Chapter 10: Coordination
Author's Commentary
Smooth movements require the synchronous interaction of sensorimotor and coordinative circuitries. Planning of a specific movement is accomplished in the prefrontal, supplementary motor and parietal cortex and is reflected in a readiness or Bereitschaft potential.
Patients have a general expectation of the results of the intended movement, which is then matched with the result (efferent copy). Initiation, postural adjustment, and its maintenance, tone, and selection of movement are components of the basal ganglia circuitry. Motivation and drive are provided by limbic circuitries.
In general, movement can be divided into thirds:
- Initiation
- Feedforward and feedback
- Terminal components
The cerebellum's contribution to movement is:
- Coordination of agonist and antagonist muscles at each joint
- The smooth termination of a movement
- Energize movements in conjunction with sustaining input from the basal ganglia. It has a major role in postural control, tone, and gait.
Excerpts From Chapter 10
Smooth movements require modulation during all of their component parts. A movement has to be planned and then executed. Planning of movements occurs in the prefrontal and supplementary motor cortex as well as the posterior parietal lobe and is reflected electrically by a cortical negative potential. The patient must have a general knowledge of the expected results of the movement, which are then matched with the actual result (efferent copy). It is convenient to divide movements into thirds so that initiation, feed forward, feedback, and terminal components can be analyzed. As a movement is initiated, the first third has a great deal to do with its planning (praxis) and the modulation is due to feed forward mechanisms from collateral fibers leaving the corticospinal tracts and synapsing in the thalamus which are then projected back to the primary sensory cortex which can effect early components of the motor output. The middle third of a movement is modulated from collaterals of the motor output that synapse with the dorsal column nuclei, that in turn project to the thalamus and primary sensory cortex. Proprioceptive feedback from the displaced joints to the cerebellar intermediate zone projects to the ventrointermediate (VIM) nucleus of the thalamus. Movement requires planning, initiation and maintenance as well as integrated feed forward and feedback mechanisms to remain correctly online. In addition, it requires the proper moderation of agonists and antagonists so that there is no difficulty with its termination or timing. The parietal lobe is required to anchor the patient in space and compare the posture to where it should be in space (the subjective visual vertical). The limbic system and its motor loops determine specific movements under stress and control the desire to move. It is clear that a great deal of the human nervous system is required to initiate, maintain, and complete a simple smooth movement.
Examination Technique Demonstration
Fig. 10.1 (a) Cerebellar drift. The hand and arm drift upward on extension. Note the uneven interplay between agonist and antagonist flexors and extensor hand muscles. This causes “spooning" of the hand. (b) Overshoot. The examiner presses down on the patient's arm and asks that the patient maintain it at its original position. (c) The patient is unable to break the agonist muscle and cannot keep the arm at the original position – it overshoots upwards.
