Basal Ganglia Flashcards
Location
Between cortex - brainstem, interconnected between each other
What structures make up basal ganglia?
Caudate nucleus
Putamen
Striatum (C + P)
Globus pallidum (external & internal segments)
Lentiform nucleus = Putamen + Pallidum
Subthalamic nucleus
Substantia nigra, just below the subthalamic nucleus
Basal ganglia are part of
Inf loop: take info from cortex, process and analyze it (filter it) —> pass it back to cortex
Mediate all automatic activity (habitual control)
Functions of basal ganglia
Learning + selecting most appropriate motor/behav programs
Control of voluntary but automatic motor movements
Eye movements
Procedural learning (new abilities)
Habit learning
Cognition and emotion
Basal ganglia loops
Motor loop: control of movement
Oculomotor loop: eye movement control
Lateral orbitofrontal loop: social behaviours
Dorsolateral prefrontal loop: executive function (perform several activities at the = time, planning and “working memory”)
Anterior Cingulate loop: reinforces the previous BG loops
Basal ganglia motor loop starts in
Motor cortex
Motor + associative + limbic loops have
Spatial topographic organization
Motor + associative + limbic loops provide
Topographically ordered input to
- post putamen (motor circuit)
- ventral striatum (limbic)
- caudate & ant putamen (associative circuit)
Motor circuit
Starts w/ 1st motor neuron in precentral cortex (1ary motor cortex).
Descends and connects with basal ganglia
Then goes to nuclei in the thalamus
From there, back to the cortex
If motor loop is activated
Thalamus will activate the cortex
If we want to stop motor loop
Thalamus will stop firing to the cortex
In the motor circuit, the associated nucleus is
Post putamen
In the associative circuit, the associated nucleus is
Caudate
In the limbic circuit, the associated nucleus is
Striatum
Each area of the precentral cortex will be connected to
A specific corresponding region in the putamen (specific topographic organization)
Main input
Striatum (C + P) —> reach post Putamen —> main action = inhibit structures it projects to
Main output
Int segment of the globus pallidum (GPi) —> main action = inhibition thalamus
Gpi
Inhibitory structure
Projects to thalamus —> projects back to cortex (closing the loop) through excitatory neurons
Gpi activated =
inhibits thalamus, thalamus stops the movement
Gpi not activated =
thalamus activates, increases activity in the cortex (“go”)
Pathways of the motor loop
direct, indirect and hyperdirect pathways
Direct pathway
Cerebral motor cortex —> excitatory act over input: striatum activates, through putamen.
Main role of putamen = inhibit Gpi: striatum connect w/ main output -> Gpi (inhibitory action over thalamus).
Inhibit inhibition = block Gpi = no thalamus inhibition.
Thalamus activate the cortex
Direct pathway is a
“GO” pathway
Indirect pathway
Cortex projects to Striatum and act it —> inhibit structures (Striatum) to which it projects.
Gpe also inhibits Subthalamic nucleus (excitatory structure that act Gpi)
(Gpe is inhibited by Striatum = Subthalamic nucleus not inhibited = it act Gpi)
- When subthalamic nucleus works = act Gpi = block the thalamus = NO movement - When subthalamic nucleus doesn’t work= won’t act Gpi = thalamus activate = GO movement
Indirect pathway is a
“STOP” pathway
Hyperdirect pathway is even shorter than direct pathway because
We won’t have info entering basal ganglia through striatum.
Hyperdirect pathway
Cortex enters basal ganglia in hyperdirect fashion by contacting Subthalamic nucleus directly, without passing through the Striatum.
Subthalamic nucleus contacts Gpi —> activate it
Gpi = INHIBITORY = inhibits thalamus
Hyperdirect pathway is a
“STOP” pathway
Main neurotransmitter in the loops of basal ganglia is
Dopamine
Dopamine effects
Opposite ones on Direct and Indirect motor pathways
Dopamine binds to
D1 receptors = direct pathway —> activated
D2 receptors = indirect pathway —> inhibited
Net result of dopamine in the brain
Promote movement
Párkinson disease
No dopaminergic neurons = difficult to move
(lack of dopamine)
Basal ganglia location
centre of the brain
