B7.038 Central Motor Systems

Question 1

motor tracts within the lateral column of the cord

Answer 1

lateral corticospinal
rubrospinal
lateral reticulospinal

Question 2

motor tracts within the ventral column of the cord

Answer 2

vestibulospinal
ventral reticulospinal
ventral corticospinal
tectospinal

Question 3

how do descending systems inhibit spinal cord reflexes

Answer 3

can switch them on/off or change the strength
synapse with and inhibit/excite interneurons within the reflex pathways (reflexes can be suppressed with voluntary effort)

Question 4

corticospinal/corticobulbar systems

Answer 4

called pyramidal tracts
originate in motor and sensory cortex
terminate on CN nuclei (corticobulbar) or a and gamma motoneurons controlling distal limb muscles as well as interneurons (corticospinal)
-90% in lateral column
-10% in ventral column

Question 5

sensory component of the corticospinal system

Answer 5

originates from primary somatosensory cortex (postcentral gyrus) and terminates in dorsal column nuclei and dorsal horn of spinal cord
can excite or inhibit dorsal column neurons
modulates activity in ascending systems and can screen out routine stimulation of the skin (from clothes)

Question 6

extrapyramidal tracts

Answer 6

rubrospinal
reticulospinal
-pontine
-medullary
vestibulospinal
tectospinal

Question 7

rubrospinal tract

Answer 7

originates in red nucleus
travels in lateral column
terminates on interneurons in spinal cord
largely crossed
controls distal limb muscles
stimulates flexors, inhibits extensors

Question 8

red nucleus input

Answer 8

contralateral deep cerebellar nuclei

motor cortex bilaterally

Question 9

reticulospinal tracts

Answer 9

originate from reticular formation of medulla and pons

Question 10

pontine reticulospinal tract

Answer 10

travel in ventral column

stimulate muscles, primarily extensors

Question 11

medullary reticulospinal tract

Answer 11

travel in lateral column

inhibit muscles, primarily extensors

Question 12

vestibulospinal tract

Answer 12

originates from vestibular nuclei
terminates on interneurons and motoneurons in anterior horn, mostly ipsilateral
facilitates anti-gravity muscles
maintains posture

Question 13

reticulospinal and vestibulospinal tract role in movements

Answer 13

limited role in extremities

main influence on trunk

Question 14

tectospinal tract

Answer 14

originates from superior colliculus in midbrain
travels in ventral column, primarily crosses
terminates on interneurons and motoneurons in cervical spinal cord, mostly crossed
plays role in reflexive control of neck muscles in response to visual stimuli

Question 15

alpha gamma coactivation

Answer 15

in voluntary movement, both alpha and gamma motoneurons are activated by descending systems
increases spindle afferent activity to assist with movement
results in automatic load compensation (bc gamma motoneurons sense changes in load)

Question 16

spindle load compensation mechanism

Answer 16

increase in external load > increased spindle afferent activity > increased alpha motoneuron excitation > increased muscle tension > overcomes load

Question 17

effect of corticospinal lesion

Answer 17

loss of fine motor control

Question 18

effect of rubrospinal lesion

Answer 18

little or no deficit or corticospinal is intact

Question 19

effect of reticulospinal lesion

Answer 19

severe impairment of axial and proximal muscles; loss of righting reflexes

Question 20

effect of vestibulospinal lesion

Answer 20

severe impairment of axial and proximal muscles; loss of righting reflexes

Question 21

decerebrate posture

Answer 21

results from damage to the upper brain stem (upper pons severed)
arms are adducted and extended
wrists pronated
fingers flexed
legs stiffly extended with plantar flexion of the foot

Question 22

decorticate posture

Answer 22

results from damage to corticospinal tracts
arms are adducted and flexed
wrists and fingers flexed on the chest
legs stiffly extended and internally rotated with plantar flexion of the foot

Question 23

why are motor cortex lesions worse than pyramidal tract lesions?

Answer 23

lesions of the pyramidal tract only destroy the direct influence of the motor cortex on motor neurons
motor cortex lesions destroy both direct and indirect influences of motor cortex on motor neurons (rubrospinal and reticulospinal)

Question 24

function of the basal ganglia

Answer 24

integrate multimodal (sensory, cognitive) cortical information (Glu) in the context of motivational information (DA) to initiate and maintain meaningful behavior

Question 25

receiving nuclei of BG

Answer 25

striatum -putamen -caudate receives inputs from cerebral cortex

Question 26

globus pallidus

Answer 26

internal segment: output nucleus of BG | external segment

Question 27

striatal medium spiny neuron

Answer 27

receives input from: cerebral cortex (glu), substantia nigra(dopamine) sends projections to GP (GABA)

Question 28

functions of BG

Answer 28

``` selection of movements gating motor function motor learning reward based conditioning habit formation ```

Question 29

function of the BG in movement

Answer 29

disinhibits CNS structures and allows initiation of voluntary movements normal output from BG is inhibitory and neurons have a high tonic firing rate

Question 30

direct route of BG

Answer 30

thalamic cells are released from inhibition (disinhibition) 1. originates from cerebral cortex 2. projects to striatum 3. striatum projects to GPi or SN 4. GPi projects to thalamus 5. thalamus projects to cortex

Question 31

indirect route of BG

Answer 31

``` corticostriatal excitation results in inhibition of GPe and disinhibition of STN results in excitation of GPi, which inhibits the thalamus and decreases excitation in motor cortec 1. originates from cerebral cortex 2. projects to striatum 3. striatum projects to GPe 4. GPe projects to STN 5. STN projects to GPi 6. GPi projects to thalamus 7. thalamus projects to cortex ```

Question 32

effect of dopamine on direct/indirect routes

Answer 32

excited direct route, causing disinhibition of thalamus inhibits the indirect rout, causing suppression of the STN and disinhibition of the thalamus dopamine = increased motor activity

Question 33

excitatory components of the BG pathways

Answer 33

1. cortical inputs to striatum 2. pathways from STN to GPi mediated by glutamate

Question 34

inhibitory components of the BG pathways

Answer 34

1. direct route from striatum to GPi 2. GPi to thalamus 3. indirect route from striatum to GPe 4. pathways from GPe to STN mediated by GABA

Question 35

mixed components of the BG pathways

Answer 35

substantia nigra pathway has mixed effects, mediated by dopamine

Question 36

rigidity

Answer 36

increased resistance to passive joint movement

Question 37

Parkinsonian tremor

Answer 37

4-8 Hz oscillation occurring in absence of voluntary movement

Question 38

akinesia/bradykinesia

Answer 38

inability to initiate voluntary movement | most troubling motor symptom

Question 39

neuropathology of Parkinson's

Answer 39

1. degeneration of nigrostriatal dopamine neurons is the cardinal feature 2. decrease in dopamine content in the striatum, symptoms appear when content drops below 20%

Question 40

abnormalities in neuronal activity in PArkinson's

Answer 40

lack of SN dopamine results in an increased activation of the indirect pathway (inhibitory to cortex) and a decrease in activity of the direct pathway (excitatory to cortex)

Question 41

hemiballismus

Answer 41

high velocity, large amplitude involuntary slinging movements generally involving the arms

Question 42

Huntington's chorea

Answer 42

genetic disorder characterized by movement abnormalities and loss of GABA neurons projecting from striatum to GPe

Question 43

choreiform movements

Answer 43

involuntary, irregular, jerky movements that are slower and smaller amplitude than movements associated with ballismus

Question 44

athetosis

Answer 44

continuous writhing movements

Question 45

abnormalities in neuronal activity in Huntingtons

Answer 45

decreased inhibitory pathway activity in the BG leads to increase in excitatory stimulation to the cortex

Question 46

laterality of effects on movement from lesions of BG

Answer 46

lesions of the BG affect limb movements contralateral to the lesion projections from BG to cortex are uncrossed projections from motor cortex to the spinal cord are crossed