Basal Ganglia Flashcards
what is the basal ganglia?
a bunch of nuclei
1st telencephalon structure- deep in the hemispheres- goes through all of the lobes
embedded in white matter of cerebrum
where does the basal ganglia lie?
lateral to the thalamus
what is the corn a radiata?
white matter that is leaving the BG- axons leaving
what are the major functions of the basal ganglia?
the integration of feelings, thoughts and movement occur in the basal ganglia
action selection hypothesis
build up on the “turn up - turn down” effects of the direct and indirect pathways
functions in postural control and descending system to BS that work with locomotion
- any movement you make requires that certain motor commands (raise arm) be executed and opposing commands (lower arm) be suppressed
- promotes proper execution commands and the indirect pathway suppresses commands related to opposing movements
- thus plays a role in the automatic or sub-voluntary integration of the various motor centers where habitual or automatic movement become organized
the sequencing of movements
smooth and accurate movement- performing a motor sequence requires that the movements be executed in the proper order. Thus, the direct pathway may “turn up” the appropriate movement commands when it is their turn while the indirect pathway may “Turn down” the commands when it is not their turn
MOTOR FUNCTION
describe how the integration of feelings, thoughts and movement occur in the basal ganglia:
this is why you jump when you’re excited, tremble when you’re nervous, freeze when you are scared or get tongue-tied when the boss is chewing you out
the basal ganglia allow for a smooth integration of emotions, thoughts and physical movement and when there is too much input they tend to lock up and do not allow a smooth transition
what is action selection hypothesis?
in this model the basal ganglia would be the arbiter of which of the potential actions that cortex might be planning actually gets executed
this fits together well with the idea that dopamine is a system mediating learning based on reward
this could train the basal ganglia to chose behaviors that have been rewarding in the past
what motor function does the BG have?
shifting and smoothing fine motor behavior
involved in suppressing unwanted motor activitiy
control of postural adjustment during voluntary movement
what are the 5 parallel loops of the BG?
how can loops be distinguished?
1- motor (from putamen)
2- cognitive loop
3- limbic loop (motication/emotion)
4-oculomotor loop
5- associative (emotion/social)
1,2,4,5 through the dorsal striatum
3 (limbic) through the ventral striatum
the cortical targets of the four loops through the dorsal striatum include the supplementary motor area, the dorsolateral prefrontal cortex, the frontal eye fields, and the lateral orbitofrontal cortex
what does the cognitive loop play a role in?
spatial memory and motor intentions
head of caudate
what does the limbic loop play a role in?
emotion and motivation function
motor expressions to emotions
what does the oculomotor loop do?
activated when a deliberate saccade is about to be made
disinhibits superior colliculus
comes from cortical eye area to BG to thalamus back to cortical eye area (remember corticobulbars do NOT go to eye)
describe the direct pathway:
what does it do?
what controls it?
what are the steps?
INCREASES EXCITATORY THALAMIC INPUT TO CORTEX
TURNS UP MOTOR ACTIVITY
wants to get rid of associative movements and only pick the right one
1-the dorsal striatum (putamen & caudate) receives excitatory input from the isocortex
“CORTICOSTRIATE FIBERS “= fibers from cortex to striatum
2-the dorsal striatum inhibits the substantia nigra reticulata and the globus pallidus using GABA and enkephalin
3-the substantia nigra and globus pallidus influence the thalamus
4- the direct loop disinhibits (excites) thalamocortical projections to the cortex
through the direct loop, information from several functionally related cortical areas funnels through one sector of the BG and results in recurrent excitation of one of these cortical regions
axons project to the dorsal striatum from neurons in all areas of the isocortex but most heavily from the ?
frontal and parietal lobes
the primary motor (4), premoter (6), supplementary motor (6) and somatosensory (3,1,2) cortices project preferentially to ?
the putamen
these projections have a tomographic organization
the frontal eye fields and association areas of the frontal and parietal lobes project heavily onto the ?
caudate nucleus
these projections have a tomographic organization
the neurons projecting from isocortex too striatum provide…
strong excitation, using glutamate as their neurotransmitter
the excitatory postsynaptic potentials results from the actions of excitatory glutamatergic cortical efferents and the inhibitory
how do the substantia nigra and globus pallidus influence the thalamus?
a major outflow of efferent fibers from the basal ganglia comes from the internal segment of the SN & GP. both these areas develop in the caudal ventral diencephalon region called the SUBTHALAMUS
fibers synapse in the intralaminar nuclei and the in the VL, VA, and MD nuclei of the thalamus.
axons from cells of the intralaminar nuclei provide feedback to the striatum
those of the VL, VA and MD nuclei complete the “basal ganglia loop” by projecting to frontal lobe cortex
each of the basal ganglia loops includes…
both direct and indirect loop fibers
describe the indirect loop:
indirect loop can be viewed as a side arm of the direct loop, through which the sub thalamic nucleus influences the outflow of the globus pallidus interna
striatal efferents reach the external segment of the globus pallidus, and after synaptic articulation, pallidal efferents cross the posterior limb of the internal capsule to reach the SUBTHALAMIC NUCLEUS.
Neurons of the sub thalamic nucleus project EXCITATORY GLUTAMATERGIC fibers back to both parts of the globus pallidus, but primarily to the internal segment and to the substantia nigra reticulate, where they excite GABA projections to the thalamus and THEREBY INHIBIT THE THALAMUS
the sub thalamic nucleus also receives direct input from the cerebral cortex
THE NET RESULT OF ACTIVATION OF THIS INDIRECT LOOP IS TO DECREASE THALAMOCORTICAL ACTIVATION
(extra loop in indirect pathway- 1st part is facilitatory like direct route until you get to the sub thalamic nucleus. sub thalamic is facility- which will facilitate an inhibitory neuron which will inhibit the VA/VL )
how do dopaminergic nigrostriatal connections modulate the direct and indirect loops?
the cells of the substantia nigra compact produce DOPAMINE
their projects to the dorsal striatum enhance cerebral cortical activation through both the direct and indirect loops. This results form differences in the types of stratal receptors that receive nigrostriatal dopaminergic input.
dopaminergic projections EXCITE stratal cells of the direct (excitatory) loop through D1 receptors on these cells
dopaminergic projections INHIBIT stratal cells of the indirect (inhibitory) loop through D2 receptors on these cells
what is dopamine? how is it produced? what effect does it have?
neuromodulator; reward system
produced from the substantia nigra
when dopamine is present it facilitates pathway (D1) or inhibits (D2)
when present you move
not present you are akinetic (Parkinson’s)
SUBSTANTIA NIGRA DOPAMINERGIC:
- Turns UP direct pathway (D1)
- Turns DOWN indirect pathway (D2)
- INCREASED VA/VL drive to cortex
- MORE MOTOR ACTIVITY
what is ACh? what effect does it have?
neuromodulator
opposite effect of dopamine
comes from the medial pontine nucleus; get less movement
facilitates indirect pathway and inhibits direct pathway
too little ACh (or too much dopamine)= hyperkinetic disorders
STRIATAL INTERNEURONS CHOLINERGIC: (ACh) -Turns DOWN direct pathway -Turns UP indirect pathway -DECREASED VA/VL drive to cortex -LESS MOTOR ACTIVITY
