Figure 2. Activation of gamma motor neurons maintains the sensitivity of unloaded muscle spindles.

When the muscle is further stretched (left), primary Ia afferents increase their firing rate until a steady-state is reached. When the muscle is shortened after activation of alpha motor neurons, muscle spindles unload and undergo relaxation (middle). Activation of gamma motor neurons (right) re-tensions spindles to the extrafusal fibres to ensure that their transduction capabilities are maintained within the appropriate range.