corticospinal tract

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cor·ti·co·spi·nal tract

a composite bundle of corticospinal fibers [TA] that descend into and through the medulla to form the lateral corticospinal tract [TA] and the anterior corticospinal tract [TA]. This massive bundle of fibers originates from pyramidal cells of various sizes in the fifth layer of the precentral motor (area 4), the premotor area (area 6), and to a lesser extent from the somatosensory cortex. Cells of origin in area 4 include the gigantopyramidal cells of Betz. Fibers from these cortical regions descend through the internal capsule, the middle third of the crus cerebri, and the basilar pons to emerge on the anterior surface of the medulla oblongata as the pyramid. Continuing caudally, most of the fibers cross to the opposite side in the pyramidal (motor) decussation and descend in the posterior half of the lateral funiculus of the spinal cord as the lateral corticospinal tract, which distributes its fibers throughout the length of the spinal cord to interneurons of the zona intermedia of the spinal gray matter. In the (extremity-related) spinal cord enlargements, fibers also pass directly to motoneuronal groups that innervate distal extremity muscles subserving particular hand-and-finger or foot-and-toe movements. The uncrossed fibers form a small bundle, the anterior corticospinal tract, which descends in the anterior funiculus of the spinal cord and terminates in synaptic contact with interneurons in the medial half of the anterior horn on both sides of the spinal cord. Interruption of corticospinal fibers rostral to the motor (pyramidal) decussation causes impairment of movement in the opposite body-half, which is especially severe in the arm and leg and is characterized by muscular weakness, spasticity and hyperreflexia, and a loss of discrete finger and hand movements. Lesions of lateral corticospinal fibers caudal to the motor decussation result in comparable deficits on the ipsilateral side of the body. The Babinski sign is associated with this condition of hemiplegia.
Farlex Partner Medical Dictionary © Farlex 2012

Corticospinal tract

A tract of nerve cells that carries motor commands from the brain to the spinal cord.
Mentioned in: Neurologic Exam
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Since corticospinal drive is directly involved in the activation of TA during the swing phase of locomotion [4, 5], after successful MEP up-conditioning, the corticospinal pathways that were trained to increase their connectivity during conditioning trials would also do so during walking.
There are strong arguments supporting the notion that the narrow central synchronization reflects input to the motoneurons from collaterals of common last order neurons [31, 47, 49], and there is also strong evidence to suggest that the coherence in the beta band reflects activity in corticospinal neurons and that the central drive responsible for these two phenomena therefore originates in the motor cortex and may possibly be explained by activity in the direct monosynaptic corticospinal pathway to the spinal motoneurons [31, 47, 49].
Capaday, "Input-output properties and gain changes in the human corticospinal pathway," Experimental Brain Research, vol.
For example, allocating spatial attention towards the hand targeted by the TMS intervention results in increased excitability in the corticospinal pathway innervating the target muscle relative to conditions in which attention was directed elsewhere [15-19].