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basal ganglia
basal ganglia
121
Anatomy
Graduate
04/25/2012

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Term
what is the basic function of the basal ganglia (3 components)?
Definition
intiation, maintenance, and termination of voluntary movements = supervising motor control
Term
does the basal ganglia project directly to LMNs?
Definition
no
Term
if the basal ganglia doesn't interact directly with LMNs, how does it influence movements?
Definition
by regulating the activity of UMNs
Term
what is a subcortical loop
Definition
a loop that's below the cortex
Term
what does the basal ganglia's subcortical loop do?
Definition
links the cortex with the basal ganglia and then to other areas of the brain and back up to the cortex again
Term
what is the function of neurons in the basal ganglia's subcortical loop
Definition
normal initiation and maintenance of voluntary movements
Term
what are the 3 major nuclei of the basal ganglia
Definition
caudate, putamen, globus pallidus
Term
what 2 additional structures are closely associated with the motor functions of the basal ganglia
Definition
substantia nigra, subthalamic nuclei
Term
what is the immediate family of the basal ganglia family unit?
Definition
caudate, putamen, globus pallidus
Term
what is the extended family of the globus pallidus family unit
Definition
substantia nigra, subthalamic nuclei
Term
what happens when anyone in the globus pallidus extended or immediate family is troubled?
Definition
the family unit doesn't work properly
Term
where is the subthalamic nuclei?
Definition
underneath the thalamus
Term
what are the 2 parts of the substantia nigra?
Definition
pars compacta, pars reticulata
Term
what are the 2 circuits within the basal ganglia
Definition
direct pathway, indirect pathway
Term
what is the main function of the direct pathway of the basal ganglia
Definition
releases UMNs from tonic inhibition
Term
what is the main function of the indirect pathway of the basal ganglia
Definition
increases tonic inhibition of UMNs
Term
using the car at the top of the hill metaphor, what does the direct pathway do?
Definition
allows the car to go down the hill
Term
using the car at the top of the hill metaphor, what does the indirect pathway do?
Definition
controls the car as it goes slowly down the hill
Term
do the pathways work at different times?
Definition
the pathways work concurrently
Term
of the direct and indirect pathways, which is the dominant pathway
Definition
direct
Term
what is the input zone of the basal ganglia
Definition
corpus striatum
Term
what is the corpus striatum
Definition
caudate + putamen
Term
what regions of the cortex project to the corpus striatum
Definition
nearly all regions of the cortex project to the corpus striatum
Term
what are the 2 types of pathways that bring infromatin to the corpus striatum?
Definition
corticostriatal pathway, nigrostriatal fibers (pathway?)
Term
through what pathway does the cortex project to the corpus striatum
Definition
corticostriatal pathway
Term
through what pathway do neurons from the substantia nigra pars compacta project to the striatum
Definition
nigrostriatal fibers
Term
where are medium spiny neurons located
Definition
in the striatum (caudate and putamen)
Term
what synapses on the medium spiny neurons
Definition
corticostriatal and nigrostriatal fibers
Term
after being synapsed on by corticostriatal and nigrostriatal fibers, what do medium spiny neurons do
Definition
project to the globus pallidus and the substantia nigra pars reticulata
Term
what are the 2 parts of the globus pallidus
Definition
internal and external segments
Term
in the direct pathway, what do axons from the striatum mostly project to?
Definition
internal segment globus pallidus and substantia nigra pars reticulata
Term
in the indirect pathway, what do axons from the striatum mostly project to?
Definition
globus pallidus external segment
Term
what are the major output sources from the basal ganglia
Definition
globus pallidus and substantia nigra pars reticulata
Term
where do efferent neurons from the internal segment of the globus pallidus project to
Definition
VA and VL nuclei of the thalamus
Term
what are the pathways of projections from the VA and VL nuclei of the thalamus?
Definition
to the primary motor and premotor cortices, completing the loop!
Term
where do efferent neurons from the substantia nigra pars reticulata project to
Definition
UMNs in the superior colliculus that command eye movements
Term
can the basal ganglia influence eye movement?
Definition
yes
Term
what are the steps of the direct pathway
Definition
Input from the cortical areas and the substantia nigra pars compacta project to the striatum. The striatum projects to the internal globus pallidus. The internal globus pallidus projects to the VA/VL complex of the thalamus. The VA/VL complex of the thalamus projects to the motor cortex.
Term
what types of synapses do all corticostriatal fibers make on the medium spiny neurons within the striatum?
Definition
excitatory glutamatergic synapses
Term
what types of synapses do nigrastriatal fibers make on the medium spiny neurons within the striatum in the direct pathway?
Definition
excitatory dopaminergic synapses
Term
area all glutamtergic synapses excitatory
Definition
yes
Term
are all dopaminergic synapses exciatory
Definition
no, but they can be. It depends on the dopamine receptor whether it's excitatory or not
Term
what types of synapses do fibers from the medium spiny neurons of the striatum make on the globus pallidus internal segment
Definition
GABAnergic inhibitory
Term
is GABA an inhibitory or excitatory neurotransmitter
Definition
inhibitory
Term
when are medium spiny neurons silent (not firing)?
Definition
always, unless we initate movement or are moving
Term
when is the globus pallidus active?
Definition
always, unless they are silenced by movement
Term
to where does the globus pallidus internus constantly fire action potentials
Definition
VA and VL nuclei of the thalamus
Term
what type of neurons project to the VA and VL nuclei of the thalamus from the GP internal segment?
Definition
GABAnergic inhibitory
Term
is the output of the basal ganglia inhibitory or excitatory
Definition
inhibitory
Term
what do the neurons from the globus pallidus interal segment do?
Definition
project to the VA/VL of the thalamus and prevent movement by inhibiting the neurons that project from the VA/VL to the motor cortex
Term
when you're at rest and the car is parked at the top of thehill, what affect does the globus pallidus have on the car?
Definition
keeps the car parked at the top of the hill, preventing the thalamus from exciting the motor cortex and letting the car go down the hill
Term
are the basal ganglia important in initating movement?
Definition
yes
Term
what are the steps of the direct pathway including excitation/inhibition at rest/with no movement
Definition
1. There is no excitation of stritatal neurons from the cortex or substantia nigra; 2. without excitation, the striatal neurons are silent; 3. without inhibition from striatum, globus pallidus is tonically inhibitory; 4. the globus palldus inhibits the VA/VL complex of the thalamus; 5. inhibited thalamic neurons can't excite motor cortex neurons so no movement occurs
Term
what are striatal neurons doing at rest
Definition
nothing
Term
what is the globus pallidus doing at rest
Definition
tonically inhiiting the thalamus
Term
what are the steps of the direct pathway including excitation/inhibition at with movement
Definition
1. striatal neurons are excited by the cortex and the substantia nigra pars compacta; 2. striatal neurons inhibit the globus pallidus; 3. the globus pallidus stops inhibiting the VA/VL nuclei of the thalamus; 4. the VA/VL nuclei of the thalamus excite the motor cortex neurons; 5. motor cortex excitement leads to movement
Term
which neurotransmitter inhibits the globus pallidus from the striatum during movement?
Definition
GABA
Term
what do we call the circuit that allows UMNs to send commands that initiate movement
Definition
disinhibitory circuit/direct pathway
Term
what has its foot on the brake in allowing movement
Definition
globus pallidus
Term
how is the direct pathway a disinhibition circuit?
Definition
activation of the direct pathway serves to release the UMNs from tonic inhibition
Term
what is the indirect pathway
Definition
the pathway that increases the level of tonic inhibition to UMNs, increasing control of movement
Term
what is the car metaphor of the indirect pathway
Definition
we let the car go down the hill, but we control it
Term
does the indirect route go through the basal ganglia
Definition
yes
Term
what population of medium spiny neurons is involved in the indirect pathway
Definition
population of medium spiny neurons in the striatum that projects to the globus pallidus externus.
Term
in the indirect pathway, where do dopamine neurons come from
Definition
substantia nigra pars compacta
Term
are dopamine neurons in the indirect pathway excitatory or inhibitory
Definition
inhibitory
Term
what type of dopamine receptors are inhibitory
Definition
D2
Term
do the indirect and direct pathways occur simultenously
Definition
yes, but the direct pathway is a little stronger
Term
what happens when any component of the basal ganglia is compromised?
Definition
movement disorders occur
Term
what are 3 examples of basal ganglia dysfunction
Definition
hemiballismus, parkinson's, huntington's
Term
symptoms of hemiballismus
Definition
violent, uncontrolled movements of the limbs confined to one side of the body
Term
what part of the brain is damaged with hemiballismus
Definition
subthalamic nucleus on opposite sideof the body
Term
a stroke of which artery would cause hemiballismus
Definition
middle cerebral artery that vascularizes the thalamus
Term
what causes the violent, uncontrolled movements in hemiballismus?
Definition
movements are initiated by abnormal discharges of UMNs that are receiving less tonic inhibition from the basal ganglia (the globus pallidus internal is not excited by subthalamus to increase its tonic inhibition to the thalamus)
Term
what is parkinson's disease
Definition
neurodegenerative disease characterized by loss of nigrostriatal dopamine neurons from the substantia nigra pars compacta
Term
what is the common age range of onset of parkinson's?
Definition
50-70 years
Term
can younger people (than 50) get parkinson's?
Definition
yes
Term
if you have parkinson's what will you have difficult with
Definition
initiating movements
Term
what are the 4 cardinal features of Parkinson's disease?
Definition
Tremor (resting); Rigidity; Akinesia (minimal facial expression) or bradykinesia; Postural changes - flexed or stooped over position
Term
describe the posture of someone with Parkinson's
Definition
stooped over, arms flexed. No arm swing during gait
Term
describe the gait of someone with Parkinson's
Definition
shuffle gait: short steps, unable to sstop
Term
describe rigidity of someone with parkinson's
Definition
affects all somatic muscles, but greater in flexors - causes stopped osture
Term
what is cogwheel rigidity
Definition
some parkinson's patients experience muscle resistance that is overcome in a series of jerks
Term
what causes resting tremors in people with PD
Definition
result of alternating contraction of agonists and antagonists caused by cerebellum
Term
why do some parkinson's patients have uncontrollable dyskinesia-like motor symptoms?
Definition
some are medication induced; some may be from imbalance of excitatory and inhibitory signals in both the direct and indirect pathways, leading to the diminished ability of the basal ganglia to properly control motor function.
Term
what are the effects on direct pathwaysdue to parkinson's
Definition
inputs from the substantia nigra pars compacta are diminished. This makes it more difficult to generate transient inhibition from the striatum. The result is to sustain the tonic inhibition from the globus pallidus to the thalamus, decreasing the excitiation of the motor cortex
Term
what is hypokinetic movement
Definition
decreased movement
Term
what happens if you don't have dopamine
Definition
you can't inhibit the globus pallidus so it tonically inhibits the thalamus
Term
what are fetal tissue grafts
Definition
implant fetal midbrain tissue into caudate and putamen for PD treatment
Term
how is gene therapy used in PD treatment
Definition
implant cells that are genetically modified to produce high levels of tyrosine hydroxylase, which converts tyrosine to L-DOPA, increasing dopamine in th ebasal ganglia
Term
how are neural stem cells used in PD treatment
Definition
implant progenitor cells that have been engineered to differentiate into dopamine neurons
Term
is deep brain stimulation an effective treatment for PD?
Definition
yes
Term
what is the set up for deep brain stimulation
Definition
battery packs are placed near clavicles and electrodes are inserted bilaterally into the globus pallidus or subthalamus.
Term
how does deep brain stimulation work
Definition
deep brain stimulation signals override pathologic circuitry with properly structured neural patterns to coordinate voluntary movements
Term
when a patient with PD receives deep brain stimulation and it is turned off, what happens?
Definition
resting tremor returns
Term
what is huntington's disease
Definition
neurodegenerative disease characterized by inappropriate motor activity
Term
what are choreiform movements
Definition
abnormal movements
Term
which basal ganglia disease is an inherited autosomal dominant disease
Definition
huntington's disease
Term
at what age range does huntington's disease usually occur
Definition
40's-50's
Term
what is the final result of huntington's disease
Definition
death in 10-20 years
Term
what is the hallmark of huntington's
Definition
choreiform movements
Term
what gene is responsible for huntington's disease
Definition
huntington gene
Term
what are the physical effects of huntington disease on the brain
Definition
caudate and putamen atrophy
Term
how does huntington's affect medium spiny neurons that project to the extneral GP?
Definition
they degenerate
Term
what is the result of huntington's disease on the indirect pathway
Definition
the absence of inhibitory input from the medium spiny neurons to the external GP causes the external GP to become overactive. The overactive external GP provides more inhibition to the subthalamic nucleus. The inhibited subthalamic nucleus provides less excitation to the internal GP. The internal GP provides less tonic inhibition to the thalamus. The result is over-activated UMNs and hyperkinetic movements
Term
aside from motor loops, what are basal ganglia involved with
Definition
other cognitive functions
Term
what are 2 non-motor subcortical loops that include the basal ganglia
Definition
limbic loop, prefrontal loop
Term
what is the function of the limbic loop
Definition
regulate emotional and motivational aspects of behavior
Term
what is the prefrontal loop important for?
Definition
important in initiating cognitive processes like planning and attention
Term
does parkinson's affect cognition
Definition
yes
Term
in the indirect pathway, where do the medium spiny neurons from the striatum project?
Definition
GPE
Term
in the indirect pathway, are the dopamine neurons from the substantia nigra pars compact inhibitory or excitatory
Definition
inhibitory
Term
in the indirect pathway, what makes the dopamine from the substantia nigra pars compacta inhibitory
Definition
D2 receptors of the striatum are inhibitory dopamine receptors
Term
how does the inhibitory dopamine in the striatum affect the excitatory input from the cortex to the striatum
Definition
dampens it
Term
what 2 places does the GPE project to
Definition
GPI, subthalamus
Term
what does the subthalamus project to
Definition
GPI
Term
is the GPE tonically/transiently excitatory/inhibitory to the subthalamus
Definition
tonically inhibitory
Term
why do the GPE's projections to the GPI not matter when we activate the indirect pathway
Definition
the GPE is shut off in the indirect pathway, so it doesn't have control over the GPI. The subthalamus will then be able to have the control of the GPI
Term
what does the subthalamus want to do to the GPI that the GPE tonically inhibits it from doing
Definition
excite the GPI
Term
what is the indirect pathway including all excitations and inhibitions when activated because of movement
Definition
excitatory signals from the cortex and inhibitory dopaminergic signals from the substantia nigra enter the striatum simultaneously. Excitation from the cortex is dampened by the inhibition from the substantia nigra, but the cortical excitation wins, and the striatum sends transient inhibition to the GPE via medium spiny neurons. The GPE is inhibited, so its tonic inhibition of the subthalamus is temporarily stopped. The subthalamus is also receiving excitatory input from the cortex, and without its inhibition form the GPE, it's able to excite the GPI. The excited GPI inhibitis the thalamus, reducing excitation to the cortex and reducing/preventing movement
Term
does the indirect pathway increase or release tonic inhibition of UMNs
Definition
increase
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