So we discussed really
briefly a spinal reflex pathway.
Now let's take a closer look
at how these reflexes occur.
A reflex is a fast involuntary, unplanned
response to a particular stimulus.
Reflexes are necessary in order
to help us maintain homeostasis.
And the grey matter of the
spinal cord is very important
as it serves as the integrating
centre for the spinal reflexes.
So now let's take a closer
look at the reflex arc.
A reflex arc is going to include
the sensory information that goes in
as well as the motor
information that goes out.
It starts with sensory receptors and parts of
the body that are going to receive a stimulus.
Next a nerve impulse is propagated down the sensory
neuron into the posterior root of the spinal cord.
In the grey matter of the spinal cord
you will have your integrating center.
After integration, a motor neuron is going
to transport a nerve impulse to an effector.
In integration, there
can be two different types.
The first type is monosynaptic where
the sensory neuron is going to synapse
directly with the motor neuron.
In the second type, we have polysynaptic.
In polysynaptic, the sensory neuron is going
to actually synapse with an interneuron first
or an association neuron and then that
neuron will synapse with the motor neuron
and then signal will go to the effector.
Also in a reflex arc, there are
different types of arcs that we can have.
The first type of arc
is an ipsilateral arc .
In an ipsilateral arc, the sensory
information is going to be received
and the output or the motor information
is going to go to the same side of the body.
Another type of reflex arc
is a contralateral reflex arc.
In this type of reflex arc, the sensory
information comes in on one side of the body
is integrated in the grey matter and
then leaves out of the other side of the body
So in the reflex arc, there are certain
vocabulary terms that you should know.
First, e'll start with ipsilateral.
In an ipsilateral reflex arc, the sensory neuron
and the motor neuron are going to come in
and exit out of the same side of the body.
An example of this type of reflex arc will be
a withdrawal reflex when you touch a hot pan.
In the contralateral reflex, the sensory neuron
is going to come in on one side of the spinal cord
and the motor neuron is going to leave
at an opposite side of the spinal cord.
An example of this would be when
you're trying to maintain your balance
such as when you're falling
over and your body corrects itself
Also, there are two types of reflex arcs.
You can have monosynaptic where the sensory neuron
is going to synapse directly with the motor neuron
and you can have polysynaptic where the sensory neuron
is going to synapse with an association or interneuron
and then that neuron is going
to synapse with a motor neuron.
Please note that a polysynaptic reflex
arc can be ipsilateral or contralateral
while a monosynaptic
reflex arc is always ipsilateral
The last term is reciprocal innervation.
In reciprocal innervation,
our body is going to make sure
that when the agonistic muscle is
contracted, the antagonistic muscle is relaxed.
This helps us maintain homeostasis so that all of
our muscles are not contracting at the same time