Activity of forelimb motor units and corticomotoneuronal cells during ramp-and-hold torque responses: comparisons with oculomotor cells

doi:10.1016/S0079-6123(08)63408-1

Progress in Brain Research

Volume 64, 1986, Pages 133-141

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To compare the functional organization of the somatomotor and oculomotor systems, it may be helpful to begin by comparing the response properties of their motoneurons and monosynaptically connected premotor neurons under behavioral conditions, which are as comparable as possible. In the somatomotor system, the activity of single forelimb motor units and input cells from precentral motor cortex, during ramp-and-hold torque responses has been sufficiently characterized to provide some basis for comparison. Such ramp-and-hold responses, alternating between flexion and extension target zones, were chosen to reveal the neural activity related to changes in force and to maintain static force; for purposes of discussion, these ramp-and-hold wrist responses may be considered analogous to saccadic eye movements followed by fixation. This chapter discusses the response properties and organization of somatic motor units and corticomotoneuronal (CM) cells, with brief comments on some interesting analogies with comparable oculomotor neurons. More information on the correlational linkages of the observed cells with their inputs and their targets would be helpful for understanding the source and consequences of their response properties.

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Skeletomotor movements can be divided into five subsystems, each having its own independent mechanism and purpose. The subsystems are: 1. Reflex 2. Position 3. Velocity 4. Pursuit 5. Simultaneous. Reflex movements are rapid, stereotyped, inflexible and specific in terms of stimulus and response. Position movements are made to a target or certain position, with or without a load. A mechanism is proposed by which the Basal Ganglia program positioning movements into the primary movement and any load is compensated for by the stretch reflexes. Velocity movements are throwing movements and a mechanism is proposed by which the Cerebellum programs velocity into the basic, primary movement. A mechanism for Pursuit movements is proposed by which sensory and pursuit neurons activate velocity neurons whose activity drives the motor pathways to make pursuit movements. Simultaneous movements could be under the direction of the Prefrontal Cortex utilizing sensory feedback and interhemispheric transfer of information. A subcortical or cerebellar pattern generator could be set up for movements such as walking and running. The purpose of this division is to provide a guide for research and to aid in the understanding and treatment of diseases and injuries that affect the motor system.
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Activity of forelimb motor units and corticomotoneuronal cells during ramp-and-hold torque responses: comparisons with oculomotor cells

Publisher Summary

Brain Res.

Progr. Brain Res.

Neurosci. Lett.

Projections of individual pyramidal tract neurons to lumbar motor nuclei of the monkey

Exp. Brain Res.

Motor units: anatomy, physiology, and functional organization.

Response of rubromotoneuronal cells identified by spike-triggered averaging of EMG activity in awake monkeys

Neurosci. Lett.

Functional classes of primate corticomotoneuronal cells and their relation to active force

J. Neurophysiol.

Corticomotoneuronal cells contribute to long-latency stretch reflexes in the rhesus monkey

J. Physiol.

Comparable patterns of muscle facilitation evoked by individual corticomotoneuronal (CM) cells and by single intracortical microstimuli in primates: evidence for functional groups of CM cells

J. Neurophysiol.

Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey

J. Neurophysiol.

Motor and sensory properties of primate corticomotoneuronal cells

Exp. Brain Res., Suppl.

Recruitment order, contractile characteristics and firing patterns of motor units in the temporalis muscle of monkeys

Exp. Neurol.

Functional organization of motor and sensory cortex: symmetries and parallels.

Postspike facilitation of forelimb muscle activity by primate corticomotoneuronal cells

J. Neurophysiol.

Motor unit and muscle activity in voluntary motor control

Physiol. Rev.

Activity of single motor units from human forearm muscles during voluntary isometric contractions

J. Neurophysiol.