Control Lecture 18: Basal Ganglia Flashcards
Which structures are included in the classical basal ganglia but not the functional Basal Ganglia?
The Amygdala and the Claustrum.
What 5 structures make up the functional Basal ganglia?
- Corpus Striatum - Made up of the Globus Pallidus (internus and externus), the Caudate Nucleus
and the Putamen - Substantia Nigra - Substantia Nigra Compacta and Substantia Nigra Reticulata
- Subthalamic Nucleus
What part of the basal ganglia originates from the telencephalon?
The Corpus Striatum
- The Substantia Nigra is an extension of the mesencephalon
- The Subthalamic Nucleus is an extension of the diencephalon
Which part of the Basal Ganglia is referred to as the Neostraitum?
The Caudate Nucleus and Putamen
The Globus Pallidus is referred to as the Paleostraitum.
Which part of the basal ganglia produces dopamine?
Substantia Nigra Compacta. As a by-product of dopamine production, we produce melanin making the SNc appear dark.
What is the default setting of the output nuclei to the thalamus?
Inhibitory
What are the output nuclei to the thalamus?
These project to the thalamus. These include GPi and the Substantia Nigra pars Reticulata.
What are the input nuclei?
The Neostraitum - Caudate and the Putamen.
Corticostriatal neurones bring fibres from the cortex and Nigrostriatal afferents bring fibres from the SNc.
Describe the direct pathway to facilaote movement.
- Corticostriatial afferents bring information from the cortex to the caudate and the putamen. These fibres are always excitatory.
- When they reach fibres at the caudate (or putamen) they excite inhibitory neurones afferents that take information from the putamen to the GPi.
- This leads to reduced activity of the inhibitory neurones. These neurones act on fibres that take information from the GPi to the thalamus. These fibres are always inhibitory. There is therefore reduced inhibition on the thalamus.
- The efferents that take information from the thalamus reach the cortex. These are always excitatory. Due to the reduced inhibition on them, there is facilitated wanted movement.
Describe how to indirect pathway inhibits unwanted movement.
- Corticostraital afferents are always excitatory. This means they excite the neurones leaving the putamen or caudate nucleus.
- Neurones from the putamen or caudate nucleus move to the GPe. These neurones are always inhibitory. As a result there is enhanced inhibition.
- These neurones act on neurone moving from the GPe to the Subthalamic neurones. These neurones are inhibitory. This means they are inhibited due to the enhanced inhibition on them.
- Neurones from the sub thalamic nucleus to the GPi therefore are uninhibited. These neurones are excitatory.
- Neurones from the GPi to the thalamus are also inhibitory. They therefore enhanced.
- Neurones from the thalamus to the cortex are always excitatory. They are therefore dampened due to the enhanced inhibition on them.
What is the effect of dopamine on movement?
- Dopamine excite the direct pathway
- Inhibits the indirect pathway - therefore leading to wanted movement
The action of both of these leads to imitated movement.
How does dopamine facilitate movement in the direct pathway?
- When dopamine releasing neurones, nigrostraital neurones, release dopamine onto the D1 receptor in the caudate nucleus or putamen, it excites them.
- The afferent fibres that bring information from the caudate to Gi are inhibitory. Since activated by D1 receptors they have enhanced inhibition.
- These act on neurones that move from the GPi to the Thalamus. These are inhibitory neurones. Due to enhanced inhibition, their effect is damped.
- These neurones act on neurones that move from the thalamus to the cortex. These thalamocortical neurones are always excitatory. Due to the reduced inhibition on them, the pathway leads to facilitated movement.
How does dopamine leads to facilitated movement through the indirect pathway?
- Nigrostraital neurones act on D2 receptors. Their effect is inhibitory.
- These fibres inhibit neurones that move from the putamen to the GPe - these are inhibitory neurones. Their effect is damped due to the inhibition on them.
- There is therefore reduced inhibition on the fibres that travel from the GPe to the sub thalamus - these are inhibitory fibres.
- Now with enhanced inhibition, there is a greater effect of the fibres that travel from the sub thalamus to the GPi. These fibres are excitatory.
- These fibres act on the fibres from the GPi to the Thalamus. With reduced excitation, their effect is inhibited. The fibres that travel from the GPi to the thalamus are inhibitory.
- There is therefore reduced action on the fibres from the thalamus to the cortex - excitatory neurone es. This therefore facilities movement.
What is the effect of degeneration of the dopamine producing neurones in the SNc?
- The direct pathway cannot facilitate movement as there is loss of action on the D1 receptors
- The indirect pathway cannot facilitate movement as there is loss of stimulation on the D2 receptors
In PD the of the neurones to the cortex are reduced. There is failure to initiate movement.
How can injury to the inhibitory fibres from the striatum to the GPi affect movement? What movement disorder does this occur in?
Chorea - Huntington’s disease
- The corticostiatal neurones are excitatory and act on neurones in the putamen that travel to the GPi.
- These however cannot act on the inhibitory neurones that move from the GPi to the thalamus.
- There is therefore no inhibition on the excitatory thalamocoritcal neurones. This leads to a hyperkinetic disorder.
