2. BASAL NUCLEI

3. Basal Ganglia Functions
Compare proprioceptive information and movement commands.
Sequence movements.
Regulate muscle tone and muscle force.
May be involved in selecting and inhibiting specific motor synergies.

4. Basal Ganglia Functions
Basal ganglia are vital for normal movement but they have no direct connections with lower motor neurons.
Influence LMNs:
Through planning areas of cerebral cortex.
Pedunculopontine nucleus of midbrain.

5. Basal Ganglia Functions
Basal nuclei set organism’s level of responsiveness to stimuli.
Extrapyramidal disorders are associated with basal nuclei pathology:
Negative symptoms of underresponsiveness:
Akinesias
i.e. Parkinson disease
Positive symptoms of over-responsiveness:
Choreas, athetoses, ballisms
i.e. Huntington’s chorea

6. Basal Nuclei Components
Corpus striatum
Substantia nigra (within the midbrain)
Subthalamic nuclei (diencephalon)
Red nucleus (?)
Claustrum (?)
Nucleus accumbens (?)

7. Corpus Striatum Composed of caudate nucleus + lentiform nucleus:
Striatum = caudate nucleus + putamen.
Pallidum = globus pallidus.
Putamen + globus pallidus = lentiform nucleus.
Controls large subconscious movements of the skeletal muscles.
The globus pallidus regulates muscle tone.

8. Corpus Striatum

10. Substantia Nigra Subdivisions
Dorsal pars compacta:
Has melanin containing neurons and dopaminergic neurons.
Ventral pars reticularis:
Has iron-containing glial cells.
Has serotonin and GABA (no melanin).

11. Substantial Nigra

12. Input Nuclei Striatum Receive widespread input from: Caudate nucleus
Putamen
Nucleus accumbens
Receive widespread input from:
Neocortex
Intralaminar nuclei
Substantia nigra
Dorsal raphe nucleus

13. Input Nuclei Striatum projects to:
Globus pallidus
Substantia nigra
Pars reticularis
Via gabaminergic fibers
Motor and sensory cortices project to putamen.
Association areas of all lobes project to caudate nucleus.

14. Output Nuclei Globus pallidus (medial part) Substantia nigra:
Pars reticularis
Ventral pallidum
Fibers project to:
VA/VL nuclei
Mostly inhibitory

15. General Core Circuit Cerebral cortex to: Striatum to:
Globus pallidus to:
Thalamus to:
Portions of motor cortex to:
Upper motor neurons

16. Thalamic Fasciculi Ansa lenticularis:
Consists of fibers from dorsal portion of globus pallidus.
Loops under internal capsule.
To VA/VL complex.

17. Thalamic Fasciculi Lenticular fasciculus:
Consists of fibers from ventral portion of globus pallidus.
Passes across the internal capsule.
To VA/VL complex.

18. Dopamine Neuronal System
Consists of nigrostriatal fibers
From pars compacta of substantia nigra
To striatum
Dopaminergic

19. Direct Basal Ganglia Circuit
Motor cortex projects to putamen:
Excitatory (glutamate)
Putamen projects to output nuclei (globus pallidus internus and substantia nigra reticularis):
Inhibitory (GABA and substance P)

20. Direct Basal Ganglia Circuit
Output nuclei project to motor thalamus (VA-VL) and pedunculopontine nuclei:
Inhibitory (GABA)
Ventrolateral (VA-VL) thalamus projects to motor cortex:
Excitatory
Therefore:
Increasing input to putamen increases activity in corticofugal fibers

21. Direct Basal Ganglia Circuit
Pedunculopontine nuclei project to reticulospinal and vestibulospinal pathways.
Stimulation of pedunculopontine nuclei elicit rhythmical behaviors such as locomotor patterns.

22. Indirect Basal Ganglia Circuit
Motor cortex to putamen:
Excitatory (glutamate)
Putamen to globus pallidus externus:
Inhibitory (GABA and enkephalins)
Globus pallidus externus to subthalamic nuclei:
Inhibition (GABA)

23. Indirect Basal Ganglia Circuit
Subthalamic nuclei to output nuclei (substantia nigra reticularis)
Excitatory (glutamate)
Output nuclei to VA-VL complex (motor thalamus)
Inhibitory (GABA)

24. Indirect Basal Ganglia Circuit
VA-VL complex to motor cortex:
Excitatory
Therefore: decrease in corticofugal pathways.

25. Input from Substantia Nigra Compacta
Projects to putamen:
Excitatory (dopamine)
Two kinds of receptors in basal ganglia circuit:
D1: facilitates activity in direct pathway
D2: inhibits activity in indirect pathway