Basal Ganglia Flashcards
general features of basal ganglia output
inhibitory: increased BG activity = reduced activity of targets.
input structures of the BG
striatum (putamen and caudate) and the subthalamic nucleus. receive excitatory input from cerebral cortex and from the substantia nigra pars compacta
output structures of the BG
globus pallidus interna and the substantia nigra pars reticulata. output to thalamus and brainstem.
What do D1 and D5 receptors do
stimulate adenylate cylase. factilitate neuronal activity
What do D2-4 receptors do?
inhibit adenylcylcase activity and decrease the effect of cortical input to striatal neurons. inhibit neuronal activity.
what are medium spiny striatal neurons?
contain GABA
are inhibitory
peptide neurotransmitters co-localized with GABA
medium spiny neurons that express D2 receptors: other neurotransmitters and projections
contain enkephalon and GABA and project to external globus pallidus.
medium spiny neurons that express D1 receptors: other neurotransmitters and projections
GABA, dynorphin, substance P. project to output nuclei: globus pallidus interna and substantia nigra pars reticulata.
Inputs to the subthalamic n.
excitatory, glutaminergic input from frontal lobes
inhibitory GABA input from GPe.
subthalamic n. output
glutamatergic and ecitatory to the BG output nuclei (globus pallidus interna and substantia nigra pars reticulata). Thus, subthalamus stimulates BG and supresses motor.
Differences in pathways to the striatum vs. the subthalamic n.
input to the STN is from frontal cortex; input to striatum from all over the cortex.
output from the STN is excitatory. output from the striatum is inhibitory
exctiatory route through STN faster than inhibitory route through striatum
STN projection to GPi is divergent and the striatal projection is more focused.
Inputs to globus pallidus internal segment and substantia nigra
excitatory input from subthalamic
inhibitory input from striatum
inhibitory input from globus pallidus externa.
project to VL, VA, and DM
Summarize BG circuits
BG outputs fire at a tonic rate to inhibit unwanted movements. when a movement is desired, the cortex projects to both the subthalamic nucleus and to the striatum. The premotor/motor cortex excites the subthalamic nucleus, which excites the globus pallidus interna broadly. this increases the brakes on most movements in the body to deselect unwanted movements. the cortex also projects to the striatum, which inhibits very selected parts of the GPi. This lifts the brake on the desired motion. Striatum can also disinhibit GPi via indirect pathways through the GPe.
Where do you damage to cause symptoms of Parkinson’s disease?
substantia nigra pars compacta.
explain some symtpoms of PD
too much GPi output makes movements slow. Rigidity due to difficulty inhibiting postural refelxes. may also explain postural instability.
basis of chorea in huntingtons
disinhibition of GPe neurons because of selective death in the striatum. inhibition of STN and GPi. leads to abnormal overactivity of motor cortical and brainstem mechanisms.
what happens with damage to the GPi
slow voluntary movements and involuntary postures. no delay in movement initiation
