08aStart of Motor Systems: Indirect tracts basal ganglia feedback loop, cerebellar feedback loop(Associated with material in Chapters 13, 14, and a bit of 15)
Overview of the motor systems • Extrapyramidal systems • Brainstem to spinal cord (indirect activation) • Feedback loop to direct system via basal ganglia • Cerebellar system • Feedback loop to direct system via cerebellum • Pyramidal systems (direct activation) • corticospinal • corticonuclear (corticobulbar)
Extrapyramidal system • Indirect activation pathways • Basal ganglia feedback loop
Major motor system/group: Extrapyramidal system (outside of pyramidal system) • Indirect activation pathways, inhibited by cortical inputs • Maintain muscle tone, body posture, and reflex responses of larger muscle groups • Tracts from brainstem to spinal cord • Reticulospinal (muscle tone, stabilize proximal body parts) • Vestibulospinal (maintain antigravity tone for overall posture) • Tectospinal (reactive orienting head and eye movements when there is a sudden visual, auditory, or somatosensory stimulus) • Rubrospinal (functions in rudimentary way like corticospinal) • Feedback loop from cortex to basal ganglia and back to cortex • Help with movement initiation (cf. hypokinetic dyskinesia) • Help with movement inhibition (cf. hyperkinetic dyskinesia)
Basal ganglia feedback loop: Helps w/ movement initiation and inhibition Cortex to basal ganglia to thalamus to cortex • Remember basal ganglia? • Caudate nucleus • Putamen • Globuspallidus • Subthalamic nucleus • Substantianigra • Problem with movement initiation: Parkinson’s disease (subst. nigra) Hypokinetic dyskinesia • Problem with movement inhibition: Hyperkinetic dyskinesia Connections between and among the basal ganglia are both excitatory and inhibitory
Major motor system/group:Cerebellar feedback loop • Cerebellar system (pp. 143-146 in W&A; pp. 354-355 in W’r; handout with “figures 42-3 and 41-12” on it) • Coordinates movements via feedback loop from cortex to cerebellum to cortex • Puts rough movements together into smooth, coordinated action • When cerebellum or cerebellar feedback loop is damaged, it results in ataxia (discoordination). In speech system, this is called ataxic dysarthria.
Feedback loop, cerebellum: coordinates movement Cortex to pons to cerebellum to VL of thalamus back to cortex When cerebellum or cerebellar feedback loop is damaged, or when sensory inputs to cerebellum are damaged it results in ataxia (discoordination). In speech system, this is called ataxic dysarthria. What inputs is cerebellum using to accomplish this job?
Thus, motor feedback loops • Help initiate and inhibit movements (basal ganglia feedback loop) • Help smoothen and coordinate movements (cerebellar feedback loop)