Functional synergies among neck muscles revealed by branching patterns of single long descending motor-tract axons.
In this chapter, we describe our recent work on the divergent properties of single, long descending motor-tract neurons in the spinal cord, using the method of intra-axonal staining with horseradish peroxidase, and serial-section, three-dimensional reconstruction of their axonal trajectories. This work provides evidence that single motor-tract neurons are implicated in the neural implementation of functional synergies for head movements. Our results further show that single medial vestibulospinal tract (MVST) neurons innervate a functional set of multiple neck muscles, and thereby implement a canal-dependent, head-movement synergy. Additionally, both single MVST and reticulospinal axons may have similar innervation patterns for neck muscles, and thereby control the same functional sets of neck muscles. In order to stabilize redundant control systems in which many muscles generate force across several joints, the CNS routinely uses a combination of a control hierarchy and sensory feedback. In addition, in the head-movement system, the elaboration of functional synergies among neck muscles is another strategy, because it helps to decrease the degrees of freedom in this particularly complicated control system.
Sugiuchi
Yuriko
Y
Department of Systems Neurophysiology, Graduate School of Medicine, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
Kakei
Shinji
S
Izawa
Yoshiko
Y
Shinoda
Yoshikazu
Y
D000818:Animals; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure; D009046:Motor Neurons / Q000502:physiology*; D009334:Neck Muscles / Q000294:innervation* / Q000502:physiology*; D009476:Neurons, Efferent / Q000502:physiology*; D011712:Pyramidal Tracts / Q000648:ultrastructure; D012154:Reticular Formation / Q000502:physiology; D012665:Semicircular Canals / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology; D003336:Tectum Mesencephali / Q000502:physiology; D014725:Vestibular Nerve / Q000502:physiology