Function and innervation of the involuntary m. retroauricularis

Area of Science:

• Neuroscience
• Ophthalmology
• Neurology

Background:

• The involuntary retroauricularis muscle (m. retroauricularis) exhibits automatic, obligatory, and tonic coinnervation during conjugate lateral gaze, a phenomenon linked to nystagmus.
• Beyond oculomotor functions, the m. retroauricularis displays other physiological coinnervation patterns during various activities.

Purpose of the Study:

• To describe and analyze the diverse physiological ways of accidental coinnervation of the m. retroauricularis.
• To explore the potential diagnostic utility of m. retroauricularis innervation patterns in neurological conditions.

Main Methods:

• Electromyographic registration of the m. retroauricularis during different physiological states and activities.
• Observation of innervation patterns during talking, chewing, swallowing, inspiration, and sleep.
• Assessment in 'nervous subjects' and patients with ocular myasthenia.

Main Results:

• Irregular bursts of innervation were recorded during talking, chewing, swallowing, and involuntary inspiration.
• Regular rhythmic inspiratory innervation and myoclonic jerks were observed during sleep, with a potential link to REM sleep.
• The m. retroauricularis demonstrated an early myasthenic reaction in patients with ocular myasthenia.

Conclusions:

• The m. retroauricularis exhibits complex and varied innervation, extending beyond oculomotor control.
• Irregular innervation in 'nervous subjects' may serve as a measure of involuntary somatomotor nervous system activity and neurotic tension.
• The study suggests potential diagnostic applications for m. retroauricularis innervation analysis in facial paralysis, strabismus, and nystagmus.