Pons is the largest and lowest structure of the brain stem. It serves as a ‘bridge’ connecting the two hemispheres of the cerebrum and supporting the transmission of almost all the information processed in every area of the brain.
Furthermore, this part of the brain is in charge of the relay of information between different brain centers, as well as the regulation of sleep. It also plays an important role in the processing and control of sensations such as hearing, eye movement, taste, bladder control, balance, swallowing, equilibrium, facial expressions, as well as facial sensation.
As one of the most active relay centers in the brain, the pons is involved in the regulation of the most vital function of the human body – breathing.
What Is the Main Function of the Pons?
As a result of its central location in the brain, the pons serves as one of the major relay centers for information, transferring it from the neuron cells to all other areas of the cerebral cortex.
This brain structure performs some of the most vital functions in the brain. It’s involved in the regulation and control of a long list of functions, including facial expression, chewing, biting, swallowing, as well as the transmission of sound from the ear to the brain.
Above all, the pons is responsible for the regulation of deep sleep and breathing by controlling the breathing rate and the pattern of inhaling and exhaling air performed by the lungs.
The Pons and Respiratory Control
The pons can be split into two centers for the regulation and control of breathing:
- Apneustic center
- Pneumotaxic center
Apneustic Center
The apneustic center is located in the lower section of the pons. When the neurons located in this center are stimulated, they signal the medulla’s inspiratory center, thus activating the phrenic nerve.
Pneumotaxic Center
This neural center is located in the upper part of the pons. It regulates the amount of air we inhale with each breath and controls both inspiration and expiration.
Where Is the Pons Located in the Brain and What Is Its Structure?
Location of the Pons
Located on the upper part of the brain stem, right above the medulla oblongata and the midbrain, the pons functions as a relay center of all information coming to or from the brain.
In this way, this part of the brain serves as a sort of a bridge (hence its name) among the other stimuli-processing structures of the brain.
Organization of the Pons
The pons is comprised of the following structures:
- The basilar part of the pons in the front (ventral portion)
- The pontine tegmentum of the pons in the back (dorsal portion)
- Tracts of the pons
- Cranial nerves
Both the basilar part of the pons in the front and the pontine tegmentum of the pons in the back are made of groups of neuronal cell bodies, as well as bundles of neurons, i.e. tracts. Their bundles of fibers connect both parts of the cerebellum.
Basilar Part of the Pons
The basilar part of the pons is made of gray and white matter and forms the characteristic appearance of the pons, in the form of a bridge. It is formed by the axons of the cortical-ponto-cerebellar tract and functions as a link to both the cerebrum and cerebellum.
The ventral portion of the pons is the area where the pontine nuclei are located. These structures are responsible for movement coordination.
Pontine Tegmentum
The pontine tegmentum is comprised of a multitude of nuclei:
- the nuclei of the cranial nerves
- the abducens nuclei
- the facial nuclei
- the vestibulocochlear nuclei
- the nuclei of the pontine reticular formation
- the mesopontine cholinergic system consists of a pedunculopontine nucleus
- the laterodorsal tegmental nucleus
- the nuclei of the pneumotaxic center, and
- the nuclei of the apneustic center.
These nuclei of the pons are involved in motor activity by supporting some of the most vital neuronal connections and the transmission of information they carry toward both cerebellar hemispheres of the brain.
The pontine tegmentum is also the location of the reticular formation – a network of nerves whose axons stem from the medulla oblongata and branch toward the spinal cord and the thalamus.
The reticular formation plays a vital role in consciousness, alertness, as well as in the sleep cycles. Also, it’s related to behavioral responses to various stimuli, sensory perception, as well as motor control.
Tracts of the Pons
There are several tracts that ascend from the pons to the other brain structures. They are described and analyzed below:
- Dorsal columns – They transmit the information on proprioception, touch, and vibration. The dysfunctional dorsal columns can lead to sensory problems reflecting on the opposite part of the body.
- Spinothalamic tracts – They transmit information from the sensory organs, translated as pain, soft touch, and temperature. The dysfunctional spinothalamic tracts of the pons can also lead to sensory problems reflecting on the opposite part of the body.
- Spinocerebellar tracts – These tracts are responsible for the transmission of sensory information from the proprioception to the cerebellum, especially regarding the balance, tone, and posture of the body.
- Corticospinal tract – The corticospinal tracts are in charge of the voluntary movements of the body since they stem from the motor areas of the brain. Damage to these tracts could lead to paralysis in the opposite part of the body.
- Corticobulbar and Corticopontine Tracts – The corticobulbar tracts are involved in the control and regulation of the head and neck muscles. Originating from the head, the corticopontine tracts link the cerebellum to the brain in order to refine and coordinate the movements of the body.
- Medial Longitudinal Fasciculus tracts – Located in the paramedian area of the pons and the midbrain, this tract branches from the brain stem and coordinates the movement of the eyes with the movements of the head and the neck. It connects the oculomotor, trochlear, abducent, and vestibulocochlear nerves.
- Central Tegmental Tracts – These structures stem from the pons and the midbrain. They provide neural pathways for the transmission of information gained from the sensory stimuli of taste and also serve as a pathway of the descending neuron fibers that connect the cerebellum and the midbrain.
Cranial Nerves
The connection of the pons to several cranial nerves makes it a vital structure for the central nervous system. Four major cranial nerves branch out from the pons:
- Trigeminal cranial nerve – This is the largest one of all 12 cranial nerves. The cranial nerve number V stems from the middle section of the ventrolateral part of the pons and supports the action of chewing, and is also responsible for facial sensation. The trigeminal cranial nerve relays the sensory data to the sinuses and skin and supports the movement of the jaw.
- Abducent cranial nerve – It’s the cranial nerve number VI, and it stems from the junction between the pons and the pyramids and aids the movement of the eyes toward the temporal field of the horizontal plane of the body.
- Facial cranial nerve – It stems from the cerebellopontine angle (angle between pons and cerebellum) and enables facial expressions and movements of the parts of the face. This is the seventh cranial nerve that controls the facial muscles and plays a role in the sensation of taste because it carries both motor and sensory fibers.
- Vestibulocochlear cranial nerve – The eighth cranial nerve which stems from the cerebellopontine angle, and is responsible for the transmission of audio stimuli, i.e. hearing, as a result of its cochlear branch. The vestibulocochlear nerve also regulates our equilibrium and balance.
Conclusion
The pons relays sensory information from the cerebrum to both the cerebellum and thalamus as primary centers, and to all other parts of the human brain, in order to regulate and control the subconscious somatic and visceral motor centers.
In other words, its main function is the control of sleep, and probably the most vital bodily functions of all – the breathing.
If any of the aforementioned structures of the pons is damaged or dysfunctional, it could lead to a wide array of medical conditions and problems with balance, chewing, hearing, vision, paralysis, numbness, incoordination, hydrocephalus, difficulties with taste, and disturbances of consciousness, etc.
Fun Facts
Did you know?
- The word pons has a Latin origin, meaning a bridge. It’s also known as Pons Varolii, or The Bridge of Varolius. This second name was derived after Constanzo Varolio (1543-75), an Italian surgeon and anatomist.
- The pons is only 2.5 cm in length and bulges outward at the top of the brain stem in a characteristic shape of a ‘knob’.
- The term pontine tegmentum also originates from the Latin, and carries the meaning of ‘covering’.
- The pontomedullary junction is an important anatomical landmark of the pons. It creates an angle between the upper boundary of the medulla oblongata and the lower part of the pons.
- The cerebellopontine angle is yet another anatomical landmark that allows us to easily identify and locate the pons. It’s the place where a small part of the cerebellum (responsible for motor movement), the facial and vestibulocochlear nerves, and the ventricular choroid plexus, encircle the foramen of Luschka.
- The ventricular choroid plexus is a network of capillaries and ependymal cells that produce cerebrospinal fluid in the central nervous system. This network also creates a sort of a barrier as protection of the brain’s tissues from toxins.
- The foramen of Luschka is a gap located at the sides of the fourth ventricle. If it becomes blocked, the flow of the cerebrospinal fluid will be disrupted, which can lead to a life-threatening medical condition called hydrocephalus – fluid accumulation in the brain.
- A phrenic nerve is both a sensory and motor nerve that stems from the spinal nerves branching in the neck. Since it supports the motor control of the diaphragm, its function is vitally important for our breathing.
- An injury to the phrenic nerve can lead to a multitude of medical conditions, such as unexplained shortness of breath, recurrent pneumonia, anxiety, insomnia, morning headache, excessive daytime sleepiness, fatigue, etc.
- Carbon dioxide is one of the most powerful breathing triggers. It makes the blood pressure in the arteries rise, thus rapidly increasing the ventilation of the lungs.