Transcript Reflex classification

General organization
• Sensory neurons
• Deliver information to CNS
• Motor neurons
• Distribute commands to peripheral effectors
• Interneurons
• Interpret information and coordinate
responses
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Neuronal pools
• Neuronal Pools- Functional group of
interconnected neurons.
• There are 5 Neural circuit patterns:
• Divergence- Spread of information from one neuron to several
neurons, or from one pool to multiple pools.
• Permits the broad distribution of a specific input.
• Convergence- Several neurons synapse on the same
postsynaptic neuron.
• Several patterns of activity in the presynaptic neurons can have
the same effect on the postsynaptic neuron.
• The same motor neurons can be subject to both conscious and
subconscious control.
• Ex.: Ribs and diaphram motion.
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5 Neural circuit patterns, continue
-Serial processing- Occurs when information is relayed in a stepwise
fashion, from one neuron to another or from one neuronal pool to the next.
-Occurs as sensory information in relayed from one part of the brain to
another.
-Parallel processing- Occurs when several neurons or neuronal pools
process the same information at one time.
-Divergence must take place first.
-Due to parallel processing many responses can occur at the same time.
-Ex.: Stepping on a nail and subsequent, simultaneous response
of moving your foot, shifting your weight, pain, and yelling.
-Reverberation- A positive feedback along a chain of neurons such that
they remain active once stimulated.
-Will continue to function until synaptic fatigue or inhibitory stimuli
break the cycle.
-May involve a single neuronal pool or a series of interconnected pools.
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Figure 13.15 The Organization of Neuronal
Pools
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Figure 13.15
An introduction to reflexes
• Reflexes are rapid automatic responses to stimuli
• Neural reflex involves sensory fibers to CNS and
motor fibers to effectors
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Reflex arc
• Wiring of a neural reflex
• Five steps
• Arrival of stimulus and activation of receptor
• Activation of sensory neuron
• Information processing
• Activation of motor neuron
• Response by effector
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Figure 13.16 Components of a Reflex Arc
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Figure 13.16
Reflex classification
• Reflexes are classified according to:
• 1). Development
• 2). Site of information processing
• 3). Nature of resulting motor response
• 4). Complexity of neural circuit involved
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Figure 13.17 Methods of Classifying Reflexes
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Figure 13.17
reflex classifications
• Innate reflexes
• Result from connections that form between
neurons during development
• Acquired reflexes
• Learned, and typically more complex motor
patterns.
• Ex.: A professional skier makes quick adjustments in
body positioning while racing.
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More reflex classifications
• Cranial reflexes
• Reflexes processed in the brain
• Spinal reflexes
• Interconnections and processing events occur
in the spinal cord
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still more reflex classifications
• Somatic reflexes
• Control skeletal muscle
• Visceral reflexes (autonomic reflexes)
• Control activities of other systems
• See chapter 16.
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and more reflex classifications
• Monosynaptic reflex
• Sensory neuron synapses directly on a motor neuron
• Polysynaptic reflex
• At least one interneuron between sensory
afferent and motor efferent
• Longer delay between stimulus and response
• Length of delay is proportional to the number of
synapses involved.
• Can produce far more complicated responses than
monosynaptic reflexes as the interneurons can control
several muscle groups.
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Figure 13.18 Neural Organization and Simple
Reflexes
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Figure 13.18
Spinal Reflexes
• Range from simple monosynaptic reflexes (single
segment of spinal cord) to polysynaptic reflexes
that involve many segments
• In the most complicated spinal reflexes, called
intersegmental reflex arcs, many segments interact to
produce a coordinated, highly variable motor
response.
• Many segments interact to form complex
response
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Monosynaptic Reflexes
• Stretch reflex automatically monitors skeletal
muscle length and tone
• Patellar (knee jerk) reflex
• Sensory receptors are muscle spindles
• Postural reflex maintains upright position
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Figure 13.19 Components of the Stretch Reflex
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Figure 13.19
Figure 13.20 The Patellar Reflex
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Figure 13.20
Figure 13.21 Intrafusal Fibers
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Figure 13.21
Polysynaptic reflexes
• Produce more complicated responses
• Tendon reflex
• Withdrawal reflexes
• Flexor reflex
• Crossed extensor reflex
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Figure 13.22 The Flexor and Crossed Extensor
Reflexes
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Figure 13.22
Polysynaptic reflexes, continue
• Involve pools of interneurons
• Occurs in pools of interneurons before motor neurons are activated.
• Result may be excitation or inhibition.
• Are intersegmental in distribution
• Interneuron pools extend across spinal segments and may activate
muscle groups in many parts of the body.
• Involve reciprocal inhibition
• Coordinates muscular contractions and reduces resistance to
movement.
• Have reverberating circuits to prolong the motor
response
• Several reflexes may cooperate to produce a
coordinated response
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Control of spinal reflexes
• Brain can facilitate or inhibit motor patterns
based in spinal cord
• Motor control involves a series of interacting
levels
• Monosynaptic reflexes are the lowest level
• Brain centers that modulate or build on motor
patterns are the highest
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Reinforcement and inhibition
• Reinforcement = facilitation that enhances spinal
reflexes
• Spinal reflexes can also be inhibited
• Babinski reflex replaced by planter reflex
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Figure 13.23 The Babinski Reflexes
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Figure 13.23
You should now be familiar with:
• The structure and functions of the spinal cord.
• The three meningeal layers that surround the
CNS.
• The major components of a spinal nerve and their
distribution in relation to their regions of
innervation.
• The significance of neuronal pools.
• The steps in a neural reflex.
• How reflexes interact to produce complicated
behaviors.
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