Control Of Movement Flashcards
What is motor control?
- 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
Which structures of the brain are involved in motor control?
- Prefrontal cortex
- Pareital cortex
- Cerebellum
- Brainstem centres
- Spinal cord
- Key structure: Basal ganglia which is connected to all of these structures
What are the structures of the basal ganglia?
- Stratium: Caudate Nucleus & Putamen
- Globus pallidus
- Subthalamic nucleus
- Substantia nigra
What type of connections does the basal ganglia receive?
- 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
How does the basal ganglia work in regards to motor control?
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
What does the Basal ganglia do?
- 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
What arises due to the abnormal function of the basal ganglia?
Movement disorders
- Neurological conditions determining slowed or absent voluntary movement (hypokinesia) or excessive and involuntary movement (hyperkinesia)
List some Hypokinectic movement disorders
Slowed or absent voluntary movement
- Parkinsonism
- Parkinson’s disease
- Atypical parkinsonisms
List some Hyperkinectic movement disorders
Excessive and involuntary movements
- Tremor
- Dystomia, Chorea
- Tics
- Myoclonus
What is Parkinson’s disease characterised by?
Bradykinesia
- Progressive reduction of amplitude
- Progressive reduction of speed
- Lack of spontaneous movements
- Difficulty to execute internally generated movements > externally paced movements
Other than motor processing, what else does the basal ganglia control?
Non motor processing
- Basal ganglia are separated anatomically (and functionally) between different loops (motor, associative, limbic) and within loops
List the non motor functions of the basal ganglia
- Attention
- Explicit and implicit learning
- Reward related behaviour
- Habit formation
- Time estimation
What basic functions does the basal ganglia controls?
- Movement
- Behaviour
- Cognition
Where are the 3 basic loops into the basal ganglia connected?
- 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
What is the importance of the basal ganglia loop?
- 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
Describe these two pathways
Called the rate model
- Has a stop pathway And a direct Go pathway
Describe the indirect stop pathway in more detail
INPUT (STRATIUM - medium spiny neurons) -> OUTPUT (Gpi/SNr) via indirect stop pathway -> Thalamus/CTX
- Reduce movement
Describe the direct go pathway in more detail
INPUT (STRATIUM - medium spiny neurons) -> OUTPUT (Gpi/SNr) via direct go pathway -> Thalamus/CTX via thalamic inhibition
- Increases movement by reducing thalamic inhibition
What does a change in the firing rate determine?
Determines the degree of thalamic inhibition and therefore the amount of movement possible
Describe the dopamine direct pathway
- 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
Describe the indirect pathway
- 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
Describe the role of dopamine in the loop
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
