Lecture 11 - Motor Control + Disorders of Action 2 Flashcards
What is the basal ganglia?
Subcortical group of nuclei
GPl: lateral globus pallidus (external)
GPm: medial globus pallidus (internal)
SNc: substantia nigra pars compacta
STN: subthalamic nucleus
Putamen – receive inputs from cortical areas (striatum), GPm – projects back to cortex
What is the excitatory direct pathway in the BG?
Excitatory signal from cortex
Increased inhibitory signal from Putamen to GPm
Reduced inhibitory signal from GPm to thalamus
Increased excitatory signal from thalamus to motor cortex
What is the inhibitory direct pathway in the BG?
Increased inhibitory signal from Putamen to GPI
Reduced inhibitory signal from GPI to STN
Increased excitatory input to GPm
Increased inhibitory output to thalamus
Reduced excitatory output to cortex
How does the BG help ‘gain control’?
Direct pathway: allows desired movements to occur
Indirect pathway: prevents undesired movement occurring
How does the BG act as selection mechanism?
Diff possible movements
Desired movement is ‘disinhibited’ (released)
Competing movements inhibited –> prevent from occurring
How does BG relate to Parkinson’s?
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 thalamus + reduced excitation of cortex
What are 4 ways we treat Parkinson’s?
L-dopa –> BUT drug induced dyskinesias (involuntary erratic movements of face/arms, etc.)
Newer dopaminergic drugs
Surgery – lesions + deep brain stimulation
Deep brain stimulation: battery-operated stimulator delivers electrical stimulation to targeted areas –> thalamus, subthalamic nucleus, globus pallidus
How does deep brain stimulation help?
Reduces effect of indirect pathway (reduced activity in STN, reduced excitation of GPm, reduced inhibition of thalamus, greater excitation of motor cortex)
What is Huntington’s disease? (HD)
Inherited, autosomal dominant condition, onset in 30s/40s
Chorea – uncontrolled movements
Degeneration of putamen/caudate
Death from complications, no treatment at present
Brain: enlarged lateral ventricles, cortical degeneration
How does BG affect HD?
Underactivity of indirect pathway (reduced inhibition of GPI/STN, reduced activity of GPm) –> too much movement
What 5 cognitive impairments does HD come with?
Attention, executive function, speed of processing, prospective memory, emotion recognition
What is Tourettes?
Simple tics (eye blinking, nose twitching), complex tics (scrating, gestures, utterances), may increase during times of stress/decrease when concentration
> 1000 per 100,000 children (greater than 1 in 1000)
Hereditary, links to obsessive/compulsive behaviours, developmental
How does BG affect TS?
Increased dopamine from substantia nigra
Overactivity of direct pathway – leads to disinhibition of unwanted movement
What is aberrant selection?
Aberrant focus of activity in striatum leads to activity in direct pathway + disinhibition of undesired movement, may explain obsessive compulsive behaviours
What is a summary of direct/indirect pathway effects?
Park: D - underactive, I - Overactive
Hunt: I - underactive
Tour: D - overactive
