Week 6: Basal Ganglia Structure and Function Flashcards
Does damage to the basal ganglia cause paralysis?
Damage of basal ganglia leads to inability to carryout smoothly executed skilled movements but not paralysis.
What are the principle structures of the basal ganglia?
- striatum:
dorsal: caudate nucleus and putamen
ventral: nucleus accumbens - globus pallidus
external segment (GPe)
internal segment (GPi) - substantia nigra
- subthalamus
Describe the divisions of the substantial nigra (SN).
- Pars compacta (SNpc)- pigmented dopamine neurons. Dorsal strip. pigment due to presence of neuromelanin
- Pars reticulata (SNpr)-non pigmented GABA neurons. Ventral strip.
Describe generally how the basal ganglia influences motor activity.
- influence on motor activity is indirect via conniptions with motor cortex. Ipsilateral.
- BG influences motor activity on contralateral side of the body (since motor cortex controls muscles on contralateral side).
Where does the predominant input to the BG come from? Where does it terminate?
From all parts of the cerebral cortex and terminates in the striatum. Excitatory pathway.
From striatum, goes to GP and SN
What is the output of the BG? Where does it go?
Output from GPi and SNpr neurons. Directed mainly to thalamus, ventral anterior (VA), and ventral lateral (VL) nuclei
-terminal output releases GABA and have tonic inhibitory effect on VA and VL
What are the afferents and efferents of the VA and VL nuclei of the thalamus?
- Afferents: from Basal ganglia, GPi and SNpr neurons
- thalamocortical efferents: project back to same areas of cortex where cortical input to BG originated (feedback back to the cortex)
- VA and VL use glutamate and are excitatory. Serves to increase activity of motor areas.
Describe the function of the direct pathway of the corticostriatal circuit.
Increases excitatory feedback from thalamus to cortex
Results in promotion of desired motor activities
What does the indirect pathway of the corticostriatal circuit result in?
- decreases excitatory feedback from the thalamus to cortex
- reduces cortical activation by thalamus
- reduces unwanted motor activities
Summarize the direct pathway of the corticostriatal circuit.
Striatum–>GPi/SNr–>Thalamus
- increases inhibition to GPi/SNr
- reduces inhibition to VA/VL nuclei of thalamus (disinhibition)
- facilitates cortical activation by VA/VL nuclei
- sustains wanted motor programs and desired motor activity
Summarize the indirect pathway of the corticostriatal circuit.
Striatum (inhibitory)–>GPe (inhibitory)–>STN (excitatory)–>GPi/SNr (inhibitory)–> thalamus
- increases STN stimulation of GPi/SNr
- increases inhibition of VA/VL nuclei
- reduces cortical facilitation by VA/VL (negative feedback that suppresses cortical activity)
- suppresses unwanted programs and undesired motor behavior
List the distinct areas of frontal cortex where corticostriatal circuits originate.
- Motor cortex: primary motor (M1), supplementary motor (SMA), premotor (PMA)
- Prefrontal cortex (executive/associative fxn): dorsolateral prefrontal (DLPFC), lateral orbitofrontal (LOFC)
- Oculomotor cortex (eye): frontal eye fields (FEF), supplementary frontal eye fields (SEF)
- Limbic cortex (emotion/motivation): ant. cingulate area (ACA), medial orbiofrontal cortex (MOFC)
Describe the motor circuit.
- from M1, SMA, PMA
- projects to putamen
- action selection, preparation for movement, sequencing of movements, control of movement parameters i.e. direction & velocity, involved in reinforcement learning
Describe the oculomotor circuit.
- from FEF and SEF
- projects to caudate
- involved in coordination of voluntary and saccadic eye movements
Describe the dorsolateral prefrontal circuit that originates from the prefrontal cortex.
- from DLPFC and projects to caudate
- involved in working memory, learning new info, planning ahead, temporal ordering of recent events
- can use Tower of London Test- how many moves to go from a a set of colored donuts to another sequence of colored donuts
- clinical syndromes: impaired reasoning, easily distracted, poor organization abilities