Sensory systems
In this workshop, we finished last week’s introduction to the nervous system. We learned how information travels within a neuron and how information gets transmitted from neuron to neuron. Contrary to our intuition, the signal that travels down the axon of a neuron is electrical, but the signal that moves across the synapse (which is where information flows from one neuron to another) is actually chemical. The conversion of the signal from electrical to chemical happens at the synaptic cleft.
We also started a new topic: sensory systems. We explored how the brain integrates information received from the different senses to figure out what is going on in the world. We discussed which of the senses we would hate to live without (students were split in their opinions and this elicited a lively discussion). We learned how some animals have senses that we don’t, such as mosquitoes’ abilities to sense carbon dioxide or platypuses’ abilities to detect electric fields generated by prey.
We then honed in on the sense of touch. We learned that the somatosensory cortex is the sensory area for the sense of touch. We explored how some areas of the skin are more sensitive than others. For instance, we had people close their eyes while their partners gently rubbed different objects on their forearms and fingertips. Generally, students were not very good at discriminating between similar objects with their forearms, but they were much better able to discriminate between similar objects with their fingertips. We tried very different types of objects like aluminum foil vs. parchment paper, paper towel vs. copy paper, penny vs. button, and rubber band vs. twist tie.
We were then introduced to the idea of sensory receptors: specialized cells that receive information from the external environment. In the skin, there are different types of receptors, some which are specific to temperature and some which are specific to pressure. Areas of the skin that are more sensitive (e.g., fingertips) have more receptors than areas of the skin that are less sensitive (e.g., forearm). We also learned that the receptive field, or the area of the skin from which a receptor receives information, is bigger in areas like the forearm than the fingertips. When asked why that would be the case, some students thought that it’s because the forearm is bigger than the fingertips. The actual reason is because in areas with more receptors like the fingertips, receptors are closer to one another, which means that the area of the skin from which each receptor is receiving information is smaller.
We ended the class by doing another activity. We measured the sensitivity of different body parts (palm of the hand, arm, forehead, leg, back, and foot) by measuring two-point discrimination (the ability to tell that two nearby objects touching the skin are two points instead of one point). We had two points 3.75 mm, 7.5 mm, 15 mm, 30 mm, and 60 mm apart. Overall, people discovered that points on the back had to be further apart in order to tell that they’re two points as opposed to one point, whereas people were generally good at making two-point discrimination at the palm of the hand even when the distance between the two points is small. We ran out of time, but next time we meet, we will learn how the somatosensory cortex contains a map of sensory space and use all our measurements from this workshop to create personalized cortical representations of our bodies.
Until next time!
Lily