Basal Ganglia (Exam 2) Flashcards
What is the basal ganglia and what does it influence?
- Collection of gray matter nuclei located deep within the white matter of the cerebral hemisphere
- Influence the descending motor system without directly projecting to periphery
What are the main components of the Basal Ganglia?
- Caudate Nucleus
- Putamen
- Globus Pallidus (Internal & External Sement)
- Subthalamic Nucleus
- Substantia nigra
What makes up the striatum?
- Caudate nucleus
- Putamen
What makes up the lentiform nucleus?
Putamen
Globus Pallidus (internal & external segment)
In the striatum what separates and connects the caudate nucleus & putamen?
- Separated by internal capsule
- Connected by cellular bridges
What is the subthalamic nucleus and what is it derived from?
- Spindle or cigar shaped structures just under thalamus
- Derived embryologically from midbrain
Substantia nigra pars reticulate is what part of the substatia nigra? what is it?
- Ventral portion
- Cells similar to globus pallidus
Substantia nigra pars compact is what part of the substantia nigra and what comes from there?
- Dorsal portion
- Dopamine producing neurons
What arteries supply blood to the basal ganglia?
- Lenticulostriate (branches of MCA)
- Anterior choroidal (branch of ICA)
- Recurrent artery of Heubner (branch of ACA)
Describe the motor channel of the Basal Ganglia
Function?
Thalamic Relay Nuclei?
Cortical Targets of Output?
Function: General motor control
Thalamic Relay Nuclei: Ventral lateral nucleus & ventral anterior nucleus
Cortical Target of Output: Supplementary motor area, premotor cortex, primary motor cortex
Describe the Oculomotor channel of the Basal Ganglia
Function?
Thalamic Relay Nuclei?
Cortical Targets of Output?
Function: Regulation of eye movements
Thalamic Relay Nuclei: Ventral anterior nucleus & Mediodorsal nucleus
Cortical Targets of Outputs: Frontal eye fields, supplementary eye fields
Describe the prefrontal channel of the Basal Ganglia
Function?
Thalamic Relay Nuclei?
Cortical Targets of Output?
Function: Cognitive functions
Thalamic Relay Nuclei: Ventral anterior nucleus & mediodorsal nucleus
Cortical Target of Output: prefrontal cortex
Describe the limbic channel of the Basal Ganglia
Function?
Thalamic Relay Nuclei?
Cortical Targets of Output?
Function: Regulation of emotions & motivational drives
Thalamic Relay Nuclei: Mediodorsal nucleus & ventral anterior nucleus
Cortical Target of Outputs: Anterior cingulate gyrus, orbital frontal cortex
What are the 3 thalamic relay nuclei?
- Ventral lateral nucleus
- Ventral anterior nucleus
- Mediodorsal nucleus
Inputs to the Basal Ganglia, what is the neurotransmitter coming from the area and is it excitatory or inhibitory?
- Cerebral Cortex
- Substantia Nigra pars compacta
- Intralaminar nuclei of thalamus
- Cerebral Cortex: glutamate (excitatory)
- Substantia Nigra pars compacts: Dopamine (excitatory/inhibitory)
- Intralaminar nuclei of thalamus: Glutamate (excitatory)
What are the modulatory inputs from subcortical systems?
- Acetylcholine
- Serotonin
- Noradrenalin
- Histamine
What is the input nuclei to the Basal Ganglia?
Striatum
What are the output nuclei from the Basal Ganglia?
- Globus pallidus internal segment (GPi) (motor control of body)
- Substantia nigra pars reticulate (SNr) (Motor control of head & neck)
Describe the Direct pathway broadly
- Input from cortex to striatum
- Striatum connect directly to GPi/SNr
- Output to thalamic nuclei
Within the Direct pathway what neurotransmitter does each area give off and it it inhibitory or excitatory?
Cortex: Glutamate (Excitatory)
Striatum: GABA & Substance P (Inhibitory)
GPi/SNr: GABA (inhibitory)
Thalamus: Glutamate (excitatory)
What does the direct pathway allow and how does it happen?
- Allows movement to occur
- Excitation of the basal ganglia by the cortex leads to increased excitation of the motor cortex by disinhibition of the thalamus
Describe broadly the Indirect Pathway
- Input from cortex to striatum
- Striatum connects indirectly to GPi/SNr by stopping at the globus pallidus external segment and then the sub thalamic nuclei
- Output to thalamic nuclei
Within the indirect pathway what neurotransmitter does each area give off and is it inhibitory or excitatory?
Cortex: Glutamate (Excitatory)
Striatum: GABA & Enkephalin (Inhibitory)
GPe: GABA (inhibitory)
STN: Glutamate (excitatory)
GPi/SNr: GABA (inhibitory)
In regards to the indirect pathway, in the resting state what is tonically active?
Both output nuclei (GPi/SNr) & GPe
In regards to the indirect pathway what is the basal ganglia doing to the thalamus and what happens with excitation?
- At rest basal ganglia is inhibiting the thalamus
- With excitation of the indirect pathway by the cortex inhibitors outflow is increased
Overall what does the indirect pathway do ti movement?
- Inhibits unwanted movements
When is dopamine excitatory and when is it inhibitory?
- Dopamine is excitatory when it bind to D1 receptors of the direct pathway
- Dopamine is inhibitory when it binds to D2 receptors of the indirect pathway
What effect does dopamine have on the direct pathway?
- Dopamine increase activity of the direct pathway
- Promotes movement
What effect does dopamine have on the indirect pathway?
- Dopamine inhibits the activity of the indirect pathway
- It inhibits movement inhibition
- Promotes movement
Who is broadly categorized as having a movement disorder?
Patients with lesions or damage to the basal ganglia present with abnormal movements and movement patterns
What is the presentation of those with a hyperkinetic movement disorder?
- Excessive
- Uncontrolled
- Involuntary movement
What is the presentation of those with a hypokinetic movement disorder?
- Rigidity
- Slowness
- Difficulty initiating movements
If a lesion is unilateral to the basal ganglia where would the movement disorder symptoms be?
Contralateral
In addition to motor symptoms what else can disorder of the basal ganglia cause?
Dysfunction in control of eye movements, cognition & emotional regulation
What is bradykinesia?
slow movement
What is hypokinesia?
Small movement or decreased amount of movement
What is akinesia?
Absence of movement
What are bradykinesia, hypokinesia & akinesia caused by?
- Increased inhibitory outflow from the basal ganglia to the thalamus
- May result from lesions in several regions
- Common symptoms associated with Parkinson’s disease
Is rigidity velocity or directional dependent?
No
What is lead pipe rigidity?
Continuous resistance through range
What is cogwheel rigidity?
ratchet-like interruptions in tone felt throughout range
what is dystonia?
Co-contraction of agonist & antagonist muscles resulting in abnormal distorting positions of limbs, trunk or face
Describe dystonia
- Tend to be slower & somewhat sustained
- Generalized, unilateral or focal
- Treated with anticholinergic medications or Botox
- Occurs with many disorders of basal ganglia
- Commonly seen with acute or long term use of dopaminergic antagonist
What is athetosis?
Writhing, twisting movements of limbs, face & trunk
What is chorea?
- Nearly continuous involuntary movements of extremities, trunk, neck, face & respiratory muscles
- Low amplitude (may conceal w/ voluntary movements)
- Large amplitude (may disrupt voluntary movements)
What is ballismus?
Larger amplitude movements of proximal limb movements with rotary or flinging quality
What is a tremor?
Rhythmic or semi-rhythmic oscillating movements
What is a resting tremor?
- Most prominent when limbs are relaxed
- Common with Parkinson’s disease
What is Postural tremor?
- Seen when holding limbs active but still
What is intention tremor?
Occurs when patients attempts to move limb to a target
What is Parkinson’s Disease?
- Common idiopathic neurodegenerative disorder
- Loss of dopaminergic neurons in substantia nigra pars compacta
What are some common symptoms of Parkinson’s disease?
- Resting tremor
- Bradykinesia
- Rigidity
- Postural instability/ gait disturbance
In Parkinson’s disease what impact would loss of dopamine have on the direct pathway?
- Less excitation of D1 receptors
- Less activation of direct pathway
- Less disinhibition
- Less Movement
In Parkinson’s disease what impact would loss of dopamine have on the indirect pathway?
- Less inhibition of D2 receptors
- Less inhibition of the indirect pathway
- More inhibitory outflow from BG to thalamus
- Less movement
Overall in Parkison individuals have less dopamine what impact does this have on movement?
- Inhibitory outflow of Basal Ganglia to thalamus is unusually high in individuals with too little dopamine
- Movement is less likely to occur
- Hypokinetic Movement Disorder
What are some red flags that would lead you to believe that it is not idiopathic Parkinsons?
- More symmetrical
- Rapidly progressing
- Little response to dopamine
- Multiple system atrophy
- Progressive supra nuclear palsy
- Dementia with Lewy bodies
- Corticobasal degeneration
- Wilson’s dises
- Drug induce Parkinsonism
What is Huntington’s Disease?
- Autosomal dominant neurodegenerative condition
- Progressive atrophy of striatum
- Initially degeneration of enkephalin containing stratal neurons
- Later degeneration of all striatal neurons
What are clinical symptoms of Huntington’s disease?
- Chromatic movement disorder
- Abnormal eye movements
- Dementia
- Psychiatric & emotional disturbances
How would degeneration of enkephalin- containing striatal neurons impact on the function & output of the basal ganglia?
- Enkephalin containing neurons are specifically those with D2 receptors that function as part of INDIRECT pathway
- Unable to inhibit GPe so it continues to inhibit the STN
- STN is unable to excite the output nuclei to increase inhibition
- Less inhibition of unwanted movement (HYPERkinetic movement disorder)
How would degeneration of all striatal neurons impact on the function & output of the basal ganglia?
- Indirect
- Reduced inhibition of unwanted movement
- Direct
- Increased inhibition of movement
Huntington’s disease is what movement in beginning and what movement disorder in end?
Beginning disease is hyperkinetic movement disorder
-Later stages more hypo kinetic
Describe stereotactic neurosurgery
- External reference system place on patient & CT or MRI performed
- Allows computer calculation of exact brain region in relation to the external reference system
- Therapeutic ablation of brain tissue in specific regions
- Lesions at specific locations can be used to alter function of basal ganglia in individuals with movement disorders
- Irreversible
Describe Deep brain stimulation
- Electrodes placed in deep brain structures
- Stimulation causes a depolarization block
- Reversible dysfunction of neurons at the tip of the electrode
- Reversible and adjustable
What locations are targeted during deep brain stimulation when treating Parkinson’s Disease?
- Subthalamic nucleus
- Globus pallidus (internal segment)
