Basal Ganglia Flashcards
What are the ‘basal ganglia’?
A set of neural structures buried deep within the cerebral hemispheres
What structures make up the basal ganglia?
Caudate nucleus, putamen, globus palidus (internal and external), substantial nigra (reticulate and pars compacta) and sub thalamic nucleus
Which structures make up the dorsal striatum?
Caudate nucleus and putamen
Which structures make up the ventral striatum?
The nucleus accumbens
Which structures make up the corpus striatum?
Globus pallidus, putamen and caudate nucleus
Which structure of the basal ganglia forms the lateral wall of the lateral ventricles in the brain?
The caudate nucleus
What is the function of the basal ganglia?
To process incoming information from the sensory and associated cortex and send the response from the thalamus to the supplementary motor cortex;
> Regulates intensity of stereotyped movement
Inhibits antagonistic movement
Regulates attention and cognition
Switch motor programmes
What are ‘medium spiny neurones’?
The neurones present in the striatum and in the basal ganglia generally; a form of GABAergic neurone that can be influenced by the action of dopamine on D1 and D2 receptors
By what two pathways is the striatum connected with the globus pallidus and substantia nigra?
The direct and indirect pathways
Describe the direct pathway which connects the striatum with the globes pallidus and substantia nigra
> Medium spiny neurones in the striatum are activated by glutamatergic neurones synapsing from the cortex
The medium spiny neurones then project from the striatum to the INTERNAL globus pallidus and release GABA
This prevents the firing of medium spiny neurones from the globus pallidus interna to the thalamus; this means that glutamatergic neurones from the thalamus to the supplementary motor cortex aren’t inhibited and therefore communication can occur (disinhibition)
What is the normal function of the direct pathway in the basal ganglia?
To allow changes in motor programmes e.g. to stop running or sitting down
What is the normal function of the indirect pathway in the basal ganglia?
Disallows changes in motor programmes as it decreases excitatory thalamocortical projections
Describe the indirect pathway which connects the striatum with the globes pallidus and substantia nigra
> Glutamatergic neurones from the cortex synapse in the striatum and activate the medium spiny neurones
The medium spiny neurones project from the striatum to the globus pallidus externa
GABAergic neurones from the globus pallidus externa travelling to the sbthalamic nucleus therefore don’t fire
The glutamatergic neurones from the sub thalamic nucleus then project to the globus pallidus interna
This stimulates the GABAergic neurones from the globus pallidus interna to project to the thalamus
There is inhibition of the glutamatergic neurones from the thalamus to the cortex which prevents changes in motor programmes
Outline the role of dopamine in the nigrostriatal pathway
Facilitates the activity of the medium spiny neurones of the DIRECT pathway but INHIBIT INDIRECT pathway –> dopamine allows motor programmes to change
Outline the function of the dopamine receptors in the nigrostriatal pathway
Dopamine is released from the substantia
Which structure secretes dopamine in the basal ganglia?
Substantia nigra pars compacta
D1 receptors - binding of dopamine increases cAMP levels, increases sensitivity of striata cells to glutamate, facilitates the direct pathway
D2 - decreases the action of the indirect pathway
Which pathways of the basal ganglia are active at rest?
Direct pathway is inactive
Indirect pathway is active
Which pathways of the basal ganglia are active during change of movement?
Direct pathway is active
Indirect pathway is less active
What two conditions are associated with dysfunction of the basal ganglia?
Parkinson’s and Huntington’s disease
What is the cause of Parkinson’s disease?
Loss of the substantia nigra pars compacta cells, leading to loss of dopamine input to the striatum (caudate nucleus and putamen)
What are the signs of Parkinson’s disease?
Don’t present until >80% of SN cells have degenerated.
> Tremor at rest
Rigidity
Bradykinesia
Loss of postural reflexes
What is the genetic cause of Huntington’s disease?
Autosomal dominant mutation in the Huntington gene
What are the symptoms of Huntington’s disease?
> Hyperkinesis
Ballismus (involuntary, sudden and jerky movements)
Athetosis (involuntary, smooth movements)
Dementia
What is ballismus?
Involuntary, sudden and jerky movements associated with Huntington’s disease
