Basal Ganglia Flashcards
What are basal ganglia?
Neural structures deep within cerebral hemispheres
What is the function of basal ganglia?
Regulate movement
Process info. relating to emotion, motivation and cognition
How do basal ganglia regulate movement?
- regulate intensity of slow/stereotypes movements
- inhibit antagonistic unnecessary movements
- switch motor programs to stop or start movements
What are the neural structures within the basal ganglia?
- caudate nucleus
- putamen
- globus pallidus
- substantia nigra (motor)
- subthalamic nucleus (motor)
What are the features of the caudate nucelus?
C shaped
in frontal lobe
head, body, tail
tail tapers ending in temporal lobe
What are the features of the putamen?
Large rounded
Forebrain
Connected to caudate at caudate head region
What are the features of the globus pallidus?
Internal segment (GPi) sends output to thalamus External segment (GPe) relays info between basal ganglia nuclei and globus pallidus
What are the features of internal capsule?
White matter structure
Separates lentiform nucleus and caudate nucleus
What is the blood supply to the caudate nucleus?
Middle cerebral artery
Anterior cerebral artery
What is the blood supply to the putamen?
Middle cerebral artery
Anterior cerebral artery
What is the blood supply to the globus pallidus?
Middle cerebral artery
Anterior choroidal
What is the blood supply to the internal capsule?
Middle cerebral artery
Anterior cerebral artery
Anterior choroidal
What is the input into the basal ganglia?
Cerebral cortex (frontal and parietal) Substantia nigra
How does the cerebral cortex project to the basal ganglia?
Project directly to caudate nucleus and putamen
From association areas in frontal and parietal cortex
Projections are corticostriatal pathway
How does the substantia nigra project to the basal ganglia?
In midbrain
Dopaminergic input to caudate nucleus and putamen
Nigrostriatal pathway
Where do the substantia nigra and cerebral cortex input into?
Input zone of basal ganglia
caudate nucleus and putamen = corpus striatum
What are the main neurons in the corpus striatum?
Medium spiny neurons
75%
What does corpus striatum convergence produce?
dendritic trees of medium spiny neurons inputs converge = - cortical neurons (glutamatergic) - substantia nigra neurons (dopaminergic) - local circuit neurons (GABAergic)
these all converge on globus pallidus and substantia nigra reticulata
What is the order of the corpus striatum convergence?
Cortex -> corpus striatum -> globus pallidus external -> globus pallidus internal or substantia nigra reticulata
What is the output of the basal ganglia?
- subthalamic nucleus
- VA/VL thalamic nuclear complex
- superior colliculus (controls eye movement)
What are the features of the subthalamic nucleus?
small paired nuclei
below thalamus
input from cerebral cortex and external globus pallidus
projects to internal globus pallidus and substantia nigra reticulata
What are the features of the VA/VL thalamus complex?
Input from internal globus pallidus
Projects directly to motor cerebral cortex areas
Loop within cerebral cortex
What is the input into the corpus striatum?
Cortical
Via excitatory glutamate neurons
Where are there inhibitory neurons?
Corpus striatum and globus pallidus
GABAergic inhibitory neurons
What is disinhibition?
Inhibition of inhibition
Produces excitation
Double inhibition
2 inhibitory neurons in sequence
What is an example of a direct pathway?
Excitatory Glutamatergic axons -> caudate and putamen -> internal globus pallidus -> motor thalamus and back to motor cortex
What is an example of an indirect pathway?
Caudate and putamen inhibit globus pallidus external which inhibits subthalamic nucleus which excites globus pallidus internal which inhibits motor thalamus so that motor thalamus remains fixed and so supplementary motor cortex output remains fixed
When is the direct and indirect pathway active/inactive?
At rest/undergoing repetitive movement => direct inactive and indirect is active
Tonic inhibitory input to motor thalamus prevents change in movement
When you want a change in movement direct pathway becomes active
What receptors are expressed by the corpus striatum neurons?
D1 or D2
What is the role of the D1 receptor?
- increases cAMP
- increases sensitivity of corpus striatum neurons to glutamate
- projects to internal globus pallidus directly
What is the role of dopamine on pathways?
Increases action of direct pathway via D1 receptors to activate motor program change
Decreases action of indirect pathway via D2 receptors to block motor program change
What is the role of dopamine?
Allows motor programs to change and stop and start
What are hypokinetic movement disorders?
e. g. Parkinson’s
- if balance of inhibitory signals in direct and indirect pathways are altered
- can also get hyperkinetic movement disorders which is not PD
What are the characteristics of Parkinson’s?
Resting tremor
Slowness of movement (bradykinesia)
Muscular rigidity
Minimal facial expressions
What is the cause of motor function defects in Parkinson’s?
- loss of dopaminergic neurons in substantia nigra compacta which project to caudate and putamen
What are the 3 stages of Parkinson’s?
- early: cardinal symptoms, no medication related complications
- PD with motor and non-motor complications, medication side effects, unrelieved symptoms
- advanced life limiting with significant disability
How to manage early PD?
Levodopa
Dopamine agonists
MAO-B inhibitor
How to manage 2nd stage PD?
COMT inhibitor
Apomorphine
Amantadine
How to manage 3rd stage PD?
Deep brain stimulation
What is an example of a hyperkinetic movement disorder?
Huntington’s
How is Huntington’s inherited?
- autosomal dominant
What are the characteristics of Huntingtons?
Mood alterations
Personality alterations
Defects in memory and attention
Involuntary movements
What causes Huntington’s?
Defects in motor function due to loss of GABAergic neurons in corpus striatum which project to globus pallidus
What is chorea?
Rapid involuntary jerk type movements, non-purposeful, dance like, distal
Greek to dance
What is athetosis?
Slow involuntary smooth writing type movements, non-purposeful, writhing, distal
Greek to throw
What is ballismus?
Rapid involuntary wild flinging type movements, non-purposeful, wild flinging, proximal
greek for not fixed
