Crossed pyramidal tract

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

The crossed pyramidal tract, also known as the lateral corticospinal tract, is a major pathway in the central nervous system responsible for the voluntary control of the muscles of the body. It is a component of the pyramidal tracts, which are named for their origin in the pyramids of the medulla in the brainstem.

Anatomy

The crossed pyramidal tract originates in the primary motor cortex, located in the precentral gyrus of the frontal lobe of the cerebral cortex. The neurons in this region 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 crus cerebri of the midbrain, the pons, and into the medulla oblongata.

In the medulla, the fibers form the pyramids of the medulla, where approximately 85-90% of these fibers decussate, or cross over to the opposite side of the central nervous system. This crossing occurs at the junction between the medulla and the spinal cord, forming the lateral corticospinal tract.

Spinal Cord

After decussation, the fibers descend in the lateral column of the spinal cord. The crossed pyramidal tract terminates at various levels of the spinal cord, where the axons synapse with lower motor neurons in the anterior horn of the spinal cord. These lower motor neurons then project to the skeletal muscles, facilitating voluntary movement.

Function

The primary function of the crossed pyramidal tract is to mediate voluntary motor control, particularly fine motor movements of the distal extremities, such as the hands and fingers. It is crucial for the execution of precise, skilled movements.

Clinical Significance

Damage to the crossed pyramidal tract can result in a variety of motor deficits, depending on the location and extent of the injury. Common clinical manifestations include:

• Upper motor neuron lesion: Characterized by spasticity, increased muscle tone, exaggerated deep tendon reflexes, and the presence of Babinski sign.
• Hemiparesis: Weakness on one side of the body, often resulting from a lesion in the cerebral hemisphere or brainstem affecting the tract before decussation.
• Paraplegia or quadriplegia: Resulting from spinal cord injuries affecting the tract bilaterally.

Associated Conditions

Several neurological conditions can affect the crossed pyramidal tract, including:

• Stroke: Often results in damage to the motor cortex or internal capsule, affecting the tract.
• Multiple sclerosis: Demyelination can disrupt the conduction of nerve impulses along the tract.
• Amyotrophic lateral sclerosis: Degeneration of upper motor neurons affects the tract.

See Also

• Pyramidal tracts
• Motor cortex
• Spinal cord
• Upper motor neuron
• Lower motor neuron