As an international student living thousands of miles away from home, one of my essential daily activities is messaging my mom. Since I work on my math or chemistry problems on a daily basis, I am usually solving problems when my mom messages me. Once I hear the Facebook messenger notification bell, and if it’s my mom, I quickly open a new tab to read the message. She asks me how things went on that day, and I ask back how her day was. We have a brief but enjoyable conversation before I have to say farewell and return to my homework. I’m breaking this activity down into three parts: first, doing my assignments; second, hearing the notification bell and opening a new tab; and finally, conversing with my mom.
The first part of the activity is doing my assignments. Solving math or chemistry problems requires me to constantly move my hands and arms as I write down the solutions. What plays a crucial role here is the brain. According to Kalat (2010), the process of my hand and arm movement initiates from the primary motor cortex which controls the body motion. From the primary motor cortex, located in the frontal lobe, electrical signals are delivered by the motor neurons, which then move downwards (Kalat, 2010, p. 83).
The cerebral cortex, however, does not directly send the signals to the muscles. After the signals exit the brain, they enter the peripheral nervous system, passing through the pons and the medulla to the spinal cord, which controls the action from the neck down (Kalat, 2010, p. 84). The brachial plexus, one of the many networks of nerves that branch out from the spinal cord, is the one that supplies signals to the chest shoulders, arms, and hands, as stated by Saladin (2014). Specifically, motor neurons in the axillary and radial nerve of the posterior cord, which all originate from the brachial plexus, are responsible for hand and arm movements.
Starting from the brachial plexus, through the posterior cord, and to the axillary and radial nerve, the action potential continues until it arrives at the neuromuscular junction, where the motor neuron and the muscle tissues meet (Saladin, 2014, p. 489-491). Here, a look at the cellular activities is essential. According to Sadava, Hillis, Heller, and Berenbaum (2012), when an action potential arrives at the neuromuscular junction, vesicles of acetylcholine are released. Then the postsynaptic membrane generates another action potential that spreads down the muscle tissue, causing several receptors to change in conformation. This triggers the release of calcium ions in the sarcoplasm, the endoplasmic reticulum of the muscle cell. As the calcium ions diffuse in the sarcoplasm, muscle contraction is stimulated, enabling me to move my hands and arms while I solve the questions (Sadava, Hillis, Heller, and Brenbaum, 2012, p. 990).
While my neurons are hard at work, I am startled by the Facebook notification bell. This initiates the second section of my action. This time, when I hear the notification bell and shift my attention from my assignment to the computer screen, the initial change occurs at the cellular level. Savada et al. (2012) illustrates that when sound waves arrive at my ears, stereocilia, or the extended cell membrane of the hair cells are bent in one direction in response to the change of the air pressure. The change in conformation causes the ion channels to open, depolarizing the hair cell membrane. The depolarization opens voltage-gated calcium ion channels, stimulating the release of neurotransmitters to the sensory neurons, which then send the signals to the brain (Savada et al., 2012, p. 1001).
Once the signals reach my brain, the temporal lobe takes charge and processes the information. As stated by Kalat (2010), the temporal lobe, being the main area for hearing and some of the complex aspects of vision, converts the signals transmitted from my sensory neurons so that I can comprehend the source of the sound. It also converts the information received from my eyes after looking at the computer screen, allowing me to detect who sent the message (Kalat, 2010, p.81). I move my hands to check the notification, and upon seeing it, I become emotional. I am both excited and anxious to talk to my mom after a long day of lectures and discussions. The swirl of emotions activates my sympathetic nervous system, as demonstrated by Savada et al. (2012), generating the signals that the preganglionic neurons transmit outwards from the spinal cord to the peripheral nervous system.
The signals are then transmitted to the postganglionic neurons at the synapses within the ganglia, Savada et al. (2012) continues to explain. Acetylcholine is released, activating the nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulation, the postganglionic neurons release norepinephrine which activates the receptors on the peripheral target tissues. The activation of such tissues causes the effects associated with the sympathetic nervous system: my palms get sweaty, my pupils expand, my heart beats faster, and my mouth becomes dry (Savada et al., 2012, p.974-975).
Joyously, I begin conversing with my mom, my final and favorite task. My nervous system is hard at work reading and preparing sentences to send back to her. In order for this communication to occur, I first need to perceive the written message sent by my mom, beginning at a cellular level. The light reflected from my laptop screen comes into my eyes and travels through layers of transparent neurons – ganglion, amacrine, bipolar and horizontal cells, Savada et al. (2012) further describes. Once it reaches the back of the retina, it is absorbed by the rods and the cones, which makes up the photoreceptive layer of the eye. The absorbed information is processed through the layers of neurons, as it moves forwards toward the ganglion cells. The processed signals finally converge on ganglion cells, which connects the brain with the sensory organ – in this case, my eyes (Savada et al., 2012, p. 1010).
Reading, comprehending, and writing are complicated processes. Once the signals reach my brain, a number of brain regions have to work together for me to read, understand, and write back to my mom. Edwards mentions that among them are the temporal lobe, responsible for distinguishing sounds; the Broca’s area in the frontal lobe that governs language comprehension; and the angular and supramarginal gyrus that links different parts of the brain so that my letters become complete words. (Reading and the brain, para.4).
These complex processes allow me to feel relieved, as they enable me to talk to someone who is always in support of me. The intense emotions I felt just moments ago subside, stimulating my parasympathetic nervous system, as acknowledged by Savada et al. (2012). The mechanism begins the same way it did for the sympathetic nervous system – the preganglionic neurons release acetylcholine at the synapse outside the central nervous system. This time, however, the postganglionic neurons are cholinergic, which means they release acetylcholine as neurotransmitters. The acetylcholine released on the peripheral target tissues activate them, and I feel the effects of the parasympathetic nervous system: my palms become dry, my pupils constrict, and my heart beat slows down (Savada et al., 2012, p, 1022-1023).
Everything from doing my assignments to conversing with my mom happens in just a few minutes. In this short period of time, a variety of chemicals, regions of the brain, and aspects of the peripheral nervous system cooperate in order for me to work on my homework and communicate with my mom. It is very easy to think that our daily, somehow mundane tasks are done habitually, but they aren’t. They are the beautiful product of activities in my body at the cellular level, in the brain, and in the peripheral nervous system.