Unit 3: Corticospinal And Corticobulbar (CN) Pathways Pg 93-101 Flashcards
Pyramidal system refers to what pathways
Corticospinal and Cortibobulbar/Corticonuclear pathways
There are many descending motor pathways that do not traverse the pyramids and are sometimes collectively called
Extrapyramidal system
What is the origin of the coritospinal and corticobulbar (corticonuclear) tracts?
Frontal lobe (several regions) and Parietal lobe
Frontal lobe:
- precentral gyrus and anterior paracentral lobule
- posterior part of the superior frontal and middle frontal gyri
- medial frontal gyrus and anterior portion fo cingulate gyrus
Parietal lobe:
- post central gyrus
- posterior paracentral lobule
- superior parietal lobule
What 2 locations of the frontal lobe individually contributes about 30% of pyramidal fibers? (So 60% together)
30% - Precentral gurus and anterior paracentral lobule
30% - premotor and supplementary motor areas of frontal lobe
Note: other 40% is from the parietal lobe
Anatomically: Precentral gurus and anterior paracentral lobule
Functionally:
Primary motor cortex (M1)
Pyramidal neurons are called
Betz cells
The primary motor cortex corresponds to Brodmann map area
4
Functionally: Premotor area
Anatomically:
Posterior part of superior frontal and middle frontal gyri; anterior to the primary motor area
Functionally: supplementary motor
Anatomically:
Medial frontal gyrus and anterior portion of the cingulate gyrus
Premotor and supplementary motor areas of frontal lobe corresponds to Brodmann Map area
6
The premotor and supplementary motor area is involved in what function?
Planning the execution of movement and the programming of skilled movements
Some of the descending fibers that originate in the parietal lobe are not upper motor neurons
True. They terminate on sensory neurons in the brainstem and spinal cord
The corticospinal fibers in the pyramids that do not decussate at the pyramidal decussations do what?
Uncrossed fibers descend in the anterior funiculus of spinal cord to form the ventral/anterior corticospinal tract and decussate at the spinal level
Corticospinal and corticobulbar (corticonuclear) tracts help provide voluntary control of motor activity’s that involve distal parts of extremities and face such as:
Eyes Tongue Facial expression Fingers Toes
Corticospinal and corticobulbar (corticonuclear) tracts confers that movements of the distal and extremity body parts (eye, tongue, facial expression, fingers, toes) can be performed with
Speed
Agility
Precision
A “pure” lesion of the Corticospinal tract can be performed in a non-human primate by abating (cutting) through a pyramid (above the decussations). The initial result if this is:
Hypotonia of contralateral muscles (esp distal extremities and face)
Initial period of flaccid paralysis contralateral to lesion (esp distal extremities)
NOTE: over a period of several months motor control returns so that
- chronic loss of voluntary motor control is minimal
- permanent difficulty with performing highly skilled activities with distal extremities
- execution of movements requires much attention and there is a permanent loss of speed, agility and precision of movements
What are long term deficits resulting from a “pure” lesion of the C-S tract (after return of motor control)
- Permanent difficulty with performing highly skilled activities with distal extremities
- Execution of movements requires much attention with permanent loss of speed, agility and precision of movements
Corticobulbar (corticonuclear) Tract originates from
UMNs located in inferior 1/3 of precentral gyrus, the premotor area and areas of parietal lobe
The motor nuclei of cranial nerves that receive C-B/C-N innervation include
Oculomotor nuclear complex including LMNs of CN III
Trochlear nucleus — CN IV
Trigeminal motor nucleus — CN V
Abducens nucleus — CN VI
Facial motor nucleus — CN VII
Nucleus ambiguus — CN IX, X, (cranial root of) XI
Hypoglossal nucleus — CN XII
Note: the only CNS not mentioned 1, 2, and 8
Which 3 nuclei receive C-B/C-N innervation, but not directly?
III
IV
VI
Most C-B/C-N fibers innervate nuclei of V, VII, nucleus ambiguus and XII on which side?
Contralateral
Note: there are significant C-B/C-N fibers to these nuclei that end ipsilaterally. Thus most LMNs of CN receive bilateral C-B/C-N innervation and there is no significant paralysis of most muscles innervated by CN following unilateral lesions of C-B/C-N fibers
What cranial nerves are included in the nucleus ambiguus?
IX
X
XI (cranial root)
What are the two exceptions to the pattern of bilateral C-B/C-N innervation?
- LMS within the caudal portion of the facial motor nucleus that innervate muscles of facial expression on the lower 1/2 of the face
- LMNs of the hypoglossal nucleus that innervate muscles of the tongue
Vergence movements
Eyes move in opposite directions
