The pons is the middle part of the brain stem and is attached to the front of the cerebellum by two stems at the back. The pons is located below the midbrain (mesencephalon) and above the medulla oblongata and is approximately 2.5 centimeters high.
Other names for the pons are the bridge of Varol or the pons Varolii.
The location of the pons in the brain:
Pons. Image from Anatomography maintained by Life Science Databases(LSDB). 日本語: 橋。 画像はLife Science Databases(LSDB)のAnatomographyというサイトより。
The word 'pons' is Latin for bridge. The name already indicates that it connects parts. The pons connects the cerebral cortex of the large brain (cortex), small brain (cerebellum) and the medulla oblongata (medulla oblongata) with each other and thus acts as an intermediate station for signals.
The pons coordinates which cranial nerves are controlled.
It carries out the coordination between the two hemispheres of the brain. The pons also transmits signals from the organs of balance and hearing to the cerebellum.
Furthermore, the pons coordinates the movements of the eyes.
The REM sleep phase, the phase in which most people dream, originates in the pons.
Also in sleep paralysis (the state between dream and wakefulness in which one cannot speak or move) the pons plays a role.
The respiratory organ is partly located in the pons and the other part in the medulla oblongata.
Consciousness and the degree of consciousness originate in the pons.
- awareness of the environment
- consciousness of one's own self
- the subjective experience of one's own body, thoughts, emotions, wishes and intentions
Injury to the pons
Injury to the pons may affect many important and autonomic movements and body functions. Several cranial nerves originate in the brainstem. In the pons these are cranial nerves V-VIII.
These nerves control many functions and all associated functions can be disrupted in case injured:
- sleep and sleep cycles and regulating deep sleep and inhibiting movements in sleep
- balance, body position/posture, muscle tension
- bladder control
- eye movements, horizontal eye movements are coordinated in the pontine gaze center. (Pontine means belonging to the pons.)
- facial expression
- feeling in the face
- production of saliva
- production of tears
Vibrations and shaking
Furthermore, it is known that pons and brain stem injuries may cause involuntary movements that resemble trembling, shaking, tonic-clonic and fasciculation-like muscle contractions. This can also occur in case of temporary oxygen deficiency of the pons and other parts of the brain stem.
The involuntary movements vary in nature, frequency and per trigger. The vibrations can occur in the late night, just before waking up. When aggravated, they can also be felt during the day, but not always visible. It causes an intensely tiring and restless feeling in the body. The vibrations can 'extinguish' over time and later 'flare up' again.
Furthermore, injury to the pons can cause the following problems:
- sensory problems,
- sleep disorders,
- loss of voluntary muscle control,
- disturbances of consciousness and coma.
A group of neurons throughout the brain stem and part of
reticular formation is particularly important for consciousness: the Ascending Reticular Activating System (ARAS). The function of the ARAS is to make the cerebral cortex active and alert to all forms of stimuli. More information on the coma page.
Pons related injuries
- Locked-in syndrome (LIS). A blood clot prevents blood flow to the part of the brain that sends signals to the spinal cord (cerebromedullospinal disconnect syndrome). More rare is intracranial hemorrhage as a cause. The result is that the person ends up in a state where he or she is trapped in his or her own body. Aware of the environment, but unable to move or communicate due to complete paralysis.
- Central Pontine Myelinolysis the white matter that covers and protects the nerve endings. It ensures rapid conduction of stimuli and prevents short circuits. In this injury, the myelin in the pons is damaged.
The literature states that breakdown of this white matter in the pons can be caused by too rapid correction of a low sodium level in the blood (hyponatremia) or by alcohol consumption. Complaints may include:
- paralysis of both arms and legs (tetraparalysis)
- problems controlling the tongue (pseudobulbar paralysis)
- swallowing disorder (pseudobulbar paralysis)
- speech disorder (pseudobulbar paralysis)
The Central Pontine Myelinolysis problem is often accompanied by disorders of other brain areas.
- Lacunar infarction due to blockage of the arteries that supply the pons with oxygen and nutrition. Complaints may include:
- loss of feeling
- problems walking
- problems speaking
Read more on our page on lacunar stroke.
- Pontine glioma or diffuse intrinsic growing pontine glioma (DIPG), a tumor that arises from the supporting cells (glia cells) of the brain cells. This type of brain tumor is mainly seen in children, most often at the age of six and seven years. This type of brain tumor is rarer at other ages, but it can als occur at other ages.
Complaints may include:
- paralysis of facial muscles such as mouth and eye muscles
- double vision
- problems with hearing
- difficulty speaking
- changes in facial sensation
- balance problems
- reduced responsiveness
- MSA-c Multiple/Multiple system Atrophy type c (olivo-ponto-cerebellar atrophy) is a progressive brain disease by which cells die. There is atrophy in several brain areas. In this type of MSA, atropy occurs in the olive nucleus (olivo), the brain stem (pons) and in the cerebellum. Complaints may include:
- ataxia (uncoordinated movements)
- balance problems and unsteady gait
- trembling when moving
- sleep disorders
- difficulty speaking, soft voice
- problems swallowing
- breathing disorders
Read more on our MSA page.
- Millard-Gubler syndrome or ventral pontine syndrome
- Foville syndrome in the dorsal part of the pontine tegmentum
- Intracranial hemorrhage in the pons. This hemorrhage is usually not only localized in the pons but also in the midbrain
(mesencephalon). You can therefore relate complaints to both parts of the brain. Complaints may include:
- severe headache
- breathing difficulties (respiratory arrest or irregular breathing)
- disturbances of consciousness / coma
- rarely body temperature dysregulation
- high blood pressure
- paralysis or loss of strength on one side or on both sides
- abnormal eye movements (horizontal or vertical gaze palsy)
The control center for vertical eye movements is located in the mesencephalon/midbrain. The control center for horizontal eye movements is located
in the pons.
Gaze palsy is a disorder in which a person cannot move both eyes in a certain direction at the same time.
Horizontal gaze palsy is a disorder in which a person cannot move the eyes to the right and left.
Vertical Gaze Palsy is a disorder in which a person cannot move the eyes upwards across the horizontal centerline of the eye. A person cannot look up or down with both eyes at the same time.
Each eye has six muscles. Cooperation between the muscles of the eyes allows the eyes to see in a coordinated manner and in this way double vision is prevented.
Brain damage can cause an eye muscle to fail. Then the muscle cannot cooperate with other muscles. As a result, the images of the two eyes do not coincide.
The central nervous system elaborated
Tectum mesencephali, Crus cerebri, Pretectum, Aqueduct of Sylvius
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