00:01
Now, let's talk a little bit about how the body feels pain.
00:04
Pain is perceived in both the central and peripheral nervous systems.
00:08
And so we're going to talk about central nervous system control of neuropathic pain
and peripheral nervous system control of pain.
00:15
In the peripheral nervous system, we know that the nerves start as the nerve roots
and then, extend into the plexus, and then end in the terminal nerve branches.
00:24
And dysfunction in any of these areas can contribute to the development of neuropathic pain.
00:30
So let's take a closer look at how the body feels pain.
00:33
Well, first, a sensory nerve feels pain in the skin.
00:37
That may be pain or a temperature response, or vibration, or some painful sensation in the skin.
00:43
This is carried by an action potential in sensory neurons towards and to the spinal cord.
00:50
Those peripheral sensory neurons, cell bodies are contained within the dorsal root ganglia.
00:56
That sensory information is relayed into the spinal cord
and there's already some modulation of that signal as a result of interneurons within the spinal cord.
01:05
But ultimately, the signal is propagated towards the brain
through the white matter tracts in the spinal cord.
01:12
Sensory pathways continue to second order neurons projecting into the thalamus.
01:17
And the thalamus is really the primary mediator and regulator of all sensory input to the brain.
01:26
Sensory information ultimately reaches the cerebral cortex,
and that's where sensory pathways reach the brain for conscious perception of pain.
01:33
The brain doesn't feel pain, but it is the part of the body that perceives pain,
that understands what it is. Is this a good pain or a bad pain?
Do I need to recoil or keep doing this?
In the circumstance of a hand feeling hot water, we want the hand to recoil away.
01:49
So that sensory stimulus that's perceived in the brain will generate a motor response.
01:56
Motor responses start in the primary motor cortex
and descend as any volitional motor action through the internal capsule to the brain stem,
down the spinal cord where there's a synapse in the ventral horn.
02:08
That information travels out the peripheral motor neuron
and motor nerve to the hand and the hand recoils.
02:16
In addition to central nervous system control and perception of pain,
the spinal cord is also important. There are a number of spinal reflexes
that allow the body to move away from a painful stimulus without even thinking about it.
02:32
And you can think about what happens if you were to step on a nail.
02:35
Before you even know that it's a nail or that you even feel pain,
your foot is moving away from the nail and moving away from that painful stimulus.
02:45
And what does this is a spinal reflex. You can see what's happening here.
02:48
First, the painful sensory response is felt in the skin in the foot.
02:53
That information is travelled quickly into the spinal cord where it will travel up to the brain.
02:59
And ultimately, the brain will realize that I'm stepping on a nail.
03:02
But before that happens, that signal is transferred through interneurons in the spinal cord to the ventral horn.
03:08
And there's an activation of motor neurons that move the leg up,
that contract the quad, that relax the muscles of the - of knee flexion
and move the leg away from the painful stimulus.
03:23
So both central nervous system and spinal reflex control of pain
are important in the body's safety mechanisms.