Defects in circuits

Defects in circuits

1. 1. Background - BASAL GANGLIA

   • b. Main components of the basal ganglia:
     • Corpus striatum
       • Putamen
       • Caudate
       • Ventral striatum
     • Globus pallidus (internal and external)
     • Substantia nigra
       • Pars reticulata
       • Pars compacta
     • Subthalamic nucleus
   • a. Function of the basal ganglia
     • ii. How does it with the motor pathway?
       • Nearly all regions of the neocortex project into the BG
         • After sensory information is filtered and 'fine-tuned' through, is passes through the thalamus and back to the cortex
     • i. Function
       • Coordination of executation by integrating information from multiple sources which feeds back to the cortex to smooth out movements
         • It both initiates and terminates voluntary movements, therefore inhibiting any unwanted movements
           • It does this alongside the cerebellum by regulating the activity of UPPER MOTOR NEURONS
             • NOTE: They do NOT project directly to local circuits/lower motor neurons (this is done by the spinal cord/motor regions of the cortex)
   • c. Anatomical organization of the inputs to the Basal ganglia
     • Multiple projections from the cortex into the BG exist (they are usually glutamatergic)
       • They project to the striatal neurons of the putamen
         • Neurons from the substantia nigra pars compacta innervate the putamen too
           • Meaning all inputs into the BG is reached via the striatum
             • From the BG are projections of medium spiny neurons to the globus pallidus via TWO pathways
               • 1. Projections from the striatum to the internal segment of the globus pallidus
                 • Directly through the thalamus and projects back to the ortex
               • 2. Indirect pathway as the medium spiny neurons project to the external part of the globus pallidus, there is a GABAergic projection to the subthalamic nucleus which is the only excitatory part of the BG circruit
                 • This then projects back to the globus pallidus intern, then the same pathway via the thalamus to the cortex

2. 2. MEDIUM SPINY NEURONS

   • a.
     • Project directly to the internal segment of the GPi
     • When excited by DA1 neurons, it leads to excitation through upregulation of adenylyl cyclase
       • Whereas the GPe GABAergic neurons contain D2 types of receptors, when excited they will be suppressed
         • Therefore, there are two pathways: one leading to the GPi and the other through the subthalamic nucleus with the medium spiny neurons either projecting to the GPi or GPe
   • b. How do they operate?
     • They form micro-circuits
   • iii. Direct and indirect pathway

3. 3. PARKINSON'S DISEASE

4. 4. SCHIZOPHRENIA