Motor Control

Question 1

what are the three levels in the motor control hierarchy?

Answer 1

> High: strategy (goal and movement strategy)
middle: tactics (sequence of muscles movements to achieve the goal)
low: execution (activation of motor neuron pools)

Question 2

what do the ventral medial pathways of the spinal cord control?

Answer 2

posture and locomotion under brain stem control

Question 3

1/3 of the corticospinal tract originate in what areas?

Answer 3

4 and 6 of the frontal motor cortex

Question 4

where does the smaller rubrospinal tract start?

Answer 4

the red nucleus of the midbrain

Question 5

what is the effect of a lesion on the corticospinal tract and the rubrospinal tract?

Answer 5

fine movements of arms and hands lost. cant move shoulders, elbows, wrist and fingers independently.

Question 6

what is the effect of a lesion on the corticospinal tract alone?

Answer 6

there is loss of fine movements of the hands and arms but after a few months functions start to reappear as they have been taken over by the rubrospinal tract.

Question 7

name the two lateral pathways controlling voluntary movement

Answer 7

> corticospinal tract

> rubrospinal tract

Question 8

name the two ventromedial pathways controlling posture

Answer 8

> vestibulospinal tracts

> tectospinal tracts

Question 9

what do the vestibulospinal tracts control?

Answer 9

head and neck stabalisation

Question 10

what do the tectospinal tracts control?

Answer 10

eye stability as the body moves

Question 11

what ventromedial pathways control the trunk and antigravity muscles?

Answer 11

the pontine and medullary reticulospinal tracts

Question 12

what is the function of the pontine and medullary reticulospinal tracts?

Answer 12

they use sensory information about balance, body position and vision to reflexly maintain body position by innervating the trunk and limb muscles

Question 13

how does the motor cortex directly activate spinal motor neurons?

Answer 13

by communicating via nuclei of ventromedial pathways

Question 14

what do lateral tracts from the cortex control?

Answer 14

precise skilled voluntary movements

Question 15

what is the primary motor cortex?

Answer 15

the precentral gyrus

Question 16

what will weak stimulation of area 4 cause?

Answer 16

a weak twitch in specific contralateral muscles

Question 17

what are the two somatotopically organised motor maps in area 6?

Answer 17

> premotor area

> supplementary motor area

Question 18

how is a mental image of the body in space produced?

Answer 18

by somatosensory, proprioceptive and visual inputs to posterior parietal cortex (areas 5 and 7)

Question 19

where are decisions made about action to take and their outcome?

Answer 19

the prefrontal and parietal cortex

Question 20

what happens when axons from the prefrontal cortex and parietal cortex converge in area 6?

Answer 20

signals encoding what actions are desired are converted into how actions will be carried out

Question 21

what does a change in body position initiate to correct postural instability?

Answer 21

a rapid compensatory feedback message from the brainstem vestibular nuclei to spinal cord motor neurons AND feedforward anticipatory adjustments by the reticular formation nuclei to stabilise posture

Question 22

what does cortical damage cause?

Answer 22

immediate flaccidity of contralateral muscles (hypotonia). then after a few days spinal circuits regain function.

Question 23

what does Babinski sign indicate?

Answer 23

incomplete upper control of spinal circuits

Question 24

what makes up the corpus striatum?

Answer 24

two principle nuclei: caudate and putamen

Question 25

what are the input zone for the basal ganglia?

Answer 25

caudate and putamen nuclei

Question 26

what does the putamen fire before?

Answer 26

limb and trunk movements

Question 27

what does the caudate fire before?

Answer 27

eye movements

Question 28

what do medium spiny neurons in putamen and caudate receive?

Answer 28

excitatory cortical inputs on dendrites

Question 29

what do medium spiny neurons integrate?

Answer 29

somatosensory, premotor and motor cortical inputs

Question 30

what do the medium spiny neurons project inhibitory axons to?

Answer 30

> globus pallidus | > substantia nigra pars reticulata

Question 31

what is the functional consequence of cortical activation of the putamen?

Answer 31

excitation

Question 32

how does cortical activation of putamen boosts cortical excitation?

Answer 32

> at rest globus pallius neurons inhibit VL > cortical excitation excites putamen > putamen inhibits the inhibitory globus pallidus > this releases cells in VLo from inhibition so activity in VLo boosts SMA activity

Question 33

what does the direct pathway of cortical input flow through the basal ganglia do?

Answer 33

selects specific motor actions

Question 34

what does the indirect pathway of cortical input flow through the basal ganglia do?

Answer 34

suppresses competing/inappropriate action

Question 35

how does the indirect pathway antagonise the direct pathway through the basal ganglia?

Answer 35

> striatum inhibits globus pallidus external which then inhibits the globus pallidus internal and the subthalmic nuclei > the cortex then excites the subthalmic nuclei which excites the GPI which inhibits the thalamus

Question 36

what is hypokinesia?

Answer 36

>slowness and difficulty in making voluntary movements > increased muscle tone > tremors of the hand and jaw

Question 37

what causes hypokinesia?

Answer 37

degeneration of neurons in the substrantia nigra and their dopaminergic (excitatory) inputs to the striatum

Question 38

what does the depletion of dopamine cause?

Answer 38

closing down activation of focused motor activation that funnel through the thalamus to the SMA

Question 39

what is the effect of dopamine on cortical inputs?

Answer 39

> enhancement through direct routes | > suppression through indirect routes

Question 40

what is characteristic chorea?

Answer 40

spontaneous uncontrolled rapid flicks and major movements with no purpose seen in huntingtons

Question 41

name a basal ganglia disorder

Answer 41

huntingtons

Question 42

what causes huntingtons effects?

Answer 42

profound loss of caudate, putamen and globus pallidus: loss of inhibitory effects of the basal ganglia

Question 43

what do lesions in the cerebellum produce?

Answer 43

uncoordinated inaccurate movements, ataxia

Question 44

what parts of the bran are a large part of cortico-ponto-cerbellar projection?

Answer 44

> layer 5 > areas 4 > area 6 > somatosensory cortex

Question 45

through what does the cerebellum communicate tot he cortex?

Answer 45

via the ventrolateral thalamus