During our class visit to Musée Fragonard at the École Veterinaire d’Alfort, we saw many cabinets full of organs, medical conditions, and abnormalities. A few cases displayed some of the first models designed to astonish the public and teach them about the structure and function of animal and human anatomy. A piece that stood out to me was the model of the lamprey’s circulatory system. Though I was not interested in the lamprey’s circulatory system, the model reminded me of the role of central pattern generators in the locomotion. The ever-famous experiment done on a cat whose spinal cord was severed and was observed to walk and run on a treadmill was a cornerstone study in the discovery of central pattern generators.
In NBB 301, we spent a lot of time discussing central pattern generators, which are described as motor control centers located in the spinal cord that can activate motion in the peripheral body without input from the brain. In other words, if the brain were separated from the spinal cord, the motor action could still occur. When I say brain input, I am referring to a series of neural pathways that send a command down the spinal cord and into the periphery to activate muscle effector neurons causing an action to occur. There are few actions that can be outsourced without a higher command, but lampreys provide a great example a central pattern generator as a means of locomotion.
When lampreys swim, they oscillate laterally from right to left. As muscles in the right-side body contract, the left-side body relaxes (Messina et al., 2017). This alternation in contraction is what allows the body to bend in either direction, and is made possible by interneurons that inhibit contraction on the side opposite to where contraction is occurring, as depicted in Figure 2. It is also important to note that although the central pattern generator can function without commands from the brain, it cannot function properly if there is a break in the chain. A singular neuron can run the full length of the spinal cord, and if any damage is done, the action cannot be expressed through the effector neurons that are located behind the damage (Messina et al., 2017). This provides evidence that there is a component of central pattern generators that rely on the interaction between both sides of the spinal cord. Additionally, by disrupting the continuation of signaling, it supports that the spinal cord is vital to neuronal communication to peripheral areas of the body.
Figure 1. In the Musée Fragonard at the École Veterinaire d’Alfort, the lamprey model if the circulatory system.
Figure 2. (a) Schematic of neural circuitry in the spinal cord, and (b) alternation of neural firing in the right-side and left-side body.
Works Cited
Messina, J. A., St. Paul, A., Hargis, S., Thompson, W. E., & McClellan, A. D. (2017). Elimination of Left-Right Reciprocal Coupling in the Adult Lamprey Spinal Cord Abolishes the Generation of Locomotor Activity. Frontiers in Neural Circuits, 11, 89. http://doi.org.proxy.library.emory.edu/10.3389/fncir.2017.00089