Varolio Bridge: characteristics and functions

The Varolio bridge is an area of ​​the brain stem responsible for regulating automatic functions. Today we show you these functions and their characteristics.

Reviewed and approved by the psychologist Elena Sanz on November 23, 2021.

Last update: 23 November, 2021

The Varolio Bridge, also known as brainstem bridge or Annular protuberance, is a section of the brain in humans and other bipeds. It is located in front of the cerebellum, above the medulla oblongata and just below the midbrain. Therefore, it is a structure of the central nervous system (CNS) with its own functions.

Although we cannot understand the function of the brain in isolation, since this organ functions as a whole, several specific activities have been attributed to this area. It receives its name in honor of Costanzo Varolio (1543-1575) and emulates a highway that allows permanent communication between the brain and the spinal cord. Let’s see everything you should know about him.

Structure of the Varolio bridge

A good part of the internal structure of the pons is neuronal nuclei that are related to the cranial nerves.

The bridge of Varolio is a protrusion found in the brain stem. It shares place with other areas such as the midbrain and the medulla oblongata. We can functionally divide its structure into the following parts:

  • Basilar part of the Varolio bridge: also known as basilar groove or ventral part. Through this the basilar artery crosses; that is, one that provides oxygenated blood to the brain. It is located in the middle area of ​​the bulge and the damage associated with it is related to alterations in motor function.
  • Dorsal part of the Varolio bridge: It is also known as pontine tegmentum. It is the anterior part of the bridge, which forms a rhomboid structure together with the dorsal cord. This section regulates many motor functions, but also sensory and arousal functions.

This is the structure understood in a macro way, but if we analyze it in more detail we find different tracts or nuclei. Among the most important we distinguish the following:

  • Special trigeminal motor nucleus: regulates proprioception of periodontal tissues and of all chewing muscles. It also regulates visceral movements.
  • Special motor core of the facial: it is characterized by being a gray mass on the bridge.
  • Somatic motor abductor nucleus: a structure related to the abducens nerve. Provides innervation to the lateral rectus muscle, one of the extraocular muscles.
  • Superior salivary nucleus: provides parasympathetic innervation to different glands associated with the oral cavity (salivary, submandibular and sublingual).

It also has other sections such as the vestibular and cochlear nuclei, the nucleus of the solitary tract, the trigeminal pontine nucleus, and many more. All of these nuclei are associated with the cranial nerves.

In turn, we can divide its structure into three large groups: sensitive part, visceral motor part and vegetative part. In any case, let this serve as an example that it is a very complex structure, one that also has a leading role.

Characteristics of the Varolio bridge

Like many areas of the brain, the Varolio bridge has some peculiar characteristics. Let’s see some that often go unnoticed when understanding their functions and structure:

  • On average, Varolio’s bridge measures only 2.5 centimeters.
  • It is the largest part of the brainstem (which is partly why it is known as boss).
  • It is made up of neurons and glia, although some specific areas lack synapses.
  • Its own nuclei are found in the ventral part of its structure, although most of its nuclei are associated with the cranial nerves (they are external or shared).
  • It is shaped like a thick roller.
  • It can be affected by conditions such as central pontine myelinolysis and Millard-Gübler syndrome.

The Varolio bridge is part of the central nervous system (CNS) and directly and indirectly regulates different functions. Let’s look at some of these to understand their importance.

Varolio bridge functions

We have already advanced some of the functions of the Varolio bridge, but now we will describe them more carefully. It is not an area that fulfills a single function, but connects with many other areas to form a whole.

Serves as a communication link

The best known function of the Varolio bridge is to serve as a communication link. The bulge allows information to flow from the brain to the spinal cord (and vice versa). Therefore, it has a regulatory or conductive function. Imagine that it is a large highway that works as a two-way communication route.

Regulates automatic functions

Daily you do automatic activities that go completely unnoticed by your consciousness. For example, standing, breathing, or blinking. The Varolio Bridge is responsible for regulating these and other associated processes. Walk, stop or resume inhalation, focus your eyes on a specific place, and so on.

Intervenes in the expression of emotions and feelings

Some of the cranial nerves make facial expressions possible, a function in which the bridge of Varolio is involved.

Emotions such as joy, anger or sadness are manifested through specific facial features. Thanks to the regulation of the nerves that pass through the protuberance, these expressions can be controlled, although most of the time it is done automatically.

Helps maintain balance

Balance is something that most people take for granted. This is because it is regulated by different systems, including the Varolio bridge processes. These receive and transmit signals to the nerves that allow you to keep your head up or walk without losing your balance.

It also intervenes in your perception of pain, taste, touch, the secretion of saliva, tears, auditory perception and many more. As we have already pointed out, these functions do not develop exclusively in this area, but are combined with other areas of the brain to process as a whole.

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