Anatomy & Organs

Bridge (Pons) – Structure, Function & Diseases

Bridge (pons)

The pons (the pons ) is a ventrally protruding section of the brainstem . It lies between the midbrain and the medulla.

What is the bridge

The bridge (from the Latin “pons”) is a section of the human brain . Together with the cerebellum , the pons belongs to the hindbrain ( metencephalon ). Even a cursory inspection of the brain reveals the bridge as a clearly raised transverse bulge. It is located between the midbrain (mesencephalon) and the cerebellum (myelencephalon) and together with both forms the brainstem of the brain in the central nervous system .

Anatomy & Structure

The bridge is divided into a front part – the base (Latin: Pars basilaris pontis) – and a rear part – the bridge cap (Latin: Pars dorsalis pontis).There are two longitudinal ridges at the base. The so-called pyramidal tract (main part of the system of movement control, tractus pyramidalis) runs through both . The basilar artery , which is an important tributary for supplying the brain with blood , runs in the middle of the groove (Latin: sulcus basilaris) . In the cross-section of the brain, a clearly visible line connecting the two halves (raphe) can be found, which is crossed by a large number of nerve fibers. The body of the trapezium (Latin: Corpus trapezoideum) is located behind the transverse fibers of the pontine base. It forms a station of the auditory pathway (central nervous part of the auditory system).

Dorsally, at the caudal edge of the bridge, in the bridge angle of the cerebellum, cranial nerves VII ( nervus facialis , facial nerve) and VIII (Latin: nerve vestibulocochlearis , equilibrium nerve) come to the surface of the brain. The VI The cranial nerve (lat.: Nervus abducens, together with other nerves responsible for the movement of the eyeball ) leaves the bridge in the bulbopontine sulcus at the base of the bridge, which points downwards. The trigeminal nerve (very strong 5th cranial nerve, “triple nerve”, conveying tactile sensations in the face and scent perception) exits or enters the bridge laterally.

Part of the floor of the rhombic fossa (lat.: fossa rhomboidea) forms the dorsal end of the bridge cap and thus of the 4th ventricle ( cavity filled with cerebrospinal fluid ). The connection to the cerebellum is established on both sides through the middle cerebellar peduncle (Latin: Pedunculus cerebelli medius).

Function & Tasks

The pons forms the passageway for all the pathways that connect the areas of the central nervous system in front of and behind it, both between brain areas and with the spinal cord . In addition to these longitudinal strands of fibers (Latin: Fibrae pontis longitudinales), the white matter of the pons also contains strong strands of fibers running transversely to them (Latin: Fibrae pontis transversae).

These connect the bridge to the cerebellum. The pathways that connect the two parts of the metencephalon originate in so-called bridge nuclei (Latin: nuclei pontis), which are considered switching stations. Above all, the cortical areas in the cerebrum -cortex are connected to those of the cerebellum (usually crossed) via this. The nuclei of the bridge (mediators of projections of the cerebral cortex and the contralateral cerebellar cortex) unfold strongly.

Embedded in the pontine formation reticularis (extended, diffuse network of neurons in the brainstem), the pontine cap contains, among other things, the motor nuclei of origin of some nerves of the brain (e.g. nucleus motorius nervi trigemini, nucleus nervi abducentis and nucleus motorius nervi facialis). The pons is the regulatory center for circulation and respiration . It also ensures the function of hearing and taste.

Diseases

Typical diseases of the bridge are central pontine myelinolysis (CPM), Millard-Gubler syndrome (so-called bridge syndrome) and tumors . Central pontine myelinolysis is a neurological disease. This leads to damage to the sheathing of nerve fibers in the pons.These diseases are caused when a pathologically reduced sodium level ( hyponatremia ) in the organism is corrected too quickly. Extrapontine myelinolysis is a particular form of CPM that involves demyelination in the cerebellum, near the ventricles, in the basal ganglia, in the bars, and in the internal capsule. Both forms of ZPM are considered osmotically demyelinating diseases, which can also occur simultaneously. Low-salt diets with high drinking quantities (e.g. in the case of malnutrition and anorexia ), side effects of medication such as diuretics or carbamazepine ), hormonal disorders (e.g. Schwartz-Bartter syndrome )., central salt wasting syndrome), so-called “water intoxication” (e.g. in the event of incorrect infusion therapy or accidental drowning) and alcoholism can trigger hyponatraemia and thus CPM.

Millard-Gubler syndrome is what is known as a bridge syndrome, in which there are circulatory disorders in the area of ​​the foot of the bridge (pars basilaris pontis) (e.g. as a result of a stroke ). So-called lateral and paramedian bridge syndromes can also occur. There are also bridge hood syndromes. Lateral bridge syndromes usually result from the occlusion of the circumferential arteries and damage the lateral pedunculus cerebellaris medius (bridge arm) on one side.

Symptoms of lateral bridge syndrome include movement and sensory disturbances . Paramedian bridge syndromes – also known as bridge foot syndromes – are the result of an occlusion of the branches of the basilar arteries and can be associated with symptoms such as spastic hemiplegia. With bridge hood syndrome, failure of the cranial nerves leads to hearing disorders , paralysis of vision, paralysis of sensation or cerebellar ataxia (disorder of movement processes).

A tumor in the pons can damage the brainstem. Signs of such a tumor can be squinting of the eyes , paralysis of the facial nerve (half of the face drooping), disturbances in the direction of vision, irregular breathing, loss of voluntary motor functions (exception: eye and lid movements) or paralysis of both arms and both legs (complete paraplegia ). The sense of hearing can also be impaired, and disturbances of consciousness can also occur.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.