Motor control - 3

Question 1

Describe directional tuning in primary motor cortex

Answer 1

Each neuron has preferred direction but responses of all neurons combine to produce popular vector - commands to perform precise movements are encoded in integrated activity of neurons

Question 2

What does an actual change in body position cause?

Answer 2

Initiates rapid compensatory feedback massages from brainstem vestibular nuclei to spinal motor neurons to correct postural instability

Question 3

What is the feedforward mechanism which control movement?

Answer 3

Before movement begins, the brainstem reticular formation nuclei initiates feedforward anticipatory adjustments to stabilise posture

Question 4

Where does the loop of information cycle?

Answer 4

Cortex to thalamus and basal ganglia to supplementary motor cortex

Question 5

Where does major subcortical input to area 6 come from?

Answer 5

Ventral lateral nucleus in dorsal thalamus (VLo)

Question 6

Where does input from VLo come from?

Answer 6

Basal ganglia

Question 7

Where are basal ganglia targets of?

Answer 7

Frontal, prefrontal and parietal cortex

Question 8

What are the major components of basal ganglia?

Answer 8

Corpus striatum - includes 2 principal nuclei
Caudate and Putamen

Question 9

What are the caudate and putamen?

Answer 9

Are input zone of the basal ganglia

Question 10

Where does corpus striatum receive inputs from?

Answer 10

All over cortex
Corticostriatal pathway - multiple parallel pathways with different functions

Question 11

What do medium spiny neurons in putamen and caudate receive?

Answer 11

Excitatory cortical inputs on dendrites

Question 12

What do large dendrite trees integrate?

Answer 12

Massive somatosensory, premotor and motor cortical inputs

Question 13

Describe the axons of the basal ganglia

Answer 13

Are inhibitory
Contacts 1000s of spiny neurons so integrating influence of 1000 cortical cells
Axons project to globus pallidus and SN pars reticulata

Question 14

When do putamen and caudate fire?

Answer 14

Putamen - before limb/trunk movements
Caudate - before eye movements
Both predict movements

Question 15

What type of pathway if from cortex to putamen?

Answer 15

Excitatory

Question 16

What type of pathway is between putamen to globus pallidus?

Answer 16

Inhibitory

Question 17

What type of pathway is between globus pallidus to VLo neurons?

Answer 17

Inhibitory

Question 18

What type of pathway is between VLo and back to SMA?

Answer 18

Excitatory

Question 19

What is the functional consequence of cortical activation of putamen?

Answer 19

Excitation

Question 20

At rest, what are the globus pallidus neurons?

Answer 20

Spontaneously active and inhibit VLo

Question 21

Explain cortical excitation

Answer 21

Excites putamen which inhibits globus pallidus - reduces inhibition of VLo cells - activity in VLo boosts SMA activity

Question 22

What does gating by basal ganglia depend on?

Answer 22

Dis-inhibitory arrangement

Question 23

What are the upper motor neurons in SMA like at rest?

Answer 23

Not excited as little cortical input

Question 24

What are the upper motor neurons in SMA like when excited?

Answer 24

Lots of cortical input into globus pallidus which is inhibited so this dis-inhibits the thalamus
Excites upper motor neurons in SMA

Question 25

What is the function of the direct pathway in cortical input flow?

Answer 25

Selects specific motor actions

Question 26

What is the function of the indirect pathway in cortical input flow?

Answer 26

Suppresses other/ inappropriate actions

Question 27

Describe the direct pathway of cortical input flow

Answer 27

Positive feedback loop Enhances initiation of movements by SMA Input from cortex releases inhibition on VLo

Question 28

Describe indirect pathways of cortical input flow

Answer 28

Antagonises the direct route Cortex excites subthalamic nuclei which excites GP internal which inhibits thalamus

Question 29

Describe Parkinson's disease

Answer 29

Hypokinesia - slowness, difficult to make voluntary movements, increased muscle tone (rigidity) and tremors in hand or jaw

Question 30

What is the cause of Parkinson's disease?

Answer 30

Degeneration of neurons in substantia nigra so loss of their dopaminergic excitatory inputs to striatum

Question 31

What is the function of dopamine?

Answer 31

Enhances cortical inputs through the direct pathway ad suppress inputs through indirect pathway

Question 32

What does depletion of dopamine cause?

Answer 32

Parkinson's - closes down focussed motor activities that funnel through thalamus to SMA

Question 33

Describe Huntington's disease

Answer 33

Hyperkinesia with dementia and personality disorders Is hereditary, progressive and rare Chorea - spontaneous uncontrolled rapid flicks and major movements of no purpose

Question 34

What is the cause of Huntington's disease?

Answer 34

Profound loss of caudate, putamen and globus pallidus So loss of ongoing inhibition by basal ganglia

Question 35

How many CNS neurons does the cerebellum have?

Answer 35

50%

Question 36

What is ataxia?

Answer 36

Uncoordinated inaccurate movements Can be due to lesions to cerebellum

Question 37

What structures are a part of cortico-ponto-cerebellar projection?

Answer 37

M1 layer 5, areas 4 and 6 and somatosensory cortex 20 mill axons

Question 38

What connects the cerebellum to cortex?

Answer 38

Ventrolateral thalamus

Question 39

What is the function of the cerebellum?

Answer 39

Instructs direction, timing and force

Question 40

Describe the motor loop through lateral cerebellum

Answer 40

Motor loop of voluntary movement through basal ganglia and VLo undergoes ongoing refinement Via involvement of feedback loop through pons, cerebellum and thalamus then back to cortex

Question 41

Describe Brain machine interfaces

Answer 41

BMI - allow patients to voluntary control prosthetic limbs and walk again after spinal cord injuries Sensory properties in prosthetics

Question 42

Describe brain brain interfaces

Answer 42

BBI - brain signals from one animal to teach another animal a task it has never seen