Pons is a term derived from the Latin word meaning ‘bridge’ and rightly so it serves as a bridge between brain and body. A horseshoe-shaped structured part of the brainstem that consists of millions of nerve fibres. Along with serving as a bridge, it also connects the cerebrum and the cerebellum in the brain. Pons can also be defined as a relay station that passes sensory information between the cerebrum and cerebellum from the peripheral nerves to the thalamus.
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Pons in the Brain
The human brain is an evolved system with connecting neurons that regulate and maintain our physical responses and mental health. When one dissects a brain the anatomy of the brain is an interesting subject that fosters many parts of the brain like the frontal lobe, parietal lobe, occipital lobe, temporal lobe, brainstem and cerebellum. The primary understanding of the brain can be easily done with the three main parts cerebrum, cerebellum and the brain stem. The brain stem has a stalk-like structure and bridges the gap between the head and body as it connects the cerebrum with the spinal cord.
Brain stem can further be divided into three parts:- the midbrain, pons, and the medulla also called the medulla oblongata. Let us now understand pons definition, pons structure and pons anatomy as this will enlighten your knowledge on what is the function of the pons.
Pons Anatomy and Pons Function
The function of pons in the brain can be better understood once the entire anatomy and location of the pons in the brain are clear.
Location of the Pons - The pons is superior to the medulla oblongata and inferior to the midbrain, so it lies above the medulla and below the midbrain. When a sectional part of the pons is dissected it can be seen that the pons lies anterior to the cerebellum that is in front of it and behind or posterior to the pituitary gland. The broad anterior bulge in the medulla is pons and it measures about the length of 2.5 cm in adults and it appears as a bridge that also connects the two hemispheres in the brain.
Structure of Pons - The pons even though appears as a bridge the basal part of it is free and not connected to anything, it is a collection of various tracts and nuclei, all aid to serve the purpose of the pons function. The fibres of tracts and nuclei that travel down from the cortex are called pontine nuclei. The middle cerebellar peduncles are formed when fibres of pontine nuclei from one side cross over to join together with the other side of the pontine nuclei this forms the major pathways for information to travel to the cerebellum from the brain and brainstem. The main artery for the blood supply of the entire brain is present in the pons called the basilar groove, it is a shallow groove that lodges the basilar artery and is present in the middle of the fibres.
Anterior Pons - Pons is also the origin point for many nerves like the trigeminal nerve which is the fifth cranial nerve and the most complex of all cranial nerves. The abducens nerve which is the sixth cranial nerve, the facial nerve and the vestibulocochlear nerve which are the seventh and eighth cranial nerves respectively. All of these nerves that originate from the pons serve very specific functions.
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Posterior Pons - When one separates the connection of the pons with the cerebellum the posterior surface is revealed and the pons covers the upper half of the fourth ventricle. It exposes the midline of the floor which is called medial eminence. The fibres of the facial nerve looping around the abducens nucleus form a bulge called facial colliculus. It also clearly shows the stria medullaris, which marks the posterior border between the pons and the medulla it is a bundle of nerve fibres crossing transversely from the lateral aspect into the midline.
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Posterior Anatomy of the Pons
Interior of the Pons
The internal part of the pons contains pontine nuclei that are located in the ventral pons and that also goes on to form the cerebellar peduncles which connect to the cerebellum. The reticular formation, a set of nuclei found throughout the brainstem is the evolutionarily older part of the pons called the tegmentum. The tegmentum also consists of oculomotor nuclei and the path of the oculomotor nerve cerebral aqueduct, red nucleus, substantia nigra and crus cerebri. The posterior part has many tracts passing through it like the ascending spinothalamic tracts and medial lemniscus tracts and the descending corticospinal tracts and corticobulbar tracts.
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The function of pons in the brain is very important and widespread due to its physiology and it caters to respiratory control and many other cranial nerve functions as well.
The two centres apneustic centre present in the lower parts of the pons and the pneumotaxic centre present in the upper part of the pons controls the rate and depth of involuntary respiration or breathing.
Signals relay is continuously occurring and it is controlled by the pontine fibres.
The trigeminal nerve provides sensory supply to the entire face, part of the neck and scalp and is thus responsible for feeling in the face. It also controls the muscles that are responsible for the eating habits like biting and chewing and even the swallowing process.
The abducens nerve allows the eyes to look from side to side due to its presence in the caudal parts of the pons it causes lateral rotation and abduction of the eyeball hence controlling its movement.
The facial expressions are controlled due to the motor signals provided by the facial nerve that is present in the pons. It also controls salivation as it carries taste sensations and it provides innervation to the salivary glands and also regulates the corneal reflex arc.
The movements of sound from the ear to the brain is controlled by the vestibulocochlear nerve that originates from the pons.
Pons being a part of the brainstem is also involved in impacting several automatic functions that are necessary for life like breathing and even the controlling of sleep cycles.
Pons is also responsible for proprioception, fine touch and vibration because of the ascending medial lemniscus tracts.
The ascending spinothalamic tracts present in the tegmentum is also responsible for pain and temperature sensation.
The descending corticospinal tracts in the pons regulates the voluntary motor control of the body and the voluntary motor control of the face, head and neck is controlled by the descending corticobulbar tracts.
The activated pons helps in REM (rapid eye movement) sleep.
The other voluntary motor control by pons is done for bladder control.
Pons Pathology and Injury
Damage in pons can lead to many problems since there are many nerves and nuclei possessed by it that connects and intersects many networks and important bodily functions. The diseases or damage can lead to severe damage.
An individual suffers from quadriplegia that disrupts voluntary muscle control. And they also lose the ability to speak if there is damage to the nerve pathways in the pons that connect the cerebrum, spinal cord, and cerebellum, this is called the Locked-in syndrome.
The locked-in syndrome is also a result of reduced blood flow, which can also result in strokes and clots or sometimes even bleeding in the pons.
Central pontine myelinolysis is caused when the myelin sheath of nerve cells in the pons is damaged and results in paralysis.
Lacunar stroke is caused when the arteries that supply blood to the pons are blocked due to any reason. And results in loss of memory, inability to speak and walk, paralysis, coma or even death.
Pons tumours result in sensory defects of the trunk and limbs, weakness in the facial muscle and even hearing impairment when the cochlear nerve is affected.
Pontine haemorrhage is caused when any of the fibres of the pontine nuclei are damaged and this also results in paralysis of the lateral rectus.
Due to decreased blood flow in the arteries arising from the basilar artery it leads to infarction of the pons that damages the functioning of the lower limbs.
The pons in the brain is visibly the most distinct part due to their horseshoe structure and bridge-like appearance. Even though from the embryonic stage to the adult stage the pons development is only a 2.5 cm length it controls most important voluntary functions like chewing and swallowing and even involuntary movements like breathing. The uniqueness of this part of the brain is that it is the starting point for many cranial nerves that also foster the diversity of multiple nuclei and fibres.
The pons has a long list of functions that it controls. Even starting with the tiniest change in facial expressions and arousal is controlled by the pons to the heavy-duty of managing sleep that is the circadian cycle and other activities through motor control. Due to its cerebellum connection posture is also maintained by the pons and importantly the equilibrium and muscle tone is also maintained by the pons. With its presence, many things run smoothly and even a small damage can create havoc in the body leading to serious effects like paralysis and death therefore proper care and regular healing through proper diet to prevent strokes and keeping it activated is important.