chapter 13 spinal control of movement. introduction motor programs –motor system: muscles and...
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Chapter 13 Spinal Control of
Movement
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Introduction
Motor Programs– Motor system: Muscles and neurons that control muscles– Role: Generation of coordinated movements– Parts of motor control
• Spinal cord coordinated muscle contraction• Brain motor programs in spinal cord
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The Somatic & Autonomic Motor Systems
Types of Muscles– Smooth:
digestive tract, arteries, related structures
– Striated: Cardiac (heart)
– skeletal (bulk of body muscle mass)
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Graded Control of Muscle Contraction by Alpha Motor Neurons– Varying firing rate of motor neurons– Recruit additional synergistic motor units
Lower Motor Neurons
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Tetanus – as painted by Sir Charles Bell in 1809.
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Types of Motor Units– Red muscle fibers: Large number of
mitochondria and enzymes, slow to contract, can sustain contraction
– White muscle fibers: Few mitochondria, anaerobic metabolism, contract and fatigue rapidly
– Fast motor units: Rapidly fatiguing white fibers
– Slow motor units: Slowly fatiguing red fibers
Lower Motor Neurons
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Figure 9.7a
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Muscle Contraction– Alpha motor neurons
release ACh– ACh produces large EPSP in
muscle fiber– EPSP evokes muscle action
potential– Action potential triggers
Ca2+ release– Fiber contracts– Ca2+ reuptake– Fiber relaxes
Excitation-Contraction CouplingExcitation-Contraction Coupling
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The Molecular Basis of Muscle Contraction– Z lines: Division of myofibril into segments by disks– Thin filaments: Series of bristles– Thick filaments: Between and among thin filaments– Sliding-filament model:
• Binding of Ca2+ to troponin causes myosin to bind to action
• Myosin heads pivot, cause filaments to slide
Excitation-Contraction CouplingExcitation-Contraction Coupling
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Figure 9.3a–c
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Figure 9.3c–e
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Figure 9.3d
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Figure 9.4
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Figure 9.6
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Figure 9.11
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Figure 9.12
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Sensory feedback from muscle spindles - stretch receptor
Spinal Control of Motor Units
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The Myotatic Reflex
Spinal Control of Motor Units
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Spinal Control of Motor Units
Two Types of Muscle Fiber– Extrafusal fibers: Innervated
by alpha motor neurons– Intrafusal fibers: Innervated
by gamma motor neurons
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Spinal Control of Motor Units
Golgi Tendon Organs– Additional proprioceptive input - acts like strain gauge -
monitors muscle tension
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Spinal Control of Motor Units
Golgi Tendon Organs– Spindles in parallel with fibers; Golgi tendon organs in
series with fibers
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Excitatory Input– Crossed-extensor
reflex: Activation of extensor muscles and inhibition of flexors on opposite side
Spinal Control of Motor Units
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Afferentfiber
Efferentfibers
Extensorinhibited
Flexorstimulated
Right arm(site of stimulus)
Left arm (site ofreciprocal activation)
Arm movements
Interneurons
Key:+ Excitatory synapse– Inhibitory synapse
Efferentfibers
Flexorinhibited
Extensorstimulated
+
–+
–
+
+
Flexes
Extends
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Information gleaned about nicotinic ACh receptors utilzed the electric organs of electric eels because of their high concentration of the Ach receptor. The Disease Myasthenia gravis is an autoimmune disease where the body's immune system has damaged receptors on your muscles causing long term weakness and eventual, premature death.
Individual showing classic, early signs of Myasthenia gravis