Neck afferents and muscle sympathetic activity in humans: implications for the vestibulosympathetic reflex

• Published in: Journal of applied physiology (1985) Vol. 84; no. 2; pp. 450 - 453
• Main Authors: Ray, Chester A, Hume, Keith M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.02.1998; American Physiological Society
• Subjects: Adult; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Head; Humans; Male; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Movement - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Neck Muscles - innervation; Neck Muscles - physiology; Reflex - physiology; Rotation; Space life sciences; Sympathetic Nervous System - physiology; Vertebrates: nervous system and sense organs; Vestibule, Labyrinth - physiology; Human; Sympathetic nerve; Reflex; Head position; Cardiovascular control; Striated muscle; Sympathetic nervous system; Inner ear; Autonomic nervous system; Bending; Afferent projection; Neck; Vestibular system; Non-programmatic
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1998.84.2.450

Autonomic and Cardiovascular Control Laboratory, Department of Exercise Science, University of Georgia, Athens, Georgia 30602 Ray, Chester A., and Keith M. Hume. Neck afferents and muscle sympathetic activity in humans: implications for the vestibulosympathetic reflex. J. Appl. Physiol. 84(2): 450-453, 1998. We have shown previously that head-down neck flexion (HDNF) in humans elicits increases in muscle sympathetic nerve activity (MSNA). The purpose of this study was to determine the effect of neck muscle afferents on MSNA. We studied this question by measuring MSNA before and after head rotation that would activate neck muscle afferents but not the vestibular system (i.e., no stimulation of the otolith organs or semicircular canals). After a 3-min baseline period with the head in the normal erect position, subjects rotated their head to the side (~90°) and maintained this position for 3 min. Head rotation was performed by the subjects in both the prone ( n  = 5) and sitting ( n  = 6) positions. Head rotation did not elicit changes in MSNA. Average MSNA, expressed as burst frequency and total activity, was 13 ± 1 and 13 ± 1 bursts/min and 146 ± 34 and 132 ± 27 units/min during baseline and head rotation, respectively. There were no significant changes in calf blood flow (2.6 ± 0.3 to 2.5 ± 0.3 ml · 100 ml 1 · min 1 ; n  = 8) and calf vascular resistance (39 ± 4 to 41 ± 4 units; n  = 8). Heart rate (64 ± 3 to 66 ± 3 beats/min; P  = 0.058) and mean arterial pressure (90 ± 3 to 93 ± 3; P  < 0.05) increased slightly during head rotation. Additional neck flexion studies were performed with subjects lying on their side ( n  = 5). MSNA, heart rate, and mean arterial pressure were unchanged during this maneuver, which also does not engage the vestibular system. HDNF was tested in 9 of the 13 subjects. MSNA was significantly increased by 79 ± 12% ( P  < 0.001) during HDNF. These findings indicate that neck afferents activated by horizontal neck rotation or flexion in the absence of significant force development do not elicit changes in MSNA. These findings support the concept that HDNF increases MSNA by the activation of the vestibular system. autonomic nervous system; cardiovascular control; graviceptors; orthostasis; sympathetic nerve activity; neck reflexes; vascular resistance The Journal of Applied Physiology 84(2):450-453 8750-7587/98 $5.00 Copyright © 1998 the American Physiological Society