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Spatial organization of human perioral reflexes
A Smith1, D H McFarland, C M Weber
1Department of Audiology and Speech Sciences, Purdue University, West Lafayette, Indiana 47907.
Experimental Neurology
|November 1, 1987
Summary
Stimulating the upper lip vermilion border elicited the largest reflex responses in the orbicularis oris muscle. This suggests the upper lip has more mechanoreceptors, influencing facial muscle activity.
Area of Science:
- Neuroscience
- Human Physiology
- Sensory Biology
Background:
- The orbicularis oris muscle, crucial for lip function, receives sensory input from the perioral region.
- Understanding the neural pathways controlling orbicularis oris reflexes is essential for elucidating facial motor control.
Purpose of the Study:
- To investigate how the location of mechanical skin stimulation affects reflex responses in the upper and lower orbicularis oris muscle divisions.
- To determine if sensory innervation density differs between the upper and lower lip vermilion borders.
Main Methods:
- Recorded reflex responses from upper and lower orbicularis oris muscle divisions.
- Applied localized, innocuous mechanical stimuli to 11 distinct perioral skin sites.
- Measured two-point discrimination thresholds on the upper and lower lip vermilion borders.
Main Results:
- Reflex response amplitude varied significantly with stimulation site.
- Ipsilateral upper and lower lip vermilion borders yielded the largest responses in both muscle divisions.
- Stimulation of the mouth corner, chin, and cheek produced minimal to no responses.
- Two-point discrimination thresholds were significantly lower on the upper lip vermilion border compared to the lower lip.
Conclusions:
- The upper and lower divisions of the orbicularis oris muscle likely share common synaptic input from reflex pathways.
- The upper lip vermilion border appears to be more densely innervated with mechanoreceptors than the lower lip vermilion border.