Flashcards in Lecture 11: Spinal Cord, Brainstem, & Cortex Control of Motor Function II Deck (74)
What is the definition of the pyramidal system?
These are tracts that pass through the medullary pyramidals. (other motor pathways are extrapyramidal)
Which two tracts make up the pyramidal system?
> corticospinal tract
> corticobulbar tract
Where do upper motor neurons originate?
What percentage of upper motor neurons decussate in pyramids and form the lateral corticospinal tracts?
Where do most upper motor neurons synapse?
With association neurons in spinal cord central gray matter.
You know that 75-85% of upper motor neurons decussate in pyramids and form the lateral corticospinal tracts. Where do the remaining upper motor neurons decussate?
Remainder decussate near synapse with lower motor neurons and form anterior corticospinal tracts.
How are upper motor neurons classified?
Classified according to where they synapse in the ventral horn:
- medial activation system
- lateral activation system
- nonspecific activating system
What muscles are innervated by the medial activation system?
postural and girdle muscles
What muscle control is the lateral activation system associated with?
Associated with distally located muscles used for fine movements.
What system of upper motor neurons facilitates local reflex arcs?
nonspecific activating system
What makes up the lateral corticospinal tract?
Corticospinal fibers that have crossed in medulla.
What makes up the anterior corticospinal tract?
Uncrossed corticospinal fibers that cross near level of synapse with LMSs.
What does the lateral corticospinal tract supply?
ALL levels of spinal cord.
What does the anterior corticospinal tract supply?
Neck and upper limbs.
What are the 3 origins of the corticospinal tract (pyramidal tract)?
> primary motor cortex
> pre-motor cortex
> somatosensory area
True or False:
In the corticospinal tract, some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract.
What is the pathway of the corticospinal tract?
site of origin -> internal capsule -> medullary pyramids -> X in lower medulla (most fibers) -> lateral columns of spinal cord (lateral corticospinal tract).
Where are giant pyramidal (Betz) cells located?
in motor cortex
What do giant pyramidal (Betz) cells do?
send collaterals back to cortex
What percentage of the fibers in the corticospinal tract are giant pyramidal (Betz) cells?
What are the functions of the corticospinal tract?
> Adds speed and agility to conscious movements.
- especially movements of the hand
> Provides a high degree of motor control.
- (i.e., movement of individual fingers)
What are some symptoms of a patient with a corticospinal tract lesion?
> reduced muscle tone
> not complete paralysis
> NOTE: complete paralysis results if both pyramidal and extrapyramidal systems are involved (as is often the case).
In the corticospinal tract, where do other fibers from the cortex, besides giant pyramidal (Betz) cells, go?
> pass into caudate nucleus and putamen
> pass to red nucleus
> pass to reticular substance and vestibular nuclei
> large numbers of fibers pass to pontine nuclei
What does the corticobulbar tract innervate?
Where do most fibers of the corticobulbar tract terminate?
In reticular formation near cranial nerve nuclei.
What do association neurons of the corticobulbar tract synapse with?
lower motor neurons
True or False:
Association neurons in the corticobulbar tract leave the reticular formation and synapse in cranial nerve nuclei and also lower motor neurons.
large neurons from the magnocellular region of the red nucleus give rise to what tract?
Where does the rubrospinal tract decussate?
decussates in lower brain stem