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Review: General Control Theory -Cortex -Basal Ganglia -Cerebellum.

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Presentation on theme: "Review: General Control Theory -Cortex -Basal Ganglia -Cerebellum."— Presentation transcript:

1 Review: General Control Theory -Cortex -Basal Ganglia -Cerebellum

2 Review: Primary M. Cortex Directionality : yellow = one cell’s firing vectors (broad) red = “best” vector No one (1) cell can generate an appropriate directional code! Population Tuning

3 Motor Cortex Topographical Orientation …great question from last time

4 Current Research Topics Conserved Topographical Organization? (Bizzi E):

5 PreMotor Cortex - Rostral Pre-Central Gyrus - Activated by cues for well-learned events (monkey) PreMotor Cortex

6 PreMotor Cortex Continued Lateral PreMotor elements - conditional tasks - fire before action - external cues (in monkey anyway) - damage = inability to select appropriate response movements Medial PreMotor elements - initiate internally / voluntarily driven motor tasks - internal cues - damage = reduced spontaneous movements

7 Primary vs. PreMotor Inputs: - Premotor Cortex - Somatosensory Cortex Inputs: - Pre-Frontal Cortex - Areas 5 and 7

8 Review Be familiar with the contribution of each particular anatomical structure / region: -Cortex 2 regions discussed -Brainstem the 3 nuclei discussed & pathways -Spinal Cord spatial significance / distribution -Local Circuitry / MNs / Muscle those properties discussed

9 Basal Ganglia (Group #3)

10

11 Anatomical Components : Globus Pallidus Corpus Striatum (striped) - caudate nucleus - putamen - ventral striatum Associated Nuclei - substantia nigra - subthalamic nuclei *

12 Basal Ganglia Function - Active before and during movements - Inputs: majority of cortex multiple parallel pathways - Output: thalamus, superior colliculus, cortex… “ Upper Motoneurons” - High levels of efferent tonic inhibition - GABAergic output Direct Pathway: interrupt tonic inhibition Indirect Pathway: internal loop increases inhibition

13 Basal Ganglia Continued Medium Spiny Neurons - majority of cells in striatum 75,000,000 (!) - labeled line - occur in patches: striosomes - normally not tonic Cerebral Cortex  Corpus Striatum (caudate & putamen)  Medium Spiny Neurons  Globus Pallidus & Substantia Nigra  Upper MNs Globus Pallidus - 1/100 number of m. spiny neurons 750,000 - INTEGRATOR - high level tonic output - GABAergic - Primary pathway back to motor cortex is via internal G. P.

14 Direct Pathway (tonic only) Normal activity of the direct pathway = hypokinesia

15 Direct Pathway (phasic activation) Reduced activity of the direct pathway (GP) = hyperkinesia

16 Enhanced activity in the indirect pathway = hypokinesia Indirect Pathway

17 Parkinson’s Disease medium spiny neurons - damage to Nigrostriatal cells - increased thalamic inhibition - seldom can coordinate movements - bursts of activity

18 Parkinson’s Disease treatments Must attenuate activity in the Globus Pallidus - l-Dopa (there are several pharmacological treatments) - thalamotomy - pallidotomy

19 Huntington’s Disease medium spiny neurons - sequence is known, protein function is not - yet - genetic test is available - excessive excitability - involuntary movements - eventual loss of mental cohesion

20 Huntington’s Disease treatments Must augment activity in the Globus Pallidus - ACh (acetylcholine) - Striatal tissue implants - genetic treatments (?)

21 Cerebellum (Group #4)

22 Anatomical Components: Cerebellar Cortex : - Spinocerebellum gross movt’s vermis - Cerebrocerebellum complex movt’s - Vestibulocerebellum posture / balance nodulus flocculus Cerebellum

23 Anatomical Components continued: Cerebellar Deep Nuclei : (All receive input from the cerebellar cortex – though functionally distinct) - Dentate (invaginations) - Fastigial - Interposed (2) Cerebellar Peduncles - Superior efferent pathways - Middle afferent pathways - Inferior Both afferent & efferent

24 Cerebellum - inputs from: pre-motor, primary motor, primary / secondary somatic, anterior parietal, secondary visual (not primary) - behavior modulation inputs: “ learning” inferior olive locus coruleus General Function (still not completely understood) - measure motor error - motor learning - output to cortex (via thalamus) and vestibular nucleus Modify activity pattern of “Upper MNs”

25 Cerebral Cortex [Report what’s happening]  Pontine Nuclei [Relay / Process]  Cerebellar Cortex [Compute error(?)]  Deep Cerebellar Nuclei  Thalamus (Cortex) & Vestibular Nucleus [Tell control centers] middle peduncle

26 Cerebellar Cell Types (inhibitory) “control the flow of information through the cerebellar cortex” Mossy Fibers : (excitatory) From:- pontine nuclei (via middle peduncle) - other pons / brainstem loci To:- deep cerebellar nuclei - granule cells Granule Cells : (most abundant in brain) From & To: cerebellar cortex… ~unipolar Give rise to: Parallel Fibers: (excitatory) Climbing Fibers : (excitatory) From:- inferior olive To:- Purkinje shaft Local Interneurons : - Basket Cells - Stellate Cells - Golgi Cells Purkinje Cells: (inhibitory) If there were a brain of the cerebellum, it would be the Purkinje cells

27 Cerebellar Cell Types Extraordinary branching integrative properties

28 Clinical Implications Normal Function (to reiterate): - Smooth motor functions (reduce error) - Coordinate target acquisition Lesion or Degeneration: - Loss of smooth movements - Rarely stop on target

29 CONCLUDING ADMONITION The ability to successfully complete an organized sequence of movements requires the appropriate coordination of MANY elements. Spatial organization (rubrospinal pathways, spinal signals, cerebellar integration) Temporal organization (cortical planning) Accuracy and uniformity (error measures, sensory integration) Sequencing (spinal circuitry)


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