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Human intersegmental reflexes from intercostal afferents to scalene muscles
Rachel A McBain1,2, Janet L Taylor1,2, Robert B Gorman1
1Neuroscience Research Australia, Randwick, Sydney, NSW 2031, Australia.
Experimental Physiology
|July 28, 2016
Summary
Researchers discovered a new inhibitory reflex between intercostal nerves and scalene muscles in humans. This reflex, absent in spinal cord injury patients, may help monitor injury recovery.
Area of Science:
- Neuroscience
- Human Physiology
- Respiratory Mechanics
Background:
- Intersegmental reflexes are well-documented in animal respiratory systems.
- In humans, documented short-latency reflexes primarily involve phrenic nerve stimulation.
- Limited understanding exists regarding intercostal afferent connections to accessory respiratory muscles like the scalenes.
Purpose of the Study:
- To investigate the existence of reflex connections between intercostal afferents and human scalene muscles.
- To determine if these reflex pathways remain functional after cervical spinal cord injury.
Main Methods:
- Surface electromyography (EMG) recorded from bilateral scalene muscles.
- Stimulation of the eighth or tenth intercostal nerve in both able-bodied and spinal cord-injured participants.
- Analysis of reflex responses, including latency and inhibition magnitude, at varying stimulus intensities.
Main Results:
- A novel short-latency (approximately 38 ms) inhibitory reflex was identified between intercostal afferents and scalene muscles in able-bodied individuals.
- This bilateral reflex was present in ipsilateral and contralateral scalene muscles.
- The intercostal-to-scalene reflex was completely absent in all participants with cervical spinal cord injury.
Conclusions:
- This study provides the first evidence of an intercostal-to-scalene inhibitory reflex in humans, likely mediated by large-diameter afferents.
- The absence of this reflex post-spinal cord injury suggests its dependence on intact spinal pathways.
- This newly identified reflex may serve as a potential biomarker for assessing the severity and recovery progress of thoracic or cervical spinal cord injuries.
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