Question

Explain Neurophysiologic pain and its pathway

Answer 1

Pain is an unpleasant emotional sensation associated with localised swelling compresses sensory nerve endings or potential tissue damage.Different types of pain are there sharp pain,prickling pain,thermal pain and aching pain. According to the origin, the pain can be somatic,viscreal,neuropathic,thalamic,psychosomatic, refeerred or illusionary.

Pain is acute and chronic in nature.

GENERAL PATHWAY OF PAIN

In this pathway, 3 types of neurons are present for carrying action potential to signalling the pain.

1. First order neurones (pseudounipolar neurons) - These neurons having cell bodies with in the dorsal root ganglion.They have one axon divided in to two branches, a peripheral branch (which extend towards the peripheries) and a central branch ( which extends centrally in to spinal cord/brainstem)

2. Second order neurons- These are found in Rexed Laminae of the spinal cord,or in the nuceli of cranial nerves with in brain stem.

3. Third order neurons- The cell bodies of this third order neuron lies within the VPL(ventral postereo lateral nucleus) of the thalamus. They project via the posterior limb of the internal capsule to terminate in the lipsilateral pst central gyrus (primary somatosensory cortex). The post central gyrus is somato topically organised.Therefor, pain signals initiated in the hand will terminate in the area of the cortex dedicated to represent sensations of the hand.

ACTIVATION OF FIRST ORDER NEURON

First order neurons having specilaised receptors called nociceptor which are acrtivated through various nervous stimuli. Each nocicpetors have its own receptive field. This means one nociceptor will transduce the signal of pain when a particular region is stimulated.

Nociceptor can be found in the skin,muscle,joints,bone and organs and fire in respose to a no. of different stimuli.Three types of nociceptors exist.

1. Mechanical- detects sharp ,prickling pain

2. Thermal and mecano-thermal nociceptors- detects sensation which elicit pain which is slow and burning or cold and sharp in nature.

3. Polymodal nociceptors - detect mechnaical,chemical and thermal stimuli

TRANSMISSION TO THE SPINAL CORD

Signal from mecanical,thermal and mechano-thermal nociceptors transmitter to the dorsal horn of the spinal cord, predominantly by AO fibres.These mylineated fibres have low threshold of firing and fast speed conduction and they are responisible for transmitting first pain felt.

Polymodal nociceptors transmit this signals to the dorsal horn through c fibres. C fibres are responsible for the secondary pain we felt.These fibres are typiically have large receptive fields and it leads to poor localisation of pain.