1. Crossed Extensor Reflex
Process Diagrams Step-by-Step
Copyright © 2007 by John Wiley & Sons, Inc.

2. 1 Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Withdrawal of right leg
(flexor reflex)

3. 2 1 + SENSORY NEURON excited Stepping on a tack stimulates SENSORY
RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Withdrawal of right leg
(flexor reflex)

4. 3 2 1 + + Spinal nerve + + Ascending interneurons + Interneurons
from other side + +
Descending
interneurons + + + + 3
Within INTEGRATING CENTER
(spinal cord), sensory neuron
activates several interneurons 2
SENSORY
NEURON
excited 1
Stepping on a tack
stimulates SENSORY
RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Withdrawal of right leg
(flexor reflex)

5. 4 4 3 2 1 + + Spinal nerve + + MOTOR NEURONS excited Ascending
interneurons +
Interneurons
from other side + + +
Descending
interneurons + 4
MOTOR
NEURONS
excited + + + + + 3
Within INTEGRATING CENTER
(spinal cord), sensory neuron
activates several interneurons 2
SENSORY
NEURON
excited 1
Stepping on a tack
stimulates SENSORY
RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Withdrawal of right leg
(flexor reflex)
Extension of left leg
(crossed extensor reflex)

6. 4 5 4 3 2 1 + + Spinal nerve + + MOTOR NEURONS excited Ascending
interneurons 5
EFFECTORS
(extensor muscles)
contract, and extend
left leg +
Interneurons
from other side + +
Flexor muscles
contract and with-
drawright leg + +
Descending
interneurons + + 4
MOTOR
NEURONS
excited + + + + + + 3
Within INTEGRATING CENTER
(spinal cord), sensory neuron
activates several interneurons 2
SENSORY
NEURON
excited 1
Stepping on a tack
stimulates SENSORY
RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Withdrawal of right leg
(flexor reflex)
Extension of left leg
(crossed extensor reflex)