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Review: General Control Theory
-Cortex-Basal Ganglia-Cerebellum
Review: Primary M. CortexDirectionality:
yellow = one cell’s firing vectors (broad)red = “best” vector
No one (1) cell can generate an appropriate directional code!Population Tuning
Motor CortexTopographical Orientation…great question from last time
Current Research TopicsConserved Topographical Organization?(Bizzi E):
PreMotor Cortex- Rostral Pre-Central Gyrus
- Activated by cues for well-learned events (monkey)
PreMotor Cortex
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
Primary vs. PreMotor
Inputs:- Premotor Cortex
- Somatosensory Cortex
Inputs:- Pre-Frontal Cortex
- Areas 5 and 7
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
Basal Ganglia(Group #3)
Anatomical Components:
Globus Pallidus
Corpus Striatum (striped)
- caudate nucleus- putamen- ventral striatum
Associated Nuclei - substantia nigra- subthalamic nuclei
*
Basal Ganglia
Function
- Active before and during movements
- Inputs: majority of cortexmultiple parallel pathways
- Output: thalamus, superior colliculus, cortex… “Upper Motoneurons”
- High levels of efferent tonic inhibition
- GABAergic outputDirect Pathway: interrupt tonic inhibitionIndirect Pathway: internal loop increases inhibition
Basal Ganglia ContinuedMedium Spiny Neurons- majority of cells in striatum
75,000,000 (!)- labeled line- occur in patches: striosomes- normally not tonic
Cerebral CortexCerebral Cortex
Corpus StriatumCorpus Striatum
(caudate & putamen)(caudate & putamen)
Medium Spiny Medium Spiny
NeuronsNeurons
Globus Pallidus &Globus Pallidus &Substantia NigraSubstantia Nigra
Upper MNsUpper 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.
Direct Pathway (tonic only)Direct Pathway (tonic only)
Normal activity of the direct pathway = hypokinesia
Direct Pathway (phasic activation)Direct Pathway (phasic activation)
Reduced activity of the direct pathway (GP) = hyperkinesia
Enhanced activity in the indirect pathway = hypokinesia
Indirect PathwayIndirect Pathway
Parkinson’s Disease
medium spiny neurons
- damage to Nigrostriatal cells
- increased thalamic inhibition- seldom can coordinate movements- bursts of activity
Parkinson’s Diseasetreatments
Must attenuate activity in the Globus Pallidus
- l-Dopa (there are several pharmacological treatments)- thalamotomy - pallidotomy
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
Huntington’s Diseasetreatments
Must augment activity in the Globus Pallidus
- ACh (acetylcholine)- Striatal tissue implants- genetic treatments (?)
http://www.macalester.edu/~psych/whathap/UBNRP/Huntington/treatmentdir.html
Cerebellum(Group #4)
Anatomical Components:
Cerebellar Cortex:- Spinocerebellum
gross movt’svermis
- Cerebrocerebellumcomplex movt’s
- Vestibulocerebellumposture / balancenodulusflocculus
Cerebellum
CerebellumAnatomical Componentscontinued:
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
Cerebellum
- inputs from:pre-motor, primary motor,primary / secondarysomatic, anterior parietal,secondary visual (not
primary)- behavior modulation inputs: “learning”
inferior olivelocus 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”Modify activity pattern of “Upper MNs”
Cerebral CortexCerebral Cortex[Report what’s happening][Report what’s happening]
Pontine NucleiPontine Nuclei
[Relay / Process][Relay / Process]
Cerebellar CortexCerebellar Cortex
[Compute error(?)][Compute error(?)]
Deep Cerebellar Deep Cerebellar
NucleiNuclei
Thalamus (Cortex) Thalamus (Cortex)
&&Vestibular NucleusVestibular Nucleus
[Tell control centers][Tell control centers]
middle peduncle
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… ~unipolarGive rise to: Parallel Fibers: (excitatory)
Climbing Fibers: (excitatory)
From: - inferior oliveTo: - 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
Cerebellar Cell Types
Extraordinarybranchingintegrative properties
Clinical ImplicationsClinical Implications
Normal Function (to reiterate):- Smooth motor functions (reduce error)- Coordinate target acquisition
Lesion or Degeneration:- Loss of smooth movements
- Rarely stop on target
CONCLUDING ADMONITIONCONCLUDING 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)