Motor Control II

Question 1

Does each neurone have a preffered direction?

Answer 1

Each neurone has a preferred direction but the responses of all neurons are combined to produce a population vector so commands to perform precise movements are encoded in the integrated activity of large populations of neurones in M1

Question 2

What does a change in body position lead to?

Answer 2

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

Question 3

What orrucs before a movement in anticipation?

Answer 3

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

Question 4

Damage to descending motor pathways causes upper motor neuron syndrome which causes cortical damage causes immediate flaccidity of contralateral muscles

initial hypotonia : “spinal shock” - spinal circuits are deprived of cortical input

but what happens a few days later?

Answer 4

days later spinal motor reflexes re-emerge in a consistent pattern – as spared connections strengthen and new connections sprout

Question 5

WHat happens to tendon reflexes in upper motor neuron syndrome?

Answer 5

Spasticity - increased muscle tone, hyperactive stretch reflex, clonus oscillatory contract/relax muscles in response to stretch - due to removal of cortical suppressive (inhibitory) influences

Question 6

What is the loop of information from the cortex to the SMA?

Answer 6

Major subcortical input to area 6 comes from ventral lateral nucleus in dorsal thalamus (Vlo)

Input to VLo comes from basal ganglia

Basal ganglia are targets of frontal, prefrontal and parietal cortex

So a loop of information cycles - from the cortex through thalamus and basal ganglia and back to the SMA in cortex (area 6)

Question 7

One major component of the basal ganglia is the corpus striatum (striped body), what are the 2 principal nuclei that make it up?

Answer 7

caudate

putamen

Question 8

What are the input zones of the basal ganglia?

Answer 8

caudate

putamen

Question 9

That caudate and putamen are _____ zones for _____

Answer 9

That caudate and putamen are modulation zones for movement

Question 10

WHat are the neurones found in the putamen and caudate?

Answer 10

medium spiny neurones

Question 11

What do the medium spicy neurons in the caudate and putamen do?

Answer 11

receive excitatory (glutamatergic) cortical inputs on dendrites

have large dendritic trees and integrate massive somatosensory, premotor and motor cortical inputs

their axons are inhibitory (GABAergic) and project to globus pallidus and to substantia nigra pars reticulata

the putamen fires before limb/trunk movements

the caudate fires before eye movements

both are predictive of movements

Question 12

Describe the motor loop: Cortex - Basal ganglia - Cortex

Answer 12

Cortex to putamen – is an excitatory pathway

Putamen to Globus pallidus – is inhibitory

Globus pallidus to VLo neurones – is inhibitory

VLo back to SMA – is excitatory

(vlo = ventral laternal nucleus)

Question 13

What are the globus pallidus neurones doing at rest?

Answer 13

At rest globus pallidus neurones are spontaneously active and inhibit VLo

Question 14

How do cortical excitation lead to the VLo not being inhibited by the globus pallidus?

Answer 14

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

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

Question 15

The gating operation of the basal ganglia depends on what type of arrangement?

Answer 15

disinhibitory arrangement

Question 16

This shows the disinhibitory circuit in the motor loop

Answer 16

A is at rest – there is little cortical input so upper motor neurones in SMA (D) are NOT excited

A is excited – there is a lot of cortical input to B (the globus pallidus) which is inhibited

C (the thalamus) therefore is disinhibited and so excites D – the upper motor neurones in SMA

Question 17

What part of the motor loop at rest is causing inhabition of the VLo and therefore the SMA?

Answer 17

globus pallidus

Question 18

What inhibits the globus pallidus?

Answer 18

cortical excitation to the putamen which then inhibits the globus pallidus

Question 19

What happens after the globus pallidus is inhibited?

Answer 19

allows the VLo to be excited to then pass signals and exctie the SMA

Question 20

Cortical input flows through the basal ganglia through a direct pathway but what is the other pathway?

Answer 20

An indirect pathway

Question 21

What is the direct pathway of cortical flow through the basal ganglia?

Answer 21

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

it enhances the initiation of movements by the SMA

globus pallidus neurones are spontaneously active at rest so they tonically inhibit (restrain) VL thalamus

And inputs from the cortex releases this inhibition

Question 22

What is the indirect pathway of cortical flow through the basal ganglia?

Answer 22

Indirect pathway – antagonizes the direct route

Striatum inhibits GPe (should be reed arrow in diagram)(globus pallidus external) which then inhibits both GPi (GP internal) and STN (subthalamic nuclei)

Cortex excites STN; this excites Gpi; which inhibits thalamus

Question 23

What is the function of the indirect pathway?

Answer 23

helps to prevent unwanted muscle contractions from competing with voluntary movements. It operates in conjunction with the direct pathway

Question 24

What is the function of the direct and indirect pathways?

Answer 24

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

Question 25

name a basal ganglia disorder?

Answer 25

parkinsons

Question 26

Parkinsons causes hypokinesia, what is it?

Answer 26

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

Question 27

What is the cause of hypokinesia in parkinsons?

Answer 27

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

dopamine can enhance cortical inputs through the “direct” pathway and suppress inputs through “indirect” pathway (there to supress non-essential functions)

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

Question 28

NHS definition of parkinsons

Answer 28

Parkinson’s disease is caused by a loss of nerve cells in the part of the brain called the substantia nigra.

Nerve cells in this part of the brain are responsible for producing a chemical called dopamine.

Dopamine acts as a messenger between the parts of the brain and nervous system that help control and co-ordinate body movements.

If these nerve cells die or become damaged, the amount of dopamine in the brain is reduced.

This means the part of the brain controlling movement cannot work as well as normal, causing movements to become slow and abnormal.

The loss of nerve cells is a slow process. The symptoms of Parkinson’s disease usually only start to develop when around 80% of the nerve cells in the substantia nigra have been lost.

Question 29

What is the nae of a second basal ganglia disorder?

Answer 29

Huntingtons disease

Question 30

What are the symptoms of huntingtons disease?

Answer 30

involves hyperkinesia with dementia and personality disorders

Question 31

Is huntingtons disease hereditary?

Answer 31

yes

Question 32

In huntingtons you get characteristic chorea, what is it?

Answer 32

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

Question 33

What causes characteristic chorea in huntingtons disease?

Answer 33

caused by profound loss of caudate, putamen and globus pallidus, so loss of the ongoing inhibitory effects of the basal ganglia

Question 34

What is the definition of huntingtons disease?

Answer 34

Huntington’s disease is a condition that stops parts of the brain working properly over time. It’s passed on (inherited) from a person’s parents.

a progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition). Adult-onset Huntington disease, the most common form of this disorder, usually appears in a person’s thirties or forties

Question 35

Does the cerebellum have a lot of neurons?

Answer 35

Cerebellum 10% of brain volume but 50% of total CNS neurones

Question 36

What is the cerebellum involved in?

Answer 36

movement

Question 37

WHat do lesions on the cerebellum cause?

Answer 37

uncoordinated inaccurate movements

ataxia

fail to touch nose with eyes shut

similar to alcohol which depresses cerebellar circuits

Question 38

Wht is the cerebellum in connection with

Answer 38

connects cortex, pontine nuclei and cerebellum

Question 39

How does the cerebellum relay information back to the cortex?

Answer 39

cerebellum back to cortex via ventrolateral thalamus

Question 40

What does the cerebellum instruct?

Answer 40

instructs direction, timing and force

Question 41

What makes up motor learning in the cerebellum?

Answer 41

based on predictions

calculations

experience (too fast for feedback control directly) – compares what is intended with what happened and compensates

Question 42

This photo is showing both the pathways together

Answer 42