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Muscles
and movement
Joanna
George-Johnson, Contributor
Muscles
are very important in mammals for
movement. There are three types of
muscles, skeletal, cardiac and
smooth. Cardiac
muscles are found only
in the heart.
Smooth
muscles, which are our
involuntary muscles, are found in
organs such as the bladder, blood
vessels and walls of the alimentary
canal.
Striated
muscles, which are voluntary
muscles, are found attached to bones.
Structure
is related to function
As
with most things in biology, 'form
follows function'. Bones are not different.
Features
of long bones (e.g., femur) and how
they are important to its function.
| Characteristic |
Importance
|
Hollow
in the centre
(a tube)
|
Increases
its tensile strength. The same
way the hollow tubular frame of
a bicycle is able to support a
grown man. |
| Light
compared to its size |
Easier
for animal to move about without
becoming too tired, too quickly. |
| Spongy
bone at head, compact bone at
perimeter |
They
maintain the rigidity of bone
without being too heavy. |
| Cartilage
at the ends |
Reduces
friction at the articulating surfaces.
Serves as a cushion. |
| *
Tendons: Attaches muscle to bone |
The
pull of the muscle is concentrated
over a very small area.
Helps to prevent rupturing of
muscle, when muscle is subjected
to a heavy load suddenly |
| **
Ligament: Attaches bone to bone |
They
confine movement of the structures
at each joint to a specific direction.
They strengthen joints. |
*
TENDONS:
Inelastic white fibrous tissue which
attaches muscle to bone. (They do
not stretch)
**
LIGAMENT: Tough elastic
white fibrous tissue that attaches
bone to bone. (They can stretch slightly)
Movement
in Humans
Movement
is brought about by the contraction
of skeleton muscles (striated muscles)
across. At joints, ligaments hold
bones together. They limit the movement,
thus preventing dislocation. The joints
move due to the force of muscles acting
on them.
Muscles
are attached to bones by tendons that
are made of collagen fibres. When
a muscle contracts, the tendon and
its attached bone are pulled towards
the contracting muscle.
Many
joints work due to the action of antagonistic
muscles; one set causes the joint
to move one way, the other set causes
it to return. When one muscle in the
pair is contracting, the other is
relaxing (not stretch-ing). An example
of this arrangement is the elbow joint
controlled by the bicep and tricep
muscles.
Ligaments
are made of connective tissue and
are elastic. Their function is to
hold bones together at a joint.
Tendons
attach muscles to bones. They are
attached to the membrane that covers
the bone called the periosteum.
They
are composed of tough non-elastic
fibres. This prevents them from stretching
when the muscles contract. Wherever
two or more bones meet, a joint is
formed. There are two main kinds of
joints.
A
fibrous joint is one where the bones
are held firmly together by fibres.
These joints are called sutures. The
bones in the cranium of the skull
are joined like this. They are held
so firmly together in an adult human
that they cannot move at all. There
are also fibrous joints between the
vertebrae.
A
synovial joint or movable joint is
formed where two bones need to move
freely.
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Joints
l
|
|
l
Immovable Joints
(Suture)
e.g. Skull, Pelvic girdle
|
------------------------------------
l
|
l
Moveable joints
l
|
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Freely
Moveable
(Synovial)
l
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Slightly
Moveable
e.g. adjacent vertebrate
Sliding joints (e.g bones in
hand)
|
|
l
Hings
joints
e.g. Elbow & Hip
|
l
Ball
& Socket Joints
e.g. Shoulder, Hip
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Questions
1.
Describe the movement at: 1) hinge
joint 2) ball and socket joint.
2.
Make a list of the functions of bones
in the human body and give examples
for each.
Joanna
George-Johnson teaches at Ardenne
High School.
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