by Tiara Paul
During sensory processes, our nervous system rapidly transfers information. Sensory organs detect stimuli from our five senses, which is converted to neural impulses through transduction. Neural impulses are sent to the brain through ascending sensory (afferent) neurons in the spinal cord; essentially, the spinal cord is the highway connecting sensory information and the brain. The brain interprets the information and formulates a response. Reversing the process, this information is transmitted back to muscles and glands through descending motor (efferent) neurons. The body carries out the response that the brain intended.
As pictured above, input toward the brain is afferent, while output toward muscles is efferent. (Source: http://droualb.faculty.mjc.edu/Course%20Materials/Elementary%20Anatomy%20and%20Physiology%2050/Lecture%20outlines/nervous_system.htm)
In contrast, reflexes are involuntary, instantaneous responses to stimuli. Interneurons, which facilitate communication among other neurons, send messages from sensory neurons directly to motor neurons. The spinal cord does its own processing, skipping the middle step where the brain puts its two cents in. Eventually, the information reaches the brain, but only after the fact; consequently, the response is carried out before the brain even processes what had occurred! Reflexes occur in situations when an especially-quick response is necessary because the sensory information is so powerful. These inherent reactions are beneficial by minimizing damage that would occur from having to wait to relay information to the brain.
As pictured, reflex actions occur rapidly and involuntarily before interpretation by the brain. (Source: https://ib.bioninja.com.au/options/option-a-neurobiology-and/a4-innate-and-learned-behav/reflex-arcs.html)
Two summers ago, I went on vacation to Singapore! My sister and I decided to venture to the more adventurous island of Sentosa, and we ended up in a forest. There was a statue of a fake snake—or so I thought. It appeared motionless and looked as if it was a painted statue, so without thinking, I reached to touch it. As my finger approached it, the snake instantly slithered back into the hole it was peeping out of. Not having known the snake was alive, I was startled and shrieked, but I instantly moved my hand back. Seconds later, I realized what happened and felt thankful to have not touched a live snake! For the rest of our venture through the forest, I was still on-edge. At one point, a bug flew close to my face, so I instinctively blinked my eyes and turned my head to the side.
Instantaneously withdrawing my hand was a reflex. Once my sensory organs detected that the snake moved, I recognized that it was alive. I perceived the live snake as an immediate threat. Thus, the information sent by my afferent neurons was processed by my spinal cord, which instantly sent information back to my motor neurons. Before I knew it, I had moved my hand; my brain was bypassed from interpreting the information. However, once the information did reach my brain, I registered what had happened and felt relieved. If my nervous system had waited to relay the information to my brain (as in typical sensory processing), my hand would have remained extended toward the snake, which could have left me in danger. Interestingly, it can also be argued that my extended hand was perceived as a threat to the snake, and the snake’s reflex action was to retreat into its hole. Afterwards, my eyes detected the incoming bug as a threat. Since the image of the bug on my retina was changing size, I perceived its motion approaching me. My reflex action was to blink and turn my head, thereby avoiding contact and minimizing potential damage. Again, my spinal cord processed the information via interneuron connections directly from sensory neurons to motor neurons. This is why I cannot recall what type of bug was approaching me; I closed my eyes so soon, before my brain even registered it, that I did not see if it was a bee, fly, or anything in between.
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