Extrapyramidal system: Basal Ganglia and
Cerebellum
10-8-09a
The more complex and
varied
motor activities of man and the monkey are more dependent on truly
conscious
effort, and are longer in being acquired, and longer in being reduced
to
automaticity. Yet we know that by constant and habitual repetition,
modes
of action which were acquired by long and painful education and
conscious
effort, ultimately become so easy as to be performed without
attention...
We have reason... to regard the corpora striata as the centers in which
these habitual or automatic movements become organized. -- David
Ferrier (1876) The Functions of the Brain
Basal Ganglia
- Part
of extrapyramidal
motor system
- Structure (and not every connection)
- Caudate & putamen (Collectively known as striatum)
- Modular organization
- Inputs
- cerebral cortex
- Topographically organized, e.g., frontal cortex to head,
visual cortex
to tail
- Common functional areas converge in striatum, e.g.,
frontal eye field
and
supplementary eye field
- Output to Globus pallidus and Substantia nigra
- Globus pallidus
- External segment (GPe)
- Internal segment (Gpi)
- Subthalamic nucleus (STN)
- Substantia nigra
- pars reticulata (SNpr)
- pars compacta (SNpc)
- Connectivity
- Loop: cortex basal
ganglia
thalamus
cortex
- Cerebral cortex projects to caudate or putamen
- Caudate/putamen projects to globus pallidus or subsantia
nigra pars
reticulata
- Globus pallidus or subsantia nigra pars reticulata projects
to thalamus
- Thalamus projects to cortex
- Four circuits
- Skeletal motor
- supplementary motor area (SMA) - putamen - globus pallidus
(GP) -
ventral
lateral (VL) nucleus of the thalamus
- skeletal motor movements
- Ocular motor
- frontal eye field and supplementary eye field - caudate -
SNpr -
ventral
anterior (VA) and medial dorsal (MD) thalamus and superior colliculus
- eye movements
- Dorsolateral prefrontal
- prefrontal cortex - caudate - GP - VA & MD thalamus
- working memory for guiding actions
- Lateral orbitofrontal
- orbital frontal cortex - caudate - GP - VA & MD thalamus
- behavioral set
- Anterior cingulate
- anterior cingulate cortex - ventral striatum - ventral GP -
MD thalamus
- motivation and reward
- Neurotransmitters and
connections (selective
list)
- Cortex to striatum is excitatory, glutamate
- Striatum to GPe / GPi is inhibitory, GABA
- GPe to STN is inhibitory, GABA
- STN to GPe / GPi is excitatory, glutamate
- GPi / SNpr to thalamus is inhibitory, GABA
- Thalamus to cortex is excitatory, glutamate
- Function
Updated Sep 21,
2009
