The Basal Ganglia Flashcards
Basic components of the basal ganglia.
5 interconnected subcortical nuclei: the putamen, caudate nuclei, globus pallidus, subthalamic nuclei and the substantia nigra.
What two components make up the ventral striatum?
The caudate nucleus and the putamen.
What is another name for the ventral striatum?
Nucleus accumbens
Name the major input nuclei of the basal ganglia.
The striatum: the caudate nucleus and putamen.
In what way are the caudate nucleus and the putamen fused together?
Partially fused together (ventrally) by mini strips of tissue forming bridge btw each. Are separated dorsally by the corticospinal tract.
From where does the BG receive inputs?
From the motor cortex, sensory cortex, association cortex and the limbic system.
What sort of motor information is sent to the BG?
Receives info from the primary motor cortex about the intended motor command to be sent to the spinal cord.
What sort of sensory information is sent to the BG?
Visual, auditory, olfactory info etc. informing BG about safety of surroundings. Some info is raw, some is sent via sensory integration in parietal lobe.
What sort of motivational / emotional inputs does the BG receive?
Info regarding hunger, thirst, temperature, fear stimuli?
What sort of info regarding memory is sent to the BG?
Info regarding mvmts / actions made in the past to inform decision re current mvmt.
How does the BG deal with all of the incoming info? (5)
Each piece of info will be weighted differently according to how relevant it is to the current situation. BG somehow integrates all of this info and determines whether motor action should or shouldn’t be carried out / is appropriate given the current internal / environmental conditions.
What is the major output nuclei of the BG?
The internal globus pallidus
What 4 substances mediate transmission within the BG?
Dopamine, substance P, GABA and dynorphin.
What kind of input does the striatum receive and from what location?
An excitatory input from the motor cortex.
What type of output signal does the BG send out and where to?
An inhibitory one to the motor cortex via the thalamus.
Describe the direct pathway of the BG.
(1) Motor cortex excites striatum.
(2) Striatum decides to release motor beh. and sends inhibitory input to the int. segment of the globus pallidus.
(3) Inhibitory input onto thalamus is lessened, increasing thalamic output to motor cortex.
(4) Allows motor behaviour to be generated.
Which pathway (direct or indirect) results in the generation of mvmt?
Direct
Which pathway, (direct or indirect) prevents the release of motor action?
Indirect
Describe the indirect pathway of the BG.
(1) Motor cortex excites striatum.
(2) Striatum decides NOT to release motor beh. so inhibits the ext. segment of the globus pallidus.
(3) Inhibition of subthalamic nucleus is lessened
(4) Subthalamic nuclei’s excitation of the internal globus pallidus increases
(5) The inhibition of the int. globus pallidus on the thalamus increases, decreasing thalamic output to the cortex
(5) Prevents motor behaviour from being generated
Where do dopaminergic inputs arise from within the BG?
The substantia nigra.
What class of receptors does dopamine act on in the direct circuit?
D1 receptors
What class of receptors does dopamine act on in the indirect circuit?
D2 receptors
Does dopamine increase or decrease the activity of the direct circuit?
Increases activity of direct circuity
Does dopamine increase or decrease the activity of the indirect circuit?
Reduces activity of indirect circuit
What kind of function does dopamine perform on the BG circuits?
Neuromodulatory function.
Functionally altering the synaptic connections btw BG neurons.
How does dopamine increase the activity of the direct circuit of the BG?
It increases the level of cAMP so increases the striatum’s inhibition of the internal globus pallidus, strongly disinhibiting the thalamus and increasing its excitatory input into the motor cortex.
How does dopamine reduce the activity of the indirect circuit of the BG?
Lessens the inhibition of the ext. globus pallidus via the striatum. Increases the inhibitory input of the ext. globus pallidus onto the subthalamic nucleus, decreasing subthalamic nucleus’ excitation of the int. globus pallidus, and decreases the int. globus pallidus’ inhibition of the thalamus , increasing thalamic output.
Ultimately, what circuit does dopamine bias activity towards?
Biases activity towards the direct circuit and away from the indirect circuit. Increases likelihood of mvmt behaviours being released.
