Corticospinal Tract Flashcards
Volitional movements for the body are carried out by what tract?
corticospinal tract
Volitional movements for the cranial nerve motor nuclei that innervate muscles of the face are carried out by what tract?
corticobulbar tract
Where do the corticospinal and corticobulbar tracts arise from?
cerebral cortex
The corticospinal and corticobulbar tracts descend through what to end where?
descend through the internal capsule to end in the brainstem motor nuclei or in the ventral horn of the spinal cord
Where do most of the descending fibers of these two pathways cross to the contralateral side?
lower medulla at the pyramidal decussation
Where do the remainder of the descending fibers of these two pathways go/do once leaving the cortex?
descend ipsilaterally to individual segments and then cross
What side of the brain controls volitional movements on the left side of the body?
right side of the brain
What is the voluntary motor pathway for the body?
corticospinal tract
Where are the primary cells of origin of the corticospinal tract located?
precentral gyrus (primary motor cortex; area 4)
In addition to area 4, where else can the primary cells of the corticospinal tract be located?
- area 6 (premotor region; lateral premotor and supplementary motor)
- area 8 (frontal eye fields)
- areas 3, 1, 2 (primary somatosensory cortex)
The fibers that make up the corticospinal tract exit the gray matter of the cortex and travel through what?
medullary white matter (the fiber bundles underlying the cortex)
What are the 5 fiber bundles of the medullary white matter?
- corona radiata
- posterior limb of the internal capsule
- cerebral peduncles
- corticospinal fibers in the ventral pons
- pyramids
85% of the descending fibers of the corticospinal tract cross where and then continue their descent as what?
cross at the pyramidal decussation and continue their descent as the lateral corticospinal tract
Where is the lateral corticospinal tract located?
lateral funiculus
The remaining fibers that do not cross at the pyramids descend as what and then cross where to innervate what?
descend as the anterior corticospinal tract then cross at the segmental level of the spinal cord where they innervate the lower motor neuronal pool
Where is the anterior corticospinal tract located?
anterior funiculus
97% of termination of the corticospinal fibers is primarily on what?
interneurons
55% of corticospinal fibers terminate in what region of the spinal cord?
cervical region
20% of corticospinal fibers terminate in what region of the spinal cord?
thoracic region
25% of corticospinal fibers terminate in what region of the spinal cord?
lumbar region
What excite or inhibit the lower motor neurons to influence the activity of a given motor unit?
interneurons
What neurons are in the ventral horn that make up the ventral root?
lower motor neurons
What type of lower motor neurons are responsible for activation of extrafusal muscle fibers (volitional movements)?
alpha motor neurons
What type of LMN are the final common pathway to the muscle or effector organ?
alpha motor neurons
What type of LMN innervate the intrafusal muscle fibers of the muscle spindle?
gamma motor neurons
What pathway runs parallel to the corticospinal tract?
corticoreticulospinal pathway
The cells giving rise to the fibers of the corticoreticulospinal pathway are located where?
supplementary motor and lateral premotor areas
The descending fibers of the cortioreticulospinal pathway synapse bilaterally at what 2 locations?
pons and medulla
After synapsing bilaterally, reticulospinal fibers then descend into the spinal cord where they synapse with what?
lower motor neuron pool (primarily interneurons) in the ventral horn of the spinal cord
What 2 motor areas of the brain provide information to the primary motor cortex for voluntary movement?
premotor and secondary motor areas
The information from the primary motor cortex then descends for fine motor control distally on the extremities. This precise individual movement is termed?
fractionated movement
The premotor areas of the brain also activate what?
reticular formation and the reticulospinal fibers
The information from the reticular formation and reticulospinal fibers is transferred where to initiate what?
transferred to the spinal cord for initiation of complementary activation of axial and proximal limb musculature (it sets the platform for movement in anticipation of the fractionated movement)
Pontine (medial) reticulospinal pathway is primarily contralateral, ipsilateral, or bilateral?
ipsilateral
Pontine (medial) reticulospinal pathway facilitates what?
axial and limb musculature, especially the extensors
Pontine (medial) reticulospinal pathway works with what other UMN pathway?
medial vestibulospinal tract
Medullary (lateral) reticulospinal pathway is contralateral, ipsilateral, or bilateral?
bilateral (greater ipsilateral)
Medullary (lateral) reticulospinal pathway facilitates what?
flexor musculature
Medullary (lateral) reticulospinal pathway inhibits what?
axial and limb extensor musculature
Lateral vestibulospinal pathway is contralateral, ipsilateral, or bilateral?
ipsilateral
Lateral vestibulospinal pathway facilitates/excites what?
extensors of lower extremity musculature
Lateral vestibulospinal pathway inhibits what?
flexor musculature
Medial vestibulospinal pathway projects contralateral, ipsilateral, or bilateral?
bilateral
Medial vestibulospinal pathway descends to only what two regions of the spinal cord?
cervical and upper thoracic levels
Medial vestibulospinal pathway facilitates what?
control of neck and upper thoracic musculature
Tectospinal pathway descends only to what level of the spinal cord?
cervical levels
Tectospinal pathway coordinates movement of what?
neck movement toward a stimulus
Rubrospinal pathway is contralateral, ipsilateral, or bilateral?
contralateral
What pathway is described as descending the entire length of the spinal cord?
Rubrospinal pathway
Rubrospinal pathway is involved in what movements?
flexor activation of the upper extremity, primarily distal musculature and plays a role in fractionated movements
What pathway has diminished in importance for bipedal locomotion?
Rubrospinal pathway
Rubrospinal pathway functions only at what level of the spinal cord?
cervical level
Which activation pathways (medial or lateral) are involved in more postural movements and activities?
medial activation pathways
Medial activation pathways are named for what two things?
- their position in the cord
- their function
Which activation system (medial or lateral) is more involved with the distal limb musculature, i.e., fractionated movement?
lateral activation system
The medial activation system is located where?
in the anterior funiculus
The medial activation system consists of what 5 pathways?
- anterior corticospinal
- medial reticulospinal
- medial vestibulospinal
- lateral vestibulospinal
- tectospinal
The lateral activation system is located where?
in the lateral funiculus
The lateral activation system consists of what 3 pathways?
- lateral corticospinal
- rubrospinal
- lateral reticulospinal
The primary somatosensory cortex sends axons caudally through what pathway?
lateral cotricospinal pathway
Termination location of the axons traveling from the primary somatosensory cortex through the lateral corticospinal pathway?
dorsal horn of the spinal cord
Function of the axons traveling from the primary somatosensory cortex through the lateral corticospinal pathway?
function as a feedback mechanism that integrates cortical understanding of sensation with incoming sensory information
What 2 pathways are also involved in the modification of afferent sensory information at the dorsal horn level?
- Raphespinal
- Cerulospinal
The raphespinal and cerulospinal pathways originate what 2 reticular formation nuclei?
- raphe nuclei
- Locus Ceruleus
What 2 pathways activate a number of reticular system components that play a role in the modulation of incoming pain stimuli?
- spinomesencephalic
- spinoreticular
The entire motor component of cranial nerves (both sides) receives bilateral input from what pathway?
corticobulbar pathway
What are the two exceptions to the motor component of CN’s receiving BILATERAL info from the corticobulbar pathway?
- The UMN for the two CN’s below ONLY provide CONTRALATERAL innervation:
- Facial Motor Nucleus (muscles of facial expression)
- Hypoglossal Nucleus (muscles controlling tongue movements)
Tongue atrophy and tongue deviation is ipsilateral or contralateral to the loss?
ipsilateral
Tongue atrophy and tongue deviation is an LMN or UMN deficit?
LMN deficit
Intrinsic muscles receive bilateral input from LMN or UMN?
UMN
Extrinsic muscles receive contralateral or ipsilateral input from LMN or UMN?
contralateral input from LMN
UMN has a contralateral or ipsilateral deficit? Why?
contralateral deviation with UMN because there is NO way to excite LMN of that side
What two areas are lower motor neurons located?
- ventral horn of the spinal cord
- cranial nerve motor nucleus
The axons of lower motor neurons leave the spinal cord or brainstem to innervate what?
motor units of skeletal muscle
Any deficit to LMN is ipsilateral or contralateral to the muscle?
ipsilateral
Four symptoms resulting from a lesion to a lower motor neuron (damage to axon or cell body)?
- flaccid paralysis (atonia or hypotonia)
- areflexia or hyporeflexia
- atrophy of muscle (muscle wasting)
- fasciculations and fibrillations
Cell bodies of UMN are located where?
suprasegmental levels of the CNS
Where do the axons of UMN terminate?
the ventral horn or cranial nerve motor nucleus
UMN synapse on what?
interneurons or alpha/gamma motor neurons
Any deficit to UMN is contralateral or ipsilateral damage to the muscle?
contralateral
UMN activate what?
LMN
Six symptoms resulting from a lesion to an UMN (damage to descending fiber tracts classified as UMN)?
- Initial flaccid paralysis followed by:
- -> abnormal cutaneous reflexes (babinski)
- -> abnormal reflexes (clonus; clasp knife)
- -> spasticity - velocity dependent hypertonia
- -> abnormal timing of muscle activation (slower onset, prolonged contraction)
- -> paresis or plegia (weakness)
What is defined as total loss of motor function?
paralysis
What is defined as a loss of activation of voluntary motor activity sometimes incorrectly referred to as paralysis?
plegia
What is defined as weakness?
paresis
What syndrome is a result of the lesion being a hemisection of the spinal cord?
Brown-Sequard Syndrome
What pathology is the result of a lesion caused by cavitation of the central canal, the remnant of the lumen of the neural tube?
Syringomyelia
Effects of the lesion resulting syringomyelia?
- lesion encroaches upon the anterior white commissure
- further ventral and lateral enlargement of the cavity will then encroach upon the ventral horn, effecting LMNs of axial then appendicular musculature
What is the disease that attacks LMNs in the ventral horn of the spinal cord and cranial nerve nuclei?
poliomyelitis
What pathology is a chronic and progressive disease of unknown origin that destroys LMNs in the ventral horn and brainstem nuclei in addition to destroying white matter pathways?
Amyotrophic Lateral Sclerosis (ALS)
What pathology is a multifocal disease an, thought to be an autoimmune attack on myelin, and is known as a disease of UMNs?
Multiple sclerosis
What 3 locations does multiple sclerosis develop?
- spinal cord
- brainstem
- optic nerve
