Descending motor tracts

Question 1

Motor plan

Answer 1

blueprint or module for movement

from premotor cx (lateral BA6&8) along with supplementary cortex

Question 2

alpha LMNs

Answer 2

innervate skeletal muscle
final common pathways (always excitatory)
don’t decussate (usually)
cell bodes in the ventral horn and CN motor nuclei
large diameter and high baseline activity

Question 3

baseline activity

Answer 3

of alpha LMNs
can be changed by excitatory or inhibitory inputs
*what causes normal resting muscle tone

Question 4

Lateral motor systems

Answer 4

control distal limb mm.

precise fractionated movements

Question 5

medial motor systems

Answer 5

axial/proximal limb mm.
postural movements
i.e. from non-cortical UMNs

Question 6

Cortical UMN systems

Answer 6

Corticospinal tract and corticobulbar tract

Question 7

LCST

Answer 7

largest motor tract of humans
contralateral projection
some UMNs synapse directly on LMNs
critical for complex, fractionated movements

Question 8

origins of LCST

Answer 8

1/3 from the Primary Motor Cortex
2/3 from frontal lobes and somatosensory cx and premotor and supplementary motor areas
runs in corticospinal tract

Question 9

Somatotopy of the internal capsule

Answer 9

all within the posterior limb:
facial expression in genu
UL is more anterior
trunk and LL are more posterior

Question 10

Pre-motor cortex

Answer 10

Lateral BA6 &8

involved with motor planning and starting a movement

Question 11

supplementary motor cx

Answer 11

medial BA6&8 located within the longitudinal fissure

interconnected with contralateral side, involved with bimanual movements

Question 12

corticobulbar tract

Answer 12

terminates in the brainstem
influences CN motor nuclei (LMNs) -bilaterally
and UMN nuclei (vestibular nuclei, reticular nuclei, red nucleus)
**gain voluntary control of medial motor systems (axial proximal mm.)

Question 13

LMN damage

Answer 13

hypo—>areflexia and atonia —>decreased stretch reflex

paralysis/paresis, flaccid
rapid, severe atrophy (neurogenic atrophy) due to lack of trophic effects

fasciculation and fibrillation due to spontaneous release of NTs

signs occur at lesion level

Question 14

UMN damage

Answer 14

normal - hyperreflexia 
hypertonia 
pathological reflexes (babinski) 
spastic 
disuse atrophy 
few EMG changes 
** all due to denervation hypersensitivity 

signs occur inferior to lesion

Question 15

denervation hypersensitivity

Answer 15

occurs when UMN inhibition on LMN is lost
LMNs release trophic factors
increases collateral from primary afferent
increases input on surface of LMN
causes hyperreflexia, hypertonia, sapsticity

Question 16

Non-cortical UMN systems

Answer 16

origin at sites outside cx
affect axial and proximal limb mm.
**reflex postural movement
also under voluntary control from cx via corticobulbar tract

**axons in the ventromedial cord (medial motor systems)

Question 17

Rubrospinal tract

Answer 17

cell bodies in the red nucleus
axons decussate in MB, descend in c/l lateral funiculus
innervate arm and forearm flexor (distal

Question 18

MVST

Answer 18

medial vestibulospinal tracts: aka descending MLF
cell bodies in the medial/inf vestibular nuc.

axons run b/l thru the cervical and upper thoracic in the descending MLF
acts on neck mm.
changes head and neck posture
damage causes less sx due to bilateral inputs

Question 19

LVST

Answer 19

lateral vestibulospinal tracts
cell bodies in the lateral vestibular nuc.
run ipsilateral in the cord to axial postural/abdomen muscles to help maintain trunk posture

lesions cause ipsilateral loss of muscle activity

Question 20

medial longitudinal fasciculus

Answer 20

ascending portion (MLF)
cell bodies in the medial/inf vestibular nuc.
ascends to innervate motor nuc of III, IV VI
b/l

Question 21

Medial RST

Answer 21

medial reticulospinal tracts 
aka pontine RST
cell bodies in the reticular formation 
ipsilateral 
backup pathway for voluntary movement if the corticospinal tract is damaged

Question 22

lateral RST

Answer 22

lateral reticulospinal tract 
aka medullary RST 
cell bodies in the reticular formation 
bilateral 
backup pathway for voluntary movement if the corticospinal tract is damaged

Question 23

Tectospinal tract

Answer 23

cell bodies in the superior colliculus
decussates in the c/l midbrain
synapse on neck mm. (tract terminates in cervical cord

**visual grasp reflex