Motor Control II

Question 1

true or false:

commands to perform precise movements are encoded in the integrated activity of large populations of neurones in M1

Answer 1

true

Question 2

how is posture instability corrected?

Answer 2

A change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones

In addition before movements begin, brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustments to stabilize postur

Question 3

what is initial hypotonia?

Answer 3

“spinal shock” - spinal circuits are deprived of cortical input

Question 4

what is the babinski sign?

Answer 4

• adult, plantar flexion – baby or cortical damage – extension : both indicate incomplete upper control of spinal circuits

Question 5

what does increased muscle tone, hyperactive stretch reflex, clonus oscillatory contract/relax muscles in response to stretch cause?

Answer 5

removal of cortical suppressive (inhibitory) influences

Question 6

where does the Major subcortical input to area 6 come from?

Answer 6

ventral lateral nucleus in dorsal thalamus (Vlo)

Question 7

where does Input to VLo comes from

Answer 7

basal ganglia

Question 8

what are te Major components of basal ganglia

Answer 8

Corpus striatum (striped body) - includes two principal nuclei the caudate and the putamen

Question 9

where does Corpus striatum receives inputs from ?

Answer 9

all over cortex –

corticostriatal pathway - multiple parallel pathways with different functions

Question 10

medium spiny neurones in putamen and caudate receive excitatory (glutamatergic) cortical inputs on?

Answer 10

dentrites

Question 11

each cortical axon contacts ….. of spiny neurones so integrating the influence of …. of cortical cells

Answer 11

1000s

Question 12

are the axons inhibitory or excitatory?

Answer 12

inhibitory (GABAergic)

Question 13

where do the axons project to?

Answer 13

globus pallidus and to substantia nigra pars reticulata

Question 14

does the putamen fire before limb/trunk movements or after?

Answer 14

before

Question 15

does the caudate fire after eye movements or before?

Answer 15

before

Question 16

what type of pathway is cortex to putamen?

Answer 16

excitatory pathway

Question 17

what type of pathway is putamen to globus pallidus?

Answer 17

inhibitory

Question 18

what type of pathway is globus pallidus to VLo neurones?

Answer 18

inhibitory

Question 19

what type of pathway is VLo back to SMA?

Answer 19

excitatory

Question 20

functional consequence of cortical activation of putamen is

Answer 20

excitation

Question 21

what happens to globus pallidus at rest?

Answer 21

neurones are spontaneously active and inhibit VLo

Question 22

function of Cortical excitation

Answer 22

excites putamen which

inhibits the inhibitory Globus pallidus which therefore

releases cells in VLo from inhibition so

activity in VLo boosts SMA activity

This acts as a positive feedback loop focussing or funnelling activation of widespread cortical areas back onto cortical SMA

Question 23

what does the gating operation of the basal ganglia depend on?

Answer 23

a type of disinhibitory arrangement

Question 24

what does the direct pathway act as? and what is its function?

Answer 24

positive feedback loop, a “GO” signal to the SMA in cortex

it enhances the initiation of movements by the SMA

Question 25

what is the indirect pathway?

Answer 25

antagonizes the direct route

Striatum inhibits GPe (globus pallidus external) which then inhibits both GPi (GP internal) and STN (subthalamic nuclei)

Cortex excites STN; this excites Gpi; which inhibits thalamus

Direct pathway selects specific motor actions
Indirect pathway suppresses competing/inappropriate action

Question 26

what is the direct pathway via?

Answer 26

caudate/putamen

Question 27

what is the indirect pathway via?

Answer 27

subthalmic nucleus

Question 28

what is are examples of basal ganglia disorders?

Answer 28

parkinsons disease

huntington’s disease

Question 29

what is hypokinesia?

Answer 29

slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.

Question 30

how is hypokinesia caused?

Answer 30

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

Question 31

true or false:

dopamine can enhance cortical inputs through the “direct” pathway and suppress inputs through “indirect” pathway

Answer 31

true

Question 32

what does the depletion of dopamine cause?

Answer 32

closes down activation of the focussed motor activities that funnel through thalamus to SMA

Question 33

what is characteristic chorea?

Answer 33

spontaneous, uncontrolled, rapid flicks and major movements with no purpose

Question 34

what is the cause of characteristic chorea?

Answer 34

profound loss of caudate, putamen and globus pallidus

so loss of the ongoing inhibitory effects of the basal ganglia

Question 35

how much of the total CNS neurones come from the cerebellum?

Answer 35

50%

Question 36

what do lesions to the cerebellum cause?

Answer 36

produce uncoordinated inaccurate movements : ataxia : fail to touch nose with eyes shut : similar to alcohol which depresses cerebellar circuits

Question 37

what are parts of the cortico-ponto-cerebellar projection?

Answer 37

Layer 5, areas 4 & 6, somatosensory cortex

Question 38

what is the cortico-ponto-cerebellar projection

Answer 38

connects cortex, pontine nuclei and cerebellum - 20 mill axons, 20x more that CST