What are the basal ganglia?
A group of inter-connected sub-cortical neurones
Givethe five different parts of the basal ganglia (with sub-groups, c'mon now).
- Globus Pallidus External (GPe)
- Globus Pallidus Internal (GPi)
- Pars Compacta (SNc)
- Pars Reticulata (SNr)
Subthalamic Nucleus (STN)
What do the caudate nucleus and putamen form together?
Together the putamen and globus pallidus make up what?
The lenticular nucleus
What is the role of the basal ganglia?
regulate the amplitude and velocity of the planned movement, particularly in relation to the use of internal (proprioceptive) information.
Outline the anatomy and role of basal ganglia at rest
At rest the basal ganglia actively inhibit movement.
At rest striatum is not stimulated by cerebral cortex (no planned movement)
Globus Pallidus Internal (GPi) inhibits the Thalamus
The inhibited Thalamus does not stimulate the Cerebral Cortex
Less stimulation of the cerebral cortex gives less movement
Give the three different pathways which can modify basal ganglia behaviour
Basal Ganglia direct
Basal Ganglia Indirect
Substantia Nigra compacta
Outline the anatomy and function of the basal ganglia direct pathway
The basal ganglia direct pathway amplifies planned movements.
Cerebral cortex stimulates Striatum (planned movement)
Striatum inhibits Globus Pallidus Internal (GPi)
Inhibition of the Thalamus is removed
Thalamus stimulates Cerebral Cortex, increasing stimulus of movements via UMNs
Outline the anatomy and function of the basal ganglia indirect pathway
The basal ganglia indirect pathway dampens down planned movements. It takes longer than the direct pathway, therefore acts slightly after it.
Cerebral Cortex stimulates Striatum (planned movement)
Striatum inhibits Globus Pallidus External (GPe)
Inhibition of the Subthalamic Nucleus is removed
Subthalamic nucleus stimulates the Globus Pallidus Internal (GPi)
Increased inhibition of the Thalamus by the stimulated GPi
Thalamus is inhibited, preventing it from stimulating the cerebral cortex
Less stimulation of cerebral cortex gives less movement due to less stimulation of UMNs
Outline the anatomy and function of the substantia nigra pathway
The Substantia Nigra Compacta amplifies the direct and inhibits the indirect basal ganglia pathways. The result of this is increased amplification of movements.
Dopaminergic neurones from the Substantia Nigra Compacta act on the Striatum
D1 Receptors – Increase inhibition of Globus Pallidus Internal (GPi)
é Direct Pathway, Movements Amplified
D2 Receptors – Decrease inhibition of Globus Pallidus External (GPe)
ê Indirect Pathway, Movements Amplified due to less dampening down
Give an example of a gypokinetic and hyperkinetic movement
. Basal ganglia dysfunction typically generates Hypokinetic (E.g. Parkinson’s) or Hyperkinetic (E.g. Huntington’s Chorea).
What is not affected in parkinson's?
Sequence of muscle activation is normal and unaffected as the cerebellum carries this out, along with upper and lower motor neurones.
What does parkinson's result from?
Results from progressive degeneration of dopaminergic neurones form the Substantia Nigra that run to the striatum
What does symptomatic parkinson's point to?
Symptoms appear at >60 years old, but only once 75-80% of the dopaminergic neurones have degenerated. Therefore by the time symptoms appear the patient has had Parkinson’s for a number of years.
Give four classic signs of Parkinson's
Tremor at rest, abolished by voluntary movement. Pill-rolling tremor is a classic sign of early onset
Hypertonia – Lead pipe / cog-wheel rigidity
Bradykinesia – Slowness of movement (Most debilitating)
Parkinsonian gait – Stooped posture, short shuffling steps, pedestal turning
What is the pathophysiology of Parkinson's?
Death of Dopaminergic Neurones in Substantia Nigra
Less Dopamine at D1 receptors
Loss of Dopamine’s stimulation of the striatum’s inhibition of Globus Pallidus Internal (GPi)
Loss of some of GPi’s inhibition gives a relative increase of inhibition of the Thalamus
Less Dopamine at D2 receptors
Loss of Dopamine’s inhibition of the striatum’s inhibition of Globus Pallidus External (GPe)
The relative increase in inhibition of GPe leads to decreased inhibition of the Subthalamic Nucleus
Increased stimulation of Globus Pallidus Internal (GPi)
Increased inhibition of the Thalamus
Suppression of the Direct Pathway and amplification of the Indirect Pathway leads to increased Thalamus inhibition and subsequent reduction in it’s excitatory output to the Cerebral Cortex
Therefore there is less output of the cerebral cortex via UMNs and LMNs and less muscle activation, giving a disorder of Hypokinesia.
What is Huntington's Chorea?
Autosomal Dominant inherited disease with complete penetrance (all gene carriers will develop the disease eventually)
What is the pathophys of huntington'?
Gene mutation produces the Huntingtin protein, which is responsible for the disease. The protein forms aggregates and causes cell death.
There is neuronal loss initially in the Caudate Nucleus (part of Neostriatum)
Reduction in the inhibitory neurotransmitter GABAA and Ach
Loss of inhibitory synaptic transmission leads to decreased Thalamic inhibition and subsequent increased stimulation of movement via the Cerebral Cortex
What is Huntington's chorea?
Jerky, involuntary movements. This is followed by the development of progressive psychiatric and cognitive symptoms.