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Peripheral cranio-spinal nerve communication for trapezius muscle control using axonal profiling through
Miri Kim1,2, In-Seung Yeo1,2, Tae-Hyeon Cho2,3
1Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea.
Scientific Reports
|October 25, 2024
Summary
This study reveals that upper cervical nerves (C3-4) significantly contribute to trapezius motor control and proprioception, challenging the traditional view of the accessory nerve (CNXI) as solely motor.
Area of Science:
- Neuroscience
- Anatomy
- Physiology
Background:
- The accessory nerve (CNXI) is traditionally considered the primary motor pathway for the trapezius muscle.
- Upper cervical nerves (C3 and C4) have been thought to primarily provide sensory feedback from the muscle.
- Direct evidence for these functional roles has been limited, leading to ongoing debate.
Purpose of the Study:
- To investigate the functional contributions of the accessory nerve (CNXI) and upper cervical nerves (C3-4) to trapezius muscle innervation.
- To clarify the roles of these nerves in motor control, proprioception, and sympathetic modulation.
- To challenge established notions regarding the sensory and motor functions of these nerves.
Main Methods:
- Immunostaining of human trapezius muscle samples using specific antibodies.
- Antibodies targeted neurofilament 200 (all axons), choline acetyltransferase (cholinergic axons), tyrosine hydroxylase (sympathetic axons), and alpha 3 sodium potassium ATPase (proprioceptive afferent axons).
Main Results:
- Upper cervical nerves (C3-4) contain both cholinergic and non-cholinergic axons, indicating roles in proprioceptive feedback and somatic efferent functions.
- These cervical nerves supply motor fibers, proprioceptive, and sympathetic axons to the trapezius muscle.
- The accessory nerve (CNXI) comprises mainly somatic efferent fibers but also contains sympathetic and sensory fibers.
- Mechanosensors, including nociceptive and sympathetic fibers, were identified within the cervical nerves.
Conclusions:
- Upper cervical nerves (C3-4) play a crucial role in trapezius motor control, proprioceptive feedback, and sympathetic modulation.
- The study challenges the long-held dichotomy of CNXI being exclusively motor and upper spinal nerves being exclusively sensory.
- These findings necessitate a re-evaluation of the functional neuroanatomy of the trapezius muscle innervation.
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