Kinematics of the freely moving head and neck in the alert cat

Abstract

In this study we examined connections between the moment-generating capacity of the neck muscles and their patterns of activation during voluntary head-tracking movements. Three cats lying prone were trained to produce sinusoidal (0.25 Hz) tracking movements of the head in the sagittal plane, and 22.5 degrees and 45 degrees away from the sagittal plane. Radio-opaque markers were placed in the cervical vertebrae, and intramuscular patch electrodes were implanted in five neck muscles, including biventer cervicis, complexus, splenius capitis, occipitoscapularis, and rectus capitis posterior major. Videofluoroscopic images of cervical vertebral motion and muscle electromyographic responses were simultaneously recorded. A three-dimensional biomechanical model was developed to estimate how muscle moment arms and force-generating capacities change during the head-tracking movement. Experimental results demonstrated that the head and vertebrae moved synchronously, but neither the muscle activation patterns nor vertebral movements were constant across trials. Analysis of the biomechanical model revealed that, in some cases, modification of muscle activation patterns was consistent with changes in muscle moment arms or force-generating potential. In other cases, however, changes in muscle activation patterns were observed without changes in muscle moment arms or force-generating potential. This suggests that the moment-generating potential of muscles is just one of the variables that influences which muscles the central nervous system will select to participate in a movement.

A preliminary modelling study on the equine cervical spine with inverse kinematics at walk

“…1998). This dependence has already been demonstrated in the feline cervical spine (Keshner et al . 1997).…”

Insight into understanding the anatomical and clinical aspects of supernumerary rectus capitis posterior muscles

“…In pertinent literature, the posterior neck muscles have been best studied in the cat (Richmond et al, 1992;Selbie et al, 1993;Keshner et al, 1997;Statler and Keshner, 2003) where the suboccipital region contains three dorsal muscles bilaterally: RCPM, RCP medius, and RCPm (Selbie et al, 1993). These muscles have been found to contain relatively large cross-sectional areas and high fast-fiber proportions.…”

“…They serve to quickly orient and then hold a new head position. Biomechanically, they provide head extension solely in the sagittal plane where they have a consistently large moment arm about the skull-C1 joint (Keshner et al, 1997). It can be speculated that these muscles exist in humans to effect well-coordinated head and neck movements, and that maintenance of these muscles protects an individual against cervicogenic headache or impaired imbalance [as suggested by the findings of Andary et al (1998) and McPartland et al (1997) with regard to RCP muscle dysfunctions].…”

“…These muscles have been found to contain relatively large cross-sectional areas and high fast-fiber proportions. They exert important phasic, as well as, postural roles during head movements (Richmond et al, 1992;Keshner et al, 1997;Statler and Keshner, 2003). They serve to quickly orient and then hold a new head position.…”

Perturbation parameters associated with nonlinear responses of the head at small amplitudes

“…However, despite the long trial periods, habituation in head position or velocity was not observed 35,36 suggesting either that subjects were continuously engaged throughout the trial or that sensory adaptation did not take place. 42 Nevertheless, further investigation of neck muscle activation is warranted. For example, in seated subjects receiving high jerk linear accelerations with the head free, head stabilizing responses were observed to be distributed on a continuum between two extreme categories-stiff and floppy.…”