Muscle spindles are nerve cells which wrap around specialized muscle cells (so-called intrafusal fibres), and are stretched in coordination with the stretching of the muscle fibres. The firing rate of muscle spindle neurons increases when muscle fibres are stretched. This neural activity is involved in a feedback process (called the stretch reflex or myotatic reflex) in which opposing muscle fibres are contracted as a result of the stretching of muscle fibres. Signals from muscle spindles are also involved in proprioception (the conscious perception of limb position).