Flashcards in 1,59 Basal Ganglia Deck (34):
What are the 5 parts of the basal ganglia?
What sends projections in the basal ganglia?
The cortical areas involved in planning and execution of movement
Where does the basal ganglia send projections to?
Motor relay areas of the thalamus
Where does the thalamus send projections to?
Cortical areas in planning and execution
Is the thalamus excitatory or inhibitory of the cortex?
Excitatory - encourgaes cortex to send messages down
Do the basal ganglia act ipsilaterally or bilaterally?
Are there descending outputs from the basal ganglia?
No descending outputs
What does a lesion in the basal ganglia result in?
Produces unwanted movements - because it acts inhibitory
Explain the putamen circuit....
Prefrontal, premotor and somatosensory cortex
Globus pallidus internal and external
Substantia nigra or subthalamic nucleus
Ventroanterior or Ventrolateral nuclei of the thalamus
Primary motor cortex or sma
What is the function of the putamen circuit?
Subconscious execution of learned patterns of movement
Writing, cutting with scissors and hammering nails etc...
Explain the caudate circuit...
Prefrontal, Premotor, Somatosensory areas
Putamen or globus pallidus
ventral anterior or lateral nuclei of thalamus
What is the function of the caudate circuit?
Cognitive planning of moving
What would happen if there was a lesion in the caudate circuit?
Lesion can cause an inability to plan and initiate a movement
What are D1 (receptor) cells?
Located in striatum
Excited by dopamine from the substantial nigra
excited by glutamergic projections from the cortex
What happens when D1 cells are excited?
Increases inhibition of Globus Pallidus internal
Releases tonic inhibition of thalamus (less inhibition) - VA/VL
Excitation of Cortex
What makes up the striatum?
Caudate and Putamen
What is the function of the direct pathway?
Increases motor activity
What is the function of the indirect pathway?
Decreases motor activity - inhibits unwanted movement
What are D2 (receptor) cells?
Located in the striatum
Excited by cortical input
Inhibited by dopamine
What happens when D2 receptors are excited?
Increases inhibition of globus palidus external
Decreases inhibition of subthalamic nucleus
Increases excitation of globus pallidus internal
Increases inhibition of the thalamus
Reduces thalamic excitation of the cortex
Which neurotransmitters stimulate and inhibit?
GLUT - stimulates
GABA - inhibits
What do the cholinergic neurones in the striatum do?
Opposite to dopamine
Inhibit the direct pathway
Excite indirect pathway
Net - decreased motor activity
What happens if the cholinergic neurones in the striatum are lost?
Increased motor activity - Huntington's disease
Explain hypokinetical disorders?
• insufficient direct pathway output
• excess indirect pathway output
Loss of dopamine
Explain hyperkinetical disorders?
• excess direct pathway output
insufficient indirect pathway output
What is the pathophysiology of Parkinson's?
Loss of nigrostriatal DA projections
What are the symptoms of Parkinson's?
Tremor at rest - pill rolling
(no tremor - everything's gone)
Impairment of postural reflexes
What happens to the direct and indirect pathways in Parkinson's?
Indirect pathway - normally inhibited by D2 is released
Direct pathway - normal excited by D1 is diminished
What is L-DOPA?
This is initially effective, but after 5-10 years, 50% of patients develop DOPA-induced dyskinesia.
What other treatment is available for Parkinson's?
Deep brain stimulation
The activity of the subthalamic nucleus (STN) is increased in Parkinson’s.
Bilateral STN stimulating electrodes: high frequency stimulation inactivates the STN.
What causes hyperkinetic disorders?
Caused by lesions to caudate /putamen / globus pallidus; Chorea (twitches) ; Athetosis (changeable or writhing movements); Dystonia (torsion spasm).
What is the pathophysiology of Huntington's disease?
• Atrophy of striatum (caudate + putamen)
• Loss of striatal GABAergic neurons reducing inhibition of thalamus leading to increased cortical excitation
• Neuropathological sequence
1st: loss of striatal GABA/enkephalin/D2-R neurons (indirect pathway)
2nd: loss of striatal GABA/dynorphin/D1-R neurons (direct pathway) & cortical atrophy
What are the symptoms of Huntington's disease?
Chorea (brief, involuntary movements)
dystonia (abnormal postures)
Executive function (complex tasks)
Recent and remote memory (poor retrieval)
Death within 10-25 years (often from pneumonia)