Control of Body Movement

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Control of Body Movement

• Dr. Jena Hamra

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Classification of Reflex Pathways

• Efferent division
• Somatic reflexes
• Autonomic (visceral) reflexes
• Location of CNS integration
• Spinal reflexes
• Cranial (supraspinal) reflexes
• Innate or learned reflexes
• Number of neurons in pathway
• Monosynaptic
• Polysynaptic

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Autonomic Reflexes

• Without conscious thought
• Integration
• Hypothalamus
• Thalamus
• Brain stem
• Polysynaptic
• Tonic control

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Skeletal Muscle Reflexes

• Control of skeletal muscles
• Excited by alpha motor neurons
• Inhibited by inhibiting alpha motor neurons
• Extrafusal muscle fibers contractile fibers
• Muscle sensory receptors
• Muscle spindles
• Golgi tendon organs
• Joint capsule mechanoreceptors
• Gamma motor neurons
• Associated with intrafusal muscle fibers

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Muscle Spindles

• Stretch receptors
• Intrafusal fibers
• Modified muscle fibers without myofibrils
• Sensory neurons wrap around middle of intrafusal
  fibers
• Project to spinal cord and synapse with alpha
  motor neuron
• Fire when center of intrafusal fiber stretches
• Tonically active
• Muscle tone

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Muscle Spindles

• Stretch Reflex
• Muscle stretches
• Intrafusal fibers stretch
• Sensory neurons fire more rapidly
• Reflex contraction of muscle
• Contraction decreases stretch
• Stimulus removed

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Muscle Spindles

• Alpha-gamma coactivation
• Gamma motor neurons activated with alpha motor
  neurons
• Gamma motor neurons
• Cause contraction of ENDS of intrafusal fibers
• Lengthens central section
• Intrafusal fibers remain stretched while
  extrafusal fibers contract

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Golgi Tendon Organ

• Stretch Receptor
• Free nerve endings
• Inside connective tissue capsule
• Respond to stretch and contraction
• Stretched muscle ? Pinched sensory fiber fires
• Contracted muscle ? Pulls tendons ? sensory
  neurons fires
• Activated Golgi tendon organ inhibits alpha motor
  neurons
• Decreases muscle contraction

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Stretch Reflexes

• Myotatic unit
• Collection of nervous pathways controlling a
  single joint
• Monosynaptic stretch reflex
• One sensory neuron and one somatic motor neuron
• ONE SYNAPSE!!
• Reciprocal inhibition
• Antagonistic muscle pairs
• Knee jerk reflex

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Flexion Reflexes

• Polysynaptic reflex pathway
• Pulls limb away
• Divergent pathways
• Excitatory interneurons ? alpha motor neurons ?
  flexor contraction
• Inhibitory interneurons ? relaxes antagonistic
  muscle
• Crossed extensor reflex
• Extensor contracts in supporting leg
• Flexors relax

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Reflex Movement

• Reflex movement
• Least complex
• Spinal integration
• Modulated by higher brain centers
• Postural reflexes
• Continuous sensory input
• Visual
• Vestibular
• Muscles
• Brain stem integration

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Voluntary Movement

• Most complex
• Cerebral cortex integration
• Initiated at without external stimuli
• Can become involuntary
• Riding a bicycle

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Rhythmic Movement

• Combination of reflex and voluntary
• Initiated and terminated by input from cerebral
  cortex
• After initiation becomes reflexive
• Maintained by spinal interneurons
• Example Running

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CNS Integration

• 3 levels of control
• Spinal cord
• Brain stem and cerebellum
• Cerebral cortex and basal nuclei
• Thalamus relay station
• Simple movements
• Spinal reflexes
• Postural reflexes
• Both can have cerebellar input

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Integration of Voluntary Movement

• Coordination between
• Cerebral cortex
• Cerebellum
• Basal ganglia
• 3 steps
• Decision making and planning
• Initiating movement
• Executing movement
• Feedforward postural reflexes
• Adjustment in anticipation of changes

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Visceral Muscle Control

• Reflex control
• Nervous and chemical
• Gap junctions
• Self generation of action potentials
• Pacemakers
• Cardiac and smooth muscle