Muscles have two important roles.
Muscles act as a force generator and as a sensory organ of proprioceptive input (balance-posture). It can also act as a source of pain, too.
Muscle is the most complex tissue in the body. Unlike other tissues such as ligaments, muscles are able to generate an internal force independent of length. Because of this reason, the forces generated by muscles are far more complex to predict. In addition to muscle’s role in generating force, muscles also act as joint position sensors.
Smaller muscles have a greater number of muscle spindles per gram than larger muscles. Muscle spindles are like stretch detector. It senses how fast a muscle is lengthened or shorten. Deep cervical muscles such as suboccipital muscles have really high spindle content. It makes sense that the proprioceptive inputs from the neck muscles play an important role in head-eye coordination and postural processes.