Neuronal pathways from low-threshold hindlimb cutaneous afferents to motoneurons innervating trunk muscles in low-spinal cats

1999 ◽  
Vol 128 (4) ◽  
pp. 543-549 ◽  
Author(s):  
N. Wada ◽  
M. Tokuriki ◽  
K. Kanda ◽  
N. Shikaki
Keyword(s):  
Trunk Muscles ◽  
Cutaneous Afferents ◽  
Low Threshold

Single low-threshold afferents innervating the skin of the human foot modulate ongoing muscle activity in the upper limbs

2013 ◽  
Vol 109 (6) ◽  
pp. 1614-1625 ◽  
Author(s):  
Leah R. Bent ◽  
Catherine R. Lowrey
Keyword(s):  
Upper Limb ◽  
Muscle Activity ◽  
Reflex Response ◽  
Cutaneous Afferents ◽  
Type I ◽  
Triceps Brachii ◽  
Median Response ◽  
Plantar Surface ◽  
Human Foot ◽  
Low Threshold

We have shown for the first time that single cutaneous afferents in the foot dorsum have significant reflex coupling to motoneurons supplying muscles in the upper limb, particularly posterior deltoid and triceps brachii. These observations strengthen what we know from whole nerve stimulation, that skin on the foot and ankle can contribute to the modulation of interlimb muscles in distant innervation territories. The current work provides evidence of the mechanism behind the reflex, where one single skin afferent can evoke a reflex response, rather than a population. Nineteen of forty-one (46%) single cutaneous afferents isolated in the dorsum or plantar surface of the foot elicited a significant modulation of muscle activity in the upper limb. Identification of single afferents in this reflex indicates the strength of the connection and, ultimately, the importance of foot skin in interlimb coordination. The median response magnitude was 2.29% of background EMG, and the size of the evoked response did not significantly differ among the four mechanoreceptor classes ( P > 0.1). Interestingly, although the distribution of afferents types did not differ across the foot dorsum, there was a significantly greater coupling response from receptors located on the medial aspect of the foot dorsum ( P < 0.01). Furthermore, the most consistent coupling with upper limb muscles was demonstrated by type I afferents (fast and slowly adapting). This work contributes to the current literature on receptor specificity, supporting the view that individual classes of cutaneous afferents may subserve specific roles in kinesthesia, reflexes, and tactile perception.

The reflex effects of nonnoxious sural nerve stimulation on human triceps surae motor neurons

1994 ◽  
Vol 71 (5) ◽  
pp. 1897-1906 ◽  
Author(s):  
C. G. Kukulka
Keyword(s):  
Motor Neurons ◽  
Sural Nerve ◽  
Short Latency ◽  
Triceps Surae ◽  
Reflex Response ◽  
Cutaneous Afferents ◽  
Onset Latency ◽  
Human Triceps Surae ◽  
Low Threshold ◽  
Stimulation Of

1. The effects of low-intensity electrical stimulation of the ipsilateral sural nerve on the reflex response of human triceps surae motor neurons were examined in 169 motor units recorded in 11 adult volunteers: 69 units from soleus (SOL), 48 units from lateral gastrocnemius (LG), and 52 units from medial gastrocnemius (MG). The reflex effects were assessed by the peristimulus time histogram (PSTH) technique, categorized according to onset latencies, and the magnitudes of effects were calculated as percent changes in baseline firing rates. 2. Sural stimulation evoked complex changes in motor-unit firing at onset latencies between 28 and 140 ms. The two most common responses seen in all muscles were a short-latency depression (D1) in firing (mean onset latency = 40 ms) in 42% of all units studied and a secondary enhancement (E2) in firing (mean onset latency = 72 ms) in 43% of all units. In LG, the D1 effect represented a mean decrease in firing of 52% which was statistically different from the changes in MG (42% decrease) and SOL (38% decrease). The magnitudes of E2 effects were similar across muscles with an average of 47% increase in firing. 3. No differences were found in the frequencies of occurrence for the enhancements in firing among the muscles studied. The main difference in reflex responses was the occurrence of an intermediate latency depression (D2) in 27% of the LG units with a mean onset latency of 72 ms. 4. Based on estimates of conduction times for activation of low-threshold cutaneous afferents, the short-latency D1 response likely represents an oligosynaptic spinal reflex with transmission times similar to the Ia reciprocal inhibitory pathway. These findings raise the question as to the possibility of low-threshold cutaneous afferents sharing common interneurons with low-threshold muscle afferent reflexes that have identical onset latencies. The complex reflex effects associated with low-level stimulation of a cutaneous nerve indicate a rich assortment of peripheral responses that may influence a given movement. The predominance of a specific effect is most likely determined by the interaction of this input with other peripheral signals and descending commands specific to a given motor task.

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