13 - Basal Ganglia Flashcards
Motor functions require a complex interaction between which areas of the brain?
Motor functions require a complex interaction between the cerebral motor cortex, the cerebellum and the basal ganglia
Describe the role of the cerebral cortex compared to the other areas involved in motor function
Although the ultimate decision to initiate an action with an intended purpose is the prerogative of the cortex, most of the precise control of starting, stopping, force, timing, duration and coordination of muscle contraction are subcortical functions
What is the specific role of the basal ganglia?
The specific role of the basal ganglia involves augmentation, facilitation or inhibition of components of complex actions including initiation and acceleration of voluntary movements, inhibition of extraneous movements and stopping volitional movements.
Corpus striatum
A subcortical part of the forebrain. It receives input from the cerebral cortex and is the primary input to the basal ganglia system
It is the “input gate” to the basal ganglia
Two nuclei of the corpus striatum
caudate nucleus
lentiform nucleus
The lentiform nucleus has two structures. What are they?
Putamen
Globus pallidus
What makes up the striatum (this is different from the corpus striatum)
Putamen (from the lentiform nucleus) Caudate nucleus (one of the two nuclei of the corpus striatum)
What is the pallidum?
The globus pallidus (from the lentiform nucleus)
Pallidum is “output gate” from basal ganglia
When we say “basal ganglia” we are actually referring to three separate structures that combine to become the basal ganglia. What are they?
1 - Corpus striatum (both nuclei)
2 - Substantia nigra
3 - Subthalamic nucleus
What is the major input to the basal ganglia?
From cortex to striatum to basal ganglia
Reminder: the striatum is made up of the putamen (from the lentiform nuclei) and the caudate nuclei
What is the main function of the caudate nuclei?
The caudate is primarily concerned with cognitive information
What is the main function of the putamen?
The putamen is primarily concerned with motor functions
Major input to basal ganglia - what do we call the fibers that run from the cortex to the striatum?
Corticostriate fibers
Major input to basal ganglia - what do we call the fibers that run from the thalamus to the striatum?
Thalamostriate fibers
Thalamus (intralaminar nuclei) to striatum (thalamus is a collection of relay nuclei)
Major input to basal ganglia - what do we call the fibers that run from the substantia nigra to the striatum?
Nigrostriatal
What is the major output from the striatum?
Striatum to pallidum- striatopallidal
Striatum to substantia nigra- striatonigral (pars reticulata)
What is the major input to the pallidum?
Striatum- Striatopallidal
Subthalamic nucleus- Subthalamic fasciculus
Major output of basal ganglia - there are many fibers that run from the pallidum to the thalamus (then to the cortex). What are they?
Pallidothalamic fibers (pars interna of globus pallidus)
1 - Lenticular fasciculus (dorsal)
2 - Ansa lenticularis (ventral)
3 - Thalamic fasciculus (joining (1) and (2) together en route to thalamic nuclei (ventral anterior (VA), ventral lateral (VL)
Note: Thalamic fasciculus also carries cerebellar fibers to same nuclei.
Major output of basal ganglia - what do we call the fibers that run from the pallidum to the subthalamus?
Pallidosubthalamic fibers- to subthalamic nucleus
Major output of basal ganglia - what do we call the fibers that run from the pallidum to the substantia nigra?
Pallidonigral fibers- to substantia nigra (pars compacta)
Major output of basal ganglia - what do we call the fibers that run from the thalamus to the cortex?
Thalamocortical fibers to premotor, supplementary motor cortex
Did you notice any RECIPROCAL connections in the above fibers? What are they?
Striatum and substantia nigra- striatonigral, nigrostriatal
Pallidum and subthalamic nucleus- subthalamic fasciculus
There are four circuits associated with the basal ganglia
There are four parallel pathways each conveying distinctive information to basal ganglia
1 - Motor loop
2 - Association (cognitive)
3 - Oculomotor
4 - Limbic
Describe the motor loop
A. Motor loop- information relayed from basal ganglia to motor cortical areas where they influence upper motor neurons of corticospinal, corticonuclear and other motor tracts.
Describe the association (cognitive) circuit
Association (cognitive)- planning and direction of movement.
Describe the oculomotor circuit
Oculomotor- integration of eye movements and visual guidance
Describe the limbic circuit
Limbic- emotional and motivational influences on movements
Each of the four circuits has two loops - what are they?
Open loops and closed loops
We will focus on CLOSED loops
Closed loops
Closed loops of each circuit originate from a particular cortical area, cycles through the basal ganglia, and returns to originating cortical area.
ALWAYS... Cortex Striatum Pallidus Thalamus
Open loops
- Open loops feed related and associated cortical information into the closed loop.
What are the four components of the closed motor loop?
Cortex (supplementary motor cortex - area 6)
Striatum (caudate nucleus and putamen)
Pallidum (globus pallidus and substantia nigra)
Thalamus (ventral lateral nucleus of the thalamus)
EMPHASIZED THIS
What are the four components of the closed association loop?
Cortex (prefrontal cortex - areas 9, 10)
Striatum (caudate nucleus - head)
Pallidum (globus pallidus and substantia nigra)
Thalamus (ventral anterior nucleus and dorsomedial nucleus of the thalamus)
What are the four components of the closed oculomotor loop?
Cortex (frontal eye field - area 8 for visual tracking)
Striatum (caudate nucleus)
Pallidum (globus pallidus and substantia nigra)
Thalamus (ventral anterior nucleus and dorsomedial nucleus of the thalamus)
What are the four components of the closed limbic loop?
Cortex (anterior cingulate gyrus - area 24, and orbitofrontal cortex - area 10, 11)
Striatum (ventral striatum and caudate nucleus)
Pallidum (globus pallidus and substantia nigra)
Thalamus (ventral anterior nucleus and dorsomedial nucleus of the thalamus)
What generalizations can you make about the thalamic nuclei?
VA and VL- relay signals related to movement
Mediodorsal- relay signals to frontal and limbic cortex
What is the direct pathway through the basal ganglia?
The direct path (disinhibition) allows voluntary moves
The direct pathway facilitates the flow of information through the thalamus resulting in greater excitation of the cortex. The function of the direct pathway is to release (disinhibits)
the thalamus from tonic pallidal inhibition allowing voluntary movements.
What is the indirect pathway through the basal ganglia?
The indirect path inhibits involuntary moves
The indirect pathway decreases activity in the thalamus (increased inhibition) lessening excitatory output to the cortex. The purpose is tonic suppression of inappropriate movements, but also to terminate volitional movements.
SUMMARY SLIDE
A. Striatum is the “input gate” to basal ganglia.
B. Pallidum is the “output gate” from basal ganglia
C. Thalamus is the interface between basal ganglia and cortex
D. Thalamus is excitatory to cortex
E. Pallidum is inhibitory to thalamus
F. “disinhibition” allows voluntary movements to occur
G. Tonic inhibition suppresses involuntary movements
H. NO PARALYSIS with lesions
Extrapyramidal syndromes
Clinical terminology- signs and symptoms of lesions of basal ganglia are referred to as “extrapyramidal syndromes”.
What are some extrapyramidal symptoms?
These symptoms include:
- Dystonia (continuous spasms and muscle contractions)
- Akathisia (motor restlessness)
- Parkinsonism (characteristic symptoms such as rigidity, bradykinesia, and tremor)
- Tardive dyskinesia (irregular, jerky movements)
Parkinson’s disease symptoms
- Rigidity
- Slowness of movement
- Slumped posture
- Excessive inhibition with lack of facilitation
- Resting tremor
What causes a resting tremor?
Lack of suppression of involuntary movement
What is the proximate cause of Parkinson’s disease?
Death of dopaminergic cells in pars compacta of substantia nigra
What is the therapy for Parkinson’s disease?
Therapy: L-Dopa metabolized to dopamine by dopaminergic cells
Dyskinesia
Dyskinesia – unintentional, purposeless, disorderly movements; can be hyper- or hypo-kinetic, and these occur at rest
Athetosis
Athetosis – display of slow, vermicular, involuntary movements; usually affects hands and feet; caused by degeneration of the lateral pallidum, which allows the VL nucleus of the thalamus to spontaneously fire to the motor cortex
Hemiballismus
Hemiballismus – involuntary, ballistic movements on one side of the body, affecting proximal muscles of the limbs; results from a cerebrovascular lesion of the ganglial branch of the posterior cerebral artery, which involves the contralateral subthalamic nucleus
Bradykinesia
Bradykinesia – reduced motion caused by increased inhibition from the basal ganglia
Chorea
Chorea – random, jerky movements
What two signs must be present to define Tourette’s
Motor and vocal tics
What one sign, in particular, makes Tourette’s unique among all extrapyramidal syndromes?
Vocal tics
Case 12
A 39-year-old man has had abnormal and uncontrollable movements for the past 6 months, as well as forgetfulness, obsessions, and compulsions. His wife notes some mild personality changes as well. He has become somewhat more irritable and withdrawn. These movements are spontaneous, unpredictable, and have become almost continuous. Initially his wife thought he had become “fidgety.” Abnormal behaviors as well as the extraneous movements have caused some social embarrassment. The patient’s mother died in her fifties at a psychiatric hospital. He has no more information about her. Family history is otherwise unrevealing. Examination shows obvious chorea consisting of involuntary, nonrhythmic, and persistent jerky movements of the head, neck, and arms that continue during conversation. Memory is mildly diminished. He seems very distractible and has difficulty completing motor tasks. Neurologic exam is otherwise unremarkable. MRI of the brain shows atrophy of the heads of both caudate nuclei.
