Kinematics of the freely moving head and neck in the alert cat |
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Authors: | E A Keshner K D Statler S L Delp |
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Institution: | (1) Sensory Motor Performance Program, Room 1406, Rehabilitation Institute of Chicago, 345 East Superior Street, Chicago, IL 60611, USA; e-mail: eak@nwu.edu, US |
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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 22.5o and 45o 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.
Received: 27 August 1996 / Accepted: 18 December 1996 |
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Keywords: | Neck muscles Videofluoroscopy Head tracking Moment arms Biomechanical model Cat |
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