ch 15 lower motor neuron circuits and motor control
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Ch. 15: Lower Motor Neuron Circuits and Motor Control. - a model for understanding the nervous system. Neural centers responsible for movement. 4 interactive subsystems contribute to motor control. Neural centers responsible for movement. Gray matter of spinal cord and brainstem

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ch 15 lower motor neuron circuits and motor control

Ch. 15: Lower Motor Neuron Circuits and Motor Control

- a model for understanding the nervous system

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neural centers responsible for movement
Neural centers responsible for movement
  • 4 interactive subsystems contribute to motor control

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neural centers responsible for movement1
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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neural centers responsible for movement2
Neural centers responsible for movement
  • Upper motor neurons

- cell bodies in brainstem or cerebral cortex

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neural centers responsible for movement3
Neural centers responsible for movement

3) Cerebellum

- regulate activity of upper motor neurons

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neural centers responsible for movement4
Neural centers responsible for movement
  • 4) Basal Ganglia
      • Regulate upper motor neurons

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slide12

Basal ganglia - caudate, putamen, globus pallidus

-subthalamic nucleus, substantia nigra

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1 gray matter of spinal cord and brainstem
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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gray matter of spinal cord and brainstem
Gray matter of spinal cord and brainstem
  • Local circuit neurons
    • Synaptic input to lower motor neurons

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gray matter of spinal cord and brainstem1
Gray matter of spinal cord and brainstem
  • Lower motor neurons convey voluntary and reflex commands to skeletel muscle

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gray matter of spinal cord and brainstem2
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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gray matter of spinal cord and brainstem3
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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2 upper motor neurons
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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2 upper motor neurons1
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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2 upper motor neurons2
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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3 cerebellum
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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3 cerebellum1
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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4 basal ganglia
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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how does thought lead to movement
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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motor neuron muscle relationships
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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motor neuron muscle relationships1
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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motor neuron muscle relationships2
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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motor neuron muscle relationships3
Motor neuron - muscle relationships
  • Spatial organization gives information about functions

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motor neuron muscle relationships4
Motor neuron - muscle relationships
  • Two types of lower motor neurons in the motor neuron pools
    • Small  motor neurons
    •  motor neurons

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small motor neurons
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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small motor neurons1
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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motor neurons
 motor neurons
  • Large
  • Innervate extrafusal muscle fibers. These generate force for movement and posture.

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