Basal Ganglia Presentation PDF

Presentation by Lois Stevens Basal Ganglia Senior Lecturer Relationship with Primary Motor Cortex If we know that the BG sends information to the motor cortex and receives information from the motor cortex what can we deduce?  Basal Ganglia Consists of 5 n...

Presentation by Lois Stevens Basal Ganglia Senior Lecturer Relationship with Primary Motor Cortex If we know that the BG sends information to the motor cortex and receives information from the motor cortex what can we deduce?  Basal Ganglia Consists of 5 nuclei found in the cerebrum and the mid-brain Caudate Putamen Globus Pallidus Subthalamic nuclei Substantia Nigra Anatomy  Task Draw a simple schematic of the Corticobasal ganglia – thalamocortical loop Corticobasal Ganglia – Thalamocortical Loop Cortex Basal Ganglia Thalamus  Basal Ganglia Input Nuclei: Caudate and Putamen Output Nuclei: SNr and GPi Anatomy  Basal Ganglia Input Nuclei Cortex (Caudate and Putamen) Output Nuclei Thalamus (GPi and SNr)  Thalamus/Cortex Thalamus is excitatory to cortex and it is tonically active Thalamus +ve Cortex Output Nuclei/Thalamus Output nuclei inhibit the thalamus Output Nuclei -ve Thalamus  Direct and Indirect Pathways In fact, there are two distinct pathways that process signals through the basal ganglia: the direct pathway and the indirect pathway. These two pathways have opposite net effects on thalamic target structures.  Direct Pathway Excitation of the direct pathway has the net effect of exciting thalamic neurons (which in turn make excitatory connections onto cortical neurons).  Indirect Pathway Excitation of the indirect pathway has the net effect of inhibiting thalamic neurons (rendering them unable to excite motor cortex neurons). The normal functioning of the basal ganglia involves a proper balance between the activity of these two pathways.  Analogy Thalamus – accelerator Basal Ganglia - brake  Basal Ganglia Impairment What happens when things go wrong? Too much inhibition – hypokinetic conditions – too little movement – PD Too little inhibition – hyperkinetic conditions – too much movement - Huntington’s Disease Tourette’s/ OCD?  Relationship with Reticular Formation and Vestibular System If we know that the BG sends information to the reticular formation and vestibular nuclei what can we deduce? TONE  Effect on Postural Tone A second important BG motor circuit: GP → midbrain → reticulospinal and vestibulospinal tracts When this pathway is interrupted there is excessive contraction of postural muscles Rigidity as seen in Parkinson’s disease.  Summary Function Involved in motor control, especially selection (and de-selection) of appropriate movement at the right time via connections with the motor cortices Influences postural tone via connections with Reticular Formation and Vestibular System