Postural reflexes in cranial muscles in man.

Using electromyographic recording techniques, tonic neck reflexes and tonic labyrinth reflexes have been analysed in cranial muscles of healthy man. The frontalis and orbicularis oculi (pars orbitalis) muscles are the site of positional reflexes of cervical origin, which are involved in the control of eyelid position during head movements. At a mandibular level, postural influences are set up in the masseter and digastric muscles upon ventral and dorsal flexion of the head. Their reciprocal character contrasts with the lack of evidence concerning reciprocal proprioceptive jaw reflexes. The genioglossal muscle is the site of an intense postural activity when the head is flexed dorsally. The latter influences appear related to the preservation of free air passage to the lungs.