Reflexes are quick reactions that occur when you come into contact with a specific stimulus, or in a specific way. The glabellar reflex is one of these reactions that do not involve in any way the higher functions of the consciousness. Let’s see how it is.

What is the glabellar reflex?

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

This reflex happens when you repeatedly hit the center of your forehead , a little above where your nose ends, so that your eyes cannot come into contact with the examiner or the object hitting that area.

Once the glabellar zone has been hit, as described above, briefly but energetically, this is when the glabellar reflex occurs, which consists of a constant and abnormal blinking by the subject being examined .

What nerve is involved in this reflex?

During this reaction the trigeminal nerve, which is the V cranial nerve, is mobilized. This nerve is located in the protrusion of the brain stem, and from there it extends to the Gasser Ganglion . This ganglion is the largest sensory root, and is located in the middle cranial fossa, hence 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 that is stimulated, by means of a contact or a visual stimulus we will be able to observe a different reflection in the eyes or in some zone of the face of the subject.

By feeling the forehead sector over the nose (glabellar zone), with the tapping and the form described above what we are doing is stimulating the ophthalmic branch (V1) of the Gasser ganglion , which is linked to the trigeminal nerve (V cranial nerve).

All these connections must be working properly for the reflex to occur, if there is any interference or anomaly at any point, then the synapse could not 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 occur. Bearing in mind that the third cranial pair (facial nerve) also intervenes in this reflex, by means of the efferent neuron, it is then understood that the glabellar zone reflex is of trigeminal-facial origin .

The importance of this physiological phenomenon

This reflex is fundamental for the protection of exaggerated muscle stretching, in this case of the eyelid muscles. The glabellar reflex is responsible for preventing the eyelids from being damaged and this in turn represents an important protection for the eyes.

This evaluation is really simple to perform by the examiner, as it is non-invasive. It is part of the person’s routine physical examination, and allows for very accurate detection of any spinal cord damage .

Medical evaluation

The examiner should be aware of the reflex response in both eyelids; if it happens that the blink is not symmetrical on both sides, then is an indicator of neurological damage . If so, it will be necessary to determine where exactly the damage is, whether in the afferent or sensory pathway, in the reflex processing centre (interneuron), the efferent or motor pathway, or in the effector muscle.

In order for the evaluation of this reflex to be satisfactory, it is necessary for the person being evaluated to be in a state of complete muscular relaxation. Otherwise the muscle will not react to the stimulus in the expected manner.

Sometimes it is difficult for the assessor to get the patient to relax as much as necessary to apply the assessment method. When these complications occur, a series of techniques can be used to achieve the appropriate state of relaxation in the subject.

Examples of techniques

Some of these techniques are as follows.

1. Use the Jendrassik maneuver

This procedure helps to obtain the reflex act by means of sudden movements in the area where the answer is sought.

For example, in the case of the glabellar zone, the examiner will ask the subject to blink quickly before proceeding with the assessment .

2. Relaxation techniques

It is convenient to use them before applying the percussion on the muscle tendon.

Bibliographic references:

  • Purves (2004). Neuroscience: Third Edition. Massachusetts, Sinauer Associates, Inc.
  • Derrickson (2006). Principles of Anatomy and Physiology.