8.4 Humans at Work – Section 5
8.4.5 While the soft tissue of the brain is protected by the bones of the skull, it can
require further protection in certain situations
8.4.5.a
recall the role of the skeletal system in maintaining humans as functioning
organisms
8.4.5.b
outline the changes in structure and function of the bones of the skull from birth
to old age
8.4.5.c
define the term concussion
8.4.5.d
describe the effects of shaking or bruising of brain tissue and blood vessels
8.4.5.e
discuss the energy transfers and transformations involved when a hard hat or
helmet protects the head from injury
8.4.5.f
Discuss the relationship between the design, construction, testing and use of
hard hats and safety helmets in areas of building construction and sport
8.4.5.g
describe situations in which hard hats and safety helmets are used and identify
limitations in their development due to technology
8.4.5.i
process and analyse information by examining a model human skull to measure
the thickness of bone and inferred strength of the bone
8.4.5.ii
identify data sources, gather, process, analyse and present information on
laws/regulations governing the use of safety helmets and hard hats and use
available evidence to discuss how the design of the protective headgear is related
to activity in one of the following
– football headgear
– softball helmet
– hard hats
– cricket helmets
– bike helmets
1
8.4.5.a
Recall the role of the skeletal system in maintaining humans as functioning
organisms
5.1 The skeleton
The human skeleton is made up of 206 bones. An important
part of the skeleton is the skull, the skeleton of the head. It
consists of the eight bones of the cranium (the protective
covering of the brain) and fourteen bones of the face. Only one
of these bones (the lower jaw) can move. The rest are firmly
united and movement between them is impossible.
Bones are not firmly attached to one another but are connected
by flexible joints. Muscles and ligaments, or tough bands of
connective tissue, run from bone to bone, and allow some
movement at the joints.
The skeleton is made up of both living and non-living material
(hard calcium salts). The non-living material makes up the
outer surface of bone and is a dense, ivory like substance
known as compact bone.
Many small channels provide
passageways for the nerves and blood vessels that nourish the
bone. Bone can grow and change because of the activities of
living cells, which dissolve away and replace the hard non-living
material. Further, skeletal bone is hard yet flexible. It owes
these properties to its composition. The hardness of bone is
due to the non-living material (mostly the mineral calcium
phosphate) and the flexibility is due to the living material (mostly
an elastic substance known as collagen).
The functions of the skeleton are to support, protect and help with movement.
Support
The skeleton supports soft tissue. The rigid support of the skeleton raises the
body from the ground and maintains the shape of the body despite vigorous
muscular activity. It keeps some of the vital organs in position and prevents
them from crushing each other,
Protection The skeleton protects parts of the body. This bone casing protects certain
delicate and important organs of the body. For example, the brain is enclosed
and protected by the skull, the backbone protects the spinal cord, while the rib
cage protects the heart and lungs.
Movement The skeleton allows the body to move. Most parts of the vertebrate skeleton
can move relative to each other. The muscles, coordinated by the nervous
system, exert forces on the bone resulting in movement.
© P Wilkinson 2002-04
2
8.4.5.b
outline the changes in structure and function of the bones of the skull from birth
to old age
5.2 The changing skull
Growing up does not just involve getting bigger. As a human ages (from birth to adulthood)
there are changes in basic body structure. As growth occurs cells of the brain and body become
specialised. The growth of these specialised cells means tissues and organs grow and change.
The process by which the cells of the brain and body become specialised into different types of
tissues is called MATURATION.
A good example of maturation is the changes that occur in the
skeleton. At birth a babies’ skeleton consists of a large amount of
cartilage. Cartilage is quite soft and it is several months before
the skeleton can fully support the baby's limbs. This temporary
cartilage skeleton is surrounded by a connective tissue jacket,
which contains bone-building cells (called osteoblasts). When
these cells become active, they absorb soluble calcium salts
from the blood, convert them into insoluble salts that are
deposited in the cartilage causing it to harden. This bone
hardening process is called ossification. The cartilage skeleton
is gradually converted to bone. Complete maturation of the
skeleton takes about 20 years.
As a result of this, adult bone is hard and rigid and more likely to fracture (break) than that of
a young child. A child has a higher amount of elastic organic matter, and over stressing
causes only a partial or greenstick fracture. In the elderly a gradual loss of elasticity makes
bone more brittle, and much more likely to fracture.
QUESTION
5-1
© P Wilkinson 2002-04
Look at the two diagrams opposite. They show
differences in the maturation of the skeleton
between a newborn and adult (constructed to
the same size). In the newborn there is still a
large amount of cartilage
3
a]
Describe the main differences in the two
skeletons.
b]
What is the same about the two
skeletons?
Besides this general change of cartilage to
bone there are some specific changes that
occur in the skull. In adults, the bones of the
skull fit together like the pieces of a jigsaw
puzzle. At birth these edges are not yet
interlocked but are held together by connective
tissue strips called sutures. A suture is formed,
by the fibrous covering of the two bones. In the
late foetus and newborn child, the sagittal
suture, which separates the right and left halves
of the roof of the skull is quite wide. This
enables one of the halves to glide over the
other during the passage of the child through
the mother’s pelvis during birth, thus reducing
the width of its skull.
In certain spots, the sutures are wide and there are soft spots called fontanelles; they lie
immediately above a large blood channel. The rear fontanelle provides an easy access for
obtaining a blood sample from the very young infant. As a child matures, the sutures fuse at
various dates from childhood to old age. Until maturity the sutures are active sites of growth
of the bones they separate. This fusion is due to the conversion of the fibrous tissue to bone.
Excepting those of the foetus and newborn infant, all sutures are narrow. After birth all
sutures become immobile joints.
QUESTION
5-2
The graph opposite shows the size
attained by various tissues.
The
measurement is given as a percentage
of final size for ages from birth to 20.
The most obvious feature that follows the
general curve is height. It also reflects
changes in the skeletal and muscular
dimensions as well as the dimensions of
the internal organs such as the liver, the
spleen, and the kidneys. Exceptions to
this general pattern exist, most notably
the brain and skull. If the brain has any
adolescent spurt at all, it is a small one.
A small but definite spurt occurs in head
length and breadth, but all or most of this
is due to thickening of the skull bones
and the scalp.
a. Write THREE sentences based on the information in the graph.
© P Wilkinson 2002-04
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8.4.5.c
define the term concussion
Concussion is a temporary disturbance of brain function caused by a sudden blow to the head
[World Book Encyclopaedia].
Signs of concussion include a temporary, loss of
consciousness, memory loss, headaches, and a loss of alertness. Injuries to the head should
always be considered serious. In the case of concussion the length of time the person is
unconscious is very important.
© P Wilkinson 2002-04
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8.4.5.d
describe the effects of shaking or bruising of brain tissue and blood vessels
5.3 HOW THE BRAIN IS HURT
What to do
1
2
Read the information below on how the brain is hurt.
Summarise this information using a two-column summary.

The first column contains the main ideas. [There are three main ideas – bleeding,
tearing and swelling].

The second column contains associated points
[source: http://www.tbiguide.con]
Thousands of people are seen by doctors because of an injury to the head. Many of these
will suffer long term problems that will affect their ability to work and/or affect their daily lives.
Car accidents are a major cause of head injuries. Even at moderate rates of speed, traumatic
brain injuries can and do occur. Three separate processes work to injure the brain: bruising
(bleeding), tearing, and swelling.
BRUISING (BLEEDING)
If a person is driving a car at 70 kilometres per hour and is struck head-on by another car
travelling at the same speed, the person's brain goes from 70 kilometres per hour to zero in
an instant. The soft tissue of the brain is propelled against the very hard bone of the skull.
The brain tissue is squashed against the skull and blood vessels may tear. When blood
vessels tear, they release blood into areas of the brain.
Medical experts are concerned about head injuries because of the possibility of bleeding in
the brain. A major problem is that there is no room for this extra blood. The skull, being hard
and brittle, does not expand. So the blood begins to press on softer things--like brain tissue.
Brain tissue is very delicate and will stop working properly or may even die off. Large
amounts of bleeding in the brain, can increase the pressure and make critical areas of the
brain stop working. Areas that control breathing or heart rate could be affected, and a life or
death situation could develop within hours of the accident. Some people with a head injury
from a car accident seem "just fine" right after at the accident. Some have even gotten out of
the car and directed traffic. However, within a short period of time, they can get more and
more confused until they eventually lapse into a coma. This is why people with head injuries
need to be carefully monitored and preferably go to a hospital following a car accident.
© P Wilkinson 2002-04
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There is also an "odd" thing that the brain goes
through during a car accident. The brain, which is
very soft, is thrown against the front part of the skull,
which is very hard, and bruising can happen. But the
injury process is not over. The brain, and rest of the
body, fly backward. This bouncing of the brain first
against the front of the skull and then against the
back of the skull, can produce bruises in different
parts of the brain. Thus people can have a bruise not
only where their foreheads hit the steering wheel, but
other areas of the brain as well. Doctors call this a
"contra coup" injury.
TEARING
In the case of the car accident, the brain is thrown forward, then bounced backward. In this
forward/backward motion, the brain can be torn. Tearing in the brain is very serious. Tearing
in the brain "cuts" the wires that make the brain work.
One of the problems with tearing is that it happens on a microscopic level (the brain has
about 100 billion of these "wires"). This tearing may not show up on typical medical tests.
Devices that take pictures of the brain will not see these small tears. Two common ways of
viewing the brain are with a CT Scan (using X-rays) and an MRI (using magnetic fields) to
create pictures of the brain. Both of these techniques are very good at seeing blood and
tumors in the brain, but they are not good with tears (which are very small). In a number of
medical studies with people who have head injuries, only 10 to 15 percent had "positive" CT
Scans or MRI findings [A "positive" finding means something abnormal was found].
SWELLING
If I drop a bowling ball on my foot, my foot will turn "black and blue" due to blood leaking
under the skin. But my foot will also do something else--it will swell up because of the release
of other fluids into the area. The body realises that the foot has been injured and sends
agents to heal the injured area. The problem with the brain is that there is no extra room and
the pressure begins to build up. This pressure pushes down on the brain and damages
structures in the brain. Sometimes, doctors will install a "relief valve" (intra-cranial pressure
monitor or ICP) to let off the excess pressure.
OPEN VERSUS CLOSED HEAD INJURY
Not too long ago, doctors made the distinction between open and closed head injury. In a
open head injury, the skull is fractured and doctors assumed this would produce a severe
head injury. In closed head injury, the skull is not broken and doctors assumed these
produce less severe injuries. Wrong! In closed head injury, pressure builds up and damages
brain tissue. If you fracture the skull, you may let off excess pressure thus saving the brain
from further damage. Because of the wide variation, these terms are no longer used.
© P Wilkinson 2002-04
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8.4.5.e
discuss the energy transfers and transformations involved when a hard hat or
helmet protects the head from injury
5.4 Energy transfers in collisions
In a collision, energy is transferred from one object to another.
The purpose of a helmet is to reduce the amount of energy
transferred to the head. This reduces the potential for injury.
A moving object possesses kinetic energy. Therefore, a person
riding a bicycle possesses kinetic energy.
The law of
conservation of energy states that, energy is neither created or
destroyed, but is transferred from one form energy into another.
The kinetic energy is converted into
 Sound energy
– you hear it
 Potential energy
– the object is deformed (ie changes
shape like a spring) and this deformation
stores energy.
 Heat energy
– friction produces heat when two objects
rub together
-- when the object breaks or tears a large
amount of heat energy is released
To protect the head a safety helmet is designed to deform and
then break apart. This means the helmet absorbs energy from
the collision reducing the energy transfer to the head. Energy
not absorbed by the helmet will be transferred to the head. The
head also deforms and can break apart to convert kinetic energy.
The helmet also works because it spreads the energy transfer
over a wider area and it prevents the head from sliding
unprotected on the ground.
© P Wilkinson 2002-04
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5.5 Helmets and head injuries
Problem
A senior science class wanted to find out how a safety helmet protects the head
from injury. They knew it had something to do with the transfer of energy. To investigate this
problem they set up the following experiment.
Method
1. A senior science dummy was strapped onto a
trolley.
2. The trolley was allowed to roll down a slope into
two different walls so that the dummy would crash
into the wall headfirst (see diagram).

Wall 1 – Solid concrete

Wall 2 – Solid foam cushioning
3. In both situations:

the speed of the dummy was kept the same.

the same dummy was used.

the same trolley was used.
4. The experiment was repeated several times using a new helmet for each test.
5. The head of the dummy was examined after each test. The results of this examination
were recorded.
Results
Describe the observations you would expect to see [to the head of the dummy].
QUESTIONS
5-3
5-4
5-5
What is the independent variable in this experiment?
What is the dependent variable in this experiment?
The wall could have been made from materials other than foam or concrete. Suggest
one such material and describe the possible results.
5-6
What are two controlled variables in this experiment?
5-7
What features of this experiment make it valid?
[Remember validity is related to right method]
5-8
What are the groups being compared in this experiment?
5-9
What is being measured in this experiment?
5-10 Why is the experiment repeated several times?
© P Wilkinson 2002-04
9
Explaining results.
What to do
1. Read the information below and then
2. Discuss the reasons why a safety helmet protects the head from injury.
3. Write a summary to provide an explanation for the problem.
Information
In both cases the dummy was stopped completely by the wall. A physics explanation is
that in both cases there was the same change in momentum.
The change in momentum equals impulse and therefore the impulse was the same.
Impulse equals force multiplied by time (I = F x t).
 The concrete wall stopped the dummy very quickly. Therefore, for Wall 1 to stop the
dummy, a large force was applied over a very small period of time. The transfer of
energy occurred over a very short period of time.
 The foam wall stopped the dummy slowly. Therefore, for Wall 2 to stop the dummy, a
smaller force was applied over a much longer period of time. The transfer of energy
occurred over a longer period of time.
The crash into the concrete wall meant a large force was applied to the head of the
dummy. The crash into the foam wall meant a smaller force was applied to the head of the
dummy. The larger the force the more damage to the head of the dummy. Therefore the
dummy suffered less injury when it crashed into the foam wall.
A safety helmet is like the foam wall. It works because it increases the time over which the
collision occurs. This in turn reduces the force applied to the head. This in turn reduces
the injury to your head. Considerable scientific research and development has occurred to
find the best materials to use in a helmet and also the best design for the helmet.
This principle is also used in the design of cars. Today, cars are designed to collapse
during a collision so that the impact of the crash is absorbed over a longer time. This in
turn means that a smaller force is applied to the people inside the car reducing possible
injury.
Other features of the helmet include the hard outer shell, which prevents penetration of
objects. Spreading of the force over a larger area.
© P Wilkinson 2002-04
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5.6 How helmets work?
Summary from Website: html://www.bhsi.org/webdocs.htm
What to do
1. Read the information below on bicycle helmets.
2. Summarise this information using a two-column summary.

The first column contains the main ideas

The second column contains associated points
It is important to always wear a bicycle helmet. Road rash and broken bones heal; scrambled
brains may not. Medical research shows that, 88 per cent of cyclists', brain injuries can be
prevented by a bicycle helmet. Even low-speed falls from bicycle can result in brain injury.
There are other benefits attained by wearing a helmet. Car drivers see you better and give
you more respect. Also, helmets may be required by law in your area.
A well-designed helmet is obviously the most important factor involved in head protection.
There are other important factors associated with wearing a helmet.
 It is important that the helmet fits. A good fit means level on your head, touching all
around, comfortably snug but not tight. The helmet should not move more than about an
inch in any direction, and must not pull off no matter how hard you try.
 Pick a bright colour for visibility to be sure that motorists and other cyclists
can see you.
 Common sense tells you to avoid a helmet with snag points sticking out, a
squared-off shell, inadequate vents, excessive vents, an extreme "aero" shape, dark
colors, thin straps, complicated adjustments or a rigid visor that could snag in a fall.
How Does a Helmet Work?
A bicycle helmet reduces the peak energy in a sharp impact. This requires a layer
of stiff foam to cushion the blow by crushing on impact. Nearly all bicycle helmets do this
with expanded polystyrene (EPS), the white picnic cooler foam used to protect eggs
and computers. Once crushed, the foam does not recover. Spongy foam is added inside
for comfort and fit. Another foam, expanded polypropylene (EPP), does recover, but
its use is spreading slowly. It may have some undesirable "rebound." A stronger EPS
called GECET appeared in 1992 and is widely used now. A third foam called EPU
(expanded polyurethane) is used for helmets made in Taiwan. It has a uniform cell
structure and good crush without rebound, but is difficult to manufacture.
The helmet must stay on your head even when you hit more than once--usually a car first,
and then the road. So it needs a strong strap and an equally strong fastener that cannot
be jiggled open. The helmet should sit level on your head and cover as much as possible.
Above all, with the strap fastened you should not be able to get the helmet off your head
by any combination of pulling or twisting. If it comes off or slips enough to leave large
areas of your head unprotected, adjust the straps again or try another helmet. Keep
the strap comfortably snug when riding.
© P Wilkinson 2002-04
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What Type do I Need?
Most current helmets are basically all EPS foam with a thin plastic outer shell. The shell
helps the helmet skid easily on rough pavement to avoid jerking your neck. The shell also
holds the EPS together after the first impact. Some excellent helmets are made by moulding
the EPS in the shell rather than adding the shell later.
You want a smooth plastic outer shell, not the alternating strips of plastic and foam on the
outside. Excessive vents mean less foam in contact with our head in a crash, which could
concentrate force on one point of your skull. "Aero" helmets are not noticeably faster unless
you ride at competition speeds, and the "tail" could snag in a fall. There is no real advantage
to using titanium in a helmet. Dark helmets are hard for motorists to see, and even those
silver stripes on many helmets that look reflective are not. Skinny straps are less
comfortable. Few riders need visors, which can snag or shatter in a fall.
Comfort Requirements
Coolness, ventilation, fit and sweat control are the most critical comfort needs. Air
flow over the head determines coolness, and larger front vents provide better air flow.
Most current helmets have adequate cooling for most riders. Sweat control can require
a brow pad or separate sweatband. A snug fit with no pressure points ensures comfort
and correct position on the head when you crash. It may take a half hour of wearing
to feel pressure points. Weight has not been an issue with today's thin shell helmets.
When Must I Replace a Helmet?
Replace any helmet if you crash. Impact crushes some of the foam,
although the damage may not be visible. Helmets work so well that you
need to examine them for marks or dents to know if you hit.
© P Wilkinson 2002-04
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8.4.5.f
Discuss the relationship between the design, construction, testing and use of
hard hats and safety helmets in areas of building construction and sport
8.4.5.g
describe situations in which hard hats and safety helmets are used and identify
limitations in their development due to technology
QUESTIONS
5-11 Look at the advertisement for the ADVENT bicycle helmet. List the design features,
which reduce head injuries.
5-12 Activity
Bring a number of different helmets or headgear to class. These may
include a bicycle helmet, a motor cycle helmet, a hard hat used in industry, a surfing
helmet, football headgear and other types of headgear worn for protection.
a. Briefly describe TWO examples of this protective headgear, stating clearly how they
protect the head.
b. List some differences and similarities.
© P Wilkinson 2002-04
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5-13 Fatal injuries in motorcycle riders according to helmet use
Information source:
Journal of Trauma 1995 Feb;38(2):242-5,
Sarkar S, Peek C, Kraus JF
Department of Epidemiology, School of Public Health, University of California-LA.
OBJECTIVE: Helmets have been shown to be effective in preventing head injuries
in motorcyclists, but some studies have suggested that helmets may cause injury to
parts of the head or neck because they add mass to the head.
DESIGN: This study examined patterns of fatal injuries in helmeted and
unhelmeted motorcyclists.
MATERIALS AND METHODS: Coroner reports, hospital records, and police reports
for motorcyclists fatally injured in crashes from July 1, 1988 through October 31,
1989 were examined. All injury diagnoses were abstracted and coded to the 1990
version of The Abbreviated Injury Scale and the International Classification of
Diseases, 9th revision. MAIN
RESULTS: Cerebral injury, intracranial haemorrhage, face, skull vault, and cervical
spine injuries were more likely to be found in fatally injured unhelmeted
motorcyclists than in helmeted motorcyclists.
CONCLUSIONS: These results expand earlier reports showing that helmets
provide protection for all types and locations of head injuries, and show that they
are not associated with increased neck injury occurrence.
a. What is a possible hypothesis for this investigation?
b. What is the independent variable?
c. What is the dependent variable?
d. Data on the injuries investigated came from many different sources. The problem
facing the investigators was how to measure the data so that it could be compared.
How did this investigation code data so that it could be validly compared?
[Remember, reliability relates to good method]
e. This data in this investigation was not collected by an experiment.
ii.
What type of investigation was completed?
iii.
Was this a first hand or second hand investigation? Give a reason.
f. How many reports and records would need to be collected for the conclusion to be
reliable?
g. What was the conclusion of the investigation?
© P Wilkinson 2002-04
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5-13
The table below shows data on the distribution of bicycle deaths by the time of day.
Time of day
Percent of deaths
Midnight – 3am
3am – 6 am
6am – 9am
9am –12 (noon)
Noon – 3 pm
3pm – 6pm
6pm – 9pm
9pm - midnight
6
4
8
8
14
22
23
16
a. Explain why a bar graph should be used to graph the data in the table above.
b. Draw a graph of the data in the table.
c. What conclusion could be drawn using the data in the table?
5-14
The table shows the distribution of bicycle deaths per million people, by gender.
Age
Male
3
1
4
2
5
3
6
4
7
7
8
7
9
7
10
10
11
10
12
10
13
14
14
12
15
9
16
6
17
5
18
6
19
3
20-24
4
>=25
5
© P Wilkinson 2002-04
Female
1
0
1
1
3
3
2
2
2
1
2
2
0
1
2
0
0
1
1
a. Explain why a line graph should be used to graph
the data in the table opposite.
b. Draw a graph of the data in the table.
c. Explain how this information would be used in an
advertisement campaign to reduce deaths
associated with bicycles.
[Source : http://www.bhsi.org/webdocs/stats.htm]
15
8.4.5.i
process and analyse information by examining a model human skull to measure
the thickness of bone and inferred strength of the bone
8.4.5.ii
identify data sources, gather, process, analyse and present information on
laws/regulations governing the use of safety helmets and hard hats and use
available evidence to discuss how the design of the protective headgear is related
to activity in one of the following
– football headgear
– softball helmet
– hard hats
– cricket helmets
– bike helmets
© P Wilkinson 2002-04
16