Effect of load disturbances during centrally initiated movements.

1. We have investigated the relative contributions of mechanical and reflex mechanisms in generating the forces produced by the neck muscles when loads were unexpectedly applied during centrally programmed head movements in monkeys. These movements, subserved by muscles well endowed with muscle spindles, are part of the coordinated eye-head response to the appearance of a stimulus in the animal's visual field. Our preparation was a chronically vestibulectomized monkey trained to make a visual discrimination. 2. Two procedures were used to evaluate the torque generated by the neck musculature when an unexpected load disturbance was applied: first, by surgically interrupting the afferent loop subserving the reflex action (section of cervical dorsal roots) and second, by building a mathematical model of the head-neck system and carrying out a process of simulation. 3. Our results indicated that the compensatory torque of reflex origin stimulated by the application of an opposing force was less than 10--30% of that required for perfect compensation, and the larger fraction of the observed compensation was due to the mechanical properties (inertial, viscous, and elastic) of the neck musculature. The combined action of reflex and mechanical processes never completely compensated for the disturbance.

[1]  R. Granit,et al.  The two routes for excitation of muscle and their subservience to the cerebellum , 1955, The Journal of physiology.

[2]  P. Daniel,et al.  MUSCLE SPINDLES IN MAN; THEIR MORPHOLOGY IN THE LUMBRICALS AND THE DEEP MUSCLES OF THE NECK. , 1963, Brain : a journal of neurology.

[3]  T. Sears.  Efferent discharges in alpha and fusimotor fibres of intercostal nerves of the cat , 1964, The Journal of physiology.

[4]  M L Shik,et al.  [Work of muscle receptors during controlled locomotion]. , 1967, Biofizika.

[5]  E. Evarts.  A technique for recording activity of subcortical neurons in moving animals. , 1968, Electroencephalography and clinical neurophysiology.

[6]  A. Lundberg,et al.  Reflex control of stepping , 1969 .

[7]  P. Rack,et al.  The effects of length and stimulus rate on tension in the isometric cat soleus muscle , 1969, The Journal of physiology.

[8]  T A Sears,et al.  The proprioceptive reflex control of the intercostal muscles during their voluntary activation , 1970, The Journal of physiology.

[9]  C. G. Phillips,et al.  Projection from low‐threshold muscle afferents of hand and forearm to area 3a of baboon's cortex , 1971, The Journal of physiology.

[10]  A. Vallbo,et al.  Slowly adapting muscle receptors in man. , 1970, Acta physiologica Scandinavica.

[11]  J. Houk,et al.  An evaluation of length and force feedback to soleus muscles of decerebrate cats. , 1970, Journal of neurophysiology.

[12]  D. Robinson,et al.  Absence of a stretch reflex in extraocular muscles of the monkey. , 1971, Journal of neurophysiology.

[13]  E. Bizzi,et al.  Eye-Head Coordination in Monkeys: Evidence for Centrally Patterned Organization , 1971, Science.

[14]  S. Grillner.  The role of muscle stiffness in meeting the changing postural and locomotor requirements for force development by the ankle extensors. , 1972, Acta physiologica Scandinavica.

[15]  M. Wiesendanger.  Input from muscle and cutaneous nerves of the hand and forearm to neurones of the precentral gyrus of baboons and monkeys , 1973, The Journal of physiology.

[16]  A. Vallbo,et al.  The Significance of Intramuscular Receptors in Load Compensation During Voluntary Contractions in Man , 1973 .

[17]  E. Evarts.  Motor Cortex Reflexes Associated with Learned Movement , 1973, Science.

[18]  P. Matthews,et al.  Mammalian muscle receptors and their central actions , 1974 .

[19]  E Bizzi,et al.  The coordination of eye-head movements. , 1974, Scientific American.

[20]  H Asanuma,et al.  Activities of neurons in area 3a of the cerebral cortex during voluntary movements in the monkey. , 1974, Brain research.

[21]  A. Taylor,et al.  Jaw muscle spindle activity in the cat during normal movements of eating and drinking. , 1974, Brain research.

[22]  V. Brooks,et al.  Cortical load compensation during voluntary elbow movements. , 1974, Brain research.

[23]  W. Willis,et al.  Responses of unmyelinated afferents in the mammalian ventral root. , 1974, Brain research.

[24]  J. Murphy,et al.  Afferent-efferent linkages in motor cortex for single forelimb muscles. , 1975, Journal of neurophysiology.

[25]  M Wiesendanger,et al.  Responses of neurones in motor cortex and in area 3A to controlled stretches of forelimb muscles in cebus monkeys. , 1975, The Journal of physiology.

[26]  Y. Lamarre,et al.  Load compensation in human masseter muscles. , 1975, The Journal of physiology.

[27]  C. Marsden,et al.  Stretch reflex and servo action in a variety of human muscles. , 1976, The Journal of physiology.

[28]  N. Barmack.  Measurements of stiffness of extraocular muscles of the rabbit. , 1976, Journal of neurophysiology.

[29]  E. Bizzi,et al.  Mechanisms underlying achievement of final head position. , 1976, Journal of neurophysiology.

[30]  J. Houk,et al.  Improvement in linearity and regulation of stiffness that results from actions of stretch reflex. , 1976, Journal of neurophysiology.

[31]  C. Marsden,et al.  Servo action in the human thumb. , 1976, The Journal of physiology.

[32]  J. Houk,et al.  Regulatory actions of human stretch reflex. , 1976, Journal of neurophysiology.