L17: Descending Pathways Flashcards
Association areas of cortex “decide” that a movement is called for, leading to the premotor areas of the cortex devising a plan for the movement.
Pre-motor areas pass on into to the motor cortex, which then issues commands to motor neurons either directly or indirectly, by way
of nuclei and interneurons of the brainstem and spinal cord.
This describes which organization of the motor system?
A. hierarchical
B. in parallel
A. hierarchical
Messages are conveyed to the SC from motor cortex and premotor areas themselves. Basal ganglia and cerebellum are involved in various aspects of planning and monitoring movements but have few or no
outputs of their own to the spinal cord (act primarily by affecting motor and
premotor cortices).
This describes which organization of the motor system?
A. hierarchical
B. in parallel
B. in parallel
Descending pathways are made of numerous descending tracts that ultimately terminate (sometimes directly, sometimes indirectly!) on a lower ___ neuron
A. motor
B. sensory
A. motor
Origin of the descending pathways is the ___ ___ (pyramidal neurons of Layer
V); for this reason, they are called corticofugal pathways and are efferent projections from cerebral cortex
cerebral cortices
ok
Voluntary control of a movement occurs via direct communication b/w cortical motor areas and the final destination of the motor output, the ____ ____ neurons located either
in the 1) motor nuclei in the brainstem or 2) in the ventral horn of the
spinal cord
The Lower Motor Neurons
Pathways associated with the voluntary movement are also grouped under the
definition of ____ because of their anatomical location
“pyramidal system”
Descending/corticofugal pathways always originate from the ____
cortex
___ pathways allow for direct communication between UMN and LMN + involve motor nuclei of C.N and motor neurons in the ventral horn
A. direct
B. indirect
A. direct
Label the indirect pathway:
In the Indirect Pathway, there is communication to LMN (lower motor neurons via an intermediate
stop in a ___ ___ of the brain stem. This system receives other
contributions from intermediate player, such as the _____
proper nucleus; cerebellum
Which two corticofugal pathways descend on only one sides (ipsilateral)?
A. Corticostriate / Corticorubral
B. Corticospinal
C. Corticoreticular / Corticonuclear
A. Corticostriate / Corticorubral
_____ is the only corticofugal pathway that is contralateral
A. Corticostriate
B. Corticorubral
C. Corticospinal
D. Corticoreticular / Corticonuclear
C. Corticospinal
Which two corticofugal pathways are bilateral?
A. Corticostriate / Corticorubral
B. Corticospinal
C. Corticoreticular / Corticonuclear
C. Corticoreticular / Corticonuclear
Three features of the voluntary motor control pathways (pathways of the pyramidal system - CST and CNT tracts)?
1) Voluntary movements
2) Monosynaptic connection
3) Fast and uninterrupted connection
Label the CST
Corticospinal fibers originate from which 4 cortical areas?
1) Primary motor*
2) Premotor
3) Supplementary motor
4) Primary somatosensory
5) Somatosensory association -
parietal motor area
CST fibers course through which four brainstem levels?
- Posterior Limb of IC
- Crus cerebri
- Basal pons
- Pyramid of medulla
- Fibers course somatotopically
What happens at the spinomedullary junction?
Pyramidal decussation
The term “pyramidal system” is applied to the _____ together with the functionally equivalent ____ fibers
corticospinal tracts ; corticonuclear
What are the two functions of the pyramidal system?
- Realization of a movement
- Fine movements
_____: Fibers of this tract
originate from large pyramidal neurons in
Layer V of the primary motor cortex (major contributor!!)
Corticospinal tract
At the spinomedullary junction, a majority of the fibers in
the pyramid decussate and enter the ___ ____ of the spinal cord to become _____ tract (LCST).
lateral funiculus; lateral corticospinal
At the spinomedullary junction, a small portion of fibers will not decussate (remaining ipsilateral)
and will enter the ___ ____ of the SC to become the ___ ___ ___.
These fibers will ultimately decussate in the anterior commissure of the spinal cord synapsing with contralateral ___ ___ ___
ventral funiculus;
ventral (anterior) corticospinal tract (ACST);
lower motor neurons
___ controls innervation
of distal musculature
A. Corticospinal Tracts
B. Lateral corticospinal tract (LCST)
C. Anterior corticospinal tract (ACST)
B. Lateral corticospinal tract (LCST)
Where is the LCST located?
A. Ventral Funiculus
B. Lateral Funiculus
D. Distal Funiculus
Projects/terminates to?
A. All levels of lateral SC
B. All levels of ventral SC
Located:
Lateral Funiculus
Projects/terminate: ALL levels of ventral SC
Which muscles do the LCST control?
Contralateral….
- hand
- fingers
- foot & toes
Complications of the LCST cause ___ ____
muscle atrophy
____ controls innervation of
axial muscles
A. Corticospinal Tracts
B. Lateral corticospinal tract (LCST)
C. Anterior corticospinal tract (ACST)
C. Anterior corticospinal tract (ACST)
True or False: Anterior corticospinal tract (ACST) has a larger tract than LCST
False - smaller tract than LCST
Where is the ACST located?
Where do fibers decussate?
Where do fibers terminate?
Located: Ventral Funiculus
Decussation: Anterior White Commisure
Terminate: Ventral horn of all spinal levels
The ACST activates neurons that innervate contralateral ____ muscles
A. distal
B. proximal
B. proximal
How is the CST organized?
Somatotopically
______: Fibers of this tract originate from large pyramidal neurons in
Layer V of the primary motor cortex, premotor
cortex, supplementary motor cortex, primary somatosensory cortex, and parietal association cortex
Corticonuclear tract
Function of the corticonuclear tract?
Voluntary fine movements
- Mostly b/l
Extrapyramidal System is mainly for ____ movements
involuntary
Which three tracts make up indirect pathway
(multineuronal)
that control, adjustment
& synchronization of
movement?
Which of the following tract influences flexor muscles?
A. Rubrospinal t.
B. Vestibulospinal t.
C. Reticulospinal t.
A. Rubrospinal t.
What is this??
A. Rubrospinal t.
B. Vestibulospinal t.
C. Reticulospinal t.
A. Rubrospinal t.
Where do the fibers of the rubrospinal tract
A. arise from?
B. decussate?
C. ends?
Arise from: Red nucleus in midbrain
Decussate: midbrain, course in lateral funiculus
Ends: contralaterally
True or False: The rubrospinal tract may partially compensate for loss of CST in primates
True
Which of the following modulates postural
adjustment in
response to
vestibular stimuli
+ influences extensor muscles?
A. Rubrospinal t.
B. Vestibulospinal t.
C. Reticulospinal t.
B. Vestibulospinal t.
Which of the following arises from the reticular formation, is important for balance, and modulates involuntary movements for extensor m.?
A. Rubrospinal t.
B. Vestibulospinal t.
C. Reticulospinal t.
C. Reticulospinal t.
Which two pathways often exercise an opposite effect
on extensors muscle for postural adjustments?
Reticulospinal and Vestibulospinal tract
Where does the tectospinal tract originate?
A. Cortex
B. Superior Colliculus
B. Superior Colliculus
Functions of tectospinal tract?
1) Reflex control and coordination of head, neck, and eyes in response to stimuli
When do axons of tectospinal tract decussate? terminate?
decussate: midbrain tegmentum
terminate: ventral spinal cord (cervical level only!!!)
True or False: The tectospinal tract originates from the cortex
False - SC!
