Anatomy and function of the basal ganglia Flashcards
Outline, from high to low, the hierarchy of motor control in terms of function and structures
HIGH- Strategy
Association areas of neocortex and basal ganglia
MIDDLE- Tactics
Motor cortex, cerebellum
LOW- Execution
Brainstem, spinal cord
In short, what is the function of the basal ganglia?
Gating proper initiation of movement
Which anatomical structures make up the basal ganglia anatomy?
Lenitform nucleus- putamen, external globus pallidus, internal pallidus
Caudate nucleus
Thalamus
Hypothalamus
Subthalamic nucleus
Substantia Nigra
What is meant by corpus striatum?
Caudate+ putamen +pallidum
Divided by the internal capsule (white matter of ascending and descending tracts)
Where do the lateral and third ventricle sit in respect to the basal ganglia
Anterior horn of the lateral ventricle sits most anterior
Third ventricle lies between the lentiform nucleus
Inferior horn of lateral ventricle lies most posterior and lateral to lentiform nucleus
Outline the motor loop
Cortical input from motor, premotor, somatosensory cortex
Striatum: Putamen
Pallidum: Lateral globus pallidus, internal segment
Thalamus- Ventral lateral and ventral anterior nuclei
State which neurotransmitter is excitatory and which is inhibitory
Excitatory - glutamate
Inhibitory - GABA
Outline the Direct Pathway
In the direct pathway, cerebral cortical input to the striatum causes activation of inhibitory neurons in the striatum which then causes an increased inhibitory output to the GPi. There is a decreased inhibitory output from GPi to ventral anterior and ventral lateral nuclei of the thalamus which then projects via excitatory pathways into the premotor cortex. The direct pathway is involved in regulating tonic excitation in the premotor cortex which is an area involved in planning and initiating movement.
PROMOTES MOVEMENT
Outline the Indirect Pathway
Excitatory projection from cerebral cortex facilitates inhibitory projection neurons in GPe by inhibiting the striatum. These then inhibit tonic inhibitory output neurons which decreases tonic inhibition of subthalamic nucleus [STN] resulting in increased excitatory output to GPi. Excitatory input to GPi increases inhibitory output from GPi to thalamus which then decreases excitatory feedback to cerebral cortex leading to inhibition of motor activity.
WITHHOLD MOVEMENT
Outline the Hyperdirect Pathway
It bypasses the striatum (which is the entry point to the basal ganglia in the direct and indirect pathways) and connects the cortex directly to the STN, which then sends excitatory projections to the GPi. Excitatory input to GPi increases inhibitory output from GPi to thalamus which then decreases excitatory feedback to cerebral cortex.
PAUSE MOVEMENT
How does the striatum know if a motor plan is to be promoted or prevented?
Dopamine is released by the substantia nigra
Medium spiny neurons with specialised dopamine receptors:
D1: in direct pathway, DA ramps up, MSN excitation
D2: In indirect pathway, DA dampens down, MSN excitation
=release of DA
tips pathways towards promotion of movement
Which NT do striatum interneurons use?
They use ACh
ACh opposes the effects of DA
=Tips pathway toward prevention of movement
The balance between interneurons and medium spiny neurons determines how likely movement will take place. It is regulated by DA and ACh and influenced by cortical inputs to striatum
