Download Cell Bio 8- Basal Ganglia Basal Ganglia: collection of gray matter

Cell Bio 8- Basal Ganglia
Basal Ganglia: collection of gray matter nuclei located deep within the white matter of the cerebral hemispheres
Striatum receives all inputs to the basal ganglia
Cell Bio 8- Basal Ganglia
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Inputs to the Basal Ganglia
The main input comes from massive projections from the entire cerebral cortex to striatum
Putamen is the most important input nucleus of the striatum for motor control pathways: most cortical inputs
are excitatory and use glutamate
Another important input is the substantia nigra pars compacta: this dopaminergic nigrostriatal pathway is
excitatory to some cells and inhibitory to others
Outputs from the Basal Ganglia
For motor control, the substantia nigra pars reticulata convey information for the head and neck, while the
internal segment of the globus pallidus conveys information for the rest of the body
 These output pathways are inhibitory and use GABA.
 The main output pathways are to the VL and VA nuclei of the thalamus via the thalamic fasciculus
Anteriolateral pathway VPL of thalamus
Sensory from face VPM
Internal Connections
 Direct pathway: travels from the striatum directly to the internal segment of the globus pallidus or the
substantia nigra pars reticulata
 Indirect Pathway: takes a detour from the striatum, first to the external segment of the globus pallidus and then
to subthalamic nucleus, before reaching the internal segment of the globus pallidus or the substantia
nigra pars reticulata
 The net effect of excitatory input from the cortex through the direct pathway will be excitation of the thalamus
 The net effect of excitation of the indirect pathway will be inhibition of the thalamus, resulting in inhibition of
movements through connections back to the cortex
GPi: globus pallidus pars interna
GPe: globus pallidus pars externa
SNr: substantia nigra pars reticulata
STN: subthalamic nucleus
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Cell Bio 8- Basal Ganglia
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Patients with basal ganglia lesions can have either hypokinetic or hyperkinetic movement disorders
Parkinson’s disease (hypokinetic): rigidity, slowness, and marked difficulty initiating movements
Huntington’s disease (hyperkinetic): uncontrolled involuntary movements produce a random pattern of jerks
and twists
Parkinson’s Disease
Is a common idiopathic disease caused by loss of dopaminergic neurons in the substantia nigra pars compacta. It
is characterized by asymmetrical ‘pill-rolling’ resting tremor, bradykinesia, rigidity, and postural instability, which
usually respond to therapy with levodopa.
The decreased blink rate and rigid and shuffling gate are typical of Parkinson’s disease. These problems result
from a decreased input from the ventrolateral (VL) nucleus of the thalamus to the motor cortex of the brain.
This input, which is modulated by the basal ganglia, normally modifies descending cortical motor output to allow
the individual to initiate voluntary movements at an appropriate pace.
o Thalamic input is modulated by the basal ganglia via two basal ganglia pathways. The extent to which
the VL nucleus is inhibited depends on the balance of activity in each pathway.
 A- Section through the midbrain from a patient who died with Parkinson’s disease. Asymmetrical pallor affecting
the right substantia nigra greater than the left can be seen, caused by degeneration of pigmented dopaminergic
neurons
 B- Typical Lewy body. It has a characteristic dense (pink) center with a lighter halo and is located in the
cytoplasm of a darkly pigmented dopaminergic neuron (Dementia with Lewy bodies for differential diagnosis)
Cell Bio 8- Basal Ganglia
Huntington’s Disease
Is an autosomal dominant neurodegenerative condition characterized by a progressive, usually choreiform
movement disorder, dementia, and psychiatric disturbances, ultimately leading to death.
 The pathologic hallmark is progressive atrophy of the striatum, especially involving the caudate nucleus.
 Usual age of onset is between 30 and 50 years, with prevalence of 4-5 cases per million.
 Subtle eye movement abnormalities can be detected before other manifestations become apparent. These are
slow saccades, impaired smooth pursuit, difficulty initiating saccades without moving the head or blinking.
 The abnormal gene is mapped on chromosome 4, and it includes a region containing multiple repeats of the
trinucleotide sequence CAG in tandem.
Behavior changes may occur before movement problems, and can include:
• Behavioral disturbances
• Hallucinations
• Irritability
• Moodiness
• Restlessness or fidgeting
• Paranoia
• Psychosis
Abnormal and unusual movements include:
• Facial movements, including grimaces
• Head turning to shift eye position
• Quick, sudden, sometimes wild jerking movements of the arms, legs, face, and other body parts
• Slow, uncontrolled movements
• Unsteady gait
Dementia that slowly gets worse, including:
• Disorientation or confusion
• Loss of judgment
• Loss of memory
• Personality changes
• Speech changes
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Cell Bio 8- Basal Ganglia
Cell Bio 8- Basal Ganglia
Bradykinetic (slowed movements) disorders can be caused by increased inhibitory basal ganglia outflow to the thalamus
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Rigidity
Increased resistance to passive movement of a limb
In spasticity, which results from upper motor neuron lesions, rigidity is velocity dependent. Resistive tone
initially increases as the muscles of the limb are stretched, but it may then decrease, giving rise to claspknife rigidity in corticospinal disorders
In contrast, rigidity caused by basal ganglia disorders tends to be more continuous throughout attempts to
bend the limb, and it has therefore been called plastic, or lead pipe rigidity
Dystonia
The patient assumes abnormal, often distorted positions of the limbs, trunk, or face that are more sustained
or slower than in athetosis
Focal dystonias include torticollis, which involves the neck muscles; blepharospasm, which involves the facial
muscles around the eyes, and spasmodic dysphonia, which involves laryngeal muscles
o Many cases of dystonia respond well to injection of botulinum toxin into the affected muscles
Athetosis is characterized by twisting movements of the limbs, face and trunk that sometimes merge with faster choreic
movements, giving rise to the term choreoathetosis
Cell Bio 8- Basal Ganglia
Ballismus: Movements of the proximal limb muscles with a larger-amplitude, more rotatory or flinging quality than
chorea
Hemiballismus (the most common type): there are unilateral flinging movements of the extremities
contralateral to a lesion in the basal ganglia
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Chorea
Is applied to movement disorders characterized nearly continuous involuntary movements that have a fluid or
jerky, constantly varying quality (dancing-like)
In mild case, low-amplitude chorea may be mistaken for fidgeting or restless movements of extremities, face or
trunk
Often incorporated into voluntary movements in an attempt to conceal their occurrence
Major cause of chorea is Huntington’s disease ( autosomal dominant neurodegenerative disorder).