Input Patterns and Pathways From the Six Semicircular Canals to Motoneurons of Neck Muscles. II. The Longissimus and Semispinalis Muscle Groups

Abstract

To reveal patterns of input from the six semicircular canals to motoneurons of various neck muscles and their relationship to the mechanical actions of individual neck muscles, patterns of input to neck motoneurons of the longissimus and the semispinalis muscle groups were investigated in the upper cervical spinal cord of anesthetized cats. Intracellular potentials were recorded from motoneurons of the longissimus muscle group (obliquus capitis superior muscle, OCS; splenius muscle, SPL; longissimus muscle, LONG) and the semispinalis muscle group (biventer cervicis muscle, BIV; complexus muscle, COMP), and effects of separate electrical stimulation of the six ampullary nerves on them were analyzed in each preparation. Neck motoneurons usually received convergent inputs from all of the six ampullary nerves, and motoneurons that supplied a particular muscle had a homogeneous pattern of input from the six ampullary nerves. Two different patterns of input were identified for motoneurons of these two muscle groups; one pattern for motoneurons of the longissimus muscle group and the other pattern for motoneurons of the semispinalis muscle group. Motoneurons of the OCS, the SPL, and the LONG muscles received excitation from the three contralateral ampullary nerves and inhibition from the three ipsilateral ampullary nerves. BIV and COMP motoneurons received excitation from the bilateral anterior canal nerves (ACNs) and the contralateral canal nerve (LCN) and inhibition from the bilateral posterior canal nerves (PCNs) and the ipsilateral LCN. Latencies of postsynaptic potentials (PSPs) evoked by stimulation of each of the six ampullary nerves indicated that the earliest component of excitatory PSPs (EPSPs) and inhibitory PSPs (IPSPs) was disynaptic in these motoneurons. However, trisynaptic IPSPs were evoked by stimulation of the contralateral PCN in a considerable number of BIV and COMP motoneurons. In OCS, SPL, and LONG motoneurons, all of the excitation from the contralateral and all of the inhibition from the ipsilateral ampullary nerves were mediated through the ipsilateral medial longitudinal fascicle (MLF). In BIV and COMP motoneurons, disynaptic excitation from the contralateral ACN and LCN and disynaptic inhibition from the ipsilateral LCN and bilateral PCNs were mediated through the ipsilateral MLF, whereas disynaptic excitation from the ipsilateral ACN was mediated through the ipsilateral lateral vestibulospinal tract. The patterns of semicircular canal input to neck motoneurons of these two muscle groups are related closely to the mechanical actions of the individual neck muscles and the optimal stimulus to the semicircular canals such that the connections will tend to stabilize head positions in response to head perturbations.

Spatiotemporal Symmetries in the Disynaptic Canal-Neck Projection

“…The muscles also form four polarity pairs; if a canal is activated by the motion of the head, then it sends an excitatory signal to one member of each pair and an inhibitory signal to the other member. Physiological investigations (Wilson and Maeda [16], Shinoda et al [13,14,15]) suggest that each muscle group is excited by a set of three mutually orthogonal canals (that is, one from each polarity pair) and inhibited by the complementary set of canals (the other members of the polarity pairs).…”

“…(1 3 7 5)(2 4 8 6) F 3 (1 5 4 8)(2 6 3 7) F 4 ( 1 8 4 5)(2 7 3 6) F 5 (1 8 6 3)(2 7 5 4) F 6 (1 3 6 8)(2 4 5 7) E 13 (1 2)(3 7)(4 8)(5 6) E 14 ( 1 5) (2 6)(3 4)(7 8) E 15 (1 2)(3 4)(5 7)(6 8) E 16 (1 3)(2 4)(5 6)(7 8)…”

“…First, we rederive the symmetry group Γ of the network of neurons that conveys signals from the six canals to eight principal muscle groups that control the position of the neck. McCollum and Boyle [12] analyzed experimental work of Shinoda et al [13,14,15] and Wilson and Maeda [16] to discover these symmetries. Our derivation makes transparent the fact that Γ is the 48-element symmetry group of the cube, which is called the octahedral group.…”

Orientation of Human Semicircular Canals Measured by Three-Dimensional Multiplanar CT Reconstruction

“…The semicircular canals (SCC) of the vestibular labyrinth encode head rotational velocity and provide input to the vestibulo-ocular reflex (VOR), vestibulocollic reflex, vestibulo-spinal system, vestibulo-reticular system, cerebellum, and cortex (Ewald 1892;Cohen et al 1964;Suzuki and Cohen 1964;Wilson et al 1995;Maeda et al 1975;Shinoda et al 1994Shinoda et al , 1997Peterson and Abzug 1975;Wilson et al 1976;Ebata et al 2004). Accurate knowledge of the absolute orientation (with respect to skull landmarks) and position of SCC is essential for design of experiments studying the vestibular system and for understanding exam findings during clinical evalua-tion of patients with vestibular disorders.…”

Symmetries of the Central Vestibular System: Forming Movements for Gravity and a Three-Dimensional World

“…In Figure 1A Although in Figure 1A the stimulating electrode is only shown on the right, all six canal nerves were stimulated in the experiments [45][46][47]. There are left-right connections in the CVS which allow stimulation from all six canal nerves to affect all the neck motor neurons recorded.…”