Provides a good description of the functional anatomy & physiology of the basal nuclei/ basal ganglia for undergraduate medical students. It also describes disorders of the basal ganglia like parkinsonism & chorea.

1. Basal Nuclei
Physiology
Card-7
Item-7

2. Parts of Basal Nuclei
Definition
• The basal ganglia are a collection of subcortical nuclei that are highly involved in regulating voluntary motor movements.
Parts
It consists of 5 parts:
1) Caudate Nucleus
2) Putamen (Caudate Nucleus + Putamen = Striatum)
3) Globus Pallidus (Putamen + Globus Pallidus = Lentiform Nucleus)
4) Subthalmic Nuclei
5) Substantia Nigra of the Midbrain

3. Connections of the Basal Nuclei
Afferents (Inputs) to the basal ganglia include
the following:
1) From the entire cerebral cortex - through
the corticostriatal pathway,
2) From the substantia nigra - fibers arising in
the pars compacta of the substantia nigra
reach the striatum, forming the nigrostriatal
connections.
3) From the thalamus - fibers from the thalamus
to the basal ganglia form the thalamostriatal
connections.
4) From the reticular formation of the
brainstem- afferents from the reticular
formation
Efferents (Outputs) of the basal ganglia include
the following:
1) Striatopallidal- From Striatum to Globus
Pallidus
2) Striatonigral- From Striatum to Substantia
Nigra pars reticulata

4. Direct Pathway
• The specific way that the basal ganglia
modifies movement depends largely on
whether it goes through the direct
pathway or the indirect pathway.
• The direct pathway generally has an
excitatory effect on the initial motor
signal

5. Indirect Pathway
• The indirect pathway takes a longer
route through the basal ganglia and
generally exerts a diminishing or
inhibitory effect on the initial motor
signal
• The indirect pathway starts out similarly
to the direct pathway in that the signal
is generated in the Cortex and travels to
the Striatum. However, it then exits the
direct pathway into the External globus
pallidus before traveling to the
Subthalamic nucleus, the Internal
globus pallidus, and finally the
Thalamus.

6. Functions of the Basal Nuclei
The functions of the basal ganglia are yet to be fully understood. However,
the following are functions have been clearly established by now:
• Planning and modulation of movement pathways
• Reward processing and motivation
• Decision making
• Working memory
• Eye movements
• Moreover, the basal nuclei use proprioceptive feedback from the periphery
to compare the movement patterns generated by the cerebral cortex with
the actual movement.
• Also, the basal ganglia have been shown to play an important role in
motivation considering that the basal ganglia circuits are influenced heavily
by extracellular dopamine.

7. Damage to Basal Nuclei
Parkinson’s Disease:
Parkinson’s disease is a neurodegenerative
disorder that primarily affects the motor system.
Specifically, Parkinson’s disease involves the
death of dopaminergic neurons in the substantia
nigra, leading to a general dopamine deficit in
the brain.
Symptoms of Parkinson’s Disease (TRAP) :
 T is for Tremor.
– It is typically a resting & slow tremor, meaning that
it is there most of the time but will disappear when
someone initiates a voluntary movement.
 R is for Rigidity.
– sustained way known as lead-pipe rigidity or in a
ratchety click-click-click manner known as
cogwheel rigidity
 A is for Akinesia and bradykinesia.
– Absence or slowness of movement
 P is for Postural instability
– A distinct lack of balance which tends to emerge
late in the disease

8. Damage to Basal Nuclei
HUNTINGTON’S DISEASE
Definition : Huntington’s disease is a movement
disorder that presents clinically as progressively
worsening movement and behavioral problems.
The hallmark movement abnormality seen in
Huntington’s disease is chorea (a series of quick,
jerky, flailing movements that resembles
dancing)
Cause:
Huntington’s disease is an autosomal dominant
genetic disorder involving mutations in the
huntingtin gene on chromosome 4.
• Here too many CAG repeats (more than 26) are
produced. The gene becomes affected and begins
to produce a mutant version of the huntingtin
protein that damages neurons in the caudate.
• Number of CAG repeats is directly correlated
with the severity & onset of the disease