Orbicularis oris reflex

Of the Orbicularis oris reflex is a pathological external 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 points to organic brain damage. The reflex is often preceded by causal ischemia in the area of ​​the pons.

What is the orbicularis oris reflex?

Reflexes are physiologically present in the human body. As a rule, the involuntary muscle contractions are protective reflexes that correspond to either monosynaptic self-reflexes or polysynaptic protective reflexes.

A reflex always has an afferent and an efferent limb. The triggering perceptual stimuli are transmitted to the central nervous system via the afferents. The efferent thighs trigger the motor reflex response.

In addition to the physiological reflexes, neurology knows pathological reflexes that can only be triggered in patients with neurological damage. These pathological reflexes include the orbicularis oris reflex, which is also Palate reflex is called.

The afferent leg of its reflex arch is the trigeminal nerve. The efferent leg corresponds to the facial nerve. The triggerability of the reflex refers to lesions of the upper motor neuron, damage to the nerve tracts between the pons and the cerebral cortex or other organic brain disorders.

In the aforementioned lesions of the nervous system, the orbicularis oris muscle contracts after tapping the corners of the mouth or irritating the palate. The contraction causes the lips to bulge.

Function & task

The orbicularis oris reflex is not a natural reflex and is therefore of no use to humans. For neurology, however, the pathological reflex arc has diagnostic value and thus helps with the assessment of organic brain damage.

The reflex movement is implemented by the motor part of the facial nerve. This is the seventh cranial nerve, which innervates a large part of the head with sensory, sensory, motor and parasympathetic fibers. The sensory-sensory part of the nerve is also called the intermediate nerve. The motor nuclei lie in the pons and connect with the fibers of other qualities only after they have circumnavigated the so-called inner facial knee. The facial nerve innervates the orbicularis oris muscle in a motorized manner and performs the contraction of the muscle in the reflex arc of the orbicularis oris reflex.

The orbicularis oris muscle is also known as the circular muscle of the mouth and, in addition to closing the mouth, is also involved in the tip of the lips. For this reason it is also called kissing muscle in English. The protrusion of the lips as part of the orbicularis-oris reflex corresponds to the kissing movement.

As the afferent leg of the reflex arch, the importance of the orbicularis-oris reflex should not be underestimated, in addition to the facial nerve and the trigeminal nerve. 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. In this way, the nerve registers tapping movements on these structures which, after passing through the reflex arc, trigger the pathological reflex movement of the lips.

The interconnection of the reflex takes place via the pyramidal nerve pathways in the spinal cord. In the anterior horn of the spinal cord, the upper and lower motor neurons of the central nervous system are connected by what are known as pyramidal tracts.

The orbicularis-oris reflex is one of the pathological external reflexes, as it is switched through the interconnection in the spinal cord via synapses lying one behind the other and therefore does not carry its effectors and affecters in the same organ.

Illnesses & ailments

The orbicularis oris reflex is always the symptom of a neurological disease or injury. Most often it accompanies pseudobulbar paralysis symptomatically. Such a paralysis arises from bilateral damage to the corticonuclear brain stem pathways that extend to the caudal cranial nerve nuclei. The damage triggers a central spastic paraparesis of the mouth and throat muscles. Speech disorders as well as restricted tongue mobility and difficulty swallowing characterize the clinical picture. An increased master reflex and pyramidal trajectory signs can be used as diagnostic indicators in addition to the orbicularis-oris reflex.

One of the most common causes of the disease is cerebral arteriosclerosis, which causes multiple ischemic cerebral infarctions in the corticonuclear pathways to the cranial nerve nuclei.

The phenomenon is rarely caused by neurological diseases such as the inflammatory autoimmune disease multiple sclerosis or syphilis. Theoretically, multiple brain metastases can also be the cause of the lesions. However, this cause is just as rare as pseudobulbar paralysis caused by MS or syphilis.

Spastic paraparesis can also provide the larger framework for the orbicularis-oris reflex. This occurs when the upper motor neuron is damaged, as can be caused, for example, by the degenerative disease ALS or immunological inflammation. With ALS, the motor nervous system breaks down bit by bit. In MS, immunological inflammation destroys nerve tissue in the central nervous system.

With motor neuronal lesions of the central nervous system, further pathological reflexes usually appear. Especially the reflexes of the Babinski group are considered indicators of damaged motor neurons. Since the central motor neurons represent the upper control instance of all reflexive and voluntary movements, various movement disorders and movement failures shape the clinical picture of a motor neuronal lesion. In order to correctly interpret the presence of the orbicularis-oris reflex, the neurologist uses imaging methods such as MRI in addition to reflex diagnostics.