Cerebral peduncle

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Brainstem and related structures.

The cerebral peduncle refers to the entire region of the midbrain (mesencephalon) located ventral (anterior) to the tectum, the part of the midbrain dorasl (posterior) to the cerebral aqueduct. It comprises the crus cerebri, tegmentum and the substantia nigra.

The crus cerebri is the most prominent part of the cerebral peduncle. It refers to the massive bundle of fibers located on the anterolateral aspects of the peduncle. These fibers are predominantly corticospinal tracts that carry somatic motor signals from the primary motor cortex down to the spinal cord, facilitating voluntary motor movements. The crus cerebri also carries corticonuclear (corticobulbar) fibers, which are responsible for motor control of the face and neck via the cranial nerves. Additionally, it contains corticopontine fibres which descend from the cerebral cortex to pontine nuclei.

The tegmentum, on the other hand, contains important nuclei and tracts including the red nucleus, periaqueductal grey matter and the reticular formation, which play roles in motor coordination, pain processing and arousal, respectively.

The substantia nigra, which is a large nucleus located posterior to the crus cerebri, is important for movement control. Its degeneration is a hallmark of Parkinson's disease.

The basis pedunculi, another term associated with this region, is used to describe the combined structure of the crus cerebri and the substantia nigra. In common usage, the terms crus cerebri, cerebral peduncle and basis pedunculi are often used interchangeably to refer to the large fiber bundle in the front part of the peduncle.