1. Ch. 15: Lower Motor Neuron Circuits and Motor Control
- a model for understanding the nervous system
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2. Neural centers responsible for movement
4 interactive subsystems contribute to motor control
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3. Neural centers responsible for movement
Gray matter of spinal cord and brainstem
- local motor neurons innervate skeletal muscle cells
- motor neurons of cranial nerves from cell bodies in the brain stem
- local circuit neurons are the major source of synaptic input to the lower motor neurons.
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5. Neural centers responsible for movement
Upper motor neurons
- cell bodies in brainstem or cerebral cortex
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8. Neural centers responsible for movement
3) Cerebellum
- regulate activity of upper motor neurons
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10. Neural centers responsible for movement
4) Basal Ganglia
Regulate upper motor neurons
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12. Basal ganglia - caudate, putamen, globus pallidus
-subthalamic nucleus, substantia nigra
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13. 1) Gray matter of spinal cord and brainstem
Lower motor neurons send axons out of the brain stem and spinal cord to innervate skeletal muscles of the head and body.
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14. Gray matter of spinal cord and brainstem
Local circuit neurons
Synaptic input to lower motor neurons
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15. Gray matter of spinal cord and brainstem
Lower motor neurons convey voluntary and reflex commands to skeletel muscle
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16. Gray matter of spinal cord and brainstem
Local circuit neurons
Receive descending projections from higher brain centers
Also receive sensory input from higher brain centers
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17. Gray matter of spinal cord and brainstem
Circuits provide co-ordination between muscle groups for movement
Are the final common path for movement.
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19. 2) Upper motor neurons Cell bodies in the brainstem or cerebral cortex
Axons descend to synapse with local circuit neurons, sometimes directly onto lower motor neurons
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20. 2) Upper motor neurons In the cortex Initiate voluntary movements
Initiate complex spatiotemporal sequences of skilled movements
E.g. descending projections from the frontal lobe (primary motor cortex and lateral pre-motor cortex)
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21. 2) Upper motor neurons In the brainstem
Regulate muscle tone for orienting eyes, head and body wrt sensory information (balance, somatic, sound, vision input)
Imp. For movement and posture
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22. 3) Cerebellum
Does not directly access local circuit neurons or lower motor neurons
Regulate the upper motor neurons
Located on the dorsal suface of the pons
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23. 3) Cerebellum
Detects the difference between an intended movement and the movement that is actually performed (servomechanism)
Reduces movement error in short term and in long term (learning) eg. Riding a bike.
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24. 4) Basal ganglia
No direct access to local circuit neurons or to lower motor neurons
Regulate upper motor neurons
Suppress unwanted movement
Prepare upper motor neurons for movements to start
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25. How does thought lead to movement?
Still poorly understood
Clear picture at the level of muscles themselves.
Start with the lower motor neurons and their targets.
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26. Motor neuron - muscle relationships
Neuronal tracer injections into the cell body show the pathway on motor neuron axons
motor neuron pools are all of the motor neurons that innervate a muscle.
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27. Motor neuron - muscle relationships
Motor neuron pools run together in the spinal cord.
An orderly arrangement between the motor neuron pools and the muscles that they innervate*** - a rule for the nervous system (mapping, topography)
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28. Motor neuron - muscle relationships
Fig. 15.3
Topography
Neurons for postural muscles are medial in the cord
Neurons for the shoulders are next most lateral
Neurons for upper arms are next lateral.
Neurons for distal extremeties are most lateral.
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29. Motor neuron - muscle relationships
Spatial organization gives information about functions
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30. Motor neuron - muscle relationships
Two types of lower motor neurons in the motor neuron pools
Small  motor neurons
 motor neurons
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32. Small  motor neurons
Innervate sensory structures in skeletal muscle (muscle spindles)
Muscle spindles are embedded in connective tissue
Are called intrafusal muscle fibers
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33. Small  motor neurons In Intrafusal muscle fibers
Sets the intrafusal muscle fiber to an appropriate length for the sensory neuron to function.
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34.  motor neurons
Large
Innervate extrafusal muscle fibers. These generate force for movement and posture.
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