Nature

Achilles, Greek hero of the Trojan War and paragon of military excellence, displays a superbly muscled physique in this statue, located in Hyde Park, London

One Finger One Thumb, Keep Moving…

WHAT IS IT THAT REALLY SEPARATES THE PLANTS FROM THE ANIMALS? NEARLY ALL ANIMALS CAN MOVE AROUND OR MOVE BITS OF THEMSELVES, WHILE PLANTS JUST SIT THERE AND LIVE

By Mike George

Mike George is our regular contributor on wildlife and the countryside in France. He is a geologist and naturalist, living in the Jurassic area of the Charente

True there are some crossovers. We have all seen a Venus Flytrap slam shut on a hapless fly, and some animals like sponges and corals just seem to sit still in a very plant-like way. But the Flytrap’s way of moving is very different from that of an animal. In fact, it is so different that, as far as I have been able to find out, noone has worked out how a Venus Flytrap manages to close so quickly. Moreover, it is a purely automatic response. No intention on the plant’s part is involved. The sponge and the coral – indeed all animals - can move parts of their bodies at will. The mechanisms which enable animals to move are muscles. Muscles have existed, therefore, as long as animals have. Even a jellyfish uses a muscle system to move itself through the water. There are three basic types of muscles in an animal:

Smooth Muscle

This is the type of muscle that is under the control of an automatic section of the brain. These muscles are involved with life processes, like breathing, digestion, and so forth. In some cases, you as the user can take temporary control of some of them (such as when the doctor asks you to “take a deep breath”) but control reverts to the central system as soon as you cease to think about operating the muscles. In other words, these are the muscles that have to function to keep your body alive, and therefore your body must have control of them without your conscious input.

Cardiac Muscle

This is your heart muscle and the muscles immediately associated with the heart’s function. If all is well, your heart just goes on pumping blood around your system for as long as it is needed. The amount it pumps is controlled by feed-back loops involving the other vital organs, and the rate of pumping is regulated by “pacemaker” cells within the heart itself. You never think about these muscles until something goes wrong – then suddenly they become a matter for deep concern! Striated muscle (also called skeletal, or striped muscle) These are the rest of the bunch; the ones you use for moving, the ones that are, generally speaking, under your control. Of course, many of them are also subject to reflex action, whereby a certain stimulus causes a muscle to operate on a signal from a nerve without involving the decision-making part of the brain. These are built in to enable the muscle to take the affected part of you out of danger, for example when you touch something hot. Striated muscles are most noticeable when causing bones to move relative to each other, and are often attached to a different bone at either end to enable this to happen, but they also enable skin to be moved, for example to change the expression of the face. There is even one muscle that is only attached at one end! This is able to wave about in a manner which can be quite frightening. It is your tongue, of course!

How do muscles work?

Muscles are used to exert a force, but they can only do this in contraction. Any movement caused by the relaxation of a muscle is due to a second force acting to restore what has been moved. This may be a muscle set to oppose the motion of the muscle you have just used (for example when you wiggle a finger). In this case you are using two sets of muscles, an extensor and an adductor, working against each other. Sometimes gravity is the opposing force, for example when you raise your arms out and then let them fall back down. This is one reason that living in zero gravity is so fatiguing for astronauts. The muscles that work against gravity have less to do, but those that are normally assisted by gravity have more to do. The harder a muscle works, or the more effort it has to exert, the larger it will be, and the stronger will be its attachment to the surface it has to move (its “insertion”). The muscles are joined to the bone (or tissue) that they move by means of sinews. It is thus that anatomists, especially palaeontologists, can judge the size and action of muscles from studying a skeleton; they look at the size of the insertion scars on the bones and the size of the joint that they have to move. Since the shape of a vertebrate’s body is largely determined by the arrangement and size of its bones and of the musculature that operates those bones, they can build up a fairly good idea of the creature’s shape in life. Of course, when we think of muscles and skeletons our minds immediately think of a vertebrate animal, but of course, invertebrates also use muscles. Insects, for example, have muscles that move their skeletons, but their skeletons are external, so all the muscles work under cover and in some senses in reverse. Shelled animals also rely on muscles to open and close their shells. These muscles are often quite powerful, and leave insertion scars on the insides of the shells.

You never think about these muscles until something goes wrong –then suddenly they become a matter for deep concern!

It is all a question of balance

To understand how muscles operate in your body you need to understand how levers work. Now that seems fairly simple, but if you think back to your science lessons at school you may remember that there are three types (or “orders”) of levers, depending on the relative positions in which the load, the point where the effort is applied, and the pivot (this last often referred to as the “fulcrum”) are arranged:

First-order (or ‘class’) lever

Here the load is at one end, the effort is applied at the other, and the pivot is between them. This is the classic “see-saw” arrangement, and is the way a pair of scissors works. It occurs in several places in the body. The muscle system that pulls your head up to look forward or upward works in this way.

Second-order lever

Here the pivot is at one end, the effort is applied at the other, and the load is in between. This is how an old-style, onehanded nut-cracker operates. The system that pulls you up onto your toes works like this.

Third-order lever

Here the load is at one end, the pivot is at the other, and the effort is applied between them. A pair of tweezers is the classic example of this. There are plenty of examples in the body. The system that allows you to lift anything you are holding in your hand by bending your elbow operates on this system. Also, your jaw bites in this way. I am sure that, if you think about it, you will be able to assign a lever order to lots of your joints. The important thing to know is where the active muscle inserts on the bone. And don’t forget; the load may be the weight of the limb or your body itself, not just something you are carrying.

Why are they called muscles?

As we know from classical art and literature, the Greeks and the Romans had as much pride in their bodies as we do today, and the art of the body beautiful was practiced then as now. Athletes and warriors took pride in developing their physiques and demonstrating their prowess. The audience would have been exclusively male in ancient Greece. It was considered shameful for a woman to watch such exhibitions as sports, which took place in the nude. Gymnasium in Greek meant “a place of nakedness”. Even in Rome, among women usually only Vestal Virgins were allowed to watch the sports. Of course, then as now, there were always onlookers who loved to scoff. “Look at him flexing his arms”, they would say. “It looks as though little mice were running about under his skin!” The Roman word for a mouse was mus, and its diminutive, little mouse, was musculus. Hence the name. Admittedly, very few of us have bodies that are worth displaying quite so decoratively, but we all, whether we are a Venus or an Adonis or a couch-potato, have an amazing body, with over 600 muscles that work in perfect coordination, and without which we could not move, or stand, or feed, or pick up a book. As long as our muscles keep on working, we can keep on going, and that is really something to be thankful for.

It was considered shameful for a woman to watch such exhibitions as sports, which took place in the nude

The highest recorded jump by an insect is 70 cm (28 in) by the froghopper (Philaenus spumarius). When it jumps, the insect accelerates at 4,000 m (13,000 ft) per second and overcomes a G-force of more than 414 times its own body weight. For comparison, astronauts and jet-fighter pilots experience a at most 7G. The bug's hind legs contain extremely strong muscles. Energy is built up in them by slow muscle contraction, and a locking mechanism allows the legs to be fastened in place under the body like a taut crossbow string ready to fire. When the legs are freed, the energy is released and the insect takes off in a millisecond.

Longest Jumping Creatures

Fastest flying insect

There has been some disagreement about this. Currently, a dragonfly has been clocked at 35 miles per hour, while a Hawk Moth is in second place

A dog flea is able to reach 200 times its own body length. It store energy in the muscles of its hind legs, which it can release instantly. However, a tiny marine creature, the copepod, about 3 mm long, can jump through water at an accelleration of 1000 body lengths per second. A copepod's leg develops 10 times more force than any animal studied to date.

Strongest Insect

This is a species of Dung-Beetle, Onthophagus taurus, which can lift 1,141 times its own weight. That's equivalent to a human lifting 6 double-decker buses!

Furthest Flying Insect

Until recently, this was thought to be the Monarch Butterfly, which annually flies from its overwintering grounds in the Sierra Madre mountains in Central America to Canada, a distance of some 3000 miles. Its offspring would make the return journey each autumn, though how they knew the way nobody knows. Now, however, a tiny yellow Australian dragonfly, Pantala flavescens, has been found to commute across oceans and between continents, and has been deemed the champion

The Most Powerful Punch In the World

Mantis Shrimp. It's claws are actually club-like, and are provided with an energy-storage device that works rather like a war-bow. This is poweredup by muscle-power, and when the shrimp swings its club the energy that is stored transfers into the club; delivering a punch with about the power of a .22 bullet. It can smash the shells of its victims; it has even been known to smash the glass of the aquarium it was kept in!