what about goosebumps ?

There’s one thing that porcupines will always do better than humans: having goosebumps. Ok, ok, we cannot raise our quills when threatened, simply because we do not have quills. But when we have goosebumps, our body hairs behave exactly in the same way as porcupine quills do. Cutis anserina, a definitely less catchy way to call it, consists in the formation of bumps on the skin. The curious thing is that this phenomenon is involuntary 🙂 let’s try to understand how this happens.

A feeling of cold, a sudden strong emotion of fear, pleasure, euphoria and, yes, also sexual arousal… Our body reacts to all these events in the simplest way possible: trying to protect itself. And we cannot control it, since it’s a reflex (click here to read about another reflex typical of human body). In a previous post we learnt an interesting thing about human body thermoregulation: homeostasic processes (that we saw also here) always try to keep our Body Temperature (BT) of 37°C despite environment conditions. When outside it’s too cold, our energy losses get more important and our BT lowers too fast. We know that, for example, if we do some physical exercise (even a short run) we’ll warm up again quite fast. This is because the activation of muscles develops that energy needed to warm up the body and restore proper BT conditions. But when a sudden feeling of cold occurs, our skin receptors immediately send this information to the brain via the sympathetic nervous system. Our brain cannot wait for us to take a decision and, as previously said, automatically activates a protective action: shivering.
By doing this, our muscles produce really fast contractions that we cannot control (don’t forget we’re always dealing with a reflex!).

The twitching movements of muscles produce heat, which helps to raise BT. The contraction of the arrector pili muscles, that are the tiny muscles at the base of each hair, pulls the hair erect. In that moment our body acts like that of a porcupine, even if the latter experiences this reflex when threatened (by appearing larger, the animal intimidates enemies).

In exactly the same way, if our jaw muscles begin to shiver, we start chattering our teeth. The mechanism is always the same: BT lowering is detected and an automatic response is activated to raise it up again. In an extremely stressful situation, it is possible to have goosebumps also after experiencing the so-called fight or flight response, when (from this webpage) “the sympathetic nervous system floods the blood with adrenaline (epinephrine), a hormone that speeds up heart rate, metabolism, and body temperature in the presence of extreme stress”. But this is another story that we’ll see later. For tonight, don’t forget to feed your porcupine with a wonderful home-made soup (possibly warm)!

other sources: uno, due e tre

muscle contraction and EMG analysis

By chance I found this interesting article on the web. I decided to collect some useful information about muscle contraction and EMG analysis. Voilà 🙂

As God Wikipedia reports, “Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles”. Skeletal muscles are, as their name suggests, attached to the bones of the skeleton by means of tendons. Such muscles are controlled by the nervous system (precisely, the somatic nervous system, which is part of the peripheral nervous system). Thus, they can be activated voluntarily.

This image clearly shows that muscle fibers are the basic cellular units of skeletal muscles. They are long, cylindrical and multinucleated cells also called myofibers or myocytes.

If we zoom in on a single muscle fiber, we find that it contains myofibrils, whose diameter is about 1-2 micrometers! Myofibrils are very long chains of sarcomeres, that are the contractile units of the cell.

The sarcomeres are composed of protein filaments, some of them are thin (actin) and some others are thick (myosin). During the muscle contraction process (video explanation here), the thick filaments pull the thin ones towards the center of the sarcomeres, thus shortening (contracting) the length of the myofibrils, of the myofibers and, as a consequence, of the muscle itself.

Muscle contraction can be seen as the production of mechanical energy caused by either a chemical imbalance or an electrical impulse (motor neurons). The electrical activity related to this process can be measured by means of EMG analysis.

An electromyograph is needed to detect the electrical potential (up to 30 mV) generated by muscle cells at the moment of their electrical or neurological activation. Electrodes (or needles) are positioned on the patient’s skin (or inserted inside the muscle) and the electrical activity is recorded. The result is a signal called electromyogram, that can be analyzed for diagnostics (detection of medical abnormalities and measure of useful parameters) or to analyze the biomechanics of the considered movement. Muscle tissue at rest is normally electrically inactive. When the muscle is voluntarily contracted, action potentials begin to appear. As the strength of the muscle contraction is increased, more and more muscle fibers produce action potentials. When the muscle is fully contracted, there should appear a disorderly group of action potentials of varying rates and amplitudes (a complete recruitment and interference pattern).