Fibres pass downwards from the motor cortical pre-central gyrus into the internal capsule, via the corona radiata. In the internal capsule fibres occupy the posterior third of the anterior limb and the anterior two-thirds of the posterior limb.
After descending through the internal capsule the corticospinal tract runs in the cerebral peduncles on the anterior apsect of the midbrain. The immediate posterior relation is the substantia nigra.
In the pons the fibres are scattered, but they regroup to form the pyramids on the anterior aspect of the medulla. In the medulla most fibres decussate to form the lateral corticospinal tract. Fibres that do not decussate descend as the anterior corticospinal tract.
Motor fibres then travel down the cord in the corticospinal tracts.
Most corticospinal neurones synapse with interneurones which then connect with the motor neurones which innervate the muscles at the motor endplate.
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