Gamma loop mechanism
To initiate all somatic motor actions the influence of motor system upon gamma motor neuron is significant. The motor pathways depolarized dominantly gamma motor neurons which in turn initiate the contraction of intrafusal fibres of muscle spindle organ. These results in activation of group Ia afferent fibres.
These fibres monosynaptically connect with alpha motor neurons and causes extra fiscal muscle contraction. This is known as “Gamma loop mechanism”
Cutting across the dorsal root blocks this mechanism and causes immobility and uncoordinated somatic motor activity.
Excitability of gamma motor neurons in proportion to alpha motor neurons is determined by particular spinal afferent under the influences of BSRF.
BSRF is under the influences of basal ganglia and cerebral cortex.
This indicates cerebellum and basal ganglia alter the motor activity directly through the involvement of red nucleus primary motor cortex and vestibular nucleus and indirectly through BSRF.