Pyramidal tract

The pyramidal tracts include both the corticospinal and corticobulbar tracts. These are aggregations of upper motor neuron nerve fibres that travel from the cerebral cortex and terminate either in the spinal cord or the brainstem and are involved in control of motor functions of the body.

• The corticospinal fibers connect the cerebral cortex to the spinal cord. They originate mainly in the motor and premotor areas of the frontal lobe, descend through the brainstem, decussate (mostly at the pyramids in the medulla), and synapse on the lower motor neurons or interneurons in the anterior gray horns of the spinal cord. These can be sub-divided into lateral and anterior corticospinal tract fibers.

• The corticobulbar (a.k.a. corticonuclear) fibers are motor neurons that connect the cerebral cortex to the motor nuclei of cranial nerves in the brainstem. They transmit voluntary motor signals from the cortex to control the muscles of the face, head, and neck.

The myelination of pyramidal tract fibers is incomplete at birth and progresses gradually in a caudo-cranial direction, allowing for the progressive acquisition of functionality. By the age of two, most myelination is complete, after which it continues at a much slower rate in a cranio-caudal direction until approximately twelve years of age.