Les X: Neuropathische pijn (Lore Dams)
A) Pathophysiology
Wat?
Pain caused by a lesion or disease of the somatosensory system (SS) (peripheral or central).
SS system
− Is a system that includes peripheral receptors and central processing systems like the
spinal cord and the brain.
− Allows the human body to perceive physical sensations of
∙ Pressure (touch)
∙ T° changes
∙ Proprioception
∙ Nociception (pain)
− The SS consists of 2 parts:
1) A peripheral part:
→ Sensory receptors
→ Peripheral nerve
→ Dorsal root ganglion. This last one carries sensory signals.
2) A central part:
→ Spinal cord (RM)
→ Brain
1
, a) The Peripheral SS (PSS)
1) Peripheral sensory receptors are found all over the body
→ including skin, muscles, bones, joints, internal organs but also the cardiovascular
systems.
These receptors as well as nerve endings are connected to a nerve fiber
specifically for the transport of a certain type of stimulus (e.g. see below)
2) Aβ fibers:
− Information about touch of a particular body part will be transported via thick Aβ
fibers.
− Have a thick insulating myelin sheets you can see in grey.
− That myelin sheet allows electrical impulses to transmit quickly.
3) C-fibers:
− Information about dull pain stimuli will be transported by thin C-fibers without a
myelin sheet.
− Resulting in a slower transduction or transmission of the stimuli regarding dull
pain or T° changes of warmth.
Aα Aβ Aδ C
Diameter 13-20 6-12 1-5 0,2-1,5
Speed 80-120 35-75 5-30 0,5-2
Sensory Proprioceptors/sk Mechanoreceptors ∙ Pain (sharp) ∙ Pain (dull)
receptors eletal muscle ∙ T° (cold) ∙ T° (heat)
∙ Itch
2
,b) The Central SS (CSS) : ‘On our way to the brain' ☺
Information from arrives via the in the RM Then it’s transmitted to the primary
peripheral nerves dorsal root via the thalamus SS cortex.
ganglion
− Parts of the CSS:
− RM
− Thalamus and
− SS cortex
− The SS cortex:
− Has a somatotopic organization.
− Better known as the sensory homunculus.
− Homunculus means little man.
− On the picture in the middle you can see a scale model of the human body
reflecting the relative space that specific body parts occupy in the SS cortex
→ As you can see lips, hands, feet and genitals send more SS projections to
the brain than do any other body parts.
This because they require greater sensation for their function.
− On the right image we can see the cortical mapping of the sensory
homunculus. Body parts are represented in specific locations in the SS
cortex, but it’s not an exact representation of the body itself.
→ You can see that the feet are located more medial
→ Shoulder and arms are located more lateral
→ Face is oriented upside down with the forehead pointing towards the
shoulders and facial structures are also represented in a different
location than the head itself.
→ However this somatotopic representation of the sensory homunculus is
also not fixed and can be altered by various changes in peripheral input.
3
, c) Normal functioning:
So we describe the PSS and CSS systems in a normal functioning SS system.
The peripheral receptors will capture peripheral stimuli. They will be transported and allow
us to consciously perceive them in the CSS.
But how does this transfer of stimuli take place from the peripheral receptors to the CZS?.
1. So a variety of receptors will capture a stimulus. You can see it on the right of the
picture.
2. The stimulus is captured and is then converted to an electrical signal.
3. This signal is generated by the opening and closing of natrium (Na) and potassium (K)
channels with the generation of an action potential.
4. This AP is transmitted through the axon into the direction of the CNS.
→ This is in case of normal functioning.
4
A) Pathophysiology
Wat?
Pain caused by a lesion or disease of the somatosensory system (SS) (peripheral or central).
SS system
− Is a system that includes peripheral receptors and central processing systems like the
spinal cord and the brain.
− Allows the human body to perceive physical sensations of
∙ Pressure (touch)
∙ T° changes
∙ Proprioception
∙ Nociception (pain)
− The SS consists of 2 parts:
1) A peripheral part:
→ Sensory receptors
→ Peripheral nerve
→ Dorsal root ganglion. This last one carries sensory signals.
2) A central part:
→ Spinal cord (RM)
→ Brain
1
, a) The Peripheral SS (PSS)
1) Peripheral sensory receptors are found all over the body
→ including skin, muscles, bones, joints, internal organs but also the cardiovascular
systems.
These receptors as well as nerve endings are connected to a nerve fiber
specifically for the transport of a certain type of stimulus (e.g. see below)
2) Aβ fibers:
− Information about touch of a particular body part will be transported via thick Aβ
fibers.
− Have a thick insulating myelin sheets you can see in grey.
− That myelin sheet allows electrical impulses to transmit quickly.
3) C-fibers:
− Information about dull pain stimuli will be transported by thin C-fibers without a
myelin sheet.
− Resulting in a slower transduction or transmission of the stimuli regarding dull
pain or T° changes of warmth.
Aα Aβ Aδ C
Diameter 13-20 6-12 1-5 0,2-1,5
Speed 80-120 35-75 5-30 0,5-2
Sensory Proprioceptors/sk Mechanoreceptors ∙ Pain (sharp) ∙ Pain (dull)
receptors eletal muscle ∙ T° (cold) ∙ T° (heat)
∙ Itch
2
,b) The Central SS (CSS) : ‘On our way to the brain' ☺
Information from arrives via the in the RM Then it’s transmitted to the primary
peripheral nerves dorsal root via the thalamus SS cortex.
ganglion
− Parts of the CSS:
− RM
− Thalamus and
− SS cortex
− The SS cortex:
− Has a somatotopic organization.
− Better known as the sensory homunculus.
− Homunculus means little man.
− On the picture in the middle you can see a scale model of the human body
reflecting the relative space that specific body parts occupy in the SS cortex
→ As you can see lips, hands, feet and genitals send more SS projections to
the brain than do any other body parts.
This because they require greater sensation for their function.
− On the right image we can see the cortical mapping of the sensory
homunculus. Body parts are represented in specific locations in the SS
cortex, but it’s not an exact representation of the body itself.
→ You can see that the feet are located more medial
→ Shoulder and arms are located more lateral
→ Face is oriented upside down with the forehead pointing towards the
shoulders and facial structures are also represented in a different
location than the head itself.
→ However this somatotopic representation of the sensory homunculus is
also not fixed and can be altered by various changes in peripheral input.
3
, c) Normal functioning:
So we describe the PSS and CSS systems in a normal functioning SS system.
The peripheral receptors will capture peripheral stimuli. They will be transported and allow
us to consciously perceive them in the CSS.
But how does this transfer of stimuli take place from the peripheral receptors to the CZS?.
1. So a variety of receptors will capture a stimulus. You can see it on the right of the
picture.
2. The stimulus is captured and is then converted to an electrical signal.
3. This signal is generated by the opening and closing of natrium (Na) and potassium (K)
channels with the generation of an action potential.
4. This AP is transmitted through the axon into the direction of the CNS.
→ This is in case of normal functioning.
4
