Sensory inputs are carried by different types of nerve fibre.
A-delta fibres are myelinated fibres. They conduct sensations quickly.
A-delta fibres carry sharp pain, high temperature (>45oC), hair follicle sensation and localisation.
A fibres (-delta and -beta) are the first fibres to be blocked by LA.
This is why acute, sharp pain disappears early but the patient may still feel touch and joint movement.
Motor blockage of myelinated alpha and gamma fibres occurs as a late effect.
A-beta fibres are myelinated fibres. They conduct sensations quickly.
A-beta fibres carry light pressure, rubbing, vibration and position sense.
A fibres (-delta and -beta) are the first fibres to be blocked by LA.
This is why acute, sharp pain disappears early but the patient may still feel touch and joint movement.
Motor blockage of myelinated alpha and gamma fibres occurs as a late effect.
C fibres are unmyelinated fibres. They conduct sensations slowly.
C fibres are polymodal and carry ‘slow’ dull aching pain, position sense, vibration, and temperature. They are sensitive to a wide range of tissue inflammatory mediators.
C fibres are blocked by LAs after the A fibres, and this action is dependent on dosage and type of blockade.
This is why acute, sharp pain disappears early but the patient may still feel touch and joint movement.
Blockade of autonomic unmyelinated, post-ganglionic fibres also occurs early.