Here is some simple information for GCSE
biology students about the different types of muscle tissues and why muscles work in
antagonistic pairs.
Index
Striped muscle is also called voluntary muscle. It
is sometimes called striped muscle because this is what it looks like through a
microscope. It is also called voluntary muscle because this is the muscle which you have
direct control over when you want to make a movement. You may also be told that it is
called Skeletal muscle, this is because it is attached to the skeleton. You can use any
one of these names.
Striped muscle is the muscle (or meat) on you legs
arms etc., you have direct control over these muscles and can make almost any movements
which you want to. These muscles are also found in your face and jaws, so they are used
when you smile or frown and when you talk, eat or drink.
Striped muscles are always found in pairs of
antagonistic muscles. A pair of muscles, the biceps and triceps, are used to bend and
straighten the elbow. When you make your biceps contract, it flexes the elbow (bends it).
When you contract your triceps, it extends the elbow (straightens it). The elbow, which is
a hinge joint, only needs one pair of muscles to make it work, but your shoulder, which is
a ball and socket joint, needs three pairs of muscles. This is because a ball and socket
joint can make three kinds of movement. Your arm can be moved forwards and backwards at
the shoulder; it can also be moved sideways up and away form your body and back down to
your side; thirdly, you can twist your arm round. In this third movement you can make the
palm of your hand point down or backwards and up and forwards. Some of this twisting
happens at the shoulder, but some of the twisting happens in your forearm.
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This is called smooth or involuntary muscle. It is
called smooth muscle because you cannot see any stripes when you look at it through the
microscope; it is also called involuntary muscle because you cannot make it contract and
relax through conscious control. Smooth muscle contracts and relaxes automatically. This
muscle is found in your intestines and in the iris of your eye. When you take a mouthful
of food, smooth muscles in your salivary gland squeeze the gland so that saliva squirts
into your mouth. Sometimes the muscles squeeze the salivary gland so strongly that it
hurts. If you bite into a sour apple, you feel a pain at the back of your jaw just
underneath your ear.
The muscles in your intestines also work in pairs.
When the circular muscles contract the make the intestines longer (and thinner) and when
the longitudinal muscles contract they make the intestines shorter (and fatter). These
muscles move food along the guts (peristalsis) and help to mix food with your digestive
juices.
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The muscle of your heart is also striped but it is
involuntary. It is called cardiac muscle: cardiac means "of the heart". Cardiac
muscle contracts and relaxes automatically without you having to think about it. When you
take exercise your heart beats faster and with a bigger volume. This increase in cardiac
output (how fast the blood is pumped around your body) is produced by a hormone called
adrenaline. The vagus nerve can make the heart go slower; this happens when you are
sitting or lying down.
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All muscles work in pairs. Whether they are striped
muscle, smooth muscle or cardiac muscle makes no difference, all muscles must work in
pairs. This is because they can contract and relax but cannot push or stretch themselves.
When your biceps contracts it flexes (bends) the
elbow joint. At the same time it also pulls the triceps to make it longer. So the triceps
is stretched by the biceps pulling it. When the triceps contracts is extends (straightens)
the elbow joint, and at the same time it pulls the biceps and makes it longer. So these
two muscles work together. Neither muscle can stretch itself, it must be stretched by its
antagonist (partner).
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Here is a diagram as seen
on my "blackboard" at Kingsbury High School:
Hope you can read my handwriting! When the biceps contracts and
the triceps relaxes, you can see that the triceps will be stretched. The elbow joint acts
as a pivot or fulcrum. As you can see, if the biceps gets shorter, the triceps must get
longer, the triceps is pulled by the end of the ulna: but if both muscles contract then
nothing will happen. The diagram shows the two muscles in red, the tendons are in yellow,
and the bone started off in blue but got turned into a multicolour mess when I converted
from a BMP file to a GIF file.
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Here the triceps is shown contracted
and the biceps has been stretched:
Now try the animated diagram
(needs Flash 5)
Technical Note: I did the drawing on my
blackboard (in this case a piece of paper); scanned it in with a flatbed scanner on
Virginia's computer; transfered to my computer; filled in some colour with Corel
PhotoPaint; converted from a bitmap (BMP) file to a GIF file; loaded it into MS FrontPage;
and here it is.
Here is an update on the two muscle diagrams:
Click Here
and
play off line (needs Flash 5).
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