Cutaneomuscular Reflexes in the Lower Limbs in Man

Bagheri, Hossein (1995) Cutaneomuscular Reflexes in the Lower Limbs in Man. PhD thesis, University of Glasgow.

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Mild electrical stimulation of the toes can produce cutaneomuscular reflexes in the muscles of the lower limb of normal adults (Gibbs et al, 1993). The general pattern is polyphasic with mixed excitations and inhibitions. In the present thesis an attempt was made to investigate the nature of the cutaneomuscular reflexes in different muscles of the lower limb such as tibialis anterior, gastrocnemius, quadriceps, hamstrings and abductor hallucis. The effects of site of stimulation, stimulus intensity, temporal summation, background force, posture and skin cooling were investigated on the nature and magnitude of the cutaneomuscular reflexes. Experiments were performed in 62 healthy subjects aged between 20 and 38 years old. The subjects were seated, stood erect, or lay relaxed during experiments. Cutaneomuscular reflexes were elicited by stimulation of the hallux, the heel, the lateral border of the foot, the plantar surface of the foot and the shank at intensities up to three times perceptual threshold. The reflexes were identified as modulations in the averaged rectified surface electromyogram of the muscles under study. Cutaneomuscular reflexes were recorded in tibialis anterior, gastrocnemius, quadriceps, hamstrings and abductor hallucis. Reflexes were elicited most frequently in tibialis anterior but even in this muscle there was some variability in the pattern of responses. Cutaneomuscular reflexes consist of up to four components designated: E1, I1, E2 and I2. The later excitation (E2) is the most consistent feature of reflexes elicited by stimulation of hallux, whereas stimulation of skin innervated by the sural elicits early inhibitions (I1) in all cases. Cutaneomuscular reflexes were much less frequently observed in quadriceps and hamstrings. The mean latency of the earliest component of cutaneomuscular reflexes is about 50 msec which suggests oligosynaptic spinal pathways. Later components have latencies of about 80 msec which would allow time for a supraspinal pathway. Pure excitations and inhibitions were seen in some subjects but mixed excitations and inhibitions were more common, particularly with stimulation at higher intensities. Cutaneomuscular reflexes can be elicited by single shocks but the amplitude increased significantly when a second or third stimulus pulse was added. The intensity of the background contraction against which the cutaneomuscular reflexes is elicited had a strong effect on the magnitude of cutaneomuscular reflexes. The magnitude of the reflexes was significantly greater when they were elicited during voluntary contraction in a seated position than when the muscle was posturally active during standing. Significant differences were found between the amplitudes of the different components of the cutaneomuscular reflexes as the standing position was adjusted. The excitatory and inhibitory components of the cutaneomuscular reflexes were decreased during the cooling of the skin and were restored when the skin was rewarmed. Excitations were easier to abolish than inhibitions. This effect can be attributed to changes in the magnitude of the afferent volleys. The results show that the E1, I1 and E2 are independent components of the reflex. In addition, it is suggested that there may be at least two populations of cutaneous afferents responsible for eliciting the mixed excitations and inhibitions observed in cutaneomuscular reflexes. Cutaneomuscular reflexes are likely to be most effective when muscles are operating in a low force range at about 20% MVC or less of their maximum force. The results in this thesis also suggest that E2 component of cutaneomuscular reflexes is modulated in task-dependant manner.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ronald Baxendale
Keywords: Neurosciences
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-74822
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 16:00
Last Modified: 27 Sep 2019 16:00

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