The crura cerebri form the two cerebral lobes and constitute part of the midbrain. They contain fibers of the capsula interna, through which nerve tracts from different areas of the brain pass, primarily to the bridge (pons). Damage to these nerve fibers can occur, for example, in the course of a stroke and lead to characteristic symptoms such as hemiplegia.
What is the crura cerebri?
The crura cerebri, or cerebral peduncles, form part of the midbrain, where they lie at its base in the anterior region. Adjacent to the crura cerebri is the substantia nigra, which is a nuclear area in the midbrain cap and is black in color because of its melanin and iron content. The distinction between the crura cerebri and other bilateral brain structures, the pedunculi cerebri, is not clear. Experts use this term to refer either to the cerebral peduncles alone or to the cerebral peduncles, to which the cerebral peduncles and the midbrain cap (tegmentum mesencephali) are combined. Between the cerebral peduncles is the interpeduncular fossa, which is a pit. It lies in the middle and thus separates the pedunculi cerebri and thus also the crura cerebri from each other. Further furrows separate it from the rest of the surrounding tissue. In each brain hemisphere (hemisphere), the midbrain includes the crus cerebri and the midbrain cap (tegmentum mesencephali) as well as the midbrain roof (tectum mesencephali).
Anatomy and structure
The oculomotor nerve exits at the interpeduncular fossa, which lies between the two cerebral peduncles. This nerve pathway forms the III. Cranial Nerve and is responsible for various eye movements. In addition, nerve fibers run through the crura cerebri, which belong to the capsula interna and transport information from other brain areas toward the brain stem. Physiology distinguishes five different fibers (fibrae) in the crura cerebri. The Arnold bundles or fibrae frontopontinae run from the frontal lobe via the capsula interna and the crura cerebri to the bridge (pons); the fibrae corticonucleares carry information from the motor cortex via the capsula interna to the brainstem. In the capsula interna, the pyramidal tract provides the fibrae corticospinales, which also transmit motor commands – they are also known as the tractus pyramidalis. Furthermore, the capsula interna in the cerebral lobes includes the Türck bundles (fibrae temporopontinae), which run from the temporal lobe across the crura cerebri to the bridge, as well as the fibrae parietopontinae.
Function and Tasks
The task of the crura cerebri is primarily tied to the neural pathways that pass through it. Through its various fibers, each crus cerebri transmits predominantly motor nerve signals that initiate voluntary movements. In this process, the command for muscle contraction originates in one of the brain’s motor control centers; most of them are located in the motor cortex in the cerebrum. When a neuronal signal arises, it propagates as an action potential through the nerve fibers of the neurons. The nerve fibers are thread-like projections of the cells. On the natural data pathways, the signals pass through the cerebrum and midbrain, where the crura cerebri are also located. From there, they pass into the adjacent pons, which lies between the midbrain and medulla oblongata. However, in order for the action potential to trigger a muscle response, it must be transported further along the spinal cord. The spinal nerves branch off from the spinal cord and thus form the transition into the peripheral nervous system. Finally, the motor signal reaches its destination via other nerves that run throughout the body: at a motor end plate, the nerve fiber irritates the innervated muscle and causes it to shorten (contract) or relax. The result is a conscious movement.
Diseases
Damage to the nerve pathways that run through the crura cerebri can result from a stroke, for example. Ischemic stroke is characterized by a circulatory disorder that leads to undersupply of the affected brain areas. Responsible for this is, for example, a thrombus or an embolism. In both cases, a clot initially forms within a blood vessel in the human body. This so-called thrombus can eventually narrow the blood vessel to such an extent that it is completely blocked.However, it can also become detached and travel with the bloodstream until it gets stuck at a narrow point. In this case, medicine refers to an embolism. If the brain is affected, a stroke occurs. Depending on which areas of the brain are affected, different signs of the disease can develop. Typical symptoms include hemiparesis or paralysis of only one arm or leg, speech and swallowing disorders, impaired consciousness, nausea, vomiting, dizziness, disturbances of the Babinski reflexes, amnesia, various cognitive or neuropsychological abnormalities, hemianopsia and numerous other symptoms. Doctors usually use computed tomography (CT) to create an image of the brain to confirm the stroke and determine which areas of the brain are affected. Initial measures are taken as soon as possible to limit the death of more nerve cells. About 60% of all stroke patients survive a stroke and the following year. In the medium and long term, treatment after a stroke involves extensive therapies that often include not only pharmacological and other medical measures, but also neuropsychological, physiotherapeutic logopedic, occupational therapy and other means. Risk factors that may contribute to the development of stroke include male gender, older age, elevated blood pressure, smoking, dyslipidemia, physical inactivity, diabetes mellitus, cardiac arrhythmias, and genetic predisposition.
