Basal Ganglia Flashcards
What is the role of basal ganglia? (4 answers)
Regulate intensity of slow movements
Inhibit unnecessary movement
Regulate cognition
Motor program switch
What five structures are included in the basal ganglia?
Caudate, putamen, globus pallidus, substantia nigra and subthalamic nucleus
Define basal ganglia.
Collection of nuclei situated deep within the cerebral hemispheres.
What is disinhibition? How does it relate to basal ganglia?
Excitation by double inhibition, i.e. when there are two inhibitory neurons in sequence. The direct pathway is excitatory to the motor thalamus by disinhibition.
How many % of substantia nigra dopamine cells have to be dead before clinical signs of Parkinson’s disease show?
More than 80%
What is the cause of Parkinson’s disease? What is the consequence on substantia nigra cells?
The loss of dopaminergic input to caudate and putamen. The cells in the substantia nigra degenerate and are lost.
What are the four classic motor signs of Parkinson’s disease?
Tremor at rest
Rigidity
Bradykinesia
Loss of postural reflexes
What three parts compose the corpus striatum?
Caudate nucleus, putamen, and globus pallidus
How many parts of the globus pallidus are there? How many of substantia nigra? Name them.
External and internal GP Pars compacta (input) and pars reticulata (output)
What comprises the dorsal striatum? What about the ventral striatum?
Dorsal = caudate and putamen Ventral = accumbens
Where is the substantia nigra? Where is the subthalamic nucleus?
Base of midbrain
Ventral thalamus
Where does the head of the caudate nucleus fit into? Where does the caudate nucleus end?
The lateral aspect of the anterior horn of the lateral ventricle (concave recess).
The temporal lobe.
Which nuclei forms the lateral wall of the lateral ventricle? (Coronal section)
Caudate
Input to the basal ganglia
Forebrain - frontal cortex, parietal cortex,temporal cortex
Midbrain - substantia nigra (pars compacta)
Output from basal ganglia
Thalamus and cortex
What is the main type of neuron involved with basal ganglia?
Medium spiny neurons
How many places does a dopaminergic axon synapse on a medium spiny neuron?
Three - cell bodies, spines and dendritic shafts
Describe convergence in terms of basal ganglia loops.
There are large dendritic trees of striatal output neurons (medium spiny neurons) and decreasing cell number.
The cortex has 150,000,000 neurons which reach 30,000 in the striatum, which reach 100 in the external GP and 1 in the internal GP.
What is ballismus? What is athetosis? What causes them?
Involuntary sudden jerky movements.
Involuntary smooth ‘sinuous’ movements.
Both caused by damage to cells in striatum, i.e. in Huntington’s.
How is Huntington’s managed?
Neuroleptics (dopamine antagonists)
Atypical antipsychotics
SSRI for depression
Benzodiazepines
What causes Huntington’s?
It is hereditary (autosomal dominant mutation).
The symptoms are caused by loss of GABA-ergic neurones in striatum.
How can Huntington’s be seen in MRI?
Enlargement of ventricles and shrinkage of basal ganglia
Symptoms of Huntington’s
Hyperkinesis
Extra involuntary movements
Dementia
How is Parkinson’s treated?
Early PD - levodopa, dopamine agonists, MAO-B inhibitors
PD with motor and non-motor complications - same PLUS COMT inhibitors, apomorphine, amantadine
Advanced life-limiting PD - deep brain stimulation
Describe the steps of the direct pathway (basal ganglia).
Excitatory (glutamate) axons from the sensory and association cortices –>caudate and putamen
- ->internal globus pallidus (VIA GABA so inhibitory)
- ->motor thalamus (EXCITATORY BY DISINHIBITION, as internal GP normally has tonic inhibition to thalamus)
- ->supplementary motor cortex (excitatory)
ALSO The substantia nigra excitatory dopaminergic axons –>caudate and putamen
Outcome is…change in cortical motor program.
Describe the steps of the indirect pathway (basal ganglia).
The output from the caudate/putamen
- -> the external globus pallidus (inhibitory)
- -> subthalamic nucleus (inhibitory)
- -> internal globus pallidus (excitatory)
- -> motor thalmus (inhibitory)
- -> supplementary motor cortex
Dopamine increases the action of which pathway? By which receptor? What does this receptor do?
Direct pathway via D1 receptors (and it decreases the action of the indirect pathway via D2 receptors).
D1 increases CAMP and increases sensitivity of striatal cells to glutamate.
