Glabelar’s reflex: what it is and how it happens

Reflexes are rapid reactions that occur upon contact with a specific stimulus, or in a specific way. The glabellar reflex is one of these reactions that the higher functions of consciousness are not involved in any way. Let’s see how it is.

    What is the glabelar reflex?

    As with all reflexes, the glabellar reflex is a process in which the sensory neuron drives the impulse directly to the motor neuron, Which is responsible for immediately sending the response to a muscle, which performs the action of the reflex act.

    This reflex occurs when the center of the forehead is repeatedly struck, A little above the tip of the nose, so that the eyes cannot come into contact with the examiner or with the object striking that area.

    Once the glabelar zone is struck, as described above, briefly but vigorously, this is when the glabelar reflex occurs, which consists constant and abnormal blinking from the subject being examined.

      Which nerve does this reflex involve?

      During this reaction, the trigeminal nerve is mobilized, which is the cranial pair V. This nerve is located in the protuberance of the brainstem, and from here it extends to Gasser’s Gangli. This ganglion is the largest sensory root and is located in the middle cranial fossa, from where its neural bodies are divided into three parts: the ophthalmic branch (V1), the maxillary branch (V2) and finally, the mandibular branch (V3 ).

      Depending on the branch stimulated, by a contact or a visual stimulus, we can observe a different reflection in the eyes or in an area of ​​the subject’s face.

      When we try the area of ​​the forehead above the nose (glabelar area), with the stroke and shape described earlier, what we do is stimulate the ophthalmic branch (V1) of the Gasser’s ganglion, Which is linked to the trigeminal nerve (cranial pair V).

      All of these connections have to work properly for the reflex to occur, if there is interference or abnormality at any given time, the synapse cannot occur properly.

      Therefore, the afferent neuron of this reflex, which belongs to the facial nerve (III cranial pair) would not send any signal to the muscle to move, and the reflex would not pass. Since the cranial pair III (facial nerve) is also involved in this reflex, through the efferent neuron, then we understand that the reflex of the glabellar region it is of trigeminal-facial origin.

        The importance of this physiological phenomenon

        This reflex is essential for the protection of excessive stretching of the muscles, in this case the muscles of the eyelids. The reflection of the glabellar area is responsible for preventing damage to the eyelids and in turn represents an important protection for the eyes.

        This assessment is very easy for the examiner to perform because it is not invasive. It is part of the person’s routine physical examination, and it can detect with great precision if there is damage to the spinal cord.

        medical evaluation

        The examiner should pay attention to the reflex response on both eyelids; if it happens that the flashing is not symmetrical on both sides, then it is an indicator of neurological damage. If this is the case, it will be necessary to determine exactly where the lesion is located, either in the afferent or sensitive pathway, in the reflex processing center (interneuron), in the efferent or motor pathway, or in the effector muscle. .

        In order for the assessment of this reflex to be given satisfactorily, the person assessed must be in a state of complete muscle relaxation. Otherwise, the muscle will not respond to the stimulus in the expected manner.

        sometimes it is difficult for the assessor to get the patient to relax as needed To apply the assessment method, when these complications arise, a number of techniques can be employed to achieve the favorable state of relaxation in the subject.

        Examples of techniques

        Some of these techniques are as follows.

        1. Use the Jendrassik maneuver

        This procedure makes it possible to obtain the reflex act by means of sudden movements in the area where the response is sought.

        For example, in the case of the glabellar area, the examiner it will ask the subject to change quickly before proceeding with the assessment.

        2. Relaxation techniques

        It is advisable to use them before applying a brutal percussion on the muscle tendon.

        Bibliographical references:

        • Purves (2004). Neurosciences: third edition. Massachusetts, Sinauer Associates, Inc.
        • Derrickson (2006). Principles of anatomy and physiology.

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