Answer:
Cell differentiation is how cells become specialized. This occurs through a process called gene expression. Gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and this is what dictates how a cell functions.
The answer is, Geographic barriers. Hope this helps!
<span>Ian Waterman was able to sense pain and temperature because his
spinothalamic pathway was intact, but could not feel touch and limb position because of damage to his
lemniscus pathway. </span>
The lateral spinothalamic tract is a sensory pathway which carries sensory information like pain and temperature to the brain, across the thalamus. Free nerve endings which are located in the peripheral tissues are sensitive to cell damage. Those are primary neurons and they pass the sensory signal. Primary neurons synapse with secondary which are located in the spinal cord (white matter). These secondary neurons will ascend through the brainstem, medulla oblongata, pons and midbrain, until synapsing in the ventroposteriorlateral (VPL) nucleus of the thalamus. From the thalamus, the information is sent to cortex (somatosensory cortex).
Posterior column-medial lemniscus pathway is ascending spinal tract, carrying sensory information to the brain (sensory pathway). It conducts localized sensations of fine touch, vibration and proprioception (position sense) from the skin and extremities (muscles) to the central nervous system (cerebral cortex).
