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45 Cards in this Set
- Front
- Back
In general, what do lesions in the basal ganglia result in?
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1. movement disorders
2. May also cause significant impairment in cognitive and perceptual functions and mentations |
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How are the basal ganglia organized?
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Anatomically and functionally in parallel circuits
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T/F - the basal ganglia operate primarily by disinhibition?
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True - excitatory effects are achieved by removal of synaptic inhibition rather than by increasing synaptic excitation
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In general, how are diseases of the basal ganglia characterized?
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Disruption of neurochemical interactions/transmission -- not all diseases result from the loss of a single NT, but rather specific neurochemical disruptions do occur in all diseases.
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The basal ganglia consists of what 5 interconnected subcortical nuclei?
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1. caudate n.
2. putamen 3. globus pallidus 4. subthalamic n. 5. substantia nigra |
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From what embryological structure does the caudate and putamen form?
Are these the major input or output to the basal ganglia? |
1. telecephalon
2. input |
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What is the major neuron in the caudate and putamen, and what is the main NT?
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1. medium spiny neuron
2. GABA |
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From what embryological structure does the globus pallidus form?
What's the main NT used? |
1. diencephalon
2. GABA |
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From what embryological structure does the subthalamic n. form?
What NT is used and what is unique about this? |
1. diencephalon
2. glutamate -- it is the only excitatory nucleus in the basal ganglia |
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In what part of the brain is the substantia nigra located?
Whats the major NTs of the pars reticulata and the pars compacta? |
1. midbrain
2. reticulata --> GABA 3. compacta --> dopamine |
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The most important input to the basal ganglia comes from the ____ and virtually all the axons terminate in the _____?
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1. cortex
2. striatum |
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From where in the cerebral cortex does the basal ganglia receive input?
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Everywhere -- including motor, sensory, association, and limbic areas
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Is the input to the basal ganglia topographically organized?
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YES
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What are the inputs to the putamen mainly involved with?
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motor control
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What are the inputs to the caudate mainly involved with?
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1. eye movements
2. cognitive function |
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What are the inputs to the ventral striatum (n. accumbens) mainly involved with?
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limbic functions
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What is the function of the Direct Pathway?
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Aids in cortically activated movement execution (facilitates the flow of information through the thalamus by disinhibition)
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Name the steps in the direct pathway.
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Cortex --> (+) putamen --> (-) globus pallidus interna --> (-) thalamus --> (+) cortex
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What is the function of the Indirect Pathway?
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Prevents unintended movements (inhibits the flow of information through the thalamus, also by disinhibition)
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Name the steps in the indirect pathway.
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Cortex --> (+) putamen --> (-) globus pallidus externa --> (-) subthalamic n. --> (+) globus pallidus interna --> (-) thalamus --> (+) cortex
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What are the NTs of the striatum?
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1. GABA / Substance P in the DIRECT pathway
2. GABA / Enkephalin in the INDIRECT pathway |
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What is the key integration point in both direct and indirect pathways?
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The GPi (firing decreases in direct pathway and increases in indirect pathway)
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What is the role of the substantia nigra in the direct and indirect pathways?
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the SNpc projects dopamine to the striatum to modulate both pathways, ultimately by promoting movement.
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How does the SNpc promote movement in both direct and indirect pathways?
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1. Direct - SNpc --> (+) striatum via D1 receptors
2. Indirect - SNpc --> (-) striatum via D2 receptors |
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Disorders/lesions of the basal ganglia lead to what types of signs?
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1. hyperkinetic (positive) signs; results from enhanced direct pathway and diminished indirect
2. hypokinetic (negative) signs; results from enhanced indirect pathway and diminished direct |
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Are negative signs in diseases of the basal ganglia a result of muscle weakness?
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No -- it's due to loss of normal control, e.g. poor reduction in tension by antagonist muscles --> leads to rigidity
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Name two examples of hypokinetic disturbances
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1. bradykinesia - slow movement
2. akinesia - impairment of the initiation of movement |
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Name three examples of hyperkinetic disturbances
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1. ballism - uncontrolled flinging of upper and lower extremities
2. choreiform movements - involuntary "dance-like" spasmodic movements of the limbs 3. athetoid movements - writhing or snake-like movements of the distal extremities |
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What will a lesion in the neostriatum (caudate + putamen) result in?
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hypokinetic disturbance; primary affects direct pathway; GPi fires more and causes thalamus to fire less
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What will a lesion in the subthalamic n. on one side result in?
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hemiballism; primarily affects indirect pathway; GPi fires less and causes thalamus fires more
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What does Parkinson's disease lead to by affecting the direct/indirect pathways?
How are firing patterns in direct/indirect pathways affected? |
1. hypokinesis
2. profound loss of DA reduces firing in direct pathway and reduces inhibition in indirect pathway |
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What are symptoms in Parkinson's disease?
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1. akinesia
2. bradykinesia 3. rigidity 4. pill-rolling tremor (resting tremor) 5. paucity of movement 6. shuffled gait and flexed posture 7. masked face (reptilian stare) |
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What is the mainstay treatment of Parkinson's disease?
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L-DOPA (can cross the BBB) + Carbidopa (inhibits peripheral DA synthesis)
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What designer drug contaminant is metabolized into a toxic compound causing a Parkinson-like syndrome?
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MPTP - a meperidine analog
(1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine) |
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What does Huntington's disease lead to by affecting the direct/indirect pathways? Which pathway is initially affected?
What's the genetic inheritance pattern? |
1. Absent mindedness, irritability, clumsiness, and falls in the early stages
2. Hyperkinesis gradually begins (e.g. chorea) --> seems to target the indirect pathway initially 3. Autosomal dominance of CAG repeats. |
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What basal ganglia structure is affected in Huntington's disease? What NTs are lost because of this?
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Striatum (primarily the caudate) that results in loss of ACh and GABA
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What is the age on onset for Huntington's? What is the prognosis?
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1. Late onset - usually in 30s-40s
2. Pts show increasing dementia and die within 15-20 years after onset. |
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What chromosome has been identified as a possible cause for the degeneration of neurons in Huntington's?
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Mutation on chromosome 4; may be related to excitotoxicity
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Name three similarities between basal ganglia and cerebellar function
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1. both form major subcortical loops that control movement
2. both receive major inputs from the cortex 3. both project back to the cortex via the thalamus |
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Name 3 important differences between basal ganglia and cerebellar function.
What do these differences suggest? |
1. BG receives input from entire cortex; CB only from sensory/motor corticies
2. CB output is direct to the premotor and motor corticies while the BG also projects to the prefrontal association cortex 3. CB receives somatic sensory info directly from the spinal cord and has many afferent/efferent connections with brainstem nuclei. The BG has few connections to the brainstem and no connections directly to the spinal cord. --> the CB is directly involved in execution of movement while the BG are involved with higher-order and cognitive aspects of movement (e.g. planning and execution of complex motor strategies). The BG also has limbic associations which suggests that it is involved with many other non-motor control functions, unlike the CB. |
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What motor function is the dentate nucleus primarily responsible for?
Interpositus? Fastigial? |
Dentate --> motor planning
Interpositus --> motor execution Fastigial --> Balance and eye movement |
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What do lesions of the cerebellum cause?
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1. hypotonia (low muscle tone)
2. ataxia (uncoordinated walking) 3. dysmetria (an aspect of ataxia, in which the ability to control the distance, power, and speed of an act is impaired) 4. dysdiadochokinesis (difficulty making rapid alternating movements) 5. intention tremor (occurs during the performance of precise voluntary movements) |
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Cooling the deep cerebellar nuclei (mainly the interposed n.) leads to what?
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Oscillating limb movements resulting from lack of cerebellar coordination of opposing muscles. In general, limb instability results.
--> CB is important for how long stretch reflexes are engaged |
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How does the movement disorders in cerebellar disease compare to Parkinson's disease?
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In a reaching motion, CB disease has longer latency and good ballistic movement, but the end position cannot be maintained
In Parkinson's, there is a delayed onset of movement and ballistic movement is slow (suggesting a problem in feed-forward control). However, the end position is stable once they get there. |
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How does the cerebellum participate in higher-order functions?
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1. activity in the dentate is significantly greater when the patient is mentally/cognitively active during movement
2. the CB also participates in motor learning |