Why do nerves cross over?
Nerves control various activities of our body, movement and sensation. The triggering information is received by the nervous system and it will immediately send the response to it. Nerves in our body have nerve tracts following which the path of the nervous system exist. The crossover junctions of the nerve fibers are called as synapses. Synapses are most complicated junctions where there is exchange of nerve signals from one nerve to the other. This communication of signals is carried out by the changes in electrical and chemical factors.
About 80 percent of cortico-spinal nerve fibers travel towards contra-lateral side of medulla oblongata region. Ten percent of them go into the same lateral side while the remaining ten percent cross over at the end of spinal cord and travel through anterior cortico spinal tract. These nerves get connected to other neurons through synapses.
The nerve axons travel downwards in the spinal cord through lateral corticospinal tract. The nerve fibers that will not crossover at the medulla region pass through this area via anterior corticospinal tract. Most of the nerve fibers were known to cross over to the contra-lateral side of the spinal cord. The motor and sensory neuron strips are available on both sides of the brain. The motor neurons on the right side were found to have control on the motor nerves on the left side and vice versa. It is believed that there is an evolutionary benefit for the neurons to get arranged in this fashion.
Vertebrates have lens in their eyes which tend to invert the image formed in it. The vision of the eye is created by the cross effect of the light that falls on each half of the eye. The central nervous system is set up and arranged in our body in such a way that the response for the visual stimulus will result in a correct posture of the object directed towards the correct side of the body. This system also has coordination with the sensory neurons in order to find variation of objects in the right side from those in the left side. The output of the motor nerves will have cross over called as decussation of pyramidal tract which trigger the control of right side parts by the left side motor nerves and vice versa.