So the next reflex that we’ll
discuss is the crossed-extensor reflex.
This reflex is actually a
response to the withdrawal reflex
and helps to maintain
balance when you withdraw.
So in this reflex, we start
First we step on a tack which is going to
stimulate the sensory receptors in the foot.
This is going to propagate a nerve impulse
from the sensory neuron to the spinal cord.
Just as we discussed
before in the withdrawal reflex
you're going to have an
intersegmental integration of this signal
where we're going to
synapse with interneurons
and multiple parts including descending
interneurons, ascending interneurons
and the interneurons of the spinal cord
segment that receives the sensory signal.
From there, the interneurons is going
to synapse with the motor neurons
and this is going to cause us to contract the
muscles and withdraw away from the pain stimulus.
So in this part, the withdrawal
reflex has taken place.
But if you've ever all of a sudden
lifted your foot up out of nowhere,
your body is going to be off-balanced.
So the next things that happens is a
contralateral reflex occurs in the opposite leg.
In this part, motor neurons are
actually excited in the opposite leg
and this causes you to contract and extend the
opposite leg so that you can maintain your balance.