Basal Nuclei Flashcards
what are the basal nuclei
*a collection of deep nuclei found within the cerebrum that contribute to the modulation of ALL OUTPUT that leaves the cortex
*important in voluntary movemements and adjusting posture
*receive cortical input, provides negative feedback to the cortex to modulate movement
striatum
*caudate + putamen
*receive major INPUT from cortex
lenticular (lentiform) nucleus
putamen + globus pallidus
5 basal nuclei structures
1) substantia nigra (2 components: pars compacta and para reticulata)
2) subthalamic nucleus
3) putamen
4) caudate nucleus
5) globus pallidus (2 components: GP externus and GP internus)
general function of the striatum
receives all of the inputs coming in to basal nuclei
general roles of the basal nuclei
-general motor commands*
-eye movements
-cognitive functions
-emotional functions
direct pathway of basal nuclei - overall function
EXCITATION of the thalamus, allowing for activation of cortex and thus stimulation of movement
indirect pathway of basal nuclei - overall function
INHIBITION of the thalamus, leading to inhibition of movement
what structure separates the caudate from the putamen
the internal capsule
what structure separates the two halves of the thalamus
third ventricle
where do all inputs to the basal nuclei arrive
striatum (caudate & putamen)
where do all outputs from the basal nuclei arise from
globus pallidus internus and pars reticulata of substantia nigra
direct pathway - steps
1) cortex sends glutamate to the striatum (caudate + putamen)
2) striatum sends GABA to GPi and SN pars reticulata, inhibiting them
3) inhibition of GPi and pars reticulata makes them STOP INHIBITING the thalamus
4) thalamus is free to activate cortex and initiate movement
indirect pathway - steps
1) cortical input (via glutamate) stimulates striatum to send GABA to the globus pallidus EXTERNUS, inhibiting the GPe
2) GPe STOPS INHIBITING (activates) the subthalamic nucleus
3) subthalamic nucleus STIMULATES the globus pallidus INTERNUS (via glutamate), causing the GPi to produce MORE GABA
4) GPi producing more GABA further INHIBITS the thalamus, preventing it from activating cortex
dopamine & its effects on the basal ganglia (direct & indirect pathways)
*dopamine from the substantia nigra pars compacta regulates the direct & indirect basal ganglia pathways via:
-binding to D1 receptor STIMULATES the direct pathway
-binding to the D2 receptor INHIBITS the indirect pathway
*in Parkinson’s, dopaminergic neurons that are projecting to the striatum (from pars compacta of substantia nigra) die
cause of hemiballism
damage to the subthalamic nucleus
dyskinesia
abnormal movements
*result from unilateral lesions of basal nuclei, causing contralateral effects
bradykinesia
slow movement
hypokinesia
decreased amount of movement
akinesia
absence of movement
hyperkinesia
increased movements
rigidity
resistive tone initially increases then decreases
*increased limb resistance to passive movement
examples = clasp-knife, cogwheel, lead pipe (characteristic of Parkinson’s)
dystonia
abnormal or distorted positions
(torticollis)
athetosis
writhing twisting movements
chorea
dance-like involuntary movements (Huntington’s)
ballismus
large amplitude flinging of limbs (hemiballismus)
lead-pipe rigidity
constant resistance throughout bending
*characteristic of Parkinson’s
cogwheel rigidity
*tremor on top of rigidity
*with Parkinson’s: ratchet-like interruptions in tone throughout limb bending
