08a08a

Start of Motor Systems: Start of Motor Systems: Indirect tracts Indirect tracts

basal ganglia feedback loop, basal ganglia feedback loop, cerebellar feedback loopcerebellar feedback loop

(Associated with material in Chapters (Associated with material in Chapters 13, 14, and a bit of 15)13, 14, and a bit of 15)

Overview of the motor Overview of the motor systemssystems

• Extrapyramidal systemsExtrapyramidal systems– Brainstem to spinal cord (indirect activation)Brainstem to spinal cord (indirect activation)– Feedback loop to direct system via basal gangliaFeedback loop to direct system via basal ganglia

• Cerebellar systemCerebellar system– Feedback loop to direct system via cerebellumFeedback loop to direct system via cerebellum

• Pyramidal systems (direct activation)Pyramidal systems (direct activation)– corticospinalcorticospinal– corticonuclear (corticobulbar)corticonuclear (corticobulbar)

Extrapyramidal systemExtrapyramidal system

• Indirect activation pathwaysIndirect activation pathways

• Basal ganglia feedback loopBasal ganglia feedback loop

Major motor Major motor system/groupsystem/group: : Extrapyramidal system Extrapyramidal system (outside of pyramidal (outside of pyramidal system)system)• Indirect activation pathways, inhibited by cortical inputsIndirect activation pathways, inhibited by cortical inputs– Maintain muscle tone, body posture, and reflex responses of Maintain muscle tone, body posture, and reflex responses of

larger muscle groupslarger muscle groups– Tracts from brainstem to spinal cordTracts from brainstem to spinal cord

•Reticulospinal (muscle tone, stabilize proximal body parts) Reticulospinal (muscle tone, stabilize proximal body parts)

•Vestibulospinal (maintain antigravity tone for overall posture)Vestibulospinal (maintain antigravity tone for overall posture)

•Tectospinal (reactive orienting head and eye movements Tectospinal (reactive orienting head and eye movements when there is a sudden visual, auditory, or somatosensory when there is a sudden visual, auditory, or somatosensory stimulus)stimulus)

•Rubrospinal (functions in Rubrospinal (functions in rudimentaryrudimentary way like corticospinal) way like corticospinal)

• Feedback loop Feedback loop from cortex to basal ganglia and back to cortexfrom cortex to basal ganglia and back to cortex– Help with movement initiation (cf. hypokinetic dyskinesia)Help with movement initiation (cf. hypokinetic dyskinesia)– Help with movement inhibition (cf. hyperkinetic dyskinesia)Help with movement inhibition (cf. hyperkinetic dyskinesia)

Basal ganglia Basal ganglia feedback loop: feedback loop: Helps w/ movement Helps w/ movement initiation and initiation and inhibitioninhibition • Remember basal ganglia?Remember basal ganglia?

– Caudate nucleusCaudate nucleus– PutamenPutamen– Globus pallidusGlobus pallidus– Subthalamic nucleusSubthalamic nucleus– Substantia nigraSubstantia nigra

• Problem with movement initiation: Problem with movement initiation: Parkinson’s disease (subst. nigra)Parkinson’s disease (subst. nigra)

Hypokinetic dyskinesiaHypokinetic dyskinesia

• Problem with movement inhibition: Problem with movement inhibition: Hyperkinetic dyskinesiaHyperkinetic dyskinesia

Cortex tobasal ganglia tothalamus tocortex

Connections between and among the basal ganglia are both excitatory and

inhibitory

Cerebellar system feedback Cerebellar system feedback looploop

Major motor Major motor system/group:system/group: Cerebellar feedback loopCerebellar feedback loop• Cerebellar system (pp. 143-146 in W&A; pp. 354-Cerebellar system (pp. 143-146 in W&A; pp. 354-

355 in W’r; handout with “figures 42-3 and 41-12” 355 in W’r; handout with “figures 42-3 and 41-12” on it)on it)– Coordinates movements via feedback loop Coordinates movements via feedback loop from from

cortex to cerebellum to cortexcortex to cerebellum to cortex– Puts rough movements together into smooth, Puts rough movements together into smooth,

coordinated actioncoordinated action

• When cerebellum or cerebellar feedback loop is When cerebellum or cerebellar feedback loop is damaged, it results in damaged, it results in ataxiaataxia (discoordination). In (discoordination). In speech system, this is called speech system, this is called ataxic dysarthriaataxic dysarthria. .

Feedback loop, Feedback loop, cerebellum: cerebellum: coordinates coordinates movementmovementCortex 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 loopsThus, motor feedback loops–Help initiate and inhibit Help initiate and inhibit movements (basal ganglia movements (basal ganglia feedback loop)feedback loop)

–Help smoothen and coordinate Help smoothen and coordinate movements (cerebellar movements (cerebellar feedback loop)feedback loop)