Musculoskeletal anatomy: WJEC A level Biology cram notes

Lesson 1 of 25

Cartilage

Fast revision of Option B, Human Musculoskeletal Anatomy, in WJEC A level Biology Unit 4. It follows the WJEC specification.

is : sit in in a firm . It has no blood vessels, so nutrients arrive by and it heals slowly.

The diagram below compares the three types.

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.

Hyaline: fine , smooth . Reduces friction and absorbs shock; ends of bones, trachea.
Yellow elastic: plus elastic fibres. Flexible and springs back; ear pinna, epiglottis.
White fibrous: dense bundles. Strongest; .

Lesson 2 of 25

Compact bone

The compact bone matrix
Component	Share	Function
Organic:	30%	Flexibility and tensile strength, so bone is not brittle
Inorganic: (calcium phosphate)	70%	Hardness; resists compression

Lesson 3 of 25

Haversian systems

The diagram below shows a 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.

: arteriole, venule, lymph vessel and .
: rings of . between them hold bone cells.
: tiny channels of tissue fluid linking ; substances diffuse through them.
carry vessels across the bone.

Lesson 4 of 25

Osteoblasts and osteoclasts

build bone, laying down and . break bone down, releasing calcium and phosphate. Bone is remodelled all through life, and the balance decides bone mass. slows ; weight-bearing exercise stimulates .

Lesson 5 of 25

Rickets and osteomalacia

Too little calcium is laid down, so bones are soft and may bend: in children (bowed legs), in adults. Cause: lack of or calcium. , from sunlight on skin and oily fish, is needed to absorb calcium from the gut.

Lesson 6 of 25

Osteoporosis and brittle bone disease

: abnormal loss of bone , because outpace . Risk rises with age, after the menopause, with smoking, alcohol, low calcium and and little exercise. Diagnosed by a ; a of −2.5 or lower .

The diagram below compares healthy bone with bone affected by .

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.

Thinner layer.
Fewer, thinner struts of and larger spaces.

Treatment: weight-bearing exercise, calcium and , drugs that reduce activity, stopping smoking, preventing falls. is inherited: a makes bones easily. Treated with drugs, physiotherapy and metal rods.

Lesson 7 of 25

Skeletal muscle structure

Muscle → → (long cells with many , many ) → → myofilaments of and . : membrane. : stores calcium ions. carry the impulse into the fibre.

Lesson 8 of 25

The sarcomere

The diagram below shows the bands of a .

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.

: Z line to Z line.
: the length of the (dark).
: only (light). : only.
Transverse sections: only in the , only in the , each surrounded by six in the overlap.

Lesson 9 of 25

Sliding filaments

The diagram below shows a relaxed and a contracted .

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.

slides over towards the M line; do not change length.
: same length. and : shorter.

Lesson 10 of 25

The calcium switch

The diagram below shows how calcium ions switch on the thin .

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, covers the binding sites on .
Calcium ions, released from the , bind to .
changes shape and moves , exposing the binding sites.

Lesson 11 of 25

The cross-bridge cycle

The diagram below shows 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.

head binds to : .
and Pi released: pulls .
binds: head detaches.
by ATPase: head re-cocks.

Relaxation: calcium ions are pumped back into the using , and covers the sites again.

Lesson 12 of 25

Fast and slow twitch fibres

Fibre types
Slow twitch	Fast twitch
Contract slowly, slowly	Contract fast, quickly
Aerobic; many and capillaries	Anaerobic; few , much
Much : red	Little : pale
Endurance, posture	Sprinting, lifting

Lesson 13 of 25

Anaerobic conditions and energy sources

( in the specification) gives a phosphate to make instantly, for about 6 to 10 seconds. Then : is to to regenerate . lowers pH and causes .

Muscle is the main fuel; when it runs low, fats and protein (deaminated amino acids) are respired. Protein also builds and repairs muscle.

Lesson 14 of 25

The skeleton and its functions

: skull, vertebral column, ribs, sternum. Appendicular: (scapula, clavicle) and forelimb (humerus, radius, ulna, hand bones); and hind limb (femur, patella, tibia, fibula, foot bones).

Five functions: support, muscle attachment, protection, red blood cell production in red marrow, and a store of calcium and phosphate.

Lesson 15 of 25

Fractures

The diagram below shows types of .

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.

Transverse, oblique, comminuted (several pieces), (bent and cracked on one side, in children).
: ends out of line. Open (compound): through the skin. Closed: skin intact.

Causes: trauma, or disease weakening bone (pathological). Treatment: realign and immobilise in a cast, or surgery with metal plates, screws or rods. Hip are operated on quickly to restore mobility and avoid deep vein thrombosis.

Lesson 16 of 25

The vertebral column

33 : 7 cervical, 12 thoracic, 5 lumbar, sacrum (5 fused), coccyx (4 fused). Discs of between them. Functions: support, protect the spinal cord, flexibility, muscle and rib attachment.

The diagram below shows the general structure of a .

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.

Body: bears weight. Vertebral arch and foramen: protect the spinal cord.
Spinous and transverse processes: muscle attachment. Facets: joints with other .

Regions
Region	Key feature
Cervical	; small body
Thoracic	Facets for the ribs; long spine
Lumbar	Large, thick body for weight

Lesson 17 of 25

Posture conditions

The diagram below compares posture conditions with a healthy spine.

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.

: thoracic curve too far outwards, hunched. Causes include Scheuermann's disease and .
: lumbar curve too far inwards. Causes include obesity, pregnancy and weak core muscles.
: sideways curve, often of unknown cause.

Treatments: physiotherapy and exercises, braces while growing, weight loss, surgery for severe curves.

Lesson 18 of 25

Types of joint

Fused or immovable: skull sutures. Gliding: between , wrist bones. Hinge, one plane: elbow, knee. Ball and socket, all planes: hip, shoulder.

Lesson 19 of 25

The synovial joint

The diagram below shows a .

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.

Articular (hyaline) : reduces friction, absorbs shock.
Synovial membrane: secretes , which lubricates and nourishes the .
Capsule holds the joint; join bone to bone and prevent dislocation.

Lesson 20 of 25

Osteoarthritis

The diagram below compares a healthy joint with the two kinds of arthritis.

: worn away, narrow joint space, bone spurs.
: inflamed, thickened synovial membrane, swelling, eroded and bone.

is degenerative: breaks down faster than it is repaired. Risks: age, being overweight, injury, repetitive use. Treatment: weight loss, exercise and physiotherapy to strengthen supporting muscles, painkillers and anti-inflammatories, joint replacement.

Lesson 21 of 25

Rheumatoid arthritis

An : the immune system attacks the synovial membrane, then and bone. Often the small joints of both hands. Causes: plus triggers such as smoking. Treatment: immune-suppressing drugs, anti-inflammatories and steroids, physiotherapy, joint replacement.

Lesson 22 of 25

Levers

The diagram below shows the three orders of .

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: in the middle (nodding the head).
Second order: load in the middle (standing on tiptoe).
Third order: effort in the middle (biceps lifting the forearm).

Lesson 23 of 25

Antagonistic muscles

The diagram below shows the biceps and triceps.

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.

Flexion: biceps contracts, triceps relaxes.
Extension: triceps contracts, biceps relaxes.

Muscles can only pull, so they work in pairs. are inelastic , so all the force of contraction reaches the bone.

Lesson 24 of 25

Data and calculations

Percentage change: difference ÷ starting value × 100.
Rate: change ÷ time, with a unit such as mV s⁻¹.
Evaluate: sample size, (age, sex, fitness, diet), overlap of data, percentages for unequal samples.

Lesson 25 of 25

Key points

gives flexibility; gives hardness.
build; break down.
constant; and shorten.
Calcium binds ; detaches and re-cocks .
: bone to bone. : muscle to bone.
: wear. : .

Cartilage

Compact bone

Haversian systems

Osteoblasts and osteoclasts

Rickets and osteomalacia

Osteoporosis and brittle bone disease

Skeletal muscle structure

The sarcomere

Sliding filaments

The calcium switch

The cross-bridge cycle

Fast and slow twitch fibres

Anaerobic conditions and energy sources

The skeleton and its functions

Fractures

The vertebral column

Posture conditions

Types of joint

The synovial joint

Osteoarthritis

Rheumatoid arthritis

Levers

Antagonistic muscles

Data and calculations

Key points

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: cram notes

Cartilage

Compact bone

Haversian systems

Osteoblasts and osteoclasts

Rickets and osteomalacia

Osteoporosis and brittle bone diseaseBWRBioWelsh 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.

Skeletal muscle structure

The sarcomereBWRBioWelsh 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.

Sliding filamentsBWRBioWelsh 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.

The calcium switchBWRBioWelsh 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.

The cross-bridge cycleBWRBioWelsh 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.

Fast and slow twitch fibres

Anaerobic conditions and energy sources

The skeleton and its functions

Fractures

The vertebral column

Posture conditions

Types of joint

The synovial joint

OsteoarthritisBWRBioWelsh 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.

Rheumatoid arthritis

Levers

Antagonistic muscles

Data and calculationsBWRBioWelsh 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.

Key points

Worksheets

Worksheet 1: Option B Musculoskeletal Anatomy (149 marks)

Check your understanding.

Osteoporosis and brittle bone disease

The sarcomere

Sliding filaments

The calcium switch

The cross-bridge cycle

Osteoarthritis

Data and calculations