Where it is
- They are the frontmost part of the midbrain, one on either side, and arise from the front (ventral) part of the pons. [1]
- The descending fibres from the internal capsule continue on through the midbrain as the fibres of the cerebral peduncles. [1]
- The substantia nigra, the largest nucleus of the midbrain, lies just behind (dorsal to) them. [2]
- The oculomotor nerve appears between the two peduncles, in the interpeduncular fossa; the trochlear nerve wraps around the lowest part of each peduncle. [1]
What it does
- They contain the large ascending (sensory) and descending (motor) tracts that run between the cerebrum and the pons, mainly the corticospinal, corticopontine and corticobulbar tracts. [1]
- The corticobulbar tract carries motor signals from the cortex to the nuclei of the cranial nerves in the brainstem. [3]
- Corticopontine fibres end in the pontine nuclei, which pass the signals on to the opposite side of the cerebellum. [1][4]
- Through these tracts they help refine motor movements and learn new motor skills, and help turn body-position (proprioceptive) information into balance and posture. [1]
Connections
- Their fibres come from three areas: the cerebral cortex, the spinal cord and the cerebellum. [1]
- They also act as connectors between the rest of the midbrain and the thalamic nuclei. [1]
Inside it
- In each crus the corticopontine fibres run in the outer and inner thirds, and the corticobulbar and corticospinal fibres in the middle third. [1]
Other names
- Also called the basis pedunculi; the large front bundle of fibres is the crus cerebri (cerebral crus, Latin crus meaning “leg”), also pes pedunculi. [1][5]
- Usage differs: older texts call the crus alone the cerebral peduncle, while the term now usually takes in more of the front of the midbrain (the source lists the tegmentum, crus cerebri and pretectum). [5][1]
- Not the cerebellar peduncles: those are three paired stalks that connect the cerebellum to the rest of the nervous system. [6]
Size
- On this model the left cerebral peduncle measures about 23 mm front to back, 17 mm top to bottom and 19 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [7]
- Centre of the left cerebral peduncle compared with the centre of the midbrain: 12 mm further forward, 13 mm further from the midline; 18 mm apart in a straight line. [7]
- Centre of the left cerebral peduncle compared with the centre of the pons: 10 mm further forward, 22 mm higher, 13 mm further from the midline; 28 mm apart in a straight line. [7]