Corticospinal Flashcards
corticospinal tract function
voluntary motor pathway for the body
corticobulbar (corticonuclear) tract function
carries out movements for the cranial nerve motor nuclei that innervate the face
corticospinal and corticobulbar tracts
- arise…
- descend through…
- end in…
arise in cerebral cortex descend through internal capsule end in -brainstem motor nuclei or -ventral horn of spinal cord
where do most of the fibers descending to the spinal cord from the corticospinal and corticobulbar tracts cross
-what about the other fibers
in the lower medulla at the pyramidal decussation
descend ipsilaterally to individual segments and then cross
corticospinal tract
-location of primary cells of origin
precentral gyrus (primary motor cortex; area 4) area 6 (premotor region; lateral premotor and supplementary motor) area 8 (frontal eye fields) primary somatosensory cortex (areas 3, 1, 2)
the fibers that make up the corticospinal tract exit the _____ of the cortex and travel through the _____
gray matter
medullary white matter (fiber bundles underlying the cortex)
medullary white matter
- what is it?
- specific names, in sequence
fiber bundles underlying the cortex names -corona radiata -posterior limb of the internal capsule -cerebral peduncles -corticospinal fibers in the ventral pons -pyramids
corticospinal tract
-at lower end of medulla, 85% of fibers cross at _____ and continue descent as _____
cross at pyramidal decussation
continue as lateral corticospinal tract
lateral corticospinal tract
- located in
- function
lateral funiculus
innervate extremities
corticospinal tract
- fibers that do not cross at the pyramidal decussation descend as the _____
- where do these cross
- function
anterior corticospinal tract
cross at the segmental level
innervate lower motor neuronal pool
anterior corticospinal tract
-located in
anterior funiculus
termination location of corticospinal tract fibers
interneurons (97%)
where do corticospinal fibers terminate?
cervical region (55%) thoracic region (20%) lumbar region (25%)
what excites or inhibits the lower motor neurons to influence the activity of a given motor unit
interneurons
lower motor neurons innervate muscles _____ to the cell body location in the spinal cord
ipsilateral
corticoreticulospinal pathways
- runs parallel to…
- cells giving rise to these fibers are located in the…
parallel to corticospinal tract
located in
-supplementary motor area
-lateral premotor area
corticoreticulospinal pathway
- axons descend to the level of the _____
- what happens at this level
descend to level of pontine and medullary reticular formation
synapse bilaterally
reticulospinal fibers
- descend into….
- what happens there?
descend into the spinal cord
synapse in the ventral horn on the lower motor neuron pool
-primarily on interneurons
corticoreticulospinal pathway
-purposes
premotor and secondary motor areas provide information to primary motor cortex for voluntary movement
premotor areas activate the reticular formation and subsequently the reticulospinal fibers
-information is transferred to the spinal cord for initiation of complementary activation of axial and proximal limb musculature
corticoreticulospinal
- information from primary motor cortex descends for _____
- this is termed….
fine motor control distally on the extremities, i.e. the fingers
this precise individual movement is termed fractionated movement
corticoreticulospinal
-purpose of complementary activation of axial and proximal limb musculature by the reticular formation and reticulospinal fibers
sets the platform for movement in anticipation of the fractioned movement
other descending pathways that are classified as upper motor neurons
pontine (medial) reticulospinal pathway medullary (lateral) reticulospinal pathway lateral vestibulospinal pathway medial vesticulospinal pathway tectospinal pathway rubrospinal pathway
pontine (medial) reticulospinal pathway
- ipsi or contra
- function
- works with the…
primarily ipsilateral
facilitory to axial and limb musculature
-especially the extensors
works with medial vestibulospinal tract
medullary (lateral) reticulospinal pathway
- ipsi or contra
- function
bilateral (greater ipsilateral)
facilitory to flexor musculature
inhibitory to axial and limb extensor musculature
lateral vestibulospinal pathway
- ipsi or contra
- function
ipsilateral
excitatory on extensors of lower extremity musculature (inhibits flexor musculature)
medial vestibulospinal pathway
- ipsi or contra
- descends to…
- function
projects bilaterally
descends only to cervical and upper thoracic levels
control of neck and upper thoracic musculature
tectospinal pathway
- descends to…
- function
descends only to cervical levels
coordinates neck movement toward a stimulus
rubrospinal pathway
- ipsi or contra
- descends how far?
- main functional level
- -why?
contralateral
descends the entire length of cord
functions mostly at cervical level
-in species with bipedal locomotion this tract has diminished in importance and functions mostly at the cervical level
rubrospinal pathway
-function
involved in flexor activation of the UE
-primarily distal musculature
plays a role in fractionated movements of the wrist and fingers
medial vs. lateral activation systems
- differentaiton defined primarily by…
- medial are involved in…
- lateral are involved in…
location of the axons of the upper motor neurons
medial
-involved in more postural movements and activities
-named for both their position in the cord and their function
lateral
-involved with distal limb musculature, i.e. fractionated movement
medial activation system
- location
- consists of what pathways
located in anterior funiculus consists of -anterior corticospinal -medial (pontine) reticulospinal -medial vestibulospinal -lateral vestibulospinal -tectospinal
lateral activation system
- location
- consists of what pathways
located in lateral funiculus consists of -lateral corticospinal -rubrospinal -lateral (medullary) reticulospinal
other descending components
primary somatosensory cortex raphespinal cerulospinal spinomesencephalic spinoreticular
primary somatosensory cortex
- sends axons caudally through _____
- axons terminate _____
- function
sends axons caudally through lateral corticospinal pathway
axons terminate in dorsal horn
though to function as a feedback mechanism that integrates cortical understanding of sensation with incoming sensory information
raphespinal and cerulospinal pathways
- where do they originate
- function
originate in reticular formation nuclei - Raphe nuclei and Locus Ceruleus
involved in modification of afferent sensory information at the dorsal horn level
spinomesencephalic and spinoreticular pathways
-function
activate a number of reticular system components
these descending components play a role in the modulation of incoming pain stimuli
