week 12 basal ganglia

week 12 basal ganglia

1. basal ganglia

   • releasing/stopping movements - group of nuclei in mid brain (can't see, have to cut into brain)
   • transmitters = glutamate, gaba and dopamine - - 2 pathways direct and indirect - motor cortex projects and receives info from basal ganglia - goes through direct pathway which is shorter and indirect which is longer - putamen = receives inputs from cortical areas -
     • direct pathway - excitatory signal from cortex -> increased inhibitory signal from putamen to gpm -> reduced inhibitory signal from GPm to thalmus -> increased excitatory signal from thalamus to motor cortex
       • indirect pathway - increased inhibitor signal from putamen to GPI -> reduced inhibitory signal from GPI to STN -> increased excitatory input to GPm -> increased inhibitory output to thalamus -> reduced excitatory output to cortex
         • BG as gain control - direct pathway - allows desired movements to occur - indirect = prevents undesired movement occurring
           • selection mechanism - different possible movements - desired movement is disinhibited - competing movements are inhibited

2. parkinsons disease

   • lack of dopamine has opposing effects on 2 pathways - underachieve direct pathway and overactive indirect pathway (increased GPm activity) - both lead to increased inhibition of the thalamus and reduced excitation of the cortex
     • treatment - L-dopa (dopamine precursor) - but can induced dyskinesias - uncontrolled movement - surgery - lesions and deep brain stimulation
       • surgery - Parkinson's from a young age particularly, surgery is quite an attractive option - deep brain stimulation- embed electrode into brain to deliver electrical stimulation to targeted area - targets = thalamus, sub thalamic nucleus, and globes pallidus -
         • deep brain stimulation - reduced effect of indirect pathway so there's less excitation of GPm so more excitation can get through to motor cortex

3. huntingtons disease

   • inherited, autosomal dominant condition - 30s or 40s - chorea - uncontrolled movements - degeneration of putmen and caudate - death from complications - no treatment at present
     • brain - cortical degeneration - enlarged lateral ventricles - under activity of indirect pathway - too much movement due to reduced inhibition of GPI so more activity going to motor cortex
       • can have difficulties with attention, executive function, speed of processing, prospective memory and emotion recognition

4. tourettes

   • simple tics e.g eye blinking, nose twitching - complex tics e.g scratching, gestures, utterances - may increase during times of stress and decrease when concentrating
     • >1000 per 100,000 (greater than 1 in 1000) - hereditary, links to obsessive compulsive behaviours - developmental
       • increased dopamine from substantia nigra - overactivity of direct pathway - leads to disinhibition of undesired movements

Images and files in the map