Behaviors observed by human beings are the effect of muscular movement (Carlson, 2012). In fact, it has been described by neuroscientist that “The primary function of the nervous system is the synchronized innervations of the musculature.” (Laemmle, Strominger, & Demarest, 2012).
Pyramidal and extrapyramidal have become indistinct anatomically; some anatomists propose they be abandoned. Clinicians, on the other hand, continue to find them functional because the clinical signs of lesions of the direct (pyramidal) motor pathways differ from those of the indirect (extrapyramidal) system.
In line, clinicians have conventionally divided the motor system into two groups of circuits, commonly called the pyramidal system and the extrapyramidal system. The pyramidal system comprises the corticobulbar and corticospinal tracts; the extrapyramidal system includes all other structures that power motor control, including the basal ganglia and the projection pathways from the brainstem to the spinal cord (Campbell, 2012). Physiologically, the pyramidal and extrapyramidal systems interrelate, so separating them on this base must be considered as artificial.
Pyramidal Motor Systems
One of the motor systems of the central nervous system (CNS) is called the pyramidal motor system, and its bases are mostly in the precentral gyrus of the cortex (motor area) (Campbell, 2012). It moves through various subcortical structures to the medulla, where an estimated 70% to 90% of the fibers arising in each hemisphere cross to the opposite side and moves within the spinal cord as the corticospinal tract (Brodal, 2010; Campbell, 2012). The area of the medulla upon which the fibers cross-over forms the shape of a pyramid, hence, the name pyramidal system.
This system involves the initiation and control of fine muscle movements and is excitatory only. Specifically, it is involved only in the initiation of movements.
Extrapyramidal Motor Systems
The extrapyramidal motor system, on the other hand, is a system that controls gross motor activities, such as those required to roll over in bed or to make postural adjustments, and it has both excitatory and inhibitory components (Augustine, 2008).
The extrapyramidal motor system has an important responsibility in motor movement. It directs the projections that transmit involuntary motor drives to the intended nervous system.
This complex system has its main foundation in the prefrontal cortex, but it also has an origin in the precentral, postcentral, and temporal cortex. The descending fibers of this system also move to the spinal cord after most of them cross over at the level of the medulla. Nevertheless, the crossover of fibers arising in either the right or left neural structure does not take place at the pyramidal area of the medulla, accordingly the name “extrapyramidal” motor system.
The cerebellum is regarded as part of the extrapyramidal motor system, and it functions as the regulation and modification of the motor activities, receiving input and sending output to the rest of the brain and the spinal cord. The impulses produced in the cortical portions of the extrapyramidal system are transported to the body by two descending tracts (the rubro-spinal tract and the reticulo-spinal tract) in the spinal cord.
The impulses from all descending spinal cord arrangements leave the spinal cord at the ventral root and reach the muscle by what is called the final common pathway. The final common pathway explains the route of the motor neuron from the spinal cord to the muscle fibers that it controls (Kandel, Schwartz, Jessell, Siegelbaum, & Hudspeth, 2013).
Reference List
Augustine, J. R. (2008). Human Neuroanatomy. San Diego, CA: Academic Press.
Brodal, P. (2010). The Central Nervous System. New York, NY: Oxford University Press.
Campbell, W. W. (2012). DeJong’s The Neurologic Examination. Philadelphia, PA: Lippincott Williams & Wilkins.
Carlson, N. R. (2012). Physiology of Behavior. Upper Saddle River, New Jersey: Pearson.
Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S. A., & Hudspeth, A. J. (2013). Principles of Neural Science. New York, NY: McGraw Hill Professional.
Laemle, L. B., Strominger, N. L., & Demarest, R. J. (2012). Noback’s Human Nervous System, Seventh Edition: Structure and Function. New York, NY: Springer.