Lecture 5 - Overview of Motor Pathways Flashcards
how many fibres cross at the pyramidal decussation before entering the spinal cord?
about 85%
what is the pyramidal decussation?
the dividing line between medulla and spinal cord
what is the corticospinal pathway
the pathway providing voluntary motor function.
in the pre central gyrus (location of motor cortex)
axons extend from UMNs to into the posterior limb of the internal capsule
and enter the pyramidal decussation where 85% cross,
then they descend to the appropriate level in the spinal cord as the lateral or anterior corticospinal tract
they enter gray matter and synapse onto dendrites of LOWER MOTOR NEURONS in the anterior horn to innervate skeletal muscles
what are the 3 anatomical divisions of the internal capsule
the anterior limb
the genu (“knee”)
and the posterior limb contains the descending axons of UMNs.
why is it important that so many axons of the UMNs are packed into such a small space in the posterior limb of the internal capsule?
Even a small lesion could damage many axons.
where do the axons go once they leave the internal capsule?
the midbrain via the crus cerebri on the superficial anterior surface
then they dive deep in the pons in the basis pontis
then into madulla on the anterior surface forming the medullary pyramids
where do the 85% of the fibres that cross over go
the lateral corticospinal tract in the lateral funiculus of spinal cord white matter
where do the 15% of fibres that do not cross at the pyramidal decussation go
they descend in the anterior corticospinal tract in the anterior funiculus
what are Lateral motor nuclei
in the anterior horn of grey matter in spinal cord
receive ipsilateral innervation from the lateral corticospinal tract to innervate limb muscles
what are medial motor nuclei
in the anterior horn of grey matter in spinal cord
receive mostly contralateral innervation from anterior corticospinal tract to innervate trunk muscles.
do all of the fibres in the anterior corticospinal tract not cross over?
90% of them end of crossing over so only a small percent actually stays on the ipsilateral side
where do 90% of the anterior cortiospinal fibres cross?
the anterior white commissure
same spot as pain and temperature crossing
How do UMNs reach the LMNs that innervate the muscles of the head and neck?
the corticobulbar tract.
they travel together with the other UMN, but through the genu instead of the posterior limb
where do the UMNs of that innervate the head and neck meet their LMN parters?
instead of going into the decussation and into the spinal cord, they find their LMN partners in certain cranial nerve nuclei
where are muscles in the body derived by
Most skeletal muscle of the body are derived from myotomes (GSE)
