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Nito M, Hashizume W, Jimenji M, Suzuki K, Sato T, Fujii H, Miyasaka T, Shindo M, Naito A. Oligosynaptic inhibition mediated by group Ia afferents from flexor digitorum superficialis to wrist flexors in humans. Exp Brain Res 2018; 236:1849-1860. [PMID: 29679107 DOI: 10.1007/s00221-018-5268-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Accepted: 04/17/2018] [Indexed: 11/24/2022]
Abstract
Effects of low-threshold afferents from the flexor digitorum superficialis (FDS) to the flexor carpi radialis (FCR), flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) motoneurons were examined using a post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods in seven healthy human subjects. Electrical conditioning stimulation to the median nerve branch innervating FDS with the intensity immediately below the motor threshold was delivered. In the PSTH study, the stimulation produced a trough (inhibition) in 19/44 (43%) of FCR and 17/41 (41%) of FCU motor units. Remaining motor units received no facilitatory and inhibitory effects. The central latency of the inhibition was 1.1 ± 0.6 ms (mean ± SD) and 0.6 ± 0.4 ms longer than that of the homonymous monosynaptic Ia facilitation of FCR and FCU, respectively. In the EMG-A study, the stimulation produced a trough (inhibition) in EMG-A of FCR and FCU in all the seven subjects. Amount of the inhibition was 14.5 ± 3.8% (FCR) and 17.9 ± 2.5% (FCU). Since the inhibition diminished after withdrawal of tonic vibration stimuli to the FDS muscle belly, group Ia afferents should be responsible for the inhibition. The stimulation did not produce facilitatory or inhibitory effect on ECU motoneurons in both the PSTH and EMG-A studies. These findings suggest that group Ia afferents from FDS inhibit excitability of motoneurons supplying FCR and FCU through an oligo (di- or tri-) synaptic path in the spinal cord. The reflex arcs would function to prevent wrist flexion during hand grasping movements.
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Affiliation(s)
- Mitsuhiro Nito
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, 2-2-2, Iida-nishi, Yamagata, 990-9585, Japan
| | - Wataru Hashizume
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, 2-2-2, Iida-nishi, Yamagata, 990-9585, Japan
| | - Manabu Jimenji
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, 2-2-2, Iida-nishi, Yamagata, 990-9585, Japan
| | - Katsuhiko Suzuki
- Department of Physical Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan
| | - Toshiaki Sato
- Department of Occupational Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan
| | - Hiromi Fujii
- Department of Occupational Therapy, Yamagata Prefectural University of Health Sciences, Yamagata, Japan
| | - Takuji Miyasaka
- Department of Judo Therapy, Teikyo University Faculty of Medical Technology, Utsunomiya, Japan
| | - Masaomi Shindo
- Graduate School of Health Science, The Graduate School of Matsumoto University, Matsumoto, Japan
| | - Akira Naito
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, 2-2-2, Iida-nishi, Yamagata, 990-9585, Japan.
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