Question

A complete and correct answer will include all organs and tissue types involved, and in what order signals are processed:

Humans reacting to unexpected pain (e.g. touching an unexpectedly hot surface)?

Answer 1

Ascending tracts like lateral spinothalamic tract through A delta and C type nerve fibres collects sensory information from the area of stimulus and takes that sensory information to dorsal root ganglion of spinal cord.

Now through dorsal root ganglion first order neurons arises. These first order neurons synapse with neurons at substantia gelatinosa ( lamina 2) and nucleus proprius (lamina 3 ) in the spinal cord

From nucleus proprius and substantia gelatinosa Second order neurons arises. These second order neurons cross to opposite side of spinal cord and ascend in lateral white column of spinal cord.

Third order neurons arises from thalamus.

Now in the parietal lobe of cerebellum the somasthetic area (area 3,1 ,2) process that sensory information.

Now descending tracts comes into action.

Pyramidal or Corticospinal Tracts The pyramidal or corticospinal tract is for med by the axons of pyramidal cells predominantly lying in the motor area of cerebral cortex. There is some contribution to it from axon of cells in premotor and sensory areas. From here, the fibres course through the posterior limb of internal capsule, mid brain, pons and medulla oblongata. At the lower level of medulla oblongata, 80% of fibres cross to the opposite side. This is known as pyramidal decussation. The fibres that have crossed enter lateral column of white matter of spinal cord and descend as lateral corticospinal tract. Most of these fibres terminate by synapsing through the inter nuncial neurons at the anterior horn cells.

The 20% of fibres that do not cross enter anterior white column of spinal cord to form anterior corticospinal tract. The fibres of this tract also cross at appropriate levels to reach gray matter of the opposite half of spinal cord and synapse with internuncial neurons similar to those of lateral corticospinal tract.

Thus the cerebral cortex through lateral and anterior corticospinal tracts controls anterior horn cells of opposite half of spinal cord.