The phylogenetically older one of two pyramidal systems that originate in the motor cortex, the other being the pyramidal system (or corticospinal tract). Together, they are responsible for the control and coordination of voluntary movements, as well as the maintenance of balance and posture. Thus, they are not functionally independent of each other, and interact at all levels of the nervous system. Moreover, both systems should be considered as functional rather than anatomical units. The extrapyramidal system serves to refine voluntary movements and postural control as well. Its constituent parts, in addition to the cerebellum, are the basal ganglia the red nucleus, and the reticular formation, the reason why it is labeled ‘extra’ as it involves structures outside the pyramidal system (see figure below). All these structures send excitatory or inhibitory information to the so-called lower motoneurons (i.e., anterior horn cells) in the spinal cord via muti-synaptic, and thus, indirect pathways. In this way, it is different from the pyramidal system that forms monosynaptic connections in the spinal cord. Lesions to the extrapyramidal system result in various sorts of dyskinesias and degenerative diseases such as Parkinson’s disease.
