Matching of muscle properties and motoneurone firing patterns during early stages of development.

In adults, muscle fibres match the functional requirements of the motoneurone that supplies them. During early stages of postnatal development of the rat neither muscle fibre properties, nor activity patterns of motoneurones supplying fast and slow muscles have completed their differentiation. Nevertheless, even at this early stage of development the muscles have characteristic properties that are well matched to the activity patterns of immature motoneurones. With further development differentiation of motoneurone activity and muscle fibre properties goes hand in hand. If during this period of linked differentiation, connections between the motoneurones and muscle fibres are disrupted, the development of fast muscles is permanently impaired.