Basal Ganglia Flashcards
4 main basal nuclei and location (telencephalon/diencephalon/midbrain)
- Striatum (telencephalon)
- globus pallidus (telencephalon)
- subthalamic nucleus (diencephalon)
- substantia nigra (midbrain)
Striatum subdivisions
- caudate
- putamen
- nucleus accumbens (ventral striatum)
Globus pallidus subdivisions
GP
external segment: GPe
internal segment: GPi
Substantia Nigra subdivisions
SN
compact part: SNc
Reticular part: SNr
what makes up the lenticular (lentiform) nucleus?
Globus pallidus (internal and external segments) and putamen of the striatum.
Substantia nigra functions
- SNc: location of dopaminergic neurons (dorsal part)
- SNr: functions with GPi as output from basal ganglia
Extrapyramidal system
nuclei and pathways of BG (outside pyramidal tracts)
Lesion in basal ganglia will/won’t cause:
general
- won’t cause paralysis
- will disrupt movement (slow/absence of spontaneous movement or inability to inhibit unwanted movements)
Hypokinetic BG disorder
example, cause, symptoms
- Parkinson’s disease
- loss of dopaminergic neurons in SNc
- with akinesia/bradykinesia, rigidity, resting tremor, postural instability
Hyperkinetic BG disorder
example, causes, symptoms
- can cause athetosis, chorea, ballism
- Huntington’s disease
- degeneration of projection neurons and local circuit neurons in caudate and putamen (mostly from indirect pathway)
athetosis
slow, writhing movements
hyperkinetic disorder
chorea
rapid, abrupt, random movements of limbs and face
hyperkinetic disorder
Caudate
cortical projection input, role
widespread input; cortical association areas and has role in cognitive functions
putamen
cortical projection input, role
input from motor and somatosensory cortices; role in motor output
nuclear accumbens
cortical projection input, role
receives inputs from limbic cortex, hippocampus and amygdala; role in emotional and behavioral functions
Name the 5 loops through basal ganglia
and basic pathway
- motor
- dorsolateral prefrontal
- orbitofrontal
- limbic
- oculomotor
cortex -> BG -> thalamus -> cortex
Motor loop
pathway/function
motor/somatosensory cortex -> putamen -> thalamus -> somatosensory/motor areas
Role in motor output
Dorsolateral prefrontal loop
pathway/function
dorsolateral prefrontal cortex -> caudate -> thalamus -> dorsolateral prefrontal cortex
role in cognitive functions
orbitofrontal loop
pathway/function
orbitofrontal cortex -> ventral caudate and nuclear accumbens -> thalamus -> orbitofrontal cortex
role in planning and initiating socially appropriate actions (OCD?)
limbic loop
pathway/function
limbic areas (like anterior cingulate) -> nucleus accumbens -> thalamas -> limbic areas
role in emotional and behavioral functions
oculomotor loop
pathway/functions
frontal and supplementary eye fields -> caudate -> thalamus -> eye fields
role in control of orientation and gaze
Projections to striatum (2)
Origin and NT
- cortical to striatum: glutamate
- SNc to striatum: dopamine
Function of direct vs. indirect pathway
Direct: facilitates motor/cognitive programs
Indirect: inhibits execution of competing motor programs
Projection neurons from striatum (two populations)
- D1 receptors excited by dopamine, project to GPi, direct pathway
- D2 receptors inhibited by dopamine, project to GPe, indirect pathway
Effect of glutamate and dopamine on Direct Pathway
INCREASED PATHWAY ACTIVITY (agonist)
- glutamate from cerebral cortex and dopamine from SNc
- D1 excited
- increased activity of GABA neurons to GPi/SNr
- decreased activity of pallidothalamic GABA fibers to thalamus
- disinhibition of glutamate neurons to motor cortex
- increased output from motor cortex
Effect of glutamate and dopamine on Indirect Pathway
DECREASED PATHWAY ACTIVITY (agonist)
- glutamate from cerebral cortex and dopamine from SNc
- D2 inhibited
- decreased activity of GABA neurons to GPe
- disinhibition of GABA neurons to subthalamic nucleus
- decreased activity of glutamate neurons to GPi/SNr
- decreased activity of GABA neurons to thalamus
- increased activity of glutamate neurons to motor cortex
- increased output from motor cortex
Effect of glutamate (NO dopamine) on Indirect Pathway
INCREASED PATHWAY ACTIVITY (antagonist)
- Glutamate from cerebral cortex
- D2 excited
- increased activity of GABA neurons to GPe
- Inhibition of GABA neurons to subthalamic nucleus
- disinhibition of glutamate neurons to GPi/SNr
- increased activity of GABA neurons to thalamus
- decreased acitivity of glutamate neurons to motor cortex
- decreased motor cortex output
