QS Study

Role of Cerebellum in Controlling Motor Functions

The cerebrum is the part of the brain involved in the higher levels of thinking and action. It is involved in the control of voluntary and involuntary movement as well as balance. The cerebellum is located behind the top part of the brain stem and is made of two hemispheres.

Control of voluntary movement by the cerebellum

Cerebellum control voluntary movement by two Mechanisms:

  • Cerebrocerebellar feedback control by intermediate zone.
  • Error control-role of climbing fiber.

Cerebrocerebellar feedback control

The intermediate zone of cerebellum receives two types of information when a movement is performed:

  • Direct information from the motor cortex and red nucleus telling the cerebellum sequential intended plan of movement by cortico-ponto cerebellar pathway.
  • Feedback information from the peripheral part of the body (proprioception by spinocerebellar tract) telling cerebellum what actual movements result.

After comparing the intended movement with actual movement the deep interposed nuclear cells send corrective output signals.

  • Back to the motor cortex through relay nuclei in the thalamus.
  • To a magnocellular portion of a red nucleus which gives rise to the rubrospinal tract.

The rubrospinal in turn joints the corticospinal tract innervating motor neurons (lateral most) of anterior horn of spinal cord gray matter. These neurons provide smooth coordinate movements of agonist and antagonist muscle of limbs for the performance of acute purposeful patterned movements. It may also be involved in some cognitive functions such as attention and language as well as in regulating fear and pleasure responses, but its movement-related functions are the most solidly established.

Fig: Cerebral and cerebellar control of voluntary movements, involving especially the intermediate zone of the cerebellum.

Error control by Purkinje cells (Error control-role of climbing fiber)

The inferior olivary complex receives full information from:

  • Corticospinal tract and motor centers in brain stem detailing the intent of each motor movement.
  • Receivers full information from sensory nerve endings in muscles and surrounding tissues detailing the movement that actually occur.

The inferior olivary complex then acts as a comparator to test how will the actual performance matches the intended performance.

If there is a match no firings of climbing fibers occur. But if there is a mismatch, the climbing fibers are stimulated or inhibited as needed in proportion to the degree of mismatch.

The climbing fibers then after long-term sensitivity of Purkinje cells to subsequent signals from the mossy fiber input.

This change in sensitivity along with other ‘learning’ function is believed to make the firing and other aspects of cerebellar control to approach the perfect movement and controlling error.