Motor Control 2

Question 1

What is the significance of a neurone having its greatest discharge in one direction of movement?

Answer 1

It means the responses of all neurones are combined to produce a population vector

Movement direction is encoded by the integrated activity of all the neurones

Question 2

Where does body position feedback information travel from? and to?

Answer 2

Travels from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability

Question 3

What is responsible for feedforward anticipatory adjustments to stabilize posture?

Answer 3

Brainstem reticular formation nuclei (controlled by the cortex)

Question 4

What is the result of cortical damage on contralateral muscles?

Answer 4

•cortical damage causes immediate flaccidity of contralateral muscles. Lift limb and release, drops passively

Question 5

Hypotonia is a feature of spinal shock, what happens several days later?

Answer 5

•days later spinal circuits regain function - spared connections strengthen and new connections sprout. A consistent pattern of motor signs emerges

Question 6

What is the babinski sign and what is it a sign of?

Answer 6

•Babinski sign – normal adult, plantar flexion – baby and cortical damage, extension – both indicate incomplete upper control of spinal circuits

Question 7

What are features of spasticity?

Answer 7

Increased muscle tone

Hyperactive stratch reflex

Clonus

Question 8

What causes spasticity?

Answer 8

Loss of cortical suppressive influences

Question 9

What is the loop that occurs within tha basal ganglia when selecting willed movements?

Answer 9

Subcortical information to the pre-motor area largely comes from the ventral lateral nucleus of the dorsal thalamus.

Input into this is called the VLo and is formed by the basal ganglia

The basal ganglia are targets of the pre-frontal cortex, the frontal cortex and the motor cortex.

Question 10

Define corpus striatum

Answer 10

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

They are the input zone of the basal ganglia

The internal capsule is also included in the corpus striatum

Question 11

What is the name given to the pathways associated with the corpus striatum?

Answer 11

•corticostriatal pathway - multiple parallel pathways with different functions

Question 12

How does the caudate nucleus and the putamen communicate with the cortex?

Answer 12

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

Question 13

The caudate and the putamen have large dendritic trees, what type of information do these dendritic trees integrate?

Answer 13

•somatosensory, premotor and motor cortical inputs

Question 14

Which nucleus is responsible for firing before limb/trunk movement?

Answer 14

Putamen

Question 15

Which nucleus is responsible for firing before eye moevements?

Answer 15

Caudate

Question 16

What are the excitatory components of the motor loop?

Answer 16

Cortex to putamen

VLo to SMA

Question 17

What are the inhibatory components of the motor circuit?

Answer 17

Putamen to globus pallidus

Globus pallidus to VLo

Question 18

What is the effect of cortical excitation on SMA activity?

Answer 18

1. excites putamen which
2. inhibits the inhibitory Globus pallidus which therefore
3. releases cells in VLo from inhibition so
4. activity in VLo boosts SMA activity

Positive FEEDBACK loop

Question 19

Explain B at rest

Answer 19

Globus pallidus neurones are spontaneoously active and inhibit the ventral lateral nucleus of the dorsal thalamus

Question 20

Explain what happens when A is transiently excited?

Answer 20

Striatum causes inhibition of the globus palidus inhibition - therefore the the VL is disinhibited and excited D - the upper motor neurones in the SMA

Question 21

Describe what happens during the indirect pathway of the motor loop

Answer 21

• 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 22

What is the difference in function between the direct and the indirect pathways of the motor loop?

Answer 22

Direct pathway - selects specific motor actions

Indirect pathway - suppresses competing / inappropriate action

Question 23

Name a disease associated with a basal ganglion disorder

Answer 23

Parkinsons

Question 24

What are the features of parkinsons?

Answer 24

Hypokinesia - slowness, difficulty to make voluntary movements

Question 25

What is the cause of parkinsons?

Answer 25

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

Question 26

What is the effect of dopamine on the direct and indirect pathway?

Answer 26

Direct - enhances cortical inputs

Indirect - Suppress inputs

Question 27

What is the effect of depletion of dopamine?

Answer 27

•Reduces the number of focussed motor activities that funnel through thalamus to SMA

Question 28

What are the features of hungtingtons disease?

Answer 28

Hyperkinesia

Dementia

Personality disorders

Characteristic chorea - Uncontrolled rapid flicks and major movement with no purpose

Question 29

What is the cause of Hungtingtons disease?

Answer 29

•Profound loss of caudate, putamen and globus pallidus

Loss of ongoing inhibatory effects of the basal ganglia

Question 30

Where do 50 % of CNS neurones come from?

Answer 30

Cerebellum

Question 31

What is the result of a lesion to the cerebellum?

Answer 31

Produce uncoordinated and innacurate movements - ataxia

Question 32

What parts of the brain are included in the cortico - ponto - cerebellar projection?

Answer 32

Layer 5, areas 4 & 6, somatosensory cortex

Question 33

What does the cortico - ponto cerebellar projection connect?

Answer 33

Cortex, pontine nuclei and cerebellum

Question 34

How does the cerebellum project back to the cortex?

Answer 34

Through the ventrolateral thalamus

Question 35

What does the cerebellum instruct?

Answer 35

Direction, timing and force

Also involved in motor learning

Question 36

Describe the feedback loop involving the cerebellum

Answer 36

pons, cerebellum, thalamus and back to cortex