6. Motor disorders

Question 1

source of dopamine in midbrain

Answer 1

substation nigra pars compacta

Question 2

how do basal ganglia communicate with motor cortex?

Answer 2

thalamus

Question 3

basal ganglia lesions
-ipsi or contraleteral? why?

-bilateral? why?

Answer 3

contralateral: decussation of CST from ipsilateral motor cortex

yes: neurodegeneration is the common cause, and usually this is symmetrical e.g Parkinson’s

Question 4

functions of basal ganglia

Answer 4

direct pathways reinforce appropriate movements (excitatory to motor cortex)

indirect pathways remove inappropriate movements (inhibitory to motor cortex)

Question 5

cause of Parkinson’s

Answer 5

degeneration of dopaminergic neurones in SNc

Question 6

explain why Parkinson’s causes tremor

Answer 6

dysfunction of indirect pathway which would normally suppress unwanted movements

Question 7

explain why Parkinson’s causes rigidity

Answer 7

lack or coordination between agonists and antagonists i.e. opposing each other

Question 8

explain why Parkinson’s causes bradykinesia

Answer 8

loss of cortical excitation = slow movements

Question 9

cause of Huntington’s chorea

Answer 9

loss of inhibitory projections from striatum to GPe

Question 10

does Huntington’s chorea cause hyper or hypokinesia? why?

Answer 10

hyper
‘brakes’ taken off thalamus

Question 11

cause of hemiballismus

Answer 11

damage to subthalamic nucleus which normally inhibits thalamus via GPi

Question 12

function of cerebellum

Answer 12

sequencing and coordinating movement

Question 13

where does the cerebellum receive sensory inputs from

Answer 13

contralateral sensory cortices
ipsilateral spinal cord
proprioceptive neurones

Question 14

how might cerebellar lesions present

Answer 14

vomiting
vertigo (poor coordination of extra ocular muscles)
difficulty walking

Question 15

explain why cerebellar lesions cause dysdiadochokinesia

Answer 15

cant sequence pronation, supination….

Question 16

explain why cerebellar lesions cause ataxia

Answer 16

difficulty sequencing lower limb muscle contractions, and loss of unconscious proprioception from lower limbs

Question 17

explain why cerebellar lesions cause nystagmus

Answer 17

poor coordination of extra ocular eye muscles

Question 18

explain why cerebellar lesions cause dysarthria

Answer 18

poor coordination of laryngeal and tongue musculature

Question 19

basal ganglia corticospinal pathway

Answer 19

instructs muscles what to do, from motor cortex UMN, decussate at medulla, synapse on LMN, goes to muscle

Question 20

basal ganglia corticostriatal pathway

Answer 20

motor cortex sends motor plan to basal ganglia

Question 21

basal ganglia pallidothalamocortical pathway

Answer 21

basal ganglias assessment of motor plan sent back to motor cortex via thalamus

Question 22

basal ganglia nigrostriatal pathway

Answer 22

source of dopamine to basal ganglia from Sac

Question 23

hypothetically, where would the signs be if basal ganglia were damaged unilaterally. why?

Answer 23

contraleteral

basal ganglia pathways all communicate with ipsilateral motor cortex, then corticospinal pathway decussates at medulla to contralateral side

Question 24

relevance of cerebellar tonsils

Answer 24

in raised ICP, can be forced down through foramen magnum and compress medulla

Question 25

cerebellar pathways: corticopontocerebellar

Answer 25

motor cortex communicates its motor plan through cerebellum, decussates in pons to contralteral cerebellar hemisphere

Question 26

cerebellar pathways: cerebellothalamocortical

Answer 26

projects from cerebellar hemisphere to contralateral thalamus then to motor cortex same side as thalamus

Question 27

cerebellar pathways: spinocerebellar

Answer 27

primary sensory neurones carry info from muscle spindles to ipsilateral cerebellar hemisphere

Question 28

why are cerebellar damage signs ipsilateral?

Answer 28

-double decussation of corticopontocerebellar and cerebellothalamocortical pathways

-ipsilateral sensory pathway via spinocerebellar pathway