L17: Descending Pathways - A Flashcards
Describe hierarchical organization of the Descending Pathways?
Premotor Cortex
Motor Cortex
A) Indirect
B) Direct
True or False: The basal ganglia and cerebellum are involved in parallel processing of motor system
True
Descending pathways are made of numerous descending tracts, which ultimately terminate on a ____
A. UMN
B. LMN
B. LMN
What is the origin of the descending pathways?
Cerebral cortices (pyramidal neurons of Layer V)
What is another name for the descending pathways?
Corticofugal pathways
True or False: The descending pathways are afferent projections from the cerebral cortex
False - the descending pathways are EFFERENT projections from the cerebral cortex
True or False: Voluntary control of movement occurs via direct communication between cortical motor areas + LMN located either in ___ or ___
1) Motor nuclei - associated with CN in brain stem
2) Ventral horn of SC
The pathways associated with the voluntary movement are also grouped under the definition ___ system
pyramidal
Three features of the Voluntary Motor Control Pathways?
1) Monosynaptic
- pyramidal cell (cortex) => LMN
2) Fast and uninterrupted communication
3) End contralaterally
The term pyramidal system is applied to the __ tracts together with the functionally equivalent ___ fibers
corticospinal; corticonucelar
What are the function of the corticospinal and corticonuclear tracts?
Realization of fine movements
Fibers of which tract originate from large pyramidal neurons in Layer V of M-I, as well as premotor cortex, supplementary motor cortex, primary somatosensory cortex, and parietal association cortex?
Corticospinal Tract
What happens at the spinomedullary junction?
Fibers in the pyramid decussate and enter lateral funiculus to become lateral corticospinal tract
What happens to the fibers that do not decussate at the spinomedullary junction (aka: remain ipsilateral)?
Enter ventral funiculus to become anterior corticospinal tract
Where do the fibers of the corticospinal tract ultimately decussate at?
Anterior commisure of SC - synapse with contralateral LMN’s
True or False: At the end, all fibers of the corticospinal tract end contralaterally
True
_____: Located in the lateral funiculus, projects somatotopically to all levels of the spinal cord, and will terminate at the ventral horn of all levels of the spinal cord
A. Ventral Corticospinal Tract
B. Anterior Corticospinal Tract
C. Lateral Corticospinal Tract
C. Lateral Corticospinal Tract
Main function of the Lateral Corticospinal Tract (LCST)?
Activate neurons in ventral horn (those that innervate distal musculature – neurons that innervate muscle of hands/fingers/feet/toes)
____: consists of 10-15% of CST that does not decussate at pyramidal decussation
A. Ventral Corticospinal Tract
B. Lateral Corticospinal Tract
A. Ventral Corticospinal Tract
True or False: In the ACST, fibers are ipsilateral until levels at which they terminate, where they then decussate in the anterior white commisure to gain contralateral ventral horn
True
Function of ACST (ventral/anterior corticospinal tract)?
Mostly unknown
- Activates neurons in ventral horn that innervate axial musculature
Fibers of the corticonuclear tract originate from which 5 areas?
1) Pyramidal neurons in Layer V of M-I
2) PMC
3) Supplementart motor cortex
4) S-I
5) Parietal Association Cortex
Fibers of which tract will directly synapse with neurons located in the motor nuclei of the cranial nerves?
A. Rubrospinal Tract
B. Corticonuclear Tract
C. Corticospinal Tract
B. Corticonuclear Tract
Some fibers of the Corticonuclear Tract terminate in the nuclei of the midbrain (CN __ and ___) while the rest descend in the ___
CN III, IV; pons
Which of the fibers of the Corticonuclear Tract terminate in the pontine nuclei?
A. CN III and IV
B. CN V, VI, VII
C. CN IX, X, XI, and XII
B. CN V, VI, VII
Which projections of the Corticonuclear Tract are not bilateral?
A. CN VII/CN XII
B. CN V, VI, VII,
C. CN III and IV
A. CN VII/CN XII
Which four CN of the corticonuclear tract will have fibers that end in synapses located in the medullar nuclei?
CN IX, X, XI, and XII
Which of the following has fibers that arise from neurons in the red nucleus in the midbrain?
A. Rubrospinal tract
B. Corticonuclear tract
C. Corticospinal tract
A. Rubrospinal tract
Where do fibers of the Rubrospinal Tract decussate? terminate?
Midbrain
Terminate
- LMN’s in the ventral horn
True or False: The red nucleus receives direct cortical inputs (corticorubral fibers) from the bilateral motor cortices
False - The red nucleus receives direct cortical inputs (corticorubral fibers) from the IPSILATERAL motor cortices
What is the primary function of the rubrospinal tract?
1) Influences flexor musculature – supplements CST
What symptoms would you expect to see if one has a lesion of the CST (aka: severing the pyramid)?
Able to: walk, climb, and pick up food
Unable to: perform fine dexterous movements w/digits
True or False: Rubrospinal system may partially compensate for loss of CST
True
Which two tracts arise from vestibular nuclei in the brainstem (terminate in ventral horn of SC) + are activate in response to vestibular stimulation?
Lateral vestibulospinal tracts
Medial vestibulospinal tracts
True or False: Vestibulospinal tracts are important mediators of postural adjustments and head movements
True
Which two tracts arise from the reticular formation of the brainstem?
1) Lateral Reticulospinal Tract
2) Medial Reticulospinal Tract
True or False: Both the Lateral/Medial Reticulospinal tracts innervates EXTENSOR muscles and projects to ALL spinal cord levels
True
Which of the following
Reticulospinal tracts have axons that descend BILATERALLY in the ventral funiculus?
descend IPSILATERALLY in the ventral funiculus?
Bilaterally - LRST
Ipsilaterally - MRST
Where do neurons of the MRST originate?
Where do neurons of the LRST originate?
Pontine reticular formation
Medullary reticular formation
Where is the Tectospinal Tract located?
A. Ventral funiculus of cervical/thoracic spinal cord
B. Ventral funiculus of cervical spinal cord
C. Lateral funiculus of thoracic spinal cord
D. Lateral funiculus of cervical/thoracic spinal cord
B. Ventral funiculus of the cervical spinal cord only!
Where does the Tectospinal Tract (TST) originate?
Neurons in the SC (superior colliculus)
Where do the fibers of the TST terminate in?
A. Ventral funiculus
B. Ventral horn
C. Lateral funiculus
D. Lateral horn
B. Ventral horn (of cervical spinal cord only!)
Which tract functions in reflex control and coordination of head, neck, and eye movements in response to visual and auditory stimuli + voluntary motor commands?
A. Reticulospinal Tract
B. Vestibulospinal Tract
C. Rubrospinal Tract
D. Corticonuclear Tract
E. Corticospinal Tract
F. Tectospinal Tract
F. Tectospinal Tract
Rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts in parallel to ____ tracts carry descending info from cerebral cortices to LMB
A. Corticospinal
B. Corticonuclear
A. Corticospinal
B. Corticonuclear
Corticospinal + Corticonuclear tract = _____ system
Rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts = ____ system
pyramidal system
extrapyramidal system
True or False: The extrapyramidal system is a genetic term that reassumes the different structures of the CNS and neuronal circuits, which guarantees involuntary movements + their adjustments
True
True or False: Reverberating circuits influences cerebral cortex and, thus, motor output
True
Which four structures belong to the extrapyramidal system?
1 = cerebral cortex
2 = basal ganglia
3 = nuclei of thalamus
4 = nuclei of brain stem
