Control Of Movement

Question 1

What is motor control?

Answer 1

• Refers to brain mechanisms that produce purposeful, coordinated movements
• The brain adapts motor outputs to responds to changing sensory inputs from the body and the external environments

Question 2

Which structures of the brain are involved in motor control?

Answer 2

• Prefrontal cortex
• Pareital cortex
• Cerebellum
• Brainstem centres
• Spinal cord
• Key structure: Basal ganglia which is connected to all of these structures

Question 3

What are the structures of the basal ganglia?

Answer 3

• Stratium: Caudate Nucleus & Putamen
• Globus pallidus
• Subthalamic nucleus
• Substantia nigra

Question 4

What type of connections does the basal ganglia receive?

Answer 4

• Receives afferent and efferent connections
• A: Basal ganglia major structures, MD medial dorsal, VA ventral dorsal, ventral nuclei of thalamus
• B: Major afferents to basal ganglia
• C: Intrinsic connections
• D: Efferent connections

Question 5

How does the basal ganglia work in regards to motor control?

Answer 5

The basal ganglia takes massive inputs from multiple cortical and brainstem regions and output to selected parts of these same areas
- Initiation of movement
- Focussing function
- Scaling movement: Amplitude, Velocity, rhythm

Question 6

What does the Basal ganglia do?

Answer 6

• Integrate diverse inputs from the entire cerebral cortex and funnel these influence via the thalamus to the motor cortex
• Focus attention on what is relevant among the plethora of activities going on at any time
• Favours certain channel activity over others

Question 7

What arises due to the abnormal function of the basal ganglia?

Answer 7

Movement disorders
- Neurological conditions determining slowed or absent voluntary movement (hypokinesia) or excessive and involuntary movement (hyperkinesia)

Question 8

List some Hypokinectic movement disorders

Answer 8

Slowed or absent voluntary movement
- Parkinsonism
- Parkinson’s disease
- Atypical parkinsonisms

Question 9

List some Hyperkinectic movement disorders

Answer 9

Excessive and involuntary movements
- Tremor
- Dystomia, Chorea
- Tics
- Myoclonus

Question 10

What is Parkinson’s disease characterised by?

Answer 10

Bradykinesia
- Progressive reduction of amplitude
- Progressive reduction of speed
- Lack of spontaneous movements
- Difficulty to execute internally generated movements > externally paced movements

Question 11

Other than motor processing, what else does the basal ganglia control?

Answer 11

Non motor processing
- Basal ganglia are separated anatomically (and functionally) between different loops (motor, associative, limbic) and within loops

Question 12

List the non motor functions of the basal ganglia

Answer 12

• Attention
• Explicit and implicit learning
• Reward related behaviour
• Habit formation
• Time estimation

Question 13

What basic functions does the basal ganglia controls?

Answer 13

• Movement
• Behaviour
• Cognition

Question 14

Where are the 3 basic loops into the basal ganglia connected?

Answer 14

• Motor circuit: connected to the primary model right up to the supplementary grand motor area?.??
• Associative circuit: Connected to the prefrontal areas
• Limbic circuit: Connected to the limbic system

Question 15

What is the importance of the basal ganglia loop?

Answer 15

• The main output of the basal ganglia is inhibitory, so more activity = less movement
• Two pathways through the basal ganglia exist, one which decreases output activity (increases movement) and one which increases output output activity (decreases movement)
• Dopamine has different effects on these two pathways

Question 16

Describe these two pathways

Answer 16

Called the rate model
- Has a stop pathway And a direct Go pathway

Question 17

Describe the indirect stop pathway in more detail

Answer 17

INPUT (STRATIUM - medium spiny neurons) -> OUTPUT (Gpi/SNr) via indirect stop pathway -> Thalamus/CTX
- Reduce movement

Question 18

Describe the direct go pathway in more detail

Answer 18

INPUT (STRATIUM - medium spiny neurons) -> OUTPUT (Gpi/SNr) via direct go pathway -> Thalamus/CTX via thalamic inhibition
- Increases movement by reducing thalamic inhibition

Question 19

What does a change in the firing rate determine?

Answer 19

Determines the degree of thalamic inhibition and therefore the amount of movement possible

Question 20

Describe the dopamine direct pathway

Answer 20

• Dopamine activates the dotted pathway to the one receptor
• The dotted pathway exert focus inhibition of the GPI
• Which is the output component of the model loop of the basal ganglia
• The reduced inhibition of GpI resulted in even increase of activity of the motor cortex because of reduced inhibition from the mouse
• So focus inhibition of these GPI is the excitatory pathway or the motor loop

Question 21

Describe the indirect pathway

Answer 21

• Mediated by the tourist sector
• Exerts divergent excitation of the STN
• The thalamic nucleus is an excitatory nucleus that produces glutamate that activate GPI to increase inhibitory action
• More inhibition from the child almost to the cortex

Question 22

Describe the role of dopamine in the loop

Answer 22

Dopamine facilitates the direct pathway
- Dopamine inhibits the indirect pathway = Promotes movement
- Loss of dopamine will lead to increase of activity in GPi/SNr and leads to inhibition of thalamocortical pathways during the inhibition of motor function