'Long-loop' reflexes can be obtained in spinal monkeys

Extensor muscles of the fore- and hindlimb were stretched in the lightly anaesthetized monkey (Macaca fascicularis) and cat. The resulting electromyogram contained a short latency peak consistent with a monosynaptic, segmental pathway; this peak was identified as the M1 peak of Tatton et al. [21]. A longer latency peak, identified as M2 and said to involve a pathway including supraspinal centres, was also present. After spinal section at a high cervical level, the electromyogram was reduced in amplitude, but both short (M1) and longer latency (M2) peaks were present. It is concluded that neither the cerebral cortex nor the cerebellum are necessary parts of the neural circuitry generating longer latency components of the electromyographic response to muscle stretch.