Pons Varolii 

Pons Varolii is located in the lower part of the brain stem, i.e., the cerebral cortex system that’s responsible for the regulation and control of the autonomic nervous system. Due to its location between the two hemispheres of the cerebrum, pons Varolii participates in relaying information from the sensory organs to all the processing centers in the brain.

Which Are the Anatomical Landmarks of the Pons Varolii in the Brain?

The cerebellopontine angle refers to the anatomical landmark that helps us identify and locate the pons more easily among other brain stem structures. At this location, small parts of the cerebellum, the facial and vestibulocochlear nerves, and the ventricular choroid plexus surround the foramen of Luschka.

Pons Varolii has another important anatomical landmark – the pontomedullary junction. This junction forms an angle between the upper bordering side of the medulla oblongata and the lower part of the pons.

 

What Are the Functions of the Pons Varolii?

As the brain stem connects the brain to all the parts of the body, the pons Varolii participates in regulating the most vital processes, monitored by this brain structure:

  • Breathing;
  • Circulation;
  • Blood pressure;
  • Chewing;
  • Swallowing;
  • Digestion;
  • Body temperature;
  • Startling;
  • Sleep/wake cycle;
  • Pupils dilatation;
  • Maintaining balance;
  • Saliva formation;
  • Alertness;
  • Vomiting. 

The long list of functions dedicated to this part of the brain is on account of the fact that the pons Varolii is one of the most significant information processing centers of the brain. It relays the received data from the sensory organs and the neuron cells’ sensory organs to all other areas of the cerebral cortex.

How Does the Pons Varolii Regulate and Control Breathing?

Being responsible for the most vital survival process, pons Varolii constitutes 2 centers for control, modulation, and regulation of breathing.

  • The pneumotaxic center of the pons
  • The apneustic center of the pons

The Pneumotaxic Center of the Pons

This breathing center of the pons is made of 2 nuclei: the suprabrachial nucleus and the medial parabrachial nucleus. They are in charge of the control and regulation of both the rhythm and rate of breathing.

The Apneustic Center of the Pons

The apneustic center of the pons Varolii modulates the involuntary control of breathing. This means it’s responsible for controlling the volume of our long and deep breaths.  Note that there’s another kind of breathing – short and shallow breathing, controlled by our abdominal muscles.

How Does the Pons Varolii Regulate and Control Sleeping?

Regulation of deep sleep is one of the essential functions of the pons Varolii. Namely, the pons inhibits movement during sleep by activating the corresponding centers in the medulla oblongata.

This brain structure also participates in the rapid eye movement (REM) phase of sleep. During this phase, the eyes rapidly move behind the closed eyelids. Thus, rapid eye movement refers to the short and ultra-speedy eye movements in different directions. The REM phase occurs 90 minutes after the person falls asleep. The first REM phase of sleep lasts less than 10 minutes.

What Is the Anatomy and Structure of the Pons Varolii?

The pons Varolli is comprised of the following elements:

  • Tracts of the pons Varolii
  • The basilar part of the pons Varolii in the ventral portion
  • The pontine tegmentum in the dorsal portion
  • Cranial nerves

Tracts of the Pons Varolii

The tracts of the pons Varolii comprise the following structures:

  • Spinocerebellar tracts;
  • Corticospinal tract;
  • Dorsal columns;
  • Spinothalamic tracts;
  • Medial longitudinal fasciculus tracts;
  • Corticobulbar tract;
  • Corticopontine tract;
  • Central tegmental tracts.

The Basilar Part of the Pons

The pons’ basilar part gives the pons a characteristic appearance because it’s made of gray and white matter in a bridge-type shape. The axons of the cortical-pontocerebellar tract are the main structures comprising the basilar part of Pons Varolii, which connects the cerebrum to the cerebellum.

The Pontine Tegmentum

The pontine tegmental nuclei support the motor neurons involved in some of the most vital neuronal connections. They also aid the relay of information delivered to both the left and right hemispheres of the brain.

 

The main structures of the pontine tegmentum are:

  • The nuclei of the pontine tegmentum
  • The reticular formation

Nuclei of the Pontine Tegmentum

The pontine tegmentum of the pons Varolii houses the following nuclei:

  • The facial nuclei;
  • The vestibulocochlear nuclei;
  • The nuclei of the apneustic center;
  • The nuclei of the pontine reticular formation;
  • The mesopontine cholinergic system (pedunculopontine nucleus);
  • The nuclei of the cranial nerves;
  • The abducens nuclei;
  • The laterodorsal tegmental nucleus;
  • The nuclei of the pneumotaxic center.

The Reticular Formation

Reticular nuclei consist of several interconnected nuclei that are organized into:

  • The median column (the raphe nuclei)
  • The medial column (gigantocellular nuclei)
  • The lateral column (parvocellular nuclei)

 

The reticular nuclei play a vital role in the modulation, control, and regulation of the brain’s following functions:

  • Sleep and consciousness,
  • Modulation of pain,
  • Control and regulation of the cardiovascular processes and functions,
  • Control and regulation of the somatic motor neuron functions.

Cranial Nerves

The cranial nerves of the Pons Varolii stem from the inferior pontine sulcus:

  • Facial cranial nerve (CN VII)
  • Vestibulocochlear cranial nerve (CN VIII)
  • Trigeminal cranial nerve (CN V)
  • Abducens cranial nerve (CN VI)

What Is the Blood-supply System of the Pons Varolli and the Brain Stem?

The Pons Varolii and the brain stem receive their blood supply via a complex network of veins, the pontine arteries, and the inferior and superior cerebellar arteries.

The pontine arteries are small basilar artery (BA) branches that carry oxygenated blood and nutrition to the Pons Varolii and the surrounding structures.

What Is the Function and Structure of the Basilar Artery?

The basilar artery is the direct supplier of blood and nutrients to the brain stem, cerebellum, and the brain’s occipital lobes. This artery branches into:

  • Superior cerebellar artery;
  • Pontine artery;
  • Posteromedial arteries;
  • Anterior inferior cerebellar artery;
  • Internal auditory (labyrinthine) artery.

This major blood-supplying vessel of the brain stems from the vertebral arteries and ends with the posterior cerebral arteries, which are part of the Circle of Willis.

What Happens If the Pons Varolii Becomes Dysfunctional?

In the case of Pons Varolii lesions, or damage caused by internal or external factors, various medical conditions and diseases may occur. The list of symptoms experienced by the affected individual include:

  • Problems with balance,
  • Difficulty chewing,
  • Difficulty in swallowing liquids or food,
  • Hearing problems,
  • Blurred vision,
  • Paralysis,
  • Numbness,
  • Inability to coordinate movements,
  • Hydrocephalus,
  • Disturbances of consciousness,
  • Sleeping problems (sleep apnea, insomnia).

Sleep Apnea

Sleep apnea is a sleep disorder characterized by continuous stopping and resuming of breathing during sleep. This interrupted sleeping pattern leads to snoring and tiredness during the day.

We can distinguish the following types of apnea:

  • Central sleep apnea
  • Obstructive sleep apnea
  • Complex sleep apnea syndrome

Central Sleep Apnea

Central sleep apnea is a syndrome that causes repeated obstructions of breathing during sleep. This is due to the inability of the brain to relay the correct information to the muscles that regulate the breathing pattern.

Obstructive Sleep Apnea

Obstructive sleep apnea is a breathing disorder that occurs during sleep. It’s characterized by restricted breathing, a result of blockage of the airways by the throat muscles. Fatigue, sore throat, and dry mouth are the typical symptoms of this syndrome.

Complex Sleep Apnea Syndrome

Complex apnea syndrome is a disordered form of sleeping that occurs as a result of the inability of the cortical structures to trigger the breathing process. The complexity of this syndrome lies in the fact that it incorporates the symptoms of all other types of apnea.

Insomnia

Insomnia is a common sleep disorder that refers to the inability to fall asleep at night. The reasons for this sleep disorder are usually based on excessive worrying, emotional problems, stress, trauma, etc.

Insomnia can be subdivided into the following types:

 

  • Acute insomnia
  • Chronic insomnia
  • Comorbid insomnia
  • Sleep-onset insomnia
  • Maintenance insomnia

Acute Insomnia

Acute insomnia lasts for a short period, usually for less than three months. A stressful or traumatic event is often the main reason why the affected individual is not able to fall asleep. After the stressful event that triggered the insomnia is resolved, the pattern of sleep goes back to normal again.

Chronic Insomnia

Chronic insomnia typically lasts for more than several months. This type of insomnia occurs after a stressful event, mental health disorders, poor sleep hygiene, unhealthy sleep habits, etc.

Comorbid Insomnia

Comorbid insomnia occurs in patients who already have an underlying medical condition, such as sleep apnea, depression, gastroesophageal reflux, etc. This is the reason why it’s mostly diagnosed in elderly people.

Sleep-onset Insomnia

Sleep-onset insomnia refers to the inability of the affected individual to fall asleep as the night falls. After going to bed, the patient always struggles to fall asleep. This type of insomnia mainly occurs as a result of psychological issues, or disturbance of the circadian cycle of the body.

Maintenance Insomnia

Maintenance insomnia is a sleep disorder characterized by instances of waking up at night and struggling to fall asleep right after. This sleep disorder results in lowered concentration during the day, irritability, and depressed mood of the affected individual.

Fun Facts

Did you know?

 

  1. If the Pons Varolii suffers damage to its structures, all the muscle functions will be obstructed.  The eyes are the only organ of the body that will still be able to move.
  2. The Pons Varolii got its name since it resembles a bridge. (Lat. pons – bridge)
  3. The pontine arteries branch out from the basilar artery, located where the medulla oblongata and the pons connect.
  4. The lower part of the Pons Varolii regulates the intensity of our breathing.
  5. The upper part of the Pons Varolii lowers the frequency of the breaths we take.
  6. Life without Pons Varolii would be unimaginable since it regulates the body’s most vital processes – breathing, sleeping, eating, and heart rate.
  7. The Circle of Willis is the area where internal carotid arteries branch into smaller arteries that supply the cerebrum’s structures with oxygenated blood.
  8. Apneustic respiration refers to an irregular breathing pattern interrupted by gasping for air.
  9. The phrenic nerve is both a sensory and motor nerve. It branches from the spinal nerves in our neck. Because it’s involved in controlling the motor neurons in the diaphragm, its function is imperative to breathing.
  10. The ventricular choroid plexus refers to the network of capillaries and ependymal cells responsible for the production of cerebrospinal fluid in the central nervous system of our brain.