Nervous Systems
Fig. 17. Aonyx cinereus. (Photograph by WhistlingKite24. “Asian Small-clawed Otter (Aonyx cinereus),” Zoo Chat [2019]. Retrieved December 2, 2021 from https://www.zoochat.com/community/media/asian-small-clawed-otter-aonyx-cinereus.447801/)
Mammals have the most complicated nervous systems on the planet (Sciencing, 2019). In most animals, this system is made up of two main divisions. The first division is the central nervous system (CNS), which is responsible for larger structures, like the brain and spinal cord. According to Thau et al, (2021) the brain is composed of nervous tissue, and is responsible for sensations (sensory neurons), movement (motor neurons), thought processes, communication, and more.
The second division is the peripheral nervous system (PNS), which consists of everything outside of the CNS. It is broken down into two subdivisions, the first of which is the somatic nervous system. This system controls the muscles that produce voluntary movements, such as snatching up a small crab for dinner. The remaining subdivision is the autonomic nervous system, which controls internal effectors, like cardiac
muscle, smooth muscles, and glands (Hill et al., 2016, 408).
Like sea otters, A. cinereus has two enhanced tactile structures, which are their facial whiskers and their paws (Strobel et al., 2018). According to the Denver Zoo (n.d.), A. cinereus has stiff whiskers, referred to as “vibrissae,” which are crucial for the otters to detect prey movement in the water. An example of these is shown in figure 17. It is believed that vibrissae function similar to the way human fingertips do, while they are exploring objects with their hands (Prescott et al., 2011, 6642). At the base of the vibrissae are nerve bundles that, when stimulated, send tactile information to the otters’ brain for processing.
As indicated by their common name, Asian Small-Clawed Otters have paws unique among their species. Their paws have incomplete webbing, and claws that do not extend beyond their toes, (figure 18). These otters also have enhanced dexterity with their paws, as seen in the juggling video, figure 19. This dexterity also allows them to use “tools,” in captivity to open shells for food access. This has led to studies concerning paw-preference for tool holding, which indicated there was an individual preference for A. cinereus (James, 2017, 19).
Fig. 19. Baisch, Beth, “Otter ‘juggling’ stones,” 2015, August 18. Puffins Pictures, 1:26. Retrieved December 1, 2021, from https://youtu.be/e2hiX38paj8
Fig. 18. Aonyx cinereus Paw. (Photograph by Yuwei, W. “Aonyx cinerea - Small-clawed otter paw,” Wiki NUS [2019]. Retrieved November 23, 2021 https://wiki.nus.edu.sg/display/TAX/Aonyx+cinerea+-+Small-clawed+otter)
Aside from giving otters the controlled use of their whiskers and paws, the brain plays a crucial role in hormone production. The hypothalamus, which is part of the CNS, is responsible for maintaining the otters' biological clocks, body temperature, the release of hormones like GnRH from the pituitary gland (see reproduction), and more.