Descending Motor Tracts

Question 1

topographical organization of ventral horn

Answer 1

medial- proximal muscles

lateral- distal muscles

ventral- extensor

dorsal- flexor

Question 2

fasciculus proprius (propriospinal tracts)

Answer 2

axons that interconnect segments that run in the white matter of the spinal cord, close to the gray matter

Question 3

medial v lateral motor systems

Answer 3

medial- ventral funiculus- regulate interneuron pools going to axial and proximal limb muscles- bilateral effects, and only involved in neck and trunk

lateral- lateral funiculus- regulate interneuron pools going to limb muscles- more precise movements

Question 4

tracts of the anterior funiculus

Answer 4

tectospinal tract
medial vesibulospinal tract
pontine reticulospinal tract
anterior corticospinal tract

Question 5

descending MLF properties

Answer 5

medial vestibulospinal, pontine reticulospinal, tectospinal tract

4 characteristics

enter anterior funiculus
affect axial muscles
dont extend beyond upper thoracic level
terminate bilaterally

Question 6

tectospinal tract

Answer 6

arises from superior colliculus

decussates at midbrain

controls head movement

Question 7

medial vestibulospinal tract

Answer 7

begins in medial vestibular nucleus (CN8 nucleus)

runs in MLF and controls neck muscle tone

Question 8

pontine reticulospinal tracts

Answer 8

arises from reticular formation at the core of the pons from PPRF

enter MLF

influence motor neurons for neck

link head turn w/ horizontal eye movement

Question 9

lateral vestibulospinal tract

Answer 9

arises from lateral vestibular nucleus

runs in lateral funiculus and descends to all spinal levels

strong activator of extensor motor neurons

“vestibular righting”- extension of muscles on right side when head tips right

Question 10

reticulospinal tract

Answer 10

runs in anterior lateral funiculus to all spinal levels

controls gross movements and regulates muscle tone via effects on gamma motor neuron

predominately activates inhibitory interneurons

can function as an indirect corticospinal tract, but would not help w/ refined movements

control genrealized, gross movements

Question 11

lateral motor systems

Answer 11

rubrospinal tract

lateral corticospinal tract

control limb movements

Question 12

rubrospinal tract

Answer 12

arises from red nucleus

decussates in midbrain- ventral tengmental

descends in lateral funiculus reaching all spinal levels, terminating on interneurons

controls movements of proximal limb flexors- crawling

can act as indirect corticospinal tract

Question 13

corticobulbar system

Answer 13

cortex to brainstem

affect cranial nerve nuclei- voluntary of head and face

affect sensory transmission cranial nuclei

activate brainstem nuclei involved in movement- indirect corticospinal movment

project to pons for relay to cerebellum

Question 14

corticospinal tract

Answer 14

arises from motor cortex in precentral gyrus

arises from pyramidal shaped neurons “upper motor neurons”

axons traverse the internal capsule and enter cerebral peduncles and eventually become medullary pyramids

Question 15

topographic distribution of motor cortex

Answer 15

feet near interior fissure
upper leg/trunk near exterior fissure
arm/hand- below upper leg/trunk
face- right above sylvian fissure

Question 16

repetitive finger tapping activates where first?

Answer 16

hand area primary motor cortex

Question 17

what do cortical neurons encode?

Answer 17

encode direction of movement and not a specific muscle

Question 18

why do neurons fire preceed movement

Answer 18

delay represents the time it takes for signal to reach and activate motor neurons

Question 19

movements that require a decision activate which cortex area first?

Answer 19

premotor cortex in general, in particular the supplementary motor area, then the primary motor cortex

Question 20

rehearsal of movements

Answer 20

premotor cortex is activated even if movement is not executed, but primary motor cortex is not

Question 21

corticalfugal fibers

Answer 21

connection between cortex and brainstem/spinal cord

runs through internal capsule

fibers controlling head are located in the genu (bend) of the internal capsule and are technically corticobulbar

fibers controlling arms are between head and legs, and legs are most posterior

following the internal capsule, the corticalfugal fibers enter the cerebral peduncles

Question 22

where do corticalspinal fibers decussate?

Answer 22

pyramidal decussation

10% remain uncrossed and run in anterior funiculus innervating axial muscles and producing crude movements

Question 23

where do corticospinal fibers synapse

Answer 23

most synapse on interneurons, but some synapse direct motor neurons to limb muscles

Question 24

corticobulbar facial and trigeminal nucleus innervation

Answer 24

innervation to the lower face for voluntary movements from motor cortex are strictly crossed, and a unilateral lesion with produce weakness

however, corticobulbar projections to facial and trigeminal distribute to bilaterally, and unilateral lesions dont produce weakness

produces scene where lower face muscles are weak but upper and jaw muscles are ok

Question 25

emotional movement of face

Answer 25

dont go thru internal capsule, run thru anterior cingulate cortex

Question 26

indirect corticospinal projetions

Answer 26

cerebral cortex influences pathways responsible for motor tone or motor patterns in movement