lee and Tatton (1975) who as well as proposed that on that point are typically 3 responses to a muscle grasp namely M1, M2 and M3. The first, M1, represents the short latency driven monosynaptic spinal stretch automatic involving primary afferents. M2 represents the delayed response agree to the, perhaps transcortical, tenacious loop instinctive reflexive responseive response and M3 represents the latency for a unpaid worker response arbitrate by the cerebellum. These 3 distinct responses sens be displayed graphically, as appearingn in figure 1. From analyzing figure 1 we support see that, using the terminology introduced by Lee Tatton (1985), M1 is the response seen about 45-60ms after the perturbation, M2 represents the increase in EMG performance 60-90ms after the perturbation and the increase in EMG activity between a latency of 90-110ms is termed M3. Any response with a latency of greater than 110ms is a intended response and is non considered to be a reflex response. These findings eat up been widely accepted and are frequently cited in later studies, for example in the account by Thilmann, A. F., Schwartz, M., Topper, R. Fellows, S.J. and Noth, J. (1991). Suminski, A.J., Rao, S.M., Mosier, K.M. and Scheidt, R.A. (2007) made a similar discovery finding short latency responses arising from monosynaptic reflexes, consistent with the latency of the M1 response. Petersen, N., Christensen, L., Morita, H., Sinkjr, T. and Nielsen, J. (1998) showed that ankle dorsiflexors typically show an M3 response. More interestingly, this paper als o claims that the M2 response in the upper offshoot seems to correspond with the M3 response in the lower tree branchs.According to Corden,D.M., Lippold,O.C.J., Buchanan, K. and Norrington, C. (2000), the second parcel of the stretch reflex response, M2, was first discovered byHammond (1955) who believes that the long latency is due to the long loop reflex travelling the extra aloofness to the cortex. Hammond (1956) studied the EMG response in the bicep muscle and engraft that the earlier voluntary muscle activation in response to mechanical taps occur after 90-100ms which contradicts with the later findings from Lee Tatton (1975) who claim voluntary response represents latencies greater than 110ms. This raises the possibility that the long loop reflex may shed voluntary input. There create been m all studies carried out investigating if the long-loop reflex is intermediate by transcortical passs. Logically, one would expect reflexes to be a hard-wired response and volunt ary movement to allow variation in responses. However, Evarts and Fromm (1981) provides evidence suggesting variableness in their study of the wrist position. They reason that the long loop reflex gives a pathway for the force back cortex to initiate closed loop feedback control to the flexors and extensors of the wrist. It can be argued that long latency responses fit both(prenominal) voluntary and reflex criteria. Arthur Prochazka, for one example, similarlyk particular interest in ambiguity for the correct definition of a reflex. For instance, is it regarded as a response which get holds too quickly for the brain to notice, in which case, the M2 response would not be classed as a reflex since it is of long latency, or can it be delimitate as an involuntary response, in which case, the M2 response would be classed as a reflex since it occurs below the time threshold for it to be a voluntary action and occurs without any conscious awareness of the movement.If the long loop reflex goes via the force cortex, it could be yieldd voluntarily. A notable study by press McCloskey (1985) proposed that long loop reflexes are variable. This report studied the EMG responses of the flexor pollicis longus when a stretch was applied to the thumb-tip. The subject was required to initially have the muscle in a fixed, contracting state generating a unvaried force to give a baseline EMG to compare any turn outs found against. Their outcomes showed that, in the i virtuallytric holding task, all participants of the study could importantly alter the long latency responses to a stretch with some subjects arranging up to 95% decrement in EMG activity when instructed to allow go as opposed to resist. This indicates that motor set has an influence on the long loop reflex. Although the results for the isometric tracking, isotonic tracking and weight lifting tasks were slight convincing, they still showed the ability to decrease EMG activity when told to let go not re sist, contradicting previously claimed results from Marsden et al (1976) which suggested that prior commandments had no influence on EMG responses. When the thumb was anaesthetised, there was no evidence of abolishment of the long latency EMG response, contrary to what was noted by Marsden, Merton Morton (1971). However, Loo McCloskey (1985) found there was a fundamental linear correlation between the percentage increase in perceived heaviness and the percentage reduction in long latency reflex. This study provides us with defining results, however, not all subjects performed all tests and not all results were significant so there still remains room for debate. Long loop reflexes were found to be abolished or depressed by lesions to the pathways to and from the cerebral cortex, again, giving the view that the long loop reflex does take a transcortical pathway. Matthews, P. B., Farmer, S. F. Ingram, D. A. (1990) also concluded from their study on the localization of the stretch reflex of intrinsic hand muscles in a patient with mirror movements that long loop reflexes are mediated transcortically.The long loop reflex, it has been suggested, has a slower onset due to the hourlong driveway the reflex has to take. A monosynaptic spinal reflex arc is intelligibly a shorter path than the long loop reflex which, as some evidence shows, could go via the cortex. In a previous study, Hammond (1954) suggests the main executable explanations for the delayed M2 response could be due to the longer aflutter pathway it takes or that the neurones involved are slower conducting. Matthews (1984) discovered the same findings as he suggested in his paper that the M2 response is mediated by muscle spindle secondary endings which by nature are slower conducting afferents. Corna, S., Grasso, M., Nardone, A. and Schieppati, M. (1995) also concluded that M2 response in the ankle muscles is mediated by convention II afferents. Marsden, C., Merton, P., and Morton, H., (1976) argued that the long loop reflex could not be change by the motor set and hence concluded that the response was to a greater extent likely to be a reflex response than voluntarily response. However, as pointed out by Loo McCloskey (1985), the subjects of the experiment were in fact the researchers themselves, hence, the results may be bias because sub-consciously they are aware of the experiment and what is going to happen and already have a prediction of what they want to happen. Rothwell, Traub and Marsden (1980) also suggested that long loop reflexes are not variable. Gassel (1970) claims that long loop reflexes occur preponderantly with stimulation of cutaneous nerves or dorsal roots. To this end, Marsden et al. (1978) studied the stretch reflex response in the humane flexor pollicis longus, which when stimulated, results in fold of the thumb. If this muscle is stabilized, for example, fixed in plasticine, then cutaneous nerve activity can be detected.It is proposed that lon g loop reflexes going via the motor cortex, have become progressively more important in effective motor control of motor skills. There is an initial judgement of the required specialty of the muscle contractions needed before any specific movement. Any shift in the estimate will result in the activation of the muscle spindle receptors and will result in a corrective long loop reflex, which causes an appropriate change in the signals from the motor cortex, correcting the response of the movement. This happens with a latency of less than 50 msec. This is about 70msec for lower limbs. This corrective hire is automatic and unconscious. The pathways for 1a receptors up to the motor cortex and hence participation in long loop reflexes have been recognized in mammals such as the cat (Landgren, 1984). Clarac, F. (2005) suggests that the long loop reflexes play an important role in the adaptation of flexors and extensors and hence are useful in posture and movement. He also suggests that they are involved in the mechanisms for anticipating movement, which supports the evidence of a transcortical route since there is input from the brain.Shemmell, J., An, J.H. and Perreault, E.J. (2009) claim transcortical long-loop reflexes are useful in adding flexibleness to the human stretch reflex allowing adaptation to a wider range of operative tasks. They also highlight in their report that reflex sensitivity is change magnitude in unstable environments. This study also provides evidence supporting the transcortical route of the long loop reflex since, similar to the findings of Loo McCloskey (1985), if the subject was disposed instruction prior to the perturbation, the long-loop reflex provides the ability to achieve the desired result even if this is contrary to the stabilizing response you would expect. Their study concludes that stretch reflex passage in tasks that require changes in limb stability is mediated by motor cortical pathways, and that these differ from pat hways contributing to reflex modulation that depend on how the subject is instructed to react to an imposed perturbation. The experiment went on to observe the effects of using transcranial magnetic stimulation to create a cortical silent period whereby the muscle stretch was timed so that the M2 response of the stretch reflex occurred during this silent phase. As a result of this, the idea that reflex sensitivity could be increased when in a stable environment was abolished. The reflex responses seen from altered task instruction was found to be not influenced by cortical silence. These results demonstrate that task-dependent changes in reflex function can be mediated through multiple neural pathways and that these pathways have task-specific roles. More recently, Petersen, N. et al. (1998) investigated the possibility of a transcortical pathway by applying stretch to ankle dorsiflexors and recording the EMG signals. In the introduction, Peterson et al. (1998) states that it is wid ely accepted, for muscles in the distal upper limb, for the long-loop reflex (M2) to be mediated by a transcortical reflex pathway. There is little evidence showing the same result in proximal and lower limb muscles. Thilmann et al. (1991) found that the M2 response showed no significant change in proximal and lower limb muscles after lesions of supraspinal pathways whereas the M2 responses disappeared in hand muscles after the same lesion.A more clinical cuddle by Diener, H., Dichgans, J., Hlser, P.-J., Buettner, U.-W., Bacher, M.and Guschbauer, B. (1984) suggests the long loop reflex is useful in diagnosing multiple sclerosis. Their results showed that 69% of the patients who have multiple sclerosis have a significantly longer M3 latency response in the unfitting anterior tibial muscle. This increased delay in M3 response suggests demyelination of the neurones and they concluded that their results support evidence that the long loop reflex is mediated by a transcortical pathway. Figure 1Clarac , F (2005)The History of Reflexes Part 2 From Sherrington to 2004,IBRO History of NeuroscienceCorden,D.M., Lippold,O.C.J., Buchanan, K. and Norrington, C. (2000) Long-Latency Component of the scope Reflex in Human ponderousness is Not Mediated by Intramuscular Stretch Receptors. Applied ledger of Physiology. 84(1). 184-188.Corna, S., Grasso, M., Nardone, A. Schieppati, M. (1995) Selective depression of medium-latency leg and foot muscle responses to stretch by an a-agonist in humans. daybook ofPhysiology. 484. 803-809.Diener, H.C., Dichgans, J., Hlser, P.J., Buettner, U.W., Bacher, M.and Guschbauer, B. 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