8.4Humans at Work – Section 5
8.4.5While the soft tissue of the brain is protected by the bones of the skull, it can require further protection in certain situations8.4.5.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
8.4.5.a / Recall the role of the skeletal system in maintaining humans as functioning organisms
5.1The 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.
SupportThe 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,
ProtectionThe 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.
MovementThe 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.
8.4.5.b / outline the changes in structure and function of the bones of the skull from birth to old age5.2The 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
5-1Look 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
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
5-2The 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.
- Write THREE sentences based on the information in the graph.
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.
8.4.5.d / describe the effects of shaking or bruising of brain tissue and blood vessels5.3HOW THE BRAIN IS HURT
What to do
1Read the information below on how the brain is hurt.
2Summarise 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:
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.
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.
8.4.5.e / discuss the energy transfers and transformations involved when a hard hat or helmet protects the head from injury5.4Energy 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.
5.5Helmets and head injuries
ProblemA 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
- A senior science dummy was strapped onto a trolley.
- 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
- In both situations:
- the speed of the dummy was kept the same.
- the same dummy was used.
- the same trolley was used.
- The experiment was repeated several times using a new helmet for each test.
- 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
5-3What is the independent variable in this experiment?
5-4What is the dependent variable in this experiment?
5-5The wall could have been made from materials other than foam or concrete. Suggest one such material and describe the possible results.
5-6What are two controlled variables in this experiment?
5-7What features of this experiment make it valid?
[Remember validity is related to right method]
5-8What are the groups being compared in this experiment?
5-9What is being measured in this experiment?
5-10Why is the experiment repeated several times?
Explaining results.
What to do
- Read the information below and then
- Discuss the reasons why a safety helmet protects the head from injury.
- 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.
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.
5.6How helmets work?