Exploratory System

When the coffee is finished, our coffee maker’s beeping creates pressure changes, which move away from the machine and radiate to the individual’s location across the room. The waves reach the outer ear, which contains structures known as the pinnae, angled such that sound waves bounce off them and resonate. They enter the auditory canal after being significantly amplified before reaching the tympanic membrane. The waves strike the membrane and cause it to vibrate, which subsequently transmits them to the middle ear. The ossicles are three bones (malleus, incus and stapes) of the middle ear through which the vibrations pass. The stapes transmits the vibrations to the membrane-covered oval window successfully through balancing pressure, which
counteracts the disparity between air pressure (from sound waves) and inner ear fluid pressure. Tympanic vibrations are transmitted through the ossicles and then concentrated onto the stapes, increasing the pressure over a smaller surface area. It also functions similar to a lever, such that when the membrane vibrates the stapes amplifies the pressure before it transmits it to the inner ear.
The inner ear contains the cochlea, filled with fluid essential to sound transmission. Stapes movement on the oval window causes the liquid to vibrate and travel up the spiraling structure, passing through the upper (scala vestibuli) and lower portion (scala tympani) to the round window, causing movement of the basilar membrane. This triggers movement of the organ of Corti, which contains cilia (hair cells) that bend from the subsequent, horizontal movements of the neighboring tectorial membrane. Cilia collectively bend due to their junction by tip links, opening ion channels in the cell, creating an inward flow of ions, while returning to their original position to close the ion channels. Repeated bending results in alternating transmission of electrical signal which releases neurotransmitters from the cells across the synapse to auditory nerve fibers. The signals are sent through a series of subcortical structures: the cochlear nucleus, superior olivary nucleus in the brainstem (signals from both ears meet here), inferior colliculus (mid-brain) and medial geniculate nucleus
(thalamus). They are then received by the auditory receiving area/primary auditory cortex (A1) of the temporal lobe. This area relays the signals to various auditory areas for sound localization, which can also be determined by the interaural time difference, or ITD, the time difference between sound waves reaching both ears. If the coffee maker is on our right and we are facing so that our right ear points towards it, then sound waves will reach the right ear quicker than the left, as the left ear is being blocked by the skull, which absorbs some of the waves.
Olfaction perception occurs in two stages and involves meeting a certain odorant concentration necessary for detection.
The coffee in this instance is our odor object (the source of the odor), and our olfactory mucosa and bulb (roof of nose) accepts odorant molecules carried into the nose by the air. Odorant molecules pass over the mucosa and come into contact with olfactory receptor neurons (ORNs) sensitive to specific odorant types. Each contains an olfactory receptor, similar to the retinal photoreceptors in the visual pathway. The olfactory receptor activates and sends a signal from the ORN to the glomeruli in the olfactory bulb, which receives sensory input, matches it to and fires for a particular odorant association. Odors leave the olfactory bulb after being mapped to the glomeruli and head to the piriform cortex, the main site for olfaction, where associations are made from learning. Chemotopic activation in the olfactory bulb and subsequently scattered ORN activation results in a pattern of neural activation in the piriform cortex across various cortices, from which we establish representations of odor for recognition, linking this pattern of activation with the associated odorant. Secondary olfactory processing is also done in the orbitofrontal cortex
(OFC).
Smell also plays a big role in the sensation of taste, as olfaction and taste converge at the mouth and nose. Taste receptors on the tongue, known as taste buds, respond to certain chemicals in food and drink and are situated at the back, sides and front of the tongue (structures on the tongue referred to as papillae contain a group of taste buds). Odorants may be released and reach the olfactory mucosa via the retronasal route, which connects the pharynx to the mouth (nasal to oral). The phenomenon of “tasting” food is a combination of sensory input from both the nose and mouth through tactile receptor stimulation (oral capture), successfully localizing flavor. From there, signals progress between the nucleus of the solitary tract of the brainstem and the thalamus and then to the insula of the cortex, the main taste area. From here, the insula works with the OFC to send and receive sensory input from the olfactory system (and also the olfactory bulb), which is processed by the hypothalamus, which handles hunger, and the amygdala, which handles emotional response to taste and smell. Coffee falls into two of the basic taste categories, sweet and bitter (absent the former without sugar). Additionally, having reduced olfaction inhibits odorant movement via the retronasal route and results in less precise taste due to the lack of olfactory sensory input from the nose to shape or identify our perception of the flavor.
Now that we have processed the finished coffee in relation to our senses of smell, sight, sound and taste, we progress to being able to physically drink the coffee. Having just finished brewing, the coffee warms the coffee cup as we reach to pick it up. Our perception of the coffee’s temperature begins with the transfer of heat from the cup’s exterior to the hand, which in turn signals touch receptors and transmits the signals to the dorsal root of the spinal cord. After being passed onto the spinal cord, the signals go one of two directions, either to the medial lemniscus, filled with large, quick-transmitting nerve fibers and accountable for grasping and touching, or the spinothalamic tract, filled with small fibers and responsible for pain sensation and temperature. Since we are feeling the warmth of the heat being transferred from the coffee to the cup’s exterior, our signals take the latter of the two pathways, but both routes ultimately proceed to the contralateral thalamus, the half opposite the side up which the signals originally came, and then subsequently transmitting them to the ventrolateral nucleus. The ventrolateral