To support their massive frames and the exerting physical activities that come with being a top predator, polar bears must have strong skeletal and muscular systems. There are many components of these systems that humans have as well, but of course there are differences that suit the polar bear and its lifestyle. Below, we will cover the muscular system of the bear and see what some of those differences are!
Note: unfortunately, there doesn't seem to be extensive research on the polar bear specifically, but the black and brown bear have been studied well and are quite similar to their Arctic relatives - remember, brown bears and polar bears are pretty closely related! In addition, many aspects are shared by other or all mammals, so with our current information we can still paint a pretty good picture.
Note: unfortunately, there doesn't seem to be extensive research on the polar bear specifically, but the black and brown bear have been studied well and are quite similar to their Arctic relatives - remember, brown bears and polar bears are pretty closely related! In addition, many aspects are shared by other or all mammals, so with our current information we can still paint a pretty good picture.
In all animals there are two types of muscle cells, or muscle fibers. Striated muscles, like heart and skeletal muscles exist in some proportion with unstriated (aka smooth) muscle cells.
Smooth muscle cells are often found in various organs, such as the uterus, where movement and contraction is involuntary. These fibers are innervated by the autonomic nervous system, so they kind of work on their own as opposed to skeletal muscles. For example, after having a meal a polar bear won't consciously contract their esophageal muscles to move the food from their mouth to their stomach. Instead, certain hormones (or other forms of input) activate the ANS to induce or modulate muscle contractions, and the food is digested without a second thought on the bear's part.
Cardiac muscles, when compared to the other muscle types, are unique in a few ways. For one, they feature intercalated discs that connect each cell to one another such that the contraction of one cell will cause the synchronous contraction of an adjacent cell.
Cardiac muscle cells also have special pacemaker cells that maintain a rhythmic contraction of the heart, and contractions can't summate as in other muscles. All of these factors ensure that the heart pumps blood consistently!
Cardiac muscle cells also have special pacemaker cells that maintain a rhythmic contraction of the heart, and contractions can't summate as in other muscles. All of these factors ensure that the heart pumps blood consistently!
Twitch fibers are an example of skeletal muscle fibers and are categorized based on their contractile speeds and capabilities, the most common being:
- slow oxidative fibers (type I), useful for long-term contractions but not very powerful
- fast oxidative fibers (type IIa), intermediates of type I and type IIx fibers
- fast glycolytic fibers (type IIx), which produce the most force but fatigue quickly
For the sake of simplicity, we're ignoring the type IIc and type IIax fibers - they're identified as intermediate fiber types and can represent multiple fiber type isoforms, but make up a small percentage.