Figure 4. Sensory control of spinal ‘functional units’ during different types of movements controlled from the brain (A) and ‘gating’ of reflex transmission during movement (B).

A, diagram illustrating spinal ‘functional units’ (in different colours) relating various muscle synergies, part of movements or more integrated motor behaviour. The diagram illustrates the idea that the brain is activating and mediating its effects through these ‘functional units’. The same interneurones are probably involved in several ‘functional units’, and these units should therefore be spatially overlapping. The drawing also illustrates that the sensory feedback is channelled through the ‘functional unit’ activated by the brain, as illustrated in more detail in Fig. 3C. B, diagram illustrating the phasic gating of reflex transmission during different phases of a movement (e.g. during locomotion).