Direct pyramidal tract

General Information
Latin	tractus pyramidalis directus
Greek
TA98
TA2
FMA
Details
System	Nervous system
Artery
Vein
Nerve
Lymphatic drainage
Precursor
Function	Voluntary motor control
Identifiers
Clinical significance
Notes

The direct pyramidal tract, also known as the corticospinal tract, is a major neural pathway in the central nervous system responsible for the voluntary control of the muscles of the body. It is a component of the pyramidal system, which is involved in the execution of voluntary motor movements.

Anatomy

The direct pyramidal tract originates in the cerebral cortex, specifically from the primary motor cortex, the premotor cortex, and the supplementary motor area. These areas are located in the frontal lobe of the brain. The neurons in these regions are known as upper motor neurons.

Pathway

The axons of the upper motor neurons descend through the corona radiata and converge to form the internal capsule, a white matter structure that carries information past the basal ganglia. From the internal capsule, the fibers continue to descend through the midbrain, forming part of the cerebral peduncles.

In the pons, the fibers are dispersed among the pontine nuclei but regroup in the medulla oblongata, where they form the pyramids of the medulla. At the junction of the medulla and the spinal cord, approximately 85-90% of these fibers decussate, or cross over to the opposite side, forming the lateral corticospinal tract. The remaining 10-15% of the fibers do not decussate and continue as the anterior corticospinal tract.

Termination

The fibers of the lateral corticospinal tract descend in the lateral column of the spinal cord and terminate in the anterior horn of the spinal cord, where they synapse with lower motor neurons. These lower motor neurons then project to the skeletal muscles, facilitating voluntary movement.

The anterior corticospinal tract fibers, which do not decussate at the medulla, eventually cross over at the level of the spinal cord where they terminate, also synapsing with lower motor neurons.

Function

The primary function of the direct pyramidal tract is to mediate voluntary motor control, particularly fine motor movements. It is crucial for the execution of precise, skilled movements, especially those involving the distal parts of the limbs, such as the fingers and hands.

The tract is also involved in the regulation of muscle tone and the facilitation of reflex actions. It plays a significant role in the motor learning process, allowing for the adaptation and refinement of motor skills.

Clinical Significance

Damage to the direct pyramidal tract can result in a variety of motor deficits. Lesions in the tract can lead to upper motor neuron syndrome, characterized by spasticity, hyperreflexia, and the presence of Babinski sign.

Conditions such as stroke, multiple sclerosis, and amyotrophic lateral sclerosis can affect the integrity of the pyramidal tract, leading to impaired voluntary motor control.

See Also

• Pyramidal system
• Extrapyramidal system
• Motor cortex
• Spinal cord

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