C J Long
Overview of Topics
- Trace the pyramidal system and discuss its basic function.
- Discuss the similarities and differences between the pyramidal and extrapyramidal systems.
- Explain the basic differences between the neostriatum and paleostriatum.
- Explain the importance of the substantia nigra in extrapyramidal functions.
- Explain the function of the COEPS.
- Definition: motor system with cell bodies in cortex & axons terminating directly on the motor neuron pool.
- Betz cells in motor cortex make up only 3% of this tract.
- Thought to be voluntary motor system while extrapyramidal is involuntary
- Involved in instigating, terminating, and altering movement.
- Functions to relate behavior to environment by use of sensory feedback.
- Precentral gyrus controls individual movements
- Premotor region (plan & integration of sequences of movements)
- Motor homunculus -- Organization inverted -- head at bottom
- Motor cortex area conforms to innervation ratio
- Muscle vs. movement localization controversy
Cortico-spinal and Cortico-bulbar paths:
- Axons arise from motor areas of neocortex
- Called the Pyramidal tract
- Pass through the Coronal radiata
- Through the Cerebral peduncles
- Decussation (cross) -- in brain stem -- 80%
- Forms Lateral Corticospinal tract
- Uncrossed fibers form the ventral corticospinal tract
- Axons originate - cortex terminate -spinal cord:
- In (motor neuron pool)
- Directly on visceral motor neurons
- Mostly on accessory cells medial to tract
- Connecting neurons -- necessary where fiber must mediate excitor and inhibitor function
- Two synapses
- One bypassed with repeated stimulation
- Corticobulbar tract
- Caudate nucleus - lateral wall of lateral ventricle,
medial to internal capsule
- Putamen -- lateral to internal capsule
- Both formed by many short axon cells
- Afferent input --
- (1) thalamus, &
- (2) cortex
- Efferent -- to other segment of globus pallidus, then to lower structures
Paleostriatum (globus pallidus)
- Separated from putamen by thin external medullary lamina
- Two globus pallidus (GP) layers separated by internal medullary lamina
- afferent -- from neostriatum mainly to outer G.P. but some to inner
- inferior thalamic peduncle relays fibers from medial nucleus & centrum medianum to G.P.
- all extrapyramidal influences to the spinal cord are relayed via the
- reticulospinal and cerebrospinal paths
- Thalamic connection considered as part of a feedback circuit to cortex
Affiliates of the Motor System
- Substantia nigra
- Neostriatum direct or paleostriatum
- Also feedback from other areas
- Feedback to basal ganglia
- RF and red nucleus
- Waystation for COEPS
- Discharge to rubo- & reticulospinal tract.
- Subthalamic nuclei
- Damage -- involuntary movements in limbs to opposite side
- Releasor phenomena
- Caudalward "cascade" conduction
- Thalamus and cortex ----> neostriatum ----->
- Structures (red & reticular nuclei) -
- Reticulo- & rubrospinal tracts ----> motor pool