Basal Ganglia
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Basal Ganglia menu
Basal Ganglia
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Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Basal Ganglia
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Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Overview of the Basal Ganglia
overview
Extrapyramidal Motor System
The basal ganglia perform two functions:
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1. Initiate movements
#1
#2a
1. Regulate stereotypic movements
#2b
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Initiate movements
Play
Movie
The basal ganglia govern the initiation changes in motor behavior - meaning
both starting AND stopping of motor actions. Sipping from a cup requires
proper initiation or stopping of multiple, sequential actions.
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Stereotypic movements #1
Play
Movie
Stereotyped movements, like other habits, often are context dependent. The
cerebellum governs the movement itself, but the initiation of the motor pattern
in context is governed by the basal ganglia. The basal ganglia have been
implicated in the expression of obsessive-compulsive disorders.
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Stereotypic movements #2
Play
Movie
Not all stereotyped behaviors are rhythmic, and the motor pattern can be
difficult to halt once it has begun. Have you ever tried to stifle a yawn?
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(return…)
Basal ganglia structures
This cartoon represents a horizontal slice through the brain at the level of the thalamus.
It is a midline view from above, with anterior at the top of the screen and posterior at
the bottom of the screen.
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Basal Ganglia menu
Basal Ganglia
Overview of Basal Ganglia structure
(next)
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Neural circuits of the Basal Ganglia
The basal ganglia form an circuitry
internal motor circuit …
Cortex
Caudate
Putamen
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The cortex receives motor
planning information, then
passes that information to the
caudate & putamen, which
govern timing of events
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The information then is
passed to the globus
pallidus …
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... which helps govern
movement magnitude,
and then passes this
basal ganglia output to
thalamus nuclei
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The thalamus combines
information from the
basal ganglia and the
cerebellum, then sends
it to the motor cortex
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Basal Ganglia menu
Basal Ganglia
Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
(next)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Modulation of input to the Basal Ganglia
Input modulation
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The caudate &
putamen receive
input from the cortex,
and …
… from the thalamus.
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The substantia nigra
also modulates input
to the basal ganglia.
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Reciprocal connections with the caudate & putamen allow exitatory inputs
from the substantia nigra to modulate the amount and type of output sent
to the globus pallidus. Dopamine is the neurotransmitter used by these
substantia nigra pathways.
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When the substantia nigra isn’t working properly, input to the basal
ganglia isn’t modulated properly, and the globus pallidus receive
progressvely less information. Without this information, the
initiation of movement (i.e., timing) message is less effective and
the person’s movements progressively become slower (i.e.,
bradykinesia).
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Parkinson’s disease is related to a deterioration of the substantia
nigra and globus pallidus, and is characterized by resting tremors
and bradykinesia.
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Basal Ganglia menu
Basal Ganglia
Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
(next)
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Modulation of output from the Basal Ganglia
Output modulation
1) The putamen provides
processed information
to the globus pallidus.
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- part 1
- part 1
In addition to
modulating input to
the basal ganglia, the
substantia nigra also
modulates the output.
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- part 1
The substantia nigra, in turn,
has many connections.
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- part 2
2) The subthalamus plays
a role in modulating
output from the basal
ganglia
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- part 2
Deterioration of the
subthalamus results in the
ballisms, or explosive
movements occurring
periodically, that
characterize Huntington’s
disease.
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Basal Ganglia menu
Basal Ganglia
Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
(next)
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Summary
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Basal Ganglia menu
Basal Ganglia
Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
(next)
Clinical signs related to the Basal Ganglia
Effects of drugs on the Nervous System
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Clinical signs related to
Basal
Ganglia clinical
signs
Basal
Ganglia
dysfunction
Parkinson’s disease
resting tremor . . . .
poverty of movement
bradykinesia . . . . .
stooped posture . . .
cogwheel rigidity . . .
masked face . . . . .
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Chorea . . . . . . . . .
Choreaform movements
Tics . . . . . . . . . . .
Ballisms . . . . . . . . .
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#1
#2
#3
#4
Select a blue
button to view
the video
#5
#6
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#7
#8
#9
#10a
#10b
(YouTube’s website also can be a good source of example videos…)
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Basal Ganglia menu
Resting tremor
Play
Movie
An hallmark feature of Parkinson’s disease is the resting tremor - involuntary,
oscillating movements at rest, often of the hands or head and neck.
It is not a resting tremor if it occurs during execution of a movement!
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Clinical signs menu
Poverty of movement
Play
Movie
Limited or no movement - often described by the person as becoming
“stuck” in position - also is characteristic of Parkinson’s disease. Remember
that the basal ganglia are responsible for initiating a change in movement
patterns. Here, the individual is attempting to rise from a chair - a complex
motor sequence where timing of the component movements is critical.
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Clinical signs menu
Bradykinesia
Play
Movie
“Slowed movement” is another feature of Parkinson’s disease, and is
particularly noticeable with walking - a motor behavior where the center of
gravity shifts forward, and placing each foot forward alternately is what keeps
you from falling. Slowed movements allows the center of gravity to shift too
far forward, too rapidly.
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Clinical signs menu
Stooped posture
Play
Movie
A biomechanical feature of many disorders, but characteristic of
Parkinson’s disease when seen in combination with other symptoms.
Here, note the resting tremor, bradykinesia, and - despite the poor quality
image - a masked facial expression.
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Clinical signs menu
Cogwheel rigidity
Play
Movie
An animation of the concept, meant to illustrate the lack of smooth
movements at the joint. The feeling is similar to that of a cogwheel:
“click - stop - click - stop...”
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Clinical signs menu
“The Phantom of the Opera”
Warner Brothers, 2004
Gerard Butler as the Phantom
Masked facial expression
Conveying emotion through facial expression requires initiation of motor
behavior. Without these behaviors, the person may have a “masked” facial
expression. Be aware, however, that emotional capacity is undiminished
even if the emotion can’t be expressed!
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Clinical signs menu
Chorea
Play
Movie
Huntington’s disease and other choreas typically are disorders in modulation of
the output from the basal ganglia. Ongoing, smoothly flowing movements are
typical - but the constant movement consumes calories rapidly. The movements
do not occur during sleep.
A different form of chorea (now called Sydenham’s chorea) was once termed St.
Vitus’ dance due to the frenzied limb movements and contorted facial
expressions. This form of chorea can appear after rheumatic fever, but also may
co-occur with obsessive-compulsive disorder - which also is associated with
basal ganglia dysfunction.
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Clinical signs menu
Choreaform movements
Play
Movie
Other intrusive movements may appear similar to those of Huntington’s
chorea and Sydenham’s chorea, but do not arise from the same causes
(genetic source or bacterial infection). These movements are termed
“choreaform” and they can be significant barrier to function. This individual
has been asked to touch her nose with each index. Unlike true choreas, her
impairment primarily is unilateral (right side).
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Clinical signs menu
Tics
Play
Movie
A tic is a sudden, repetitive, stereotyped, nonrhythmic, involuntary movement
(motor tic) or sound (phonic tic) that involves discrete groups of muscles. Tics
can be invisible to the observer - such as abdominal tensing or toe crunching.
Tics must be distinguished from symptoms of other disorders, such as
choreas, autism, seizures, or obsessive-compulsive disorder.
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Clinical signs menu
Ballisms #1
Play
Movie
Ballisms are sudden, explosive, large-amplitude, flinging motions of the limbs.
If confined to one limb or one side of the body, they are termed “hemiballisms.”
This motor intrusion may cause postural instability and lead to falls and cause
problems with everyday activities (such as eating, cooking, or dressing), but
frequently also is a significant social barrier.
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Clinical signs menu
Ballisms #2
Play
Movie
Caused by a lesion of the contralateral subthalamic nucleus or its connections,
ballisms may be less severe, more severe, or may progressively become
worse over time. The severity may relate to the size or to the frequency of the
ballism. This individual has been asked to touch his nose with his left index
finger.
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Clinical signs menu
Basal Ganglia
Overview of Basal Ganglia structure
Basal Ganglia circuitry (the Striato-Pallido-Thalamic loop)
Modulation of inputs to the Basal Ganglia
Modulation of outputs from the Basal Ganglia
Summary of extrapyramidal circuitry
Clinical signs related to the Basal Ganglia
(next)
Effects of drugs on the Nervous System
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Effects ofDrugDrugs
effects on the
nervous system
Click on a button
to view the video
video #1
Tardive dyskinesia
- a side effect of many anti-psychotic drugs
video #2
L-dopa therapy
- side effects related to treatment
of Parkinson’s disease
video #3
Catatonic rigidity
- side effect of Phenothiazine, an
anti-psychotic medication
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Drug side effects may
occur when a drug is
introduced into a
system that already is
malfunctioning, or when
the drug acts on brain
regions other than just
the intended target
area.
Basal Ganglia menu
Tardive dyskinesia
Tardive dyskinesia
Play
Movie
Tardive dyskinesia occurs as a result of long-term use of certain
anti-psychotic medications, such as those used in the treatment of
schizophrenia. Characterized by periodic involuntary movements
(tongue & mouth movements in particular), tardive dyskinesia is
addressed by halting the use of that particular drug - but the damage is
done, and the presence of these intrusive movements cannot be
reversed.
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Drug Effects menu
L-dopa therapy
L-dopa
Play
Movie
L-dopa is used to treat Parkinson’s disease.
While very effective in the earlier
stages of the disorder, symptoms continue to develop and larger doses of drug are
required. Eventually the side effects if high doses of L-dopa will impair function
and diminish quality of life. This is an example of a drug regime that allows the
symptoms of a disorder to be managed - at least for a time - but is NOT a cure for
the disorder. This example also shows three stages of drug action - prior to
treatment (poverty of movement; resting tremor; stooped posture; shuffling gait),
soon after administration (intrusive movements), and later on - during the
therapeutic phase of the drug’s action.
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Drug Effects menu
Catatonic rigidity
Play
Movie
Catatonic rigidity occurs as a side effect after long-term use of
certain anti-seizure medications. Use of modern medications has
limited the incidence of this iatrogenic disorder.
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Drug Effects menu
That ends the Basal Ganglia tutorial!
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Basal Ganglia menu