Motor Control II

Question 1

how is the overall movement direction encoded?

Answer 1

Each neurone has a preferred direction but responses of all neurons are combined to produce a population vector

Question 2

what adjustments are made before movements begin?

Answer 2

anticipatory feedforward adjustments

Question 3

what initiates feedforward anticipatory adjustments to stabilize posture?

Answer 3

brainstem reticular formation nuclei (controlled by the cortex)

Question 4

what does cortical damage cause?

Answer 4

causes immediate flaccidity of contralateral muscles. Lift limb and release-drops passively

Question 5

what is the babinski sign?

Answer 5

(normal adult, plantar flexion)

baby and cortical damage, extension – both indicate incomplete upper control of spinal circuits

Question 6

describe Spasticity

Answer 6

increased muscle tone, hyperactive stretch reflex – due to removal of cortical suppressive influences

Question 7

where does Major subcortical input to area 6 come from?

Answer 7

ventral lateral nucleus(VLo) in dorsal thalamus

Question 8

what does the Basal ganglia motor loop do?

Answer 8

selects and initiates willed movements

Question 9

describe the Basal ganglia motor loop

Answer 9

cycles via - cortex through basal ganglia and thalamus(VLo) - back to SMA in cortex

Question 10

what is the input zone of the basal ganglia?

Answer 10

Corpus striatum - includes 2 principal nuclei the caudate and the putamen

Question 11

what is the corticostriatal pathway?

Answer 11

multiple parallel pathways with different functions

Question 12

when do the caudate and the putamen fire?

Answer 12

putamen fires before limb/trunk movements

caudate fires before eye movements

both are predictive of movements

Question 13

what is glutamatergic?

Answer 13

excitatory axons

Question 14

what is gabaergic?

Answer 14

axons are inhibitory

Question 15

where do putamen and caudate project?

Answer 15

globus pallidus and to substantia nigra pars reticulata

Question 16

what type of neurones go from Cortex to putamen?

Answer 16

excitatory

Question 17

what type of neurones go from Putamen to Globus pallidus ?

Answer 17

inhibitory

Question 18

what type of neurones go from Globus pallidus to VLo neurones?

Answer 18

inhibitory

Question 19

what type of neurones go from VLo to SMA?

Answer 19

excitatory

Question 20

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

Answer 20

excitation

Question 21

Why does cortical activation of putamen boost cortical excitation?

Answer 21

At rest globus pallidus neurones are spontaneously active and inhibit VL
So Cortical excitation excites putamen, which
inhibits the inhibitory Globus pallidus. Which therefore releases cells in VLo from inhibition so activity in VLo boosts SMA activity

Question 22

describe the Cortical input flow by direct pathway

Answer 22

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

it enhances the initiation of movements by the SMA

input from cortex releases Globus pallidus inhibition

Question 23

describe the Cortical input flow by indirect pathway

Answer 23

antagonizes the direct route

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

Cortex excites STN; this excites Gpi; which inhibits thalamus

Question 24

what is the role of the direct and indirect pathways?

Answer 24

Direct pathway selects specific motor actions

indirect pathway suppresses competing/inappropriate action

Question 25

what is Parkinson’s disease?

Answer 25

type of hypokinesia

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

Question 26

what causes Parkinson’s disease?

Answer 26

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

Question 27

describe Huntington’s disease

Answer 27

involves hyperkinesia with dementia and personality disorders

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

Question 28

what causes Huntington’s disease?

Answer 28

profound loss of caudate, putamen and globus pallidus

so loss of the ongoing inhibitory effects of the basal ganglia

Question 29

what do lesions to cerebellum produce?

Answer 29

uncoordinated inaccurate movements

eg ataxia : fail to touch nose with eyes shut

Question 30

what makes up the huge cortico-ponto-cerebellar projection?

Answer 30

Layer 5, areas 4 & 6, somatosensory cortex

Question 31

what is the cortico-ponto-cerebellar projection?

Answer 31

connects cortex, pontine nuclei and cerebellum

Question 32

what connects the cerebellum back to cortex?

Answer 32

via ventrolateral thalamus

Question 33

what is the role of the cerebellum?

Answer 33

instructs direction, timing and force

Question 34

describe the feedback motor loop through lateral cerebellum

Answer 34

through pons, cerebellum, thalamus and back to cortex