The pons is a crucial part of the brainstem that lies between the brain and the spinal cord. It is a broad horseshoe-shaped structure with individual functions as well as functions related to nearby organs like the medulla oblongata and the cerebellum.
The pons in the brainstem connects the brain and spinal cord. This connection provides a physical route for information to travel between the brain and the body. It also controls the sleep cycle, manages pain signals, and works with other organs to maintain breathing rhythm.
The pons has many vital junctions for four of the twelve cranial nerves, each having its own functions. Any injury to the pons can result in severe disorders and ultimately poor conduction of signals from the brain to various body parts.
Description Of The Pons
The pons, known as Pons Varolii in Latin, means 'the bridge'. It was named by the Italian anatomist and surgeon Costanzo Varolio as he claimed that the most prominent part of the pons looked like a bridge between the brain hemispheres.
The brainstem sits at the bottom of the brain and has a stork-like shape. The brainstem consists of 4 parts – the diencephalon, midbrain, pons, and medulla oblongata. The pons makes up part of the brainstem. As a whole, it mainly connects the brain to the spinal cord.
Located at the second-lowest part of the brainstem is the pons. This location is below the midbrain and above the medulla oblongata. Although it is a crucial connection from the brain to the spinal cord, it is also the point of origin and termination of 4 cranial nerves. Each cranial nerve has various functions, including managing motor and sensory information to the face.
What does the pons itself look like? It is a horseshoe-shaped mass of transverse fibers. The color is beige or off-white, and it seems like a broad version of the upper stem of a branch of cauliflower. The pons is about 1.06 inches in height, 1.49 inches in width, and 0.98 inches deep.
The mass that makes up the pons consists of two parts: the ventral section and the dorsal section. The ventral part is the white matter, and the dorsal part includes all the nuclei of the cranial nerves in the pons.
What Does The Pons Consist Of?
The pons comprises many different types of cells that form part of the nervous system. The pons has many nuclei. Nuclei are clusters of brain cells that have the same or similar functions. Two main structures make up nuclei: neurons and glial cells.
Neurons are cells that fundamentally make up the brain and nerves; their job is to transmit signals. Structures like a cell body, axons, dendrites, and myelin make up each neuron. Each of these smaller structures plays a vital role in allowing electric signals to be transmitted.
For instance, the dendrites get the information for the neuron; then, the data passes through the cell body to the axon. The signal continues to be passed along to dendrites of other neurons, and these neural messages go on throughout the nervous system.
Glial cells are the supporting cells essential for neurons to work correctly. They protect neurons from infections and disease. They also control the chemical balance in the central nervous system and create a shielding coat on the neuron's axons.
Function Of The Pons
The pons is a fundamental brainstem structure that connects the brain and spinal cord. This connection means that the pons comprises a crucial part of the central and peripheral nervous systems.
Whereas the central nervous system and the peripheral system are different in function, they need to communicate with each other via pathways. By being in the brainstem, it is part of the route that is responsible for carrying signals to and from the brain to the rest of the body.
It literally acts as a bridge between the brain and spinal cord that can carry all the information we need to move and sense things. Although the spinal cord actually receives and sends messages between the central and peripheral nervous systems, the pons in the brainstem attach to the brain and the spinal cord.
Although it may be better to see the pons as a structure that houses various nuclei and tracts with their own functions, some of its primary functions include neurotransmitters that oversee specific functions, like sleep and pain signals. These are called autonomic functions, meaning they are not under our conscious control.
Pons Influences The Sleep Cycle
One of the main functions of the pons is that it controls the sleep cycle. Managing the sleep cycle means that the pons helps to alert your body to wake up. There are certain levels of alertness, and the pons ensures that the correct one is signaled to wake a person up.
Related to controlling the sleep cycle, the pons is also responsible for REM (rapid eye movement) sleep. During REM sleep, the pons, together with the medulla, send signals to the muscles to relax them.
This relaxation is important for the body not to act out dreams at night. The pons is usually implicated when sleep paralysis occurs. Some also suggest that the pons may play a role in dreams too.
Pons Manages Pain Signals
The pons is responsible for messages that give a sensation of pain. It is a route for these signals to travel, but it also regulates the signals that provide pain sensation everywhere in the body below the neck.
Pons Works With The Brainstem And Cerebellum
Although the pons has individual functions, it also works together with other structures in the brain close to it. Underneath the pons lies the medulla oblongata, and these two structures manage the respiratory rhythm of breathing.
The role that the pons plays in breathing has to do with the breathing rate – how many breaths happen per minute. The pons also works with the cerebellum, which is posterior to it. They are together responsible for functions like balance and movement.
Located in the pons is the pneumotaxic center, which contains specific nuclei that control and regulate the change from inhaling to exhaling. These particular systems in the pons also explain how the pons is involved in breathing rhythm regulation.
Functions Of The Cranial Nerves Connections Of The Pons
Besides the individual functions of the pons, like managing the sleep cycle and pain signals, it is also a point of origin for 4 out of 12 cranial nerves, each having its own functions. These cranial nerves connect directly to the brain and the structures they innervate.
The first cranial nerve is the Trigeminal nerve (Cranial nerve V), which provides facial sensation. Sensations of pain or touch (like feeling heat or cold on your face) make up part of the Trigeminal nerve's function. Regarding motor function, this cranial nerve controls the muscles used for mastication (otherwise known as chewing).
There are three main branches of the Trigeminal nerve that have different functions. The ophthalmic branch sends signals to the brain from the eyes and upper parts of the face. The second branch is the maxillary branch which allows sensation to the middle sections of the face as well as to the cheeks, upper jaw, and nose.
The third branch is the mandibular branch that gives sensation to the lower part of the face, like the jaw, lower lip, and gums. This specific branch also provides motor function, so it involves functions such as biting and swallowing. All these functions of the Trigeminal branches are important regarding the pons, as the main nerve originates in the pons.
The second nerve is called the Abducens nerve (Cranial nerve VI) and controls eye movement. Specifically, it controls one of the muscles that are needed to move your eyes voluntarily.
The Facial nerve (Cranial never VII) is the second one that is a key junction in the pons. This nerve controls facial expressions. It also controls the muscles in the inner ear to regulate the loudness of sounds entering the ear. The Facial nerve has both sensory and motor functions.
The Facial nerve is also responsible for helping to produce tears. Regarding sensation, it is responsible for the taste sensation on the front of the tongue.
Lastly, the Vestibulocochlear nerve (Cranial nerve VIII) manages the sense of balance and hearing. It does this as it connects to the vestibular and cochlear nerves in the ear. The vestibular nerve, in particular, is responsible for balance and the cochlear nerve gives the sense of hearing.
What Happens If The Pons Is Damaged?
If the pons is damaged, there will be poor conduction of neural signals from the brain to parts of the body. There will be reduced or complete loss of sensory signals that travel to parts that receive their stimulation by the pons.
A sodium deficiency can cause a demyelinating disease known as Central pontine myelinolysis. This deficiency causes the substance myelin to break down. Myelin is the substance that surrounds neuro axons and is crucial for the conduction of stimulations.
When a disease or condition destructs the myelin, it results in poorer conduction of these signals that are required to stimulate various body parts. It can cause difficulty with multiple functions, including balance, swallowing, speaking, walking as well as the sense of touch. It can result in a severe condition, leading to potential locked-in syndrome and even death.
Other damages that can affect the pons include brain tumors, concussions or traumatic brain injuries, disorders acquired from birth, possibly genetic in nature, poisoning from toxins, infections from bacteria or viruses, and inflammatory conditions like multiple sclerosis.
Symptoms That The Pons Is Damaged
Different parts of the pons can be damaged, and the signs and symptoms will be related to this. However, there are a few common signs that you can look out for, regardless of what precisely has been injured. Deafness and loss of the sense of touch can be two symptoms.
The pons house some cranial nerves. Each of these nerves is responsible for producing a sensation or motor signals to specific body parts. A loss in the ability to feel pain, temperature, or vibration can indicate an issue in the pons. The pons itself specifically plays a role in pain sensation management.
Ataxia, which refers to a lack of coordination, is another symptom of pons damage. This symptom is likely due to one of the pons' functions being balance and movement, both required for correct coordination. If you have double vision, formally called diplopia, it could also be a consequence of pons damage.
The cranial nerve 7, the Abducens nerve, controls eye movement and is one of the nerves originating in the pons. Damage to this nerve specifically can cause diplopia. Paralysis that affects any part of the head, face, or other parts of the body can mean severe damage to the pons. If these symptoms occur, then it could also result in the condition of locked-in syndrome.
Vertigo and tinnitus are another two symptoms to look out for to know whether the pons has been compromised. Vertigo refers to a dizzy or spinning feeling, even if you are only standing or sitting still. Tinnitus is when a person hears a constant ringing in their ears when there is no actual sound.
These symptoms most likely arise when there has been damage to the Vestibulocochlear cranial nerve, which has its nuclei in the pons. This nerve is responsible for the sense of hearing as well as balance.
The pons is mainly a connection between the brain and the spinal cord responsible for carrying signals to the rest of the body. Managing pain sensation and breathing regulation are also functions of the pons.
The four cranial nerves that form essential junctions in the pons also have individual functions, for instance, providing sensation to the face and motor signals to the eyes. If the pons is damaged, you could expect symptoms like a decreased ability to feel pain or temperature.