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B213-12-Reflexes

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Daniel Howell

on 12 November 2018

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Transcript of B213-12-Reflexes

Reflexes
Reflexes are rapid, predictable, automatic responses to stimuli
Neural reflex involves sensory fibers to CNS and motor fibers to effectors
May involve only the spinal cord, or the spinal cord & higher brain centers
May be monosynaptic or polysynaptic
Reflexes
The Reflex Arc
Five steps:
Activation of
receptor
by stimulus
Reflex Classification
1. Development
innate vs acquired

2. Site of information processing
spinal vs cranial

3. Nature of motor response
somatic vs visceral

4. Complexity of neural circuit
monosynaptic vs polysynaptic
Neural Organization & Simple Reflexes
Spinal Reflexes
Range from simple monosynaptic to complex polysynaptic and intersegmental

Intersegmental = many spinal cord segments interact to form a complex response
Monosynaptic Reflexes
Stretch reflexes are monosynaptic

Stretch reflex automatically monitors skeletal muscle length and tone

Example: Patellar (knee jerk) reflex

Sensory receptors of stretch reflex are muscle spindles

Postural reflexes maintains upright position
The Patellar Stretch Reflex
Components of a Stretch Reflex
Components of a Stretch Reflex
Polysynaptic Reflexes
Produce more complicated responses
Response is less stereotyped (more tailored), but
Response is slower

Involve pools of interneurons (ie, neuronal pools)
Pools are intersegmental in distribution
Involve reciprocal inhibition
Have reverberating circuits to prolong the motor response
Several reflexes may cooperate to produce a complex, coordinated response
Withdrawal Reflex
Crossed Extensor Reflex
Diagnostic Tools
Reflexes are used to assess damage to CNS or peripheral nerves.

Babinski sign = injury to CNS spinal segments S1 or S2
Biceps reflex = injury to C5, C6
Triceps reflex = injury to C6, C7
Abdominal reflex = injury to T7-T12
Ankle jerk reflex = injury to S1, S2
blown pupil = CN3 or brain damage
Daniel Howell, PhD
Liberty University

Components of a Stretch Reflex
Components of a Stretch Reflex
Withdrawal reflexes are polysnaptic, sending signal to multiple muscles to achieve withdrawal
Crossed-extensor reflexes send signals to opposite side of body
Activation of
sensory neuron
Information processing
(Integration)
Activation of
motor neuron
Response by
effector
Full transcript