Desscending tracts Flashcards
What is the origin of the pyramidal tract
From neurons in cerebral cortex
The majority of the fibers arise from area 4 and premotor area 6
Some fibers arise firing post-central sensory cortex and the parietal cortex
Fibers from sensory cortex descend to terminate in the contralateral dorsal horn of the spinal cord for modulation of sensation
What is the lamination of the pyramidal tract
In cerebral cortex:
The body is represented upside down with the face lowermost and the foot mod medial of the cerebral hemisphere
In internal capsule:
Fibers from the face in the genu, upper limb is most anterior and lower limb is most posterior in posterior limb of internal capsule
In the midbrain and spinal cord:
Cervical fibers are medial and sacral fibers are lateral
Describe the course of the pyramidal tract
Axons of neurons in the cerebral cortex-descend and converge in the corona radiate
Pass in the anterior 2/3 of the posterior limb of internal capsule
Descend in the 3/5 of the crus cerebri
(basis pedunculi of midbrain)
Descend as scattered bundles in the basis Pontus transverse debt transverse pontine fibers
Fibers collect and form the pyramid of the medulla oblongata
80% of fibers cross in the lower part of medulla forming motor decussation then descend in the spinal cord as the lateral cortecospinal tract which lies in the lateral white column
The uncrossed fibers descend as anterior corticospinal tract
The uncrossed corticospinal fibers usually cross at a lower level
What is the termination of the pyramidal system
In spinal cord
The crossed fibers : on the lateral group of anterior horn cells which supply the limbs
The uncrossed fibers: on the medial group of anterior horn cells which supply the trunk
Some fibers from the ipsilateral cortex descend directly forming ipsilateral corticospinal tract that joins the lateral corticospinal tract from the opposite side it helps in recovery of upper motor neuron lesion
In brain stem:
Some pyramidal tract fibers do not reach the spinal cord but end on motor nucleiof cranial nerves in brain stem
These fibers form the corticonuclear tract which controls muscles of the head
Fibers of corticonuclear tract descend in corona radiate , genu of internal capsule ,reach the brain stem to terminate on the contralateral nuclei and on ipsilateral motor nuclei
Two exception for this double control are:
1-The part of motor nucleus of the facial nerve that controls the muscles of the lower pat of the face
2-The part of hypoglossal nucleus that controls the geniiglissus muscle
What are the functions of pyramidal and extrapyramidal system
The pyramidal system is responsible for skilled voluntary movement
The extrapyramidal system is responsive for muscle tone, posture , semi-autonomic movements
Compare between tectospinal and rubrospibal tract
Tectospinal tract:
Origin: superior colliculus in upper level of midbrain
Crossing: in dorsal tegmental decussation
Site: Anterior white column of cervical segments
End: medial group of cervical AHCs
Neck muscles
Functions: Turning of the head in response of auditory, visual, and cutaneous stimuli
Rubrospinal tract:
Origin: Red nucleus in upper level of midbrain
Crossing: ventral tegmental decussation
Site: in lateral white column of cervical segments
End: lateral group of AHCs upper limb
Functions:Controls muscle tone in upper limb
What is the origin of olivo -spinal tract
Inferior olivary cells of medulla oblongata which receives input from cerebellum
Axons cross and descend in AHCs
Compare between medial and lateral vestibulospinal tract
Medial:
Origin: medial vestibular nucleus
Crossing:crossed and uncrossed
Site:anterior column (down to T3)
End:alpha and gamma neurons of extensor muscles
Lateral:
Origin: lateral vestibular nucleus
Crossing:uncrossed
Site:anterior column (whole cord)
End:Alpha and gamma neurons of external muscles
Compare between medial and lateral reticule spinal tracts
Medial:
Origin: pontine RF
Crossing: uncrossed
Site:Anterior column
End:gamma motor neuron of lamina 9
Lateral/
Origin: medullary RF
Crossing:crossed
Site:Lateral column
End gamma motor neurons of lamina 9
