A cut /lesion above the pyramidal tract decussation results in: September 2007
Correct Answer: Paralysis of the opposite half of the body
Description: Ans. A: Paralysis of the opposite half of the bodyThe Pyramidal Tract/coicspinal tract is group of fibers carries messages for voluntary motor movement to the lower motor neurons in the brain stem and spinal cord.Approximately 80% of the cell bodies of the pyramidal tract are located on the precentral gyrus of the frontal lobe (the motor strip). Approximately 20% of the pyramidal tract fibers also originate in the postcentral gyrus of the parietal lobe, in Brodmann's areas 1, 2, and 3. Regardless of the location of their cell bodies, pyramidal tract fibers begin their descent from the coex as a corona radiata (radiating crown) before forming the internal capsule.This tract is direct and monosynaptic which allows messages to be transmitted very rapidly from the central nervous system to the periphery.The fibers of the pyramidal tract that synapse with spinal nerves sending information about voluntary movement to the skeletal muscles form the coico-spinal tract. As they descend through the brain, they form pa of the posterior limb of the internal capsule.At the pyramids in the inferior pa of the medulla, eighty-five to ninety percent of coico-spinal fibers decussate, or cross to the other side of the brain. The remaining ten to fifteen percent continue to descend ipsilaterally. The fibers that decussate are called the lateral coico-spinal tract or the lateral pyramidal tract. Because they descend along the sides of the spinal cord, the uncrossed or direct fibers that synapse with spinal nerves on the ipsilateral side of the body are called the direct pyramidal tract. They may also be referred to as the ventral pyramidal tract or the anterior coico-spinal tract since they travel down the ventral aspect of the spinal cord.The spinal nerves receive only contralateral innervation from the coico-spinal tract. This means that unilateral pyramidal tract lesions above the point of decussation in the pyramids will cause paralysis of the muscles served by the spinal nerves on the opposite side of the body. For example, a lesion on the left pyramidal tract above the point of decussation could cause paralysis on the right side of the body.
Category:
Physiology
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