Basal Ganglia Flashcards
What is the purpose of the basal ganglia
Action selection: selecting and promoting one action while suppressing competing actions
Name 3 neuropsychiatric disorders related to problems with the basal ganglia
OCD, ADHD, Tourette syndrome
What is the “default” setting of the basal ganglia
To suppress movement
How are habits formed
There is a repeated selection of actions with positive outcomes, which leads to these actions being chunked/hardwired together
What results from the ability to group chunks together
Complex behaviors, which allows for multitasking
Is it easy or difficult to interrupt actions that are chunked together?
Difficult
What is operational learning?
Unconscious process by which we associate our chunked actions with their immediate consequences; this biases our actions toward ones associated with reward and away from those associated with negative consequences
Which is greater in the basal ganglia, number of inputs or number of outputs?
inputs
What type of neurons maintain the default state of the basal ganglia?
Tonic GABA-ergic, inhibitory neurons
What makes up 90% of the striatal neurons?
Medium, spiny neurons; GABAergic, spine-covered dendrites
What is efference copy?
Bias toward current actions, behavioral continuity
What are the 4 major components of the basal ganglia
- Striatum = caudate + putamen (dorsally) + nucleus accumbens (ventrally)
- Globus pallidus = lateral + medial GP, found ventral to putamen
- Substantia Nigra = Pars reticulata + pars compacta (dopaminergic)
- Subthalamic nucleus
What is the dorsal dopaminergic projection of the basal ganglia?
Substantia nigra pars compacta (cell body) –> caudate + putamen
Does movement result from the dorsal or ventral dopaminergic projection of the basal ganglia?
Dorsal
What is the ventral dopaminergic projection of the basal ganglia?
Ventral tegmental area (cell body) –> nucleus accumbens
Do reward-driven behaviors result from dorsal or ventral dopaminergic projections of the basal ganglia?
Ventral
What type of movements is dopamine required for?
Goal-directed movements
What is the function of the hyperdirect pathway
To stop current movement immediately
What is the function of the direct pathway
To release a selected movement from suppression
What is the indirect pathway
It has mixed effects, but the most dominant is to suppress competing, non-selected movements
What is the hyper direct pathway, starting from stimulation of myelinated fibers of the motor cortex
Glutamate release by motor cortex neurons onto subthalamic neurons, resulting in glutamate release on the internal globus pallidus, causing inhibition by the GABAergic neuron onto the VL/VA thalamus so that it cannot release glutamate onto the motor cortex to continue the loop
What is the prevalence of Parkinson’s disease
1% of the U.S. population over the age of 50
What is the etiology of Parkinson’s Disease
Degeneration of substantia nigra PARS COMPACTA (dopaminergic region)
What are the 3 symptoms commonly associated with Parkinson’s disease
Akinesia, resting tremor, rigidity
Which of the 3 skeletomotor loop pathways is affected in Parkinson’s Disease
Direct, resulting in little to no movement
What are the 3 treatment options for PD?
L-Dopa (DA precursor)
Pallidotomy (medial globus pallidus)
Subthalamic nucleus deep brain stimulation
What is the prevalence of Huntington’s Disease?
4-5/million in the U.S., adult onset
What is the etiology of Huntington’s disease
CAG repeat mutation on chromosome 4, resulting in degeneration of striatal neurons (starting with the caudate)
Which pathway is first affected in Huntington’s disease
Indirect (D2 –> lateral globus pallidus), resulting in excessive movement
What are the 2 main symptoms associated with Huntington’s Disease
Initial hyperkinesia, chlorea
Why is there initial hyperkinesia
Striatal neuron projection to the external globus pallidus dies, affecting the indirect pathway
What is chlorea
Quick, jerky, dancing movements of the extremities, symptomatic of HD
What is the treatment for Huntington’s disease
No cure, focus therapy on treating symptoms
Which group of people is Hemiballism most prevalent in?
Individuals with East Asian origin
What are the symptoms of Hemiballism
Violent “throwing” movements of one of the arms or legs
What is the etiology of hemiballism
Damage to the contralateral subthalamic nucleus
Which pathways is affected in hemiballism
Indirect at the glutamatergic neuron of the subthalamic nucleus
What are the 3 most common causes of hemiballism
Focal stroke, hyperglycemia (secondary to diabetes), and toxoplasmosis lesions in individuals with HIV
What are the treatments for hemiballism
They are aimed at the cause of the lesion; dopamine receptor ANTagonists
What is the striatal component of the dorsal extra-pyramidal system?
Caudate and putamen
What is the pallidal component of the dorsal extra-pyramidal system?
Globus pallidus, substantia nigra, pars reticulata
What is the dopaminergic innervation of the dorsal extra-pyramidal system?
Substantia nigra, pars compacta
What is the cortical input of the dorsal extra-pyramidal system?
Neocortex
What is the thalamic target of the dorsal extra-pyramidal system?
Ventral lateral and ventral anterior (VL/VA thalamus)
What is the striatal component of the ventral limbic striatal system
Nucleus accumbens, olfactory tubercle
What is the pallidal component of the ventral limbic striatal system
Ventral pallidum
What is the dopaminergic innervation of the ventral limbic striatal system
Ventral tegmental area (VTA)
What is the cortical input of the ventral limbic striatal system
Limbic cortex
What is the thalamic target of the ventral limbic striatal system
Mediodorsal
What are the 2 main components of the ventral striatum?
Nucleus accumbens (ventral to caudate) and olfactory tubercle
What is the function of the ventral striatum?
Motivation to action, expression of motivated behaviors
Describe the location of the ventral pallidum
Ventral to the globus pallidus and anterior commisure
What are the components of the ventral pallidum
Nucleus basalis of Meynert (cholinergic), nucleus of diagonal band, septal nuclei
What is the function of the ventral pallidum?
To regulate eye-head movements for attention, visceral autonomic responses (emotion), and it is implicated in induction and expression of motivated behaviors like addiction
What is the prevalence of schizophrenia in the U.S.
1% of the population
What is the etiology of schizophrenia
Excessive dopamine in the ventral striatum and dysregulation of prefrontal cortex glutamate
Which receptor do anti-psychotics bind most strongly to?
D2 receptors, which are highly expressed in the nucleus accumbens
Which loop is affected in OCD?
Indirect
