VPB 121: Veterinary Physiology - II (2+1)

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.