Why Doesn't Your Sphincter Get Tired?

TL;DR

The anal sphincter doesn't get tired because it is made of smooth muscle, which is more energy efficient compared to skeletal muscle.

Transcript

[INTRO ♪] I don’t know about you, but I consider any day I don’t poop my pants to be a good day. When you think about it, though, it's kind of weird that we’re able to do that. The muscle that keeps things from leaking out of your body, your anal sphincter, is always clenching— So why doesn’t it get tired like any other muscle if you always clenche... Read More

Key Insights

• 👻 Smooth muscle in the anal sphincter is energy efficient, allowing for prolonged clenching without fatigue.
• 💪 The slower contraction speed of smooth muscle is beneficial for sphincters but not for skeletal muscles used in activities like running.
• 💪 Smooth muscle in the anal sphincter avoids the production of metabolic byproducts that cause fatigue in skeletal muscle.
• ❓ The anal sphincter consists of both internal and external layers, with the ability to contract involuntarily and voluntarily.

Questions & Answers

Q: Why doesn't the anal sphincter get tired even though it is constantly clenched?

The anal sphincter is made of smooth muscle, which is more energy efficient compared to skeletal muscle. It uses less ATP and avoids the buildup of metabolic byproducts that cause fatigue.

Q: How does smooth muscle in the anal sphincter differ from skeletal muscle?

Smooth muscle has more actin than myosin and lacks troponin, allowing the myosin strand to always have a spot to hook onto the actin strand. This enables smooth muscle to stay contracted for a long time without using much ATP.

Q: What are the advantages and disadvantages of smooth muscle in the anal sphincter?

The advantage of smooth muscle is its energy efficiency, allowing for prolonged clenching without fatigue. The trade-off is a slower contraction speed, which may be disadvantageous in certain situations where quick muscular response is required.

Q: How does the internal and external anal sphincter work together?

The internal anal sphincter contracts involuntarily but relaxes when it receives the signal to defecate. The external anal sphincter, which is skeletal muscle, can contract voluntarily and serves as a backup to the internal sphincter.

Summary & Key Takeaways

• The anal sphincter, along with other sphincters in the body, is made of smooth muscle, which is energy efficient.

• Smooth muscle contracts differently from skeletal muscle, using less ATP and avoiding the production of metabolic byproducts that cause fatigue.

• The slower contraction speed of smooth muscle in the anal sphincter allows for prolonged clenching without getting tired.