Musculoskeletal anatomy: WJEC A level Biology revision notes

Lesson 1 of 25

What are the three types of cartilage?

These notes cover Option B, Human Musculoskeletal Anatomy, in WJEC A level Biology Unit 4: , Inheritance and Options. The option has three sections: skeletal tissues, the structure and function of the human skeleton, and joints. Each lesson follows the WJEC specification, and the exam tips come from BioWelsh analysis of WJEC past papers.

is a : living cells spread out in a that they make themselves. The cells are called , and each one sits in a small space in the called a . The is firm but flexible, and it contains protein fibres. The kind and amount of fibre decides which of the three types of you are looking at.

The diagram below compares the three types of as they look under a light microscope.

Three rectangular panels of tissue side by side. The first, hyaline cartilage, shows purple oval cells in white rings scattered in pairs and singly across a plain lilac background. The second, yellow elastic cartilage, shows the same cells among many dark wavy lines crossing in all directions. The third, white fibrous cartilage, shows thick pink wavy bands running across the panel with rows of small cells between them. Labels point to a chondrocyte, a lacuna, the matrix, the elastic fibres and the thick collagen bundles. — The three types of cartilage as seen with a light microscope. Original BioWelsh diagram.

In every type, sit in surrounded by .
has a smooth, glassy . It contains a high proportion of , but the fibres are too fine to see.
has a dense network of elastic fibres as well as , so it springs back into shape after bending.
has thick bundles of fibres lined up in the direction of stress, with in rows between them.

The three types of cartilage
Type	Structure	Properties	Where it is found
Hyaline	Fine fibres in a smooth	Smooth, reduces friction; firm but slightly compressible, so absorbs shock	Ends of bones at joints (), rings of the trachea, ends of the ribs, nose
Yellow elastic	plus many elastic fibres	Flexible and returns to its shape after bending	Outer ear (pinna), epiglottis
White fibrous	Dense, parallel bundles of	Strongest type; high tensile strength and resists compression	, pads in the knee joint, where join bone

has no blood vessels. get oxygen and nutrients by slow through the , so damaged repairs itself very slowly.

The photograph below shows from the wall of a trachea, stained and seen with a light microscope.

Light micrograph with a deep pink band along the top edge and below it a broad pale pink area scattered with many small dark pink oval spots, each in a small pale space. — Hyaline cartilage from the wall of a trachea, stained and seen with a light microscope. Photo: Berkshire Community College Bioscience Image Library, CC0.

The pale pink area is the . It looks smooth because the fibres are too fine to see.
The small dark spots are , each in its own .
The deep pink band at the top is the lining of the trachea, which is not .

Lesson 2 of 25

What is compact bone made of?

Bone is also a , but its is hardened with minerals. There are two kinds of bone tissue. is dense and forms the hard outer layer of every bone. , found at the ends of long bones and inside , is a lattice of thin struts with spaces filled with marrow.

The two components of the compact bone matrix
Component	Share of the matrix	Main substance	Function
Organic	About 30%	The protein	Gives flexibility and tensile strength, so bone bends slightly instead of snapping
Inorganic	About 70%	, a mineral of calcium and phosphate	Makes bone hard and rigid, so it resists compression

The two work together, like steel rods set in concrete. Without , bone would be hard but brittle. Without , bone would be flexible but soft, which is what happens when too little calcium is laid down in .

The illustration below shows a block cut from a long bone, with on the outside and inside.

Labelled illustration of a cylinder cut from a bone. The outer wall is made of tall cylinders labelled osteons, one pulled out and labelled with lamellae, lacunae and canaliculi. Blood vessels in red run along a Haversian canal and across in a Volkmann's canal. The inner part is a lattice labelled trabeculae of spongy bone. The outer covering is labelled periosteum. — A block of long bone showing compact bone on the outside and spongy bone inside. Photo: SEER, US National Cancer Institute, Public domain.

The outer layer is , built from cylinders called , or .
Blood vessels run down the Haversian canals and across the bone in .
The inner lattice is . Its struts are called .
The periosteum is the tough membrane covering the outside of the bone.

Lesson 3 of 25

How is compact bone built from Haversian systems?

is made of many , also called . Each is a cylinder about a millimetre across that runs along the length of the bone. Bone cells are trapped deep in hard mineral, so the whole structure is arranged to keep every cell supplied with oxygen and nutrients.

The diagram below shows one cut in transverse section.

A large circle made of concentric rings on a beige background, with small dark almond shapes arranged in rings between the lines and fine short lines running from each shape. In the centre is a round canal containing a red circle, a blue circle and a small yellow circle. A pale channel with a red line runs from the canal out to the right edge. Partial rings fill the corners. Labels identify the Haversian canal, arteriole, venule, nerve fibre, lamella, lacuna, canaliculi, Volkmann canal, the edge of the system and interstitial bone. — A Haversian system in transverse section. Original BioWelsh diagram.

The in the centre carries an arteriole, a venule, a lymph vessel and fibres.
Rings of bone called surround the canal like the rings of a tree trunk.
Bone cells sit in between the .
Tiny channels called link the to each other and to the canal. They hold tissue fluid and fine extensions of the bone cells.
run across the bone and connect Haversian canals to each other and to the blood supply at the surface.

Oxygen, glucose and amino acids leave the blood in the and diffuse through the tissue fluid in the to the bone cells. Carbon dioxide and other wastes move the opposite way. The layered also make very strong, because they resist forces from many directions.

The photograph below shows a thin slice of real , ground down until light passes through it. You can look at slides like this in class, as the specification suggests.

Grey and white micrograph showing several roughly circular systems of faint rings. At the centre of two systems is a dark oval hole. Many small dark marks are arranged in rings, each with very fine dark lines radiating from it, and paler irregular lines mark the borders between systems. — A thin ground section of compact bone seen with a light microscope. Photo: Berkshire Community College Bioscience Image Library, CC0.

The dark holes are Haversian canals, each at the centre of its own system of rings.
The small dark marks arranged in rings are .
The very fine dark lines radiating from the are .

Lesson 4 of 25

What do osteoblasts and osteoclasts do?

Bone is living tissue that is broken down and rebuilt all through life. Two types of cell do this. build bone: they secrete and lay down the inorganic of the , and some become trapped in in the they have made. are large cells with several that break bone down, dissolving the and releasing calcium and phosphate ions into the blood.

The diagram below shows the two cells at work and how the balance between them decides bone mass.

Top half: a long beige strip of bone. On the left a large lilac dome-shaped cell with four dark nuclei sits in a scooped pit containing the red labels Ca two plus, captioned osteoclast, breaks bone down. On the right a row of eight small green square cells sits on a thin pale layer labelled new matrix, collagen then hydroxyapatite, captioned osteoblasts, build bone up. Bottom half: three pairs of bars labelled build in green and break in lilac. For a growing child the build bar is taller; for a healthy young adult they are equal; for osteoporosis the break bar is taller. — Osteoclasts break bone down and osteoblasts build it up. Original BioWelsh diagram.

An sits in a pit it has dissolved in the bone surface, releasing calcium ions.
A row of lays down new on another part of the surface.
In a growing child, building is faster than breaking down, so bone mass rises.
In a healthy young adult the two are balanced. If breakdown becomes faster than building, as in , bone mass falls.

Remodelling lets bone repair small cracks, reshape itself along the lines of stress when it bears weight, and act as a store that keeps blood calcium steady. Weight-bearing exercise stimulates . The hormone normally slows down, which is why bone loss speeds up in women after the menopause, when falls.

Lesson 5 of 25

What causes rickets and osteomalacia?

and are the same disorder at different ages. Too little calcium is laid down in the bone , so bones become soft, weak and painful, and they may bend under the weight of the body.

Rickets and osteomalacia compared
Feature	Rickets	Osteomalacia
Who	Children, whose bones are still growing	Adults, whose bones have stopped growing
Signs	Bowed legs or knock-knees, deformed spine or , slow growth	Bone pain and tenderness, muscle weakness,
Cause	Lack of or calcium	Lack of or calcium

is needed to absorb calcium from food in the small intestine. The skin makes when sunlight falls on it, and it is also found in oily fish, eggs and fortified foods. Calcium comes mainly from dairy products and green vegetables. So the risk rises with little time outdoors, skin always covered, darker skin in regions with weak sunlight, or a diet low in these foods.

Treatment replaces what is missing: and calcium supplements, a diet with more dairy products and oily fish, and safe exposure to sunlight. Severe bone deformities in children may need braces or surgery.

Lesson 6 of 25

What are osteoporosis and brittle bone disease?

is an abnormal loss of bone mass and . break bone down faster than rebuild it, so both compact and lose mineral. The bones become fragile and break after minor falls, most often at the hip, the wrist and the .

Age: bone mass peaks around 30 and then slowly falls.
Being female, especially after the menopause, because normally restrains .
Low calcium or intake, and little weight-bearing exercise.
Smoking, heavy drinking, family history and long-term use of steroid drugs.

The diagram below compares cross sections through the end of a healthy bone and a bone with .

Two circles side by side. The left one, healthy bone, has a thick beige outer ring labelled compact bone and inside it a dense network of short beige struts on a pink background labelled spongy bone. The right one, bone with osteoporosis, has a much thinner outer ring labelled thinner compact layer and only scattered thin struts with large pink gaps labelled larger spaces. — Cross sections through the end of a healthy bone and a bone with osteoporosis. Original BioWelsh diagram.

The layer of around the outside is much thinner in .
The struts of are thinner and fewer, leaving larger spaces.
Less lower bone , so the bone breaks under smaller forces.

The graph below shows how the bone mineral at the hip changes with age in males and females. The data are illustrative, written to show the typical pattern.

Line graph. The horizontal axis is age from 0 to 90 years and the vertical axis is bone mineral density from 0.4 to 1.3 grams per square centimetre. A solid blue line for males rises from 0.62 at 10 years to a peak of 1.20 at about 30, then falls slowly to 0.93 at 90. A dashed red line for females rises from 0.64 to a peak of 1.10 at about 30, stays level to about 40, then falls more steeply after 50 to 0.70 at 90. A dotted grey horizontal line at 0.80 is labelled osteoporosis threshold; the female line crosses it at about 72 years. — Mean bone mineral density at the hip at different ages in males and females, using illustrative data. Original BioWelsh graph.

rises quickly through childhood and the teens, and peaks at about 30 years.
Males reach a higher peak than females.
falls faster in females after about 50, the typical age of the menopause.
The for females falls below the at about 72 years, but the for males does not by 90.

often causes no symptoms until a bone breaks, although of the can cause loss of height and a hunched back. It is diagnosed with a , a low-dose X-ray that measures bone mineral . The result is given as a : the number of standard deviations above or below the for a healthy young adult. A of minus 2.5 or lower .

Regular weight-bearing exercise, such as walking, which stimulates and increases bone .
A diet rich in calcium and , or supplements.
Drugs that reduce activity so less bone is broken down, and hormone replacement therapy in some women.
Stopping smoking, drinking less alcohol, and preventing falls.

, or , is different: it is inherited. A affects the for , so too little is made or it is faulty. Without normal the bone is brittle, and bones very easily, sometimes even before birth. There is no cure. Treatment includes drugs that increase bone , physiotherapy to strengthen muscles, and surgery to place metal rods inside long bones.

Lesson 7 of 25

How is skeletal muscle organised?

Skeletal muscle is the muscle attached to the skeleton by . It is also called striated muscle, because it looks striped under a microscope, and voluntary muscle, because we it consciously. A whole muscle is a bundle of bundles, and each level is wrapped in .

The diagram below zooms in from a whole muscle to a single .

Four circles in a row joined by arrows labelled zoom in. The first, muscle, contains seven large pink circles. The second, fascicle, is packed with many small pink circles. The third, muscle fibre, is filled with tiny pink dots, with purple oval nuclei around its edge and a few yellow ovals labelled mitochondrion. The fourth, myofibril, shows a regular pattern of larger lilac circles, labelled thick filament myosin, each surrounded by small green dots labelled thin filament actin. — Skeletal muscle is a bundle of bundles, from whole muscle to myofibril. Original BioWelsh diagram.

A muscle is made of many bundles called .
Each contains many . A is one long cell, formed when many cells fuse in the embryo, so it has many around its edge.
Each is packed with long , with many between them to supply .
Each contains thick of and thin of in a regular pattern.

Special names for parts of a muscle fibre
Term	Meaning
	The cell surface membrane of a
Sarcoplasm	The cytoplasm of a
	Specialised endoplasmic reticulum that stores calcium ions
	Infoldings of the that carry the impulse deep into the fibre
	A long bundle of thick and thin inside the fibre

The photograph below shows skeletal cut lengthways, stained and seen with a light microscope.

Light micrograph of several long pink bands running from top to bottom with pale gaps between them. Each band has fine regular cross stripes. Dark purple oval nuclei lie along the edges of the bands. — Skeletal muscle fibres in longitudinal section, stained and seen with a light microscope. Photo: Berkshire Community College Bioscience Image Library, CC0.

Each pink band running from top to bottom is one .
The fine cross stripes, or striations, are the repeating light and dark bands of the lined up side by side.
The dark purple ovals at the edges of the fibres are . One fibre has many of them.

Lesson 8 of 25

What do the bands of a sarcomere show?

Along each the are arranged in repeating units called , each about 2 to 3 µm long. A runs from one Z line to the next. The thin are attached to the Z lines, and the thick sit in the middle, held together at the M line. Where the overlap, they can pull on each other.

The diagram below shows one , and what you would see in transverse sections cut at three positions.

A long horizontal diagram of filaments. Thin green lines run in from two zigzag vertical lines labelled Z line, and thick lilac bars with small angled heads lie in the middle, crossed by a dashed line labelled M line. Brackets show the sarcomere from Z line to Z line, the A band across the full length of the lilac bars, the H zone in the centre where there are no green lines, and the I bands either side of each Z line where there are only green lines. Orange dashed lines numbered 1, 2 and 3 cut through the I band, the overlap region and the H zone and lead to three circles below: circle 1 contains only small green dots, labelled actin only, circle 2 contains large lilac dots each surrounded by six green dots, labelled actin and myosin, and circle 3 contains only lilac dots, labelled myosin only. — The structure of a sarcomere, with transverse sections at three positions. Original BioWelsh diagram.

The is the dark band. Its length is the length of the .
The is the light band either side of a Z line. It contains only.
The is the paler region in the middle of the . It contains only.
A section through the shows only thin , a section through the shows only thick , and a section through the overlap region shows each thick surrounded by six thin ones.

The bands of a sarcomere
Band	What it contains	Appearance
	The whole length of the , including where it overlaps	Dark
	only	Light
	only, in the centre of the	Lighter part of the
Z line	The anchor for the at each end of the	Thin dark line
M line	The centre of the , where are joined	Thin line in the

The electron micrograph below shows part of a human at very high .

Black and white electron micrograph of broad grey bands running diagonally, each crossed at regular intervals by dark zigzag lines, with darker and paler regions between the lines. A pale speckled strip runs diagonally across the middle of the image. — Electron micrograph of human skeletal muscle. Photo: Louisa Howard, Dartmouth College, Public domain.

The dark zigzag lines crossing each are Z lines, so the distance between two of them is one .
The darker middle part of each is the , and the paler parts beside the Z lines are the I bands.
The pale band running diagonally across the picture is the gap between two .

Lesson 9 of 25

What happens to the bands when a muscle contracts?

The explains contraction. The slide between the towards the centre of the . Neither kind of changes length. Instead, the overlap increases, so each shortens, each shortens, and the whole muscle shortens.

The diagram below compares the same relaxed and contracted, drawn to the same scale.

Two filament diagrams, one above the other, labelled relaxed and contracted. Each has green thin filaments attached to zigzag Z lines at each end and two lilac thick filaments with heads in the middle. In the contracted diagram the Z lines are closer together, the green filaments reach almost to the centre, the bracket labelled H zone is very narrow and the I band bracket is shorter, while the A band bracket below is the same length as in the relaxed diagram. Text underneath says the A band stays the same length, the I band gets shorter and the H zone gets shorter. — A sarcomere relaxed and contracted, drawn to the same scale. Original BioWelsh diagram.

The Z lines move closer together, so the is shorter.
The stays the same length, because the do not change length.
The gets shorter, because the slide further over the .
The gets shorter and may disappear, because the ends of the move towards each other.

The graph below shows how the tension a produces depends on the length of its . The data are illustrative, written to show the typical pattern.

Line graph with crosses joined by straight lines. The horizontal axis is sarcomere length from 1 to 4 micrometres and the vertical axis is tension as a percentage of maximum from 0 to 100. The line starts at 0 at 1.3, rises to 60 at 1.65 and 100 at 2.0, stays at 100 until 2.25, then falls in a straight line to 0 at 3.65. — Tension produced by a muscle fibre at different sarcomere lengths, using illustrative data. Original BioWelsh graph.

Tension is highest between about 2.0 and 2.25 µm, where the most heads overlap .
Above 2.25 µm the is stretched, overlap falls, and fewer can form.
At about 3.65 µm there is no overlap at all, so no form and no tension is produced.
Below 2.0 µm the collide in the middle and the pushes against the Z lines, so tension falls again.

Lesson 10 of 25

How do calcium ions switch on contraction?

Each thin is mostly : globular molecules joined into two chains twisted around each other. has binding sites for . Two accessory proteins whether these sites can be used. is a long strand lying along the groove of the , covering the binding sites at rest. is a smaller protein attached to at intervals, and it can bind calcium ions.

Each thick is a bundle of molecules. A molecule has a long tail and a head that sticks out towards the . The head can bind to , and it is also an , ATPase, which .

The diagram below shows the thin at rest and after calcium ions have been released.

Two rows. Top row, muscle at rest, no calcium ions: a double row of green beads, the actin, with a thick orange strand, tropomyosin, lying along the top, blue ovals, troponin, sitting on it at intervals, and lilac myosin heads above that do not reach the actin. Bottom row, after an impulse: the orange strand has moved down into the groove, small orange squares on the green beads are labelled binding site exposed, each blue troponin has a yellow circle labelled Ca attached, and three lilac myosin heads now touch the actin. — Calcium ions switch the thin filament on. Original BioWelsh diagram.

At rest, lies over the binding sites, so heads cannot attach.
When calcium ions arrive, they bind to , which changes shape.
The change in pulls aside, exposing the binding sites.
heads can now bind to and form .

From impulse to exposed binding sites

1) An impulse arrives at the
2) spreads along the and down the
3) Calcium ions are released from the
4) Calcium ions bind to , which changes shape
5) moves, exposing binding sites on
6) heads bind to , forming

Lesson 11 of 25

How do cross-bridges pull the actin?

Once binding sites are exposed, each head goes through a repeating cycle. Every cycle pulls the a tiny distance towards the M line, and each head repeats the cycle many times a second while calcium ions and are available.

The diagram below shows the four stages of the cycle.

Four panels arranged in a square with arrows between them going clockwise. Each shows a row of green beads, actin, above a lilac bar, myosin, with one myosin head on a neck. Panel 1, cross-bridge forms: the upright head carrying ADP plus Pi touches the actin. Panel 2, power stroke: the head is tilted to the right, ADP plus Pi is shown leaving, and an arrow shows the actin pulled to the right towards the M line. Panel 3, head detaches: ATP is bound and the tilted head has left the actin. Panel 4, head re-cocks: the head is upright again holding ADP plus Pi. Text says the cycle repeats while calcium ions are present and ATP is available. — The cross-bridge cycle. Original BioWelsh diagram.

A head, holding and a phosphate ion, binds to an exposed site on , forming a .
and phosphate are released and the head tilts. This pulls the towards the centre of the .
A new molecule binds to the head, which makes the head detach from .
ATPase the , and the energy released returns the head to its upright position, ready to bind further along.

is needed in two places: to detach the head from , and, through its , to re-cock the head. is also used to pump calcium ions back into the . After death no is made, heads cannot detach, and the muscles lock stiff.

When impulses stop, calcium ions are actively transported back into the . returns to its original shape, covers the binding sites again, and the muscle relaxes.

Lesson 12 of 25

How do fast and slow twitch fibres differ?

Skeletal muscles contain a mixture of two kinds of fibre. contract slowly but keep going for a long time, so they suit endurance. contract quickly and powerfully but tire fast, so they suit short bursts such as sprinting and lifting.

Slow and fast twitch fibres compared
Feature	Slow twitch	Fast twitch
Speed of contraction	Slow	Fast and powerful
	slowly	quickly
Main type of	Aerobic	Anaerobic
	Many	Few
Capillaries	Dense network	Fewer
	Lots, so the muscle looks red	Little, so the muscle looks pale
Stores	Little	Lots of and
	Little made	Much made
Examples	Back muscles for posture; marathon runners' leg muscles	Eye muscles; sprinters' and weightlifters' leg muscles

is a red , similar to haemoglobin, that stores oxygen in the muscle and releases it when oxygen levels are low. Together with a rich blood supply, it explains why muscle is darker, as in the dark meat of a chicken's leg compared with the pale breast meat.

The proportion of each fibre type is partly inherited, but training changes the fibres. Endurance training increases the number of and capillaries, and the amount of , so more is possible.

Lesson 13 of 25

How do muscles get energy when oxygen runs short?

A contracting muscle uses very quickly, but it only stores enough for a couple of seconds. When exercise is intense, oxygen cannot be delivered fast enough for to keep up, and the muscle turns to two anaerobic sources of .

The first is , a store of phosphate in the sarcoplasm. (The specification calls it .) It passes its phosphate to , making immediately: + → creatine + . This keeps levels up for only about 6 to 10 seconds of maximum effort, but it needs no oxygen. The store is rebuilt at rest, when from is plentiful.

The second is . continues, and is to , which regenerates the that needs. This gives only 2 per glucose, and builds up. The acid lowers the pH in the muscle, which slows and makes the contractile proteins less sensitive to calcium, so the muscle fatigues and may cramp. Later, is carried to the liver and converted back to or glucose, which uses extra oxygen after exercise. (If the steps of are unfamiliar, read the respiration lesson on anaerobic respiration.)

is a fall in the force a muscle can produce.
Causes include , a build-up of , and a lack of when stores of and run low.

Muscle is the main fuel for contraction. It is to glucose inside the , and that glucose can only be used by the muscle itself. When runs low, for example late in a marathon, muscles rely more on fats and on protein: amino acids are deaminated and their remains enter . Protein in the diet is also needed to build and repair muscle. Athletes may eat extra carbohydrate before an event, called carbohydrate loading, to fill their stores. (How amino acids enter is covered in the respiration lesson on lipids and proteins.)

Lesson 14 of 25

How is the human skeleton organised, and what does it do?

The skeleton has two parts. The runs down the midline of the body: the skull, the vertebral column, the ribs and the sternum. The is attached to it: the and forelimbs, and the and hind limbs.

The diagram below shows the main bones of the human skeleton from the front.

Drawing of a whole human skeleton in pale yellow standing facing forwards with arms at the sides. Small labels on either side name the skull, the cervical, thoracic and lumbar vertebrae, sacrum and coccyx, clavicle, scapula, sternum, ribs, humerus, ulna, radius, pelvic girdle, carpals, metacarpals, phalanges, femur, patella, tibia, fibula, tarsals and metatarsals. — The human skeleton seen from the front, with the main bones labelled. Photo: Mariana Ruiz Villarreal (LadyofHats), Public domain.

The skull, vertebral column, ribs and sternum form the .
The clavicle and scapula form the , which attaches the arm to the .
The forelimb contains the humerus, radius, ulna, carpals, metacarpals and phalanges.
The attaches the leg, whose bones are the femur, patella, tibia, fibula, tarsals, metatarsals and phalanges.

The five functions of the skeleton
Function	How the skeleton carries it out
Support	It gives the body its shape and holds up the soft tissues; the limbs hang from girdles attached to the spine
Muscle attachment	attach muscles to bones, which act as so the body can move
Protection	The skull protects the brain, the ribcage the heart and lungs, and the the spinal cord
Red blood cell production	Red bone marrow, in of the , , ribs, sternum and ends of long bones, makes blood cells
Calcium store	Bone stores calcium and phosphate, releasing them to keep blood calcium steady

Lesson 15 of 25

What types of fracture are there, and how are they treated?

A is a break in a bone. It is caused when a force on the bone is greater than the bone can withstand. A traumatic comes from a large force, such as a fall, a sports injury or a road accident. A pathological happens after only a small force, because disease has weakened the bone, as in , or bone cancer. Repeated small forces, as in long-distance running, can cause stress .

The diagram below shows some of the ways a long bone can break.

Five pale beige long bones side by side, each with rounded knobbly ends. The first is broken straight across. The second is broken along a sloping line. The third has its middle broken into several small separate pieces. The fourth is bent at the middle with a short red crack on one side only. The fifth is broken straight across with the lower piece shifted sideways out of line. — Some ways a long bone can break. Original BioWelsh diagram.

A transverse runs straight across the bone.
An oblique runs at an angle to the long axis.
A comminuted leaves the bone in several pieces.
A bends the bone and cracks one side only. It happens in children, whose bones contain more and so are more flexible.
In a the broken ends have moved out of line; in a non- they stay in place.

Other ways fractures are described
Term	Meaning
Closed (simple)	The skin is not broken
Open (compound)	The broken bone breaks through the skin, so there is a high risk of infection
Stress	A small crack caused by repeated stress rather than one large force

are confirmed with an X-ray. Treatment realigns the broken ends, then keeps them still while lay down new bone. A cast or splint holds a simple . or unstable may need surgery to fix them with metal plates, screws, pins or rods. Hip , common in older people with , are usually repaired by surgery quickly, because lying still for weeks risks blood clots such as deep vein thrombosis, chest infections and muscle wasting, and the hip bears the weight of the body.

Lesson 16 of 25

How do vertebrae differ along the spine?

The vertebral column is a flexible chain of 33 . From the top there are 7 cervical in the neck, 12 thoracic in the chest, 5 lumbar in the lower back, 5 fused sacral forming the sacrum, and 4 small fused forming the coccyx. Pads of , the , sit between the bodies of the and absorb shock.

The diagram below shows the vertebral column from the side, with each region coloured.

Drawing of the spine from the side, curving gently. The top seven vertebrae, labelled C1 to C7, are orange; the next twelve, T1 to T12, are blue; the next five, L1 to L5, are yellow; the fused sacrum is green and the small coccyx at the bottom is purple. — The human vertebral column seen from the side, with each region coloured. Photo: Henry Vandyke Carter, Gray's Anatomy (1918), Public domain.

The seven cervical , C1 to C7, are at the top. The first two, the atlas and axis, let the head nod and turn.
The twelve thoracic , T1 to T12, are where the ribs attach.
The five lumbar , L1 to L5, are the largest.
The sacrum and coccyx at the bottom are fused and do not move.

The diagram below shows the parts that almost every has, seen from above.

Beige outline drawing of a vertebra from above with posterior at the top and anterior at the bottom. A large oval body sits at the bottom. Above it a curved arch encloses a large white hole. A long narrow spinous process points up from the top of the arch and two transverse processes stick out sideways. Two small oval articular facets sit on the arch. Labels name each part and its function. — The general structure of a vertebra, seen from above. Original BioWelsh diagram.

The body, or centrum, is a thick block of at the front that bears the weight of the body above it.
The vertebral arch surrounds the , a hole through which the spinal cord passes, protecting it.
The spinous and transverse processes are projections where muscles and attach.
Articular facets form joints with the above and below.

Cervical, thoracic and lumbar vertebrae compared
Region	Distinctive features	How they relate to function
Cervical	Small body; a in each transverse process; short spinous process, often split	Little weight to carry; foramina protect the arteries to the brain; allow wide movement of the head
Thoracic	body; long spinous process pointing down; facets for the ribs on the body and transverse processes	Articulate with the ribs to form the ribcage; limited movement protects the chest
Lumbar	Large, thick body; short, thick processes; no rib facets	Bear the most weight; large surfaces for the powerful back muscles

Lesson 17 of 25

Which conditions affect posture?

Seen from the side, a healthy spine has gentle S-shaped curves: it curves inwards at the neck, outwards at the chest and inwards again at the lower back. These curves help absorb shock and keep the body balanced over the feet, and they are held in place by muscles, and the shape of the and discs. If the curves become too large, or the spine bends sideways, posture is affected.

The diagram below compares a healthy spine with three conditions that affect posture.

Four spines drawn as chains of small beige blocks. The first, healthy spine side view, has gentle S-shaped curves with labels cervical, thoracic and lumbar. The second, kyphosis side view, curves strongly backwards in the chest region with the neck pushed forwards. The third, lordosis side view, curves strongly forwards in the lower back. The fourth, scoliosis viewed from behind, curves to the right and then to the left. Words front and back, or left and right, mark the directions. — Curves of the spine in a healthy person and in three posture conditions. Original BioWelsh diagram.

In the thoracic region curves outwards too much, so the upper back is rounded and the person hunches forwards.
In the lumbar region curves inwards too much, giving a hollow lower back.
In the spine curves sideways, seen from behind, often in an S shape.

Posture conditions: causes and treatment
Condition	Possible causes	Treatment
	Poor posture; that grow wedge-shaped in adolescence (Scheuermann's ); of in	Posture exercises and physiotherapy, a back brace while growing, pain relief, surgery if severe
	Being overweight, pregnancy, weak core muscles, poor posture	Exercises to strengthen core muscles, physiotherapy, weight loss
	Often no known cause; runs in families; uneven muscle strength; some other conditions	Monitoring, physiotherapy, a brace while the skeleton is growing, surgery with rods to straighten severe curves

The X-ray below shows the spine of a person with , seen from the front.

Black and white X-ray of the chest and abdomen from the front. The column of vertebrae curves to one side in the chest and back the other way lower down, forming a sideways S shape. — X-ray of the spine of a person with scoliosis, seen from the front. Photo: Unknown author, Public domain.

The column of runs down the middle of the chest and abdomen.
Instead of forming a straight line, the curve to one side and then back, making a sideways S shape.

Lesson 18 of 25

What types of joint are there?

A joint is where two or more bones meet. The specification names four types, which differ in how much movement they allow. Immovable or fused joints allow none. The other three are movable, .

The diagram below shows simple models of the four types of joint.

Four simple models in a row. Fused: two beige blocks meeting along a zigzag line. Gliding: two flat blocks with thin blue layers of cartilage sliding past each other, with arrows left and right. Hinge: a bone with a rounded end sitting in a curved trough lined with blue cartilage, with curved arrows showing swinging in one direction. Ball and socket: a round ball on a neck sitting in a deep cup lined with blue cartilage, with curved arrows in several directions and a circular arrow for rotation. Captions give examples: skull sutures, between vertebrae and wrist bones, elbow and knee, hip and shoulder. — Types of joint shown as simple models. Original BioWelsh diagram.

Fused joints: the bones interlock and are joined, so no movement is possible, as in the sutures of the skull and the fused of the sacrum.
Gliding joints: flat surfaces slide a small distance over each other, as between the articular processes of and between the small bones of the wrist and ankle.
Hinge joints: movement in one plane only, like a door, as at the elbow and knee.
Ball and socket joints: a rounded head fits into a cup, allowing movement in all planes and , as at the hip and shoulder.

Lesson 19 of 25

How is a synovial joint built?

Movable joints are called . They are built to let bones move smoothly over each other for a lifetime, while holding them firmly in place.

The diagram below shows the structure of a typical .

Two beige bones meeting end to end vertically, the upper with a rounded end and the lower with a shallow cup, each capped with a thick blue layer. The space between them is pale yellow. A grey capsule with a red inner lining encloses the space, and a brown band runs outside it on each side from bone to bone. Labels name the bone, articular cartilage, synovial fluid in the joint cavity, synovial membrane, fibrous capsule and ligament. — The structure of a synovial joint. Original BioWelsh diagram.

The ends of the bones are covered with smooth , which is .
The joint cavity between the bones is filled with .
The synovial membrane lines the fibrous capsule and secretes the .
run from bone to bone across the joint, outside the capsule.

The parts of a synovial joint and their roles
Part	Role
	Gives a smooth surface that reduces friction, and absorbs shock
Synovial membrane	Secretes
	Lubricates the joint, absorbs shock, and supplies nutrients to and removes wastes from the , which has no blood vessels
Fibrous capsule	Encloses the joint and holds the bones together
	Tough, slightly elastic bands joining bone to bone; they allow movement but prevent dislocation

Lesson 20 of 25

What causes osteoarthritis and how is it treated?

Arthritis of a joint. is the most common kind. It is a degenerative disease: the wears away faster than it can be repaired. As the thins, the joint space narrows, bone rubs on bone, and bony spurs grow at the edges of the joint. The joint becomes painful, stiff and swollen, and movement is . It is most common in the knees, hips and hands.

The diagram below compares a healthy joint with joints affected by and .

Three simplified synovial joints side by side. Healthy joint: smooth, even blue cartilage caps and a clear yellow space. Osteoarthritis: only thin patches of blue cartilage remain, the two bones almost touch, and small triangular spurs of bone stick out at the edges. Rheumatoid arthritis: a thick bright red lining bulges outwards around a swollen yellow cavity, the blue cartilage is shortened, and small red-edged pits are eaten into the bone ends. — A healthy joint compared with osteoarthritis and rheumatoid arthritis. Original BioWelsh diagram.

In the healthy joint the is smooth and even, and there is a clear joint space.
In the is worn away in places, the joint space is narrow and bone spurs grow at the edges.
In the synovial membrane is inflamed and thickened, the joint is swollen, and and bone are eaten away at the edges.

Increasing age, as is worn over many years.
Being overweight, which puts more load on the knees and hips.
Previous joint injuries, and heavy or repetitive use of a joint in some sports and jobs.
Family history, and being female.

The X-ray below shows a hip joint with severe .

Black and white X-ray of a hip joint. The rounded head of the femur lies against the socket in the pelvis with almost no dark gap between them. The bone edges around the joint look rough and irregular. — X-ray of a hip joint with severe osteoarthritis. Photo: Mikael Häggström, CC0.

The rounded head of the femur and the socket of the are almost touching, because the between them has worn away.
The bone surfaces are rough and irregular, with extra bone at the edges of the joint.

There is no cure. Weight loss reduces the load on the joint.
Exercise and physiotherapy strengthen the muscles around the joint so they support it, and keep the joint flexible.
Painkillers and anti-inflammatory drugs, and sometimes steroid injections into the joint.
Joint replacement in severe cases, especially of the hip or knee, with a metal and plastic artificial joint.

Lesson 21 of 25

What causes rheumatoid arthritis and how is it treated?

is an . The immune system recognises proteins in the joint as foreign and attacks the synovial membrane, which becomes inflamed and thickened. The joint swells with extra fluid and becomes warm, painful and stiff, and over time the and bone are destroyed. It usually affects the small joints of the hands and feet, often on both sides of the body at once. The causes are a mix of inherited and environmental triggers, especially smoking.

Osteoarthritis and rheumatoid arthritis compared
Feature	Osteoarthritis	Rheumatoid arthritis
Cause	Wear of over time	The immune system attacks the joint
Tissue first affected		Synovial membrane
Typical joints	Knees, hips, hands	Small joints of the hands and feet, on both sides
Typical age	Mostly over 50	Often begins between 30 and 50

There is no cure, but the disease can be slowed.
Drugs that suppress the immune response slow the damage to the joint.
Anti-inflammatory drugs and steroids reduce pain and swelling.
Physiotherapy keeps the joints moving, and badly damaged joints can be replaced.

Lesson 22 of 25

How do joints act as levers?

A is a rigid bar that turns about a point called the . A force called the effort is applied to move a load. In the body, a bone is the rigid bar, a joint is the , a muscle provides the effort, and the load is the weight of the body part plus anything it holds. The order of a depends on which of the three is in the middle.

The diagram below shows the three orders of with an example of each in the body.

Three beams balanced on grey triangles labelled fulcrum. In the first, the fulcrum is under the middle, a red effort arrow pushes down at the left end and a blue box labelled load sits at the right end. In the second, the fulcrum is at the left end, the load box is in the middle and a red effort arrow points up at the right end. In the third, the fulcrum is at the left end, a red effort arrow points up in the middle and the load box is at the right end. Captions give first, second and third order with body examples: nodding the head, rising onto tiptoe and the biceps lifting the forearm. — Three orders of lever, with an example of each in the body. Original BioWelsh diagram.

First order: the is between the effort and the load, like a seesaw. Nodding the head uses one, with the where the skull sits on the atlas.
Second order: the load is between the and the effort, like a wheelbarrow. Rising onto tiptoe uses one, with the ball of the foot as the and the calf muscles as the effort.
Third order: the effort is between the and the load, like tweezers. The biceps lifting the forearm is the classic example.

Most in the body are third order. The muscle is attached close to the joint, so it must pull with a force much larger than the load. The benefit is that a small shortening of the muscle moves the hand a long way and quickly.

The diagram below shows the forearm as a third order , with the distances used in calculations.

A vertical beige bar labelled humerus meets a long horizontal beige bar labelled forearm at a grey circle labelled fulcrum, elbow joint. A pink oval labelled biceps lies in front of the humerus, attached by a short grey line to the forearm near the elbow, where a red arrow labelled effort points upwards. A blue box labelled load hangs at the far end of the forearm with a blue arrow pointing down. Measurements below show a short effort distance from the elbow to the biceps and a long load distance from the elbow to the load. Text reads: at balance, effort times effort distance equals load times load distance. — The forearm as a third order lever. Original BioWelsh diagram.

The is the elbow joint.
The effort is applied by the biceps where it inserts on the radius, a short distance from the elbow.
The load is the weight in the hand, much further from the elbow.
At balance, effort × effort distance = load × load distance.

Lesson 23 of 25

How do antagonistic muscles move the forearm?

Muscles can only pull, by contracting. They cannot push. To move a joint back and forth, muscles work in : as one contracts, the other relaxes and is stretched. At the elbow the pair is the biceps, in front of the humerus, and the triceps, behind it.

The diagram below shows the biceps and triceps moving the forearm.

Two side views of an arm. Left, flexion: a vertical humerus hangs from a scapula, and the forearm sticks out horizontally from the elbow. A fat pink biceps in front of the humerus is joined by grey tendons to the scapula and to the forearm near the elbow; a thin pink triceps behind is joined to the back of the elbow. Labels say biceps contracts, shorter and fatter, and triceps relaxes and is stretched. Right, extension: the forearm hangs straight down, the triceps is fat and the biceps is thin, labelled triceps contracts and biceps relaxes and is stretched. — Antagonistic muscles move the forearm at the elbow. Original BioWelsh diagram.

In flexion the biceps contracts, becoming shorter and fatter, and pulls the radius up, so the elbow bends. The triceps relaxes and is stretched.
In extension the triceps contracts and pulls on the ulna behind the elbow, so the arm straightens. The biceps relaxes.
Each muscle has an , the end attached to a bone that does not move, here the scapula, and an on the bone that moves.

join muscles to bones. They are made of tightly packed parallel fibres, so they are very strong and do not stretch. When the muscle contracts, all of its pull is passed straight to the bone instead of being lost in stretching the . The quadriceps and hamstrings work the same way at the knee.

Lesson 24 of 25

How are Option B data and calculation questions marked?

Every Option B question in recent WJEC papers has included a calculation or a question about evaluating data, usually set in an unfamiliar study of patients or athletes. The biology is often simple; the marks come from careful working and clear evaluation.

Calculations that come up in this option
Calculation	How to do it
Percentage change or difference	(difference ÷ starting or comparison value) × 100
Rate of change	change in the quantity ÷ time taken, with a unit such as mV s⁻¹
	image size ÷ actual size, in the same units
forces	effort × effort distance = load × load distance; mass in kg × 9.8 gives weight in N
Length of a from a graph	use the lengths where the graph changes, then halve differences where two are involved

Sample size: a larger sample, from more places, makes results more reliable.
variables: age, sex, ethnicity, fitness, diet and family history can all affect bones and muscles, so they must be kept the same or recorded.
Overlap: if the ranges of two groups overlap, the difference may not be real.
Percentages: use them rather than totals when samples are different sizes, so groups can be compared.
Repeats and : measuring many or patients gives a and shows the spread.
Correlation is not proof of cause.

Lesson 25 of 25

Putting the option together

Option B links the tissues of the skeleton to the way the body moves. Bone and give the skeleton its structure, muscles pull on the bones through , joints act as , and things go wrong when tissues are poorly made, worn or attacked.

How the ideas in this option connect

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Zoom in to read each branch. Swipe or scroll sideways to explore.

Human musculoskeletal anatomy
- Skeletal tissues
  - : hyaline, elastic, fibrous
  - Bone: and ,
  - and ; , , brittle bones
- Skeletal muscle
  - and the
  - Calcium, and ; and
  - Fast and ; and
- The skeleton
  - Axial and ; five functions
  - ; ; posture conditions
- Joints
  - Joint types and the
  - and
  - and muscles

gives hardness; gives flexibility.
build bone; break it down.
The stays the same length; the and shorten.
Calcium ions bind to , not .
detaches and re-cocks the head.
join bone to bone; join muscle to bone.
is wear of ; is .
Third order : the effort is in the middle.

What are the three types of cartilage?

What is compact bone made of?

How is compact bone built from Haversian systems?

What do osteoblasts and osteoclasts do?

What causes rickets and osteomalacia?

What are osteoporosis and brittle bone disease?

How is skeletal muscle organised?

What do the bands of a sarcomere show?

What happens to the bands when a muscle contracts?

How do calcium ions switch on contraction?

How do cross-bridges pull the actin?

How do fast and slow twitch fibres differ?

How do muscles get energy when oxygen runs short?

How is the human skeleton organised, and what does it do?

What types of fracture are there, and how are they treated?

How do vertebrae differ along the spine?

Which conditions affect posture?

What types of joint are there?

How is a synovial joint built?

What causes osteoarthritis and how is it treated?

What causes rheumatoid arthritis and how is it treated?

How do joints act as levers?

How do antagonistic muscles move the forearm?

How are Option B data and calculation questions marked?

Putting the option together

Worksheets

Worksheet 1: Option B Musculoskeletal Anatomy (149 marks)

Check your understanding.

The intervertebral discs between the vertebrae must withstand large compressive and pulling forces. Which type of cartilage forms them, and why is it suited to this role?

Human musculoskeletal anatomy

What are the three types of cartilage?

What is compact bone made of?

How is compact bone built from Haversian systems?

What do osteoblasts and osteoclasts do?

What causes rickets and osteomalacia?

What are osteoporosis and brittle bone disease?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 15 marks in total. This is a revision priority, not a prediction of your exam.

How is skeletal muscle organised?

What do the bands of a sarcomere show?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.

What happens to the bands when a muscle contracts?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.

How do calcium ions switch on contraction?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 10 marks in total. This is a revision priority, not a prediction of your exam.

How do cross-bridges pull the actin?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.

How do fast and slow twitch fibres differ?

How do muscles get energy when oxygen runs short?

How is the human skeleton organised, and what does it do?

What types of fracture are there, and how are they treated?

How do vertebrae differ along the spine?

Which conditions affect posture?

What types of joint are there?

How is a synovial joint built?

What causes osteoarthritis and how is it treated?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 9 marks in total. This is a revision priority, not a prediction of your exam.

What causes rheumatoid arthritis and how is it treated?

How do joints act as levers?

How do antagonistic muscles move the forearm?

How are Option B data and calculation questions marked?BWRBioWelsh recommendedWe recommend revising this because it has appeared regularly in past papers. Asked in 6 of 7 WJEC exam series (2017 to 2025), 14 marks in total. This is a revision priority, not a prediction of your exam.

Putting the option together

Worksheets

Worksheet 1: Option B Musculoskeletal Anatomy (149 marks)

Check your understanding.

What are osteoporosis and brittle bone disease?

What do the bands of a sarcomere show?

What happens to the bands when a muscle contracts?

How do calcium ions switch on contraction?

How do cross-bridges pull the actin?

What causes osteoarthritis and how is it treated?

How are Option B data and calculation questions marked?