Living for Disco

A couple of days ago, Heather A asked me whether insects have muscles like we do. I like a challenge, especially when I get to show off about how clever I am at the end of it, so I looked it up on the internet, which is the source of truth and light, as we all know.

What I found out from the internet is that this is a very difficult question, particularly for someone who didn’t even do GCSE biology.

I did a bit of reading, and then I realized that I don’t actually know much about human musculature, so I looked that up. Did you know that the tongue is actually sixteen different muscles? And that the uterus is the strongest muscle in the human body?

Anyway, I digress. There are basically three types of muscles in humans (excuse me if you already know this): skeletal or striated, smooth and cardiac. Skeletal muscles are the ones we control in order move around. They contain fibres that are arranged into tight bundles, like drinking straws tied together with string. Skeletal muscles are further broken down into fast twitch and slow twitch muscles. Slow twitch muscles contract more slowly and with less force than fast twitch muscles.

Insects have three kinds of muscle – tubular, fibrillar and microfibrillar (found in moths, apparently). Tubular muscles are found in insect legs. Fibrillar muscles are usually used for flight , and are characterized by large spaces between the fibres. Each fibre is a single multinucleated cell, and so I guess this would answer your question about how many muscle cells they have. Humans have densely packed fibres, whereas insects, at least in fibrillar muscles, don’t, ergo they have fewer muscle cells in each muscle. I hope that this is the case, as I couldn’t confirm it anywhere. It’s purely conjecture. Any entomologists out there?

There are some insects (moths, for example) that have tubular and microfibrillar flight muscles, and they tend to have much slower wing beats – between 4 and 20 a second, as opposed to bees, which beat their wings around 190 times a second.

Also, insects don’t have haemoglobin, so their muscles tend to be grey, or translucent.

So to answer your question, vaguely, I think the answer is yes, they have skeletal muscles, but no, they’re not like ours. I had to stop though, because I kept coming up against paragraphs like the following, which I found on this highly informative website, and which make my brain twitch in distress:

In the presence of calcium, which is released from the sarcoplasmic reticulum due to nerve impulses, myosin ATPase splits ATP during oscillatory work. Stretch itself increases the activity of calcium-activated myosin ATPase – here stretch acts like an increase in calcium. This is also consistent with differences between myogenic and neurogenic systems. In neurogenic systems, each wing beat may be associated with a contraction-relaxation cycle, with substantial movement of calcium out of and back into the sarcoplasmic reticulum. Asynchronous muscles are less sensitive to calcium flux, which is also correlated with reduced development of sarcoplasmic reticulum.

Anyway, it was all very interesting, so thanks, Heather, for that. I will certainly never look at insects the same way again.

This entry was posted on Wednesday, May 23rd, 2007 at 3:37 pm and is filed under Miscellanea. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.