Motor control 2

Question 1

How is direction of movement control?

Answer 1

• In M1: primary motor complex
• Made by a large integrated system of neurones
• Discharge of neurones is in the preferred direction
• Each neurone has a preferred direction- however all the discharges get put together to create one large vector

Question 2

How is change in stability controlled?

Answer 2

1- Messages from the brainstem Vestibular nuclei to the spinal cord- CORRECTS POSTURAL INSTABILITY - Feedback
2- BEFORE MOVEMENT: Brainstem reticular formation nuclei initiate FEEDFORWARD system to prevent instability and maintain postural balance- feedforward

Question 3

Basic structure of the basal ganglia loop

Answer 3

Cortex- basal ganglia- cortex

• Basal ganglia are one of the major output zones for the pre-frontal , fortal and parietal cortex
• The basal ganglia supply inputs to the ventral lateral nucleus of the the thalamus
• The ventral lateral nucleus of the thalamus supplies lots of imputs to the cortex

Question 4

Anatomy of the basal ganglia

Answer 4

• Caudate nucleus and the putamen make up the corpus stratum
• Globus pallidus is another basal ganglia

Question 5

Function of the corpus striatum

Answer 5

Main source of imput from the cortex via the corticospinal pathway

Question 6

what kind of imputs does the corpus striatum receive from the cortex

Answer 6

Spiny neurones: Excitatory impulses

• These are glutaminergic
• They receive thousands of these impulses due to their enormous dendritic trees
• These carry somatosensory, motor and pre-motor information
• From the substation nigra onto D1

Question 7

The impulses sent from the caudate and the putamen are predictive of?

Answer 7

MOVEMENT

• caudate: eye movement
• Putamen: limb and trunk movement

Question 8

Pathways pf these impulses

Answer 8

1- cortex to putamen: excitatory
2-Putamen to globus pallidus: inhibitory
3-Globus pallidus to Vlo: inhibitory
4-Vlo to cortex: excitatory

Overall: excitatory so an impulse is sent to the cortex

Question 9

What does the globus pallidus do to the Vlo at rest?

Answer 9

Inhibits it

Question 10

What is the functional purpose of thus pathway?

Answer 10

It inhibits the globus pallidus form inhibiting the vlo

Question 11

Direct pathway

Answer 11

• Motor cortex stimulates the striatum
• The striatum inhibits the globus pallidus interna
• The vLO is no longer inhibited by a globus pallidus
• Boosts activity of SMA
• More fine movement in distal motounits

Question 12

Indirect pathway

Answer 12

• Striatum inhibits the external unit of the globus pallidus
• The external globes pallidus no longer inhibits the sub thalamic nuclei
• The subthalamic nuclei would usually inhibit the internal GP
• The internal GP is excited and so inhibits the Vlo

Question 13

Involvement of the cerebellum in movement

Answer 13

Basically the basal ganglia loop gets refined via the cortico-pontico-cerebellar projection

• Cortex to pontine nuclei to cerebellum
• Cerebellum back to cortex via the thalamus
• Helps correct timing, direction and force

Question 14

What is the function of the cerebellum in terms of movement control?

Answer 14

The cerebellum helps refine

• timing
• intensity
• duration of contractions

Through the cortico-pontine- cerebellum loop

Question 15

what happens when the cerebellum is injured?

Answer 15

Many inaccurate, uncoordinated measurements

Question 16

Disorders which affect the basal ganglia loop

Answer 16

Parkinson

Huntingtons

Question 17

Parkinsons

Answer 17

Hypokinesia :

• Increased muscle tone
• Tremors
• Unco-ordinated movement

Due to loss of dopamine: involved in sending impulses via direct pathway and inhibiting impulses via indirect pathway

Question 18

Huntingtons

Answer 18

Hyperkinesia
-Due to loss of caudate, putamen and globus pallidus so loss of inhibitory effect on globus pallidus

• chorea
• personality disorder

Question 19

Damages to UMN

Answer 19

Depends on the site of injury

• Immediate damage to contralateral muscles
• Reduced imputs to spinal circuits leads to hypotonia
• Motor reflex patterns develop
• Babinski sign:plantar extension n rather than plantar flexion
• Loss of fine finger movement
• Hyperreflexia and hypertonia can occur due to loss of inhibition to the cortex

Question 20

what kind of impulses does the corpus striatum send?

Answer 20

Their axons are Inhibitory:

These are GABAinergic to the Globus pallidus externa and the substantial nigra

Question 21

what happens when the cerebellum is injured?

Answer 21

-Lots of inaccurate, uncoordinated movement.

Question 22

Function of dopamine

Answer 22

Dopamine is released from the substantial nigra
Dopamine can either bind to D1 or D2 receptors on striatum

If they bind to D1: They trigger the direct pathway
If they bind to D2: they trigger the indirect pathway