English: Musclespindel model, developed by Mileusnic et al. (2006): the muscle spindle are described as consisting of several nuclear chain fibres, and two different nuclear bag fibres, connected in parallel. The muscle fibres respond to three inputs: fascicle length, dynamic fusimotor input and static fusimotor input. The bag_1 fibre is mainly responsible for detecting dynamic fusimotor input, while the bag_2 and chain fibres are mainly responsible for detecting static fusimotor input. All fibres respond to changes in the fascicle length. The responses of the three types of fibres are summed to generate the primary and secondary afferent activities. The primary afferent activity is affected by the response of all three types of muscle fibres, while the secondary afferent activity only depends on the bag_2 and chain fibre responses.