basal ganglia

Question 1

describe the basal ganglia

Answer 1

• strategic aspects of movement
• no direct connections to spinal cord
• reciprocal connections to almost all areas of cerebral cortex
• damage.= problems initiating and terminating movement

Question 2

what is the cortex loop?

Answer 2

• behaviour and emotion
• movement
• connects to sensorimotor areas of cerebral cortex via thalamus
• input from brainstem and spinal cord

Question 3

what is the gross anatomy of the basal ganglia?

Answer 3

• 5 nuclei
• 1 caudata
• putamen
• globus pallidus (internal and external
• STN (subthalamatic nucleus)
• substantia nigra (pars compacta, pars reticulata)
• caudate and putamen of the striatum

Question 4

what are the inputs of the basal ganglia?

Answer 4

• striatum
• direct and indirect via thalamus connections from cerebral cortex

Question 5

internal connections of the basal ganglia

Answer 5

• striatum projects to globes pallidus and substantial nigra
• STN forms indirect pathway between GP internal and GP external
• GPi and Sar re the output centre of basal ganglia and send inhibitory signals to thalamus

Question 6

outputs of the basal ganglia

Answer 6

• GPi and SNr
• provides tonic inhibitory output to thalamus

Question 7

how does the feedback loop in the basal ganglia work?

Answer 7

• receives excitatory input from cerebral cortex which sends inhibitory signals to thalamus suppressing motor cortical activity
• excessive basal ganglia input = slow movement
• reduced input = enhanced movement

Question 8

what are the three stages of the cortical loop?

Answer 8

1. striatum receives array of inputs from cerebral cortex
2. outputs from GPi and Sir project an inhibitory signal to thalamus
3. inhibited thalamus projects to motor cortex suppressing movement

Question 9

direct and indirect motor pathways in basal ganglia

Answer 9

• tonic inhibitory output from basal ganglia to thalamus
• neurotransmitters
• STN is a relay from striatum to GPi/SNr, forming indirect motor pathway
• direct pathway - w inhibitory synapses result in disinhibition facilitating movement
• indirect pathway - excitation of inhibition suppressing movement

Question 10

how does dopamine affect the striatum?

Answer 10

• excitatory or inhibitory depending on receptor it binds to
• has opposite actions in direct and indirect pathways
• excited direct pathway D1R or inhibited indirect D2R
• both disinhibit thalamic output facilitating movement

Question 11

pathology of the basal ganglia

Answer 11

• imbalance in action of direct and indirect pathways
• parkinsons - increased activation of indirect pathway (inhibitory) and decreased activations of direct pathway (excitatory) so suppressed movement
• huntingtons - decreased activation of indirect pathway and increase activation of direct so facilitated movement

Question 12

how is parkinsons disease apparent?

Answer 12

• hypokinetic
• less of dopaminergic cells in substantia nigra
• increases tonic inhibitory output of basal ganglia
• 1% people over 50
• reduced dopamine uptake in striatum

Question 13

what are the symptoms of parkinsons?

Answer 13

• Bradykinesia (slow movement)
• akinesia (inability to initiate movement)
• rigidity (increased muscle tone)
• tremor
• postural instability (stooped, right)

Question 14

describe Huntingtons disease

Answer 14

• hyperkinetic
  rapid, jerky movements with no clear purpose
• choreiform
• mutation of Huntington gene = selective atrophy of striatum
• decreases activation of indirect pathway (inhibitory) resulting in movement facilitation