Week 11 Lecture 11 - Motor control part 2 Flashcards
What are the connections in the Basal ganglia?
GPl = Lateral Globus Pallidus (external)
GPm = Medial Globus Pallidus (internal)
SNc = Substantia Nigra pars compacta
STN = Subthalamic nucleus
- putamen
- thalamus
What are the 2 pathways through the basal ganglia?
- direct
- indirect
What does the circuitry of the basal ganglia look like?
see summary sheet
Where does putamen recieve inputs from?
cortical areas (Striatum) –> excitatory
Where does GPm project back to?
cortex –> inhibitory
Is the direct pathway excitatory or inhibitory?
excitatory
What is the direct pathway?
- Excitatory signal from cortex
- Increased inhibitory signal from Putamen to GPm
- Reduced inhibitory signal from GPm to Thalmus
- Increased excitatory signal from thalamus to motor cortex
Is the indirect pathway inhibitory or excitatory?
inhibitory
What is the indirect pathway?
- Increased inhibitory signal from Putamen to GPl
- Reduced inhibitory signal from GPl to
STN - Increased excitatory input to GPm
- Increased inhibitory output to thalamus
- Reduced excitatory output to cortex
What does the direct pathway allow?
desired movements to occur
What does the indirect pathway prevent?
undesired movement occurring
What does Parkinson’s Disease look like in the basal ganglia?
Lack of dopamine has opposing effects on 2 pathways
Underactive direct pathway (increased GPm activity)
Overactive indirect pathway (increased GPm activity)
Both lead to increased inhibition of the thalamus and reduced excitation of the cortex
True or false?
Different BG loops project to different cortical areas
True
Cognitive as well as motor functions
What are treatments for Parkinson’s disease?
L-dopa
but drug induced dyskinesias
- Newer dopaminergic drugs
- Surgery – lesions and deep brain
stimulation
What is deep brain stimulation as a treatment for Parkinson’s?
Battery-operated stimulator delivers electrical stimulation to targeted areas
Targets - thalamus, subthalamic nucleus, and globus pallidus
What does deep brain stimulation do the the pathways in the basal ganglia?
Reduces effect of indirect pathway:
* Reduced activity in the STN
* Reduced excitation of the GPm
* Reduced inhibition of the thalamus
* Greater excitation of the motor cortex
What is Huntington’s disease?
- inherited, autosomal dominant condition
- Onset in 30’s or 40’s
- Chorea – uncontrolled movements
- Degeneration of putamen and caudate
- Death from complications
- No treatment at present
How does HD affect the basal ganglia?
Underactivity of Indirect pathway
- Reduced inhibition of GPl
- Increased inhibition of STN
- Reduced activity of GPm
- Too much movement
What cognitive impairments can occur with HD?
Can include difficulties with the following:
* Attention
* Executive function
* Speed of processing
* Prospective memory
* Emotion recognition
What is Tourette’s syndrome?
- Simple tics e.g. eye blinking, nose
twitching - Complex tics e.g. scratching, gestures,
utterances - May increase during times of stress
and decrease when concentrating
> 1000 per 100,000 children (greater than
1 in 1000)
* Hereditary
* Links to obsessive-compulsive behaviours
* Developmental
How does TS affect the basal ganglia?
Increased dopamine from substantia nigra
- Overactivity of the direct pathway –
leads to ‘disinhibition’ of an unwanted movement
What is aberrant selection in TS?
‘Aberrant focus’ of activity in striatum leads to activity in the direct pathway
And disinhibition of undesired movement
May also explain obsessive compulsive behaviours
How can TS sometimes be treated?
by blocking dopamine
Give a summary of which BG pathways are affected in PD, HD and TS
see summary sheet
