The pons called Pons Varolii, in Latin, is known as the ‘Bridge’. it is called so as it connects both the hemispheres of the cerebrum and it is named after the Italian anatomist and surgeon Costanzo Varolio. This region in the brain stem consists of neural pathways and tracts that help to send signals from the brain down to the cerebellum and medulla oblongata and the tracts that carry signals from the pons up into the thalamus.
The largest part of the brainstem which is located above the medulla oblongata and below the midbrain is Pons Varolii. Pons is a horseshoe-shaped nerve fibre that is present in the hindbrain.
Let us look at the anatomy of the pons - location, structure, function, and clinical relevance.
The pons is a collection of nerve fibres located in the anterior part of the posterior cranial fossa.
The bulging transverse pontocerebellar fibres is considered as the anterior surface or ventral surface. These are the fibres that are wrapped around the vertically oriented brainstem which can measure up to the height of 2.5 cm in adults.
The midline of the ventral surface is divided by a groove called the basilar groove, it is the location where the basilar artery is present.
The angle between the lower border of the pons and the superior border of the medulla is a pontomedullary junction, which is an important anatomical landmark.
The cranial nerves that originate from the ventral surface of the pons are:
Cranial Nerve V: It is called trigeminal, which originates from the lateral aspect of the mid pons.
Cranial Nerve VI: It is called abducens, which originates from the pontomedullary junction that is close to the midline.
Cranial Nerve VII: It is the facial nerve that originates from a cerebellopontine angle that is lateral to the pontomedullary junction.
Cranial Nerve VIII: It is the vestibulocochlear nerve that is located lateral to the facial nerve.
The pons is related to the cerebellum and it is connected to the cerebellum by the middle cerebellar peduncles. The underlying fourth ventricle is revealed when the cerebellum is removed.
The midline of the floor of the fourth ventricle is marked by medial eminence.
The fibres of the facial nerve that are looping around the abducens nucleus are facial colliculus.
A bundle of fibres that are crossing transversely from the lateral aspect into the midline is the stria medullaris of the fourth ventricle. The posterior border of the pons and medulla is marked by them.
The pons is composed of two major components:
It consists of pontine nuclei that are responsible for the coordination of movement. The fibres from these pontine nuclei form middle cerebellar peduncles on their way to the cerebellum by crossing the midline of the nuclei.
Tegmentum of Pons:
In Latin tegmentum is known as covering. The Tegmentum of the pons is the location for several types of cranial nerve nuclei, where the CN III and CN IV are located in the tegmentum.
There are certain divisions of the tegmentum in the midbrain, pons, and medulla.
Lateral tegmental field
Pons: Important Cranial Nerves Nuclei
The sensory nucleus and the trigeminal motor nuclei are located in the mid pons. The main sensory nucleus receives somatic sensory information from the face. The two other nuclei which receive sensory information from the trigeminal nerve are the Spinal trigeminal nucleus and the Mesencephalic nucleus.
The cerebellopontine angle is clinically important since it is often the place of intracranial growths, which can lead to impairment of nearby structures. Symptoms start with mild impairment of the cranial nerve in the area.
The major function of the pons in the brain are:
It helps along with the medulla oblongata to serve a special role in the generation of the respiratory rhythm of breathing.
The active functioning of the pons is responsible for rapid eye movement (REM) sleep.
The blood supply of the pons is by branches of the vertebrobasilar system. The pons contains nuclei that rely on the signals that come from the forebrain to the cerebellum, along with nuclei pons deal primarily with the functions like sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.