Basal Ganglia Flashcards
What is the function of the basal ganglia?
Important in voluntary movements, adjusting posture
What makes up the striatum?
Which are motor and which are cognitive?
Putamen -motor
Caudate - cognitive
What makes up the lentiform nucleus?
Putamen - motor
Globus pallidus
What is another name for the substantia innominata?
Substantia nigra
What are the two parts of the substantia nigra?
Pars reticulata
Pars compacta
For the basal ganglia, which pathway is excitatory and which pathway is inhibitory?
And what receptors do they have?
Direct = D1 receptor = excitatory
Indirect = D2 receptor = inhibitory
If dopamine acts thru D1, what is the effect?
Excitatory pathway is stimulated
If dopamine acts thru D2, what is the effect?
Inhibitory pathway is inhibited
How does the direct/excitatory pathway of basal ganglia work?
SNc input —> striatum, releases GABA
GABA —> inhibits GPi
GPi cant inhibit thalamus
=increased motion
How does the indirect/inhibitory pathway work?
SNc —> striatum, releases GABA
GABA—> inhibits GPe —> activates Sub-thalamic nucleus (STN)
STN —> stimulates GPi —> GABA released and goes to thalamus
=inhibits thalamus, decreased motion
What is the blood supply for the basal nuclei?
primary from MCA - lenticulostriate As.
Also ACA and Anterior choroidal
What is the classic triad associated with Parkinson’s disease?
Tremor- pill rolling
Cogwheel Rigidity
Bradykinesia
What are symptoms of Parkinson’s disease?
Classic triad
Hypokinesia Postural instability Dementia Visuoperceptive impairments Can affect walking (sloooow walking) Speech affected and facial expressions
What is the underlying cause of Parkinson’s?
No dopamine via Pars Compacta** of substantia nigra
No dopamine = striatum not stimulated = no GABA released to act on Pars reticulata and GPi = thalamus still inhibited
What are some cause so f Parkinsonian Syndyrome?
Idiopathic Parkinson’s disease Encephalitis lethargically Head trauma • Dementia pugilistica MPTP • Designer drug CO and Manganese poisoning Drug induced • Neuroleptic (dopamine blocking drugs) Wilson Diseae • Heptolenticular degeneration Rigidity • + other deficits in multiple neurodegenerative diseases
What are some treatments for Parkinson’s?
Drugs that increase dopamine or prevent its breakdown
Deep brain stimulation
What defect does Huntington’s Chorea result from?
Degeneration of neurons in striatum (mostly the putamen) that leads to decreased GABA
When does Parkinson’s disease start?
Late in life (~60/70 y.o)
What is the average onset of Huntington’s CHorea?
Progressive disease beginning at 45 y.o.
What is the heritability of Huntington’s?
Autosomal dominant HTT gene mutation - CAG Trinucleotide repeat
What is Huntington’s chorea characterized by?
‣ Involuntary, jerky, and rapid movements
‣ Dementia
‣ Unsteady gait, slurred speech, trouble maintaining tongue protrusion, irregular breathing
‣ Many pts. Also diagnosed w/ depression
• Not just due to chronic illness
• Higher risk of suicide
What are treatments for Huntington’s chorea?
Tetrabenazine (serotonin antagonist)
Typical antipsychotic (antagonize dopamine)
Reserpine, tetrabenazine (depleting dopamine)
What is chorea?
Spontaneous rapid, jerky, arrhythmic, and involuntary movements which are purposeless, or fragments of motor programs
What is Ballismus caused by?
Lesion of the CONTRALATERAL subthalamic nucleus
What is Ballismus characterized by?
Flailing, flinging movement of whole extremity
What is Ballismus related to?
Stroke, inflammation or tumor
What is Athetosis?
Inability to sustain body part in one positions, w/ movements of a snake-like or writhing fashion
What is Athetosis often seen with?
Chorea
What characterizes Athetosis?
Slow, writhing, continuous movements
What is Athetosis dcaused by?
Dopamine blocking drugs, or hypoxicischemic injury
What is focal Dystonia?
What kind of pain does it cause?
Writer’s cramp - a persistence or fixing of posture at extreme of an athetoid movement of extremities or trunk
Not painful, just impaired ability to write bc of involuntary , sustained muscle contracture of extensor and/or flexors of hand
What are other kinds of Dystonia seen?
Torticollis (cervical Dystonia)
Blepharospasm
Drug induced
What is Sydneham’s Chorea?
Neurological disorder of childhood resulting form acute rheumatoid fever.
What is the JONES criteria for syndenham’s chorea?
- J = joints (arthritis)
* <3 = heart (-carditis)
* N = Nodules (subcutaneous)
* E = Erythema marginatum
* S = Sydenham’s chorea
What is Syndenham’s chorea characterized by?
Who does it affect more?
rapid, irregular, and aimless involuntary movements of the arms and legs, trunk, and facial muscles
It affects girls more often than boys and typically occurs between 5 and 15 years of age.
The basal ganglia provide feedback tot he cortex to either ___ or ____
What does this allow for?
Stimulate motor activity OR inhibit motor activity
Allowing for complex movements
What is the modifier in the direct pathway?
Cortex activates pars Compacta to modify striatum via D1 and dopamine
Pars compacta will stimulate straitum to further release gaba to GPi and Pars Reticulata
What is the modifier in the indirect pathway?
Cortex activates Pars compacta to modify striatum via D2 and dopamine
Will inhibit striatum and allow for GABA to work on GPe, allowing for STN to activate GPi and further inhibit thalamus
What is affected to cause Wilson’s disease?
Globus pallidus Internus and striatum
What does GPi do?
Inhibit thalamus via GABA
What does GPe do?
Inhibit STN via GABA
What 2 things inhibit the thalamus at rest?
What is this called?
GPi
Substantia nigra Pars reticulata
Tonic inhibition of thalamus
How is the striatum activated during the direct pathway?
What does this allow it to do?
Cortex releases glutamate to striatum
Striatum releases gaba to
GPi —> can no longer inhibit thalamus
Pars Reticulata —> can no longer inhibit thalamus
What is the role of the subthalamic nucleus during the indirect pathway?
Once uninhibited from GPe
STN will stimulate GPI which will then go and inhibit thalamus
What is the skeletomotor loop?
Role of it?
Motor cortex —> putamen —> VA and VL
role in control of glacial, limba and musculature
What is the Oculomotor Loop?
Role?
from eye field (posteiror parietal, prefrontal) —> Caudate —> VA and Medial dorsal
role in control of saccadic eye movements
What is the associative loop?
Role?
from post. Parietal and middle and inferior temporal lobe —> caudate —> Va and Medial Dorsal
Role in cognition and executive behavioral functions
What is the limbic loop?
Role?
from medial and lateral temporal lobes and hippocampal formation (ant. cingulate gyrus)
—> ventral striatum
—> Ventral pallidum
—> Medial dorsal and VA
Participates in the motivational regulation of behavior and emotions
