08a
Start 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
• Remember basal ganglia?
–
–
–
–
–
Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia nigra
Cortex to
basal ganglia to
thalamus to
cortex
• 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
Cerebellar system feedback loop
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
What inputs is
cerebellum using to
accomplish this job?
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.
• Thus, motor feedback loops
–Help initiate and inhibit movements
(basal ganglia feedback loop)
–Help smoothen and coordinate
movements (cerebellar feedback
loop)