KEY STAGE 3 | LEsslES AND BONES RESOURCE SHEET 1.3
JOINTS
Our bodies contain 206 bones and over 640 named muscles.
Working together, our skeletons and muscles allow us to move around. Our muscles are
attached to our skeletons at both ends by tendons. Tendons are tough and don’t stretch
much when they are pulled.
3
Joints occur where two bones meet. They make the skeleton flexible and no matter how
many muscles you have, without joints movement would be impossible.
The structure of a joint
is shown in the diagram
opposite. The joint is enclosed
in a tough capsule. Just
beneath this is the synovial
membrane. This membrane
produces synovial fluid, which
acts as a lubricant allowing the
two bones to slide smoothly
against each other. The ends
of the bones are made from
cartilage. This provides a good
smooth surface between the
two bones and prevents the
grinding you would get with
bone touching bone. Joints
with this kind of structure are
called synovial joints.
cartilage - prevents the
bones from rubbing aganst
each other, absorbs shock
and reduces friction
pelvis
ligament – holds the
bones together
ligament
synovial fluid –
reduces friction
synovial membrane
– encloses the
synovial fluid
femur
capsule – tough
fibrous tissue;
helps to hold the
bones together
Task 1
Investigate some of your own synovial joints. Move your arms and shoulders around – being
careful not to hit anyone close to you. How does your elbow allow your lower arm to move?
Compare this with your shoulder – how does your shoulder joint allow your arm to move?
Write down the different ways in which these joints allow you to move.
Synovial Joints
There are different types of synovial joint, allowing different ranges of movement:
• Your shoulder joint is a ball and socket joint, the ball is at the top of the humerus and
F EThis kind of joint allows a wide range
E ofL
the socket is formed by the shoulder girdle.
movement in any plane.
• Your elbow joint is different. This is a hinge joint.L Two knobs at the base of the humerusF
fit into two grooves at the top of the radius and ulna. These are the two bones that
make up your forearm. Your elbow will only allow movement in one plane.
NAME
E
KEY STAGE 3 | LEsslES AND BONES RESOURCE SHEET 1.3
Your Spine
front of spine
Synovial joints are not the only kind of joint to be found in
your body. Think about your spine. Here, one vertebra is
separated from another by a disc of cartilage and can only
move a little. However, put lots of vertebrae together to
form a backbone and together they allow the backbone to
bend easily.
back of spine
vertebra
disc
© Photographer: Linda Bucklin | Agency: Dreamstime.com
joint
Section of a human spine (back bone)
Non-moving Joints
There are other joints in your body where the bones
cannot move at all. These are found in your skull
and pelvis and are a result of the way your bones
grow. If your teacher has a skeleton available, see if
you can find examples of these joints.
Human skull showing joints between the skull plates
Levers
Moveable joints act like levers. There are three different kinds of lever found in the human body.
L
E
L
look upwards
F
E
F
L
F
E
stand on tiptoe
lift an object
F
L
EL F
E
L
F
F
E
F
EL
E
L
In the diagram E stands for effort force, L for load force and F for fulcrum. Fulcrum is another word
for pivot.
Task 2
Force and Distance Multipliers
Take a look at a model skeleton
and see if you can find places
where joints are acting as force
multipliers and other places
where joints are acting as
distance multipliers.
Remember that a lever is a force multiplier if the force it exerts
(the load) is closer to the pivot than the force applied to it (the
effort). This means that a small force applied to one end of the
lever produces a bigger force at the other end.
A lever is a distance multiplier if the force it exerts (the load)
is further away from the pivot than the force applied to it (the
effort). This means that a small movement applied to one end
of the lever produces a bigger movement at the other end.
L
F