The orbicularis oris reflex is a pathologic extraneous reflex of the orbicularis oris muscle that is triggered by tapping the corners of the mouth. In neurological diagnostics, the presence of the reflex movement refers to brain-organic damage. Often, the reflex is preceded by causative ischemia in the region of the pons.
What is the orbicularis oris reflex?
The orbicularis oris muscle contracts in the aforementioned lesions of the nervous system after tapping the corners of the mouth or irritation of the palate. Reflexes are physiologically present in the human body. As a rule, involuntary muscle contractions are protective reflexes corresponding to either monosynaptic intrinsic reflexes or polysynaptic protective reflexes. A reflex always has an afferent and an efferent limb. The afferents transmit the triggering perceptual stimuli toward the central nervous system. The efferent legs trigger the motor reflex response. In addition to physiological reflexes, neurology recognizes pathological reflexes that can only be triggered in patients with neurological damage. Among these pathological reflexes is the orbicularis oris reflex, also called the palatal reflex. The afferent limb of its reflex arc is the trigeminal nerve. The efferent limb corresponds to the facial nerve. The triggerability of the reflex refers to lesions of the upper motoneuron, damage to the neural pathways between the pons and the cerebral cortex, or other brain-organic disorders. The orbicularis oris muscle contracts in the aforementioned lesions of the nervous system after tapping the corners of the mouth or irritation of the palate. The contraction causes the lips to bulge forward.
Function and task
The orbicularis oris reflex is not a natural reflex and thus has no benefit to humans. However, for neurology, the pathological reflex arc has diagnostic value and thus helps in the assessment of brain-organ damage. The reflex movement is implemented by the motor part of the facial nerve. This is the VII cranial nerve, which innervates much of the head with sensory, sensory, motor, and parasympathetic fibers. The sensory-sensory portion of the nerve is also called the intermediary nerve. The motor nuclei are located in the pons and connect with fibers of other qualities only after going around the so-called internal facialis knee. The facial nerve innervates the orbicularis muscle motorically and performs the contraction of the muscle in the reflex arc of the orbicularis oris reflex. The orbicularis oris muscle is also called the ring muscle of the mouth and, in addition to closing movements of the mouth, is also involved in the peaking of the lips. For this reason, it is also called kissing muscle in English. The protrusion of the lips within the orbicularis oris reflex corresponds to the kissing movement. As the afferent limb of the reflex arc, the trigeminal nerve, in addition to the facial nerve, plays an important role in the orbicularis oris reflex that should not be underestimated. This fifth cranial nerve carries sensory and motor nerve fibers that reach large parts of the head area in three branches. The corners of the mouth are sensitively innervated by the nerve. Thus, the nerve registers tapping movements on these structures, which, after passing through the reflex arc, trigger the pathological reflex movement of the lips. The circuitry of the reflex runs through the pyramidal nerve tracts in the spinal cord. In the anterior horn of the spinal cord, the superior and inferior motoneurons of the central nervous system are connected by the so-called pyramidal tracts. The orbicularis oris reflex is one of the pathologic foreign reflexes because it is connected by the circuitry in the spinal cord via back-to-back synapses and thus does not carry its effectors and affectors in the same organ.
Diseases and complaints
The orbicularis oris reflex is always a symptom of neurologic disease or injury. Most often, it symptomatically accompanies pseudobulbar paralysis. Such paralysis results from bilateral damage to the corticonuclear brainstem tracts that extend to the caudal cranial nerve nuclei. The damage triggers central spastic paraparesis to the muscles of the mouth and pharynx. Speech disorders as well as limited tongue mobility and swallowing difficulties characterize the clinical picture.An increased master reflex and pyramidal tract signs can be used as diagnostic indicators in addition to the orbicularis oris reflex. One of the most common causes of the clinical picture is cerebral arteriosclerosis, which causes multiple ischemic cerebral infarcts in the corticonuclear pathways connecting to the cranial nerve nuclei. Only rarely is the phenomenon caused by neurological diseases, such as the inflammatory autoimmune disease multiple sclerosis or, for example, syphilis. Theoretically, multiple brain metastases may also be a cause of the lesions. However, this cause is as rare as pseudobulbar paralysis due to MS or lues. Spastic paraparesis may also be the larger frame for the orbicularis oris reflex. Such a paraparesis occurs when there is damage to the upper motor neuron, such as can be caused by the degenerative disease ALS or immunological inflammation. In ALS, the motor nervous system degrades piece by piece. In MS, immunological inflammation destroys the nervous tissue in the central nervous system. In motoneuronal lesions of the central nervous system, other pathological reflexes usually appear. Specifically, Babinski group reflexes are considered indicators of damaged motoneurons. Since the central motoneurons represent the upper control authority of all reflexive and voluntary movements, various movement disorders and movement failures characterize the clinical picture of a motoneuronal lesion. To correctly interpret the presence of the orbicularis oris reflex, the neurologist resorts to imaging techniques, such as MRI, in addition to reflex diagnosis.
