Case 7 Summary - ILOs

Case 7 Summary
General ILOs:

- To demonstrate knowledge of the roles of the basal ganglia and of the cerebellum
in the initiation and co-ordination of voluntary movement

The basal ganglia facilitate conscious movement. Neurons travel from the cortex to medium
spiny neurons (MSNs) in the corpus striatum (the corticostriatal pathway). Once in the corpus
striatum, spiny neurons converge in the globus pallidus and Substancia nigra par reticulata
(the main output sources from the basal ganglia):

 Firing of MSNs in the putamen – body movement.
 Firing of MSN in the caudate – eye movement

The structures involved in the basal ganglia pathway are:

 Caudate
 Putamen
 Substancia Nigra
 Subthalamic nucleus
 Globus pallidus (external and internal)

The caudate and putamen are collectively known as the striatum. The basal ganglia have a
direct and indirect pathway (as a rule of thumb: glutamate = excitatory; GABA = inhibitory):

Direct pathway

 Projections from the thalamus to the cerebral cortex stimulate movement
 The globus pallidus internal and Substancia nigra reticulate inhibit the thalamus
(suppressing movement)
 The cerebral cortex excites the striatum, which inhibits the globus pallidus internal




1
Guillaume Antem – MBChB Y2

,Indirect pathway

 Involved in the inhibition of movement (specifically the direct pathway).
 Globus pallidus external typically inhibits the subthalamic nucleus.
 This is stopped when the cerebral cortex activates the striatum, which inhibits the
globus pallidus external.
 This results in greater activation of the subthalamic nucleus, resulting in greater
activation of the globus pallidus internal, which inhibits the thalamus.




The indirect pathway is thought to be necessary for the suppression of unwanted movements.
The substantia nigra pars compacta modulates striatum activity using GABA. Hence,
reduction in function to that area (ie: Parkinson’s) can destabilise the indirect pathway. This
is theorised to cause the unwanted tremors experienced in Parkinson’s.

The direct and indirect pathways work together to facilitate a desired movement (direct
pathway) whilst inhibiting undesired movements (indirect pathway).

The cerebellum

The cerebellum can be considered in three parts:

 Cerebrocerebellum – regulation of extremities for dextrous movements
 Vestibulocerebellum – regulation of posture, equilibrium and balance
 Spinocerebellum - regulation of gross limb movements and proprioception (ie:
walking)
 Vermis – Regulation of posture, limb and eye movements

The cerebellum communicates with the rest of the brain via the cerebellar peduncles, of
which there are three: superior, middle and Inferior.



2
Guillaume Antem – MBChB Y2

, The superior cerebellar peduncle carries outputs from the cerebellum whilst the middle and
inferior cerebellar peduncles primarily carry input.




Information from the cerebral cortex travels to the Purkinje fibres of the cerebellum. These
communicate with the deep cerebellar nuclei, which in turn relay the signal to other structures
such as those mentioned with the basal ganglia.

Purkinje fibres receive two types of input from the cerebral cortex:

 Climbing fibres
 Parallel fibres of granule cells

As Purkinje fibres are GABAergic, local neurons are used to modulate inhibitory activity
from the fibres:

 Basket cells – receive excitatory input from parallel fibres and inhibit Purkinje fibres
 Stellate cells – receive excitatory input from parallel fibres and inhibit Purkinje fibres
 Golgi cells – receive input from parallel fibres and inhibit granule cells




3
Guillaume Antem – MBChB Y2