5.1Unit 5: Respiration, Internal Environment, Coordination and Gene Technology
Muscles & Movement — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 11 parts Lesson 2 of 36 1 quiz
Curriculum Equation Key معادلة التنفس الخلوي الهوائي الموزونة - Balanced Cellular Respiration EquationFast Exam Solution
C₆H₁₂O₆ + 6O₂ ➔ 6CO₂ + 6H₂O + 36-38 ATP
Word Equation & Conditions: Glucose + Oxygen -> Carbon Dioxide + Water + Energy (36-38 ATP) | جلوكوز + أكسجين ← ثاني أكسيد كربون + ماء + طاقة
Location & Specifications: الميتوكوندريا (Mitochondria) والسيتوسول.
Lesson summary
5.1 Muscles and Movement — IAL EDEXCEL LINEAR notes: Describe how muscles and the skeleton produce movement, the structure of muscle fibres and sarcomeres, fast and slow twitch fibres, and the sliding filament mechanism.Skeleton and muscle — effective movement needs muscles pulli…
- Skeletal muscles
- Synovial joint
- Antagonistic pair
- Sarcoplasm contents
- Sarcoplasmic reticulum
- Thick filaments
Part 1 of 9The musculoskeletal system
The musculoskeletal system
Skeleton and muscle
- Skeleton and muscle effective movement needs muscles pulling on an incompressible skeleton,
- because muscles produce movement only by pulling on a structure that does not shorten or bend.
Skeletal muscles
- Skeletal muscles over 600 muscles are effectors stimulated by impulses from motor neurones.
Tendons
- Tendons strong, flexible connective tissue joining muscle to bone that does not stretch when the muscle contracts.
Ligaments
- Ligaments strong connective tissue joining bone to bone and keeping the skeleton intact.
Synovial joint
- Synovial joint cartilage reduces friction and absorbs shock, synovial fluid lubricates and nourishes cartilage, the synovial membrane secretes the fluid,
- and the capsule and ligaments give stability.
Part 2 of 9Antagonistic muscle action
- Antagonistic pair
- muscles can only pull, so they work in pairs pulling in opposite directions at a joint.
| Movement | Contracting muscle | Relaxing muscle |
|---|---|---|
| Raise the lower arm (flexion) | Biceps (flexor) | Triceps |
| Lower the lower arm (extension) | Triceps (extensor) | Biceps |
- Reset
- the contracting muscle stretches the relaxed muscle back to full length so it can contract again.
Part 3 of 9Structure of a muscle fibre
- Muscle fibre
- a specialised multinucleate cell-like unit surrounded by a cell surface membrane, containing contractile proteins in the cytoplasm.
| Muscle fibre term | Equivalent in a normal cell |
|---|---|
| Sarcolemma | Cell surface membrane |
| Sarcoplasm | Cytoplasm |
| Sarcoplasmic reticulum (SR) | Endoplasmic reticulum |
Structure of a muscle fibre
T-tubules
- T-tubules deep tube-like folds of the sarcolemma that run close to the SR and spread electrical impulses through the fibre.
Sarcoplasm contents
- Sarcoplasm contents mitochondria make ATP by aerobic respiration, and myofibrils are bundles of actin and myosin filaments.
Sarcoplasmic reticulum
- Sarcoplasmic reticulum membrane pumps transport calcium ions into its lumen, and calcium is needed for contraction.
Part 4 of 9Myofibrils and the sarcomere
Myofibril
- Myofibril it has thick filaments of myosin and thin filaments of actin in a regular arrangement that creates bands.
Thick filaments
- Thick filaments many myosin molecules lie side by side with globular heads pointing away from the M line.
Thin filaments
- Thin filaments two chains of globular actin twist together, with tropomyosin twisted round them and troponin attached at intervals.
Sarcomere
Sarcomere the unit between two Z discs, with sarcomeres end to end giving a striated appearance.
- The A band is dark and contains myosin.
- The I band is light and contains only actin.
- The H zone is the centre, with myosin only.
- The Z line anchors actin and the M line anchors myosin.
Contraction
- Contraction the Z discs move closer, so the sarcomere, I band and H zone shorten while the A band stays the same length.
- This shows the filaments slide and do not shorten.
Part 5 of 9Fast and slow twitch fibres
| Feature | Fast twitch | Slow twitch |
|---|---|---|
| Contraction | Rapid, myosin heads cycle about five times faster | Slower, sustained |
| ATP supply | Anaerobic respiration | Aerobic respiration |
| Fatigue | Quickly, because of lactate | Slowly, suited to endurance |
| Capillaries | Fewer | Denser network with short diffusion distance |
| Myoglobin and mitochondria | Low amounts, so paler | High amounts, so dark red |
| Calcium | Large amounts needed | Less |
| Examples | Cheetah legs, robin wings, human eyelids | Wolf legs, goose wings, human back muscles |
Myoglobin
Myoglobin a red pigment like haemoglobin that stores oxygen in muscle and speeds oxygen absorption from capillaries.
Fibre proportions
- Fibre proportions they are partly genetic and altered by training, with sprinters having more fast twitch and endurance athletes more slow twitch fibres.
Part 6 of 9Sliding filament mechanism
1
An action potential reaches the neuromuscular junction, where acetylcholine depolarises the sarcolemma.
2
The depolarisation spreads along the sarcolemma and down the T-tubules, and calcium ions are released from the sarcoplasmic reticulum.
3
Calcium ions bind to troponin, which changes shape and moves tropomyosin, exposing myosin-binding sites on actin.
4
Myosin heads bind to actin, forming cross-bridges.
5
The heads bend in the power stroke, pulling the actin filaments towards the centre of the sarcomere and releasing ADP and phosphate.
6
ATP binds to the myosin heads, which detach from actin.
7
ATPase hydrolyses ATP to ADP and phosphate, returning the heads to their original position (recovery stroke).
8
The heads bind to new sites closer to the Z disc and the cycle repeats while calcium and ATP are available.
Relaxation
- Relaxation when stimulation stops, calcium leaves troponin and is actively transported back to the sarcoplasmic reticulum using ATP.
- Troponin returns to its shape, tropomyosin blocks the binding sites again and actin slides back as the antagonist pulls.
Rigor mortis
- Rigor mortis after death there is no ATP to detach the myosin heads, so muscles stay contracted.
Part 7 of 9ATP supply in muscle
ATP supply in muscle
ATP hydrolysis
- ATP + H2O → ADP + Pi releases about 30.5 kJ mol−1 and is needed for detaching and re-cocking myosin heads and for calcium pumping.
Creatine phosphate
- Creatine phosphate it regenerates ATP quickly: creatine phosphate + ADP → creatine + ATP.
Aerobic and anaerobic respiration
- Aerobic and anaerobic respiration slow twitch fibres use aerobic respiration,
- and fast twitch fibres rely on anaerobic respiration that produces lactate.
Part 8 of 9More from the specification
More from the specification
Musculoskeletal lever mechanical advantage
- Musculoskeletal lever mechanical advantage calculating load effort arm ratios provides a biomechanical means to analyze torque across synovial joints.
Musculoskeletal system
- Musculoskeletal system bones, joints, muscles and tendons work together as levers to produce movement.
Antagonistic muscles
- Antagonistic muscles biceps and triceps work in pairs, one contracting while the other relaxes.
Cardiac output
- Cardiac output heart rate times stroke volume gives the volume of blood pumped per minute and rises in exercise.
Breathing changes
- Breathing changes tidal volume and ventilation rate increase to supply more oxygen to the lungs and blood.
Exercise response
- Exercise response blood flow shifts to muscles, and training enlarges the heart and raises stroke volume.
Minute ventilation
- Tidal volume multiplied by breathing rate.
Volume
- The amount of space something takes up.
Breathing
- Moving air into and out of the lungs.
Ventricle
- Lower chamber pumping blood out.
Ventilation
- Movement of air into and out of the lungs.
Spirometer
- Instrument that measures the volume of air breathed.
Cardiac output
- Heart rate multiplied by stroke volume.
Tidal volume
- The volume of air breathed in or out in one normal breath.
Medulla oblongata
- The brain region controlling heart rate and breathing.
Part 9 of 9More on this topic
- Muscle contraction
- a nerve impulse releases calcium ions in the muscle fibre, and calcium exposes binding sites on actin.
- Myosin heads attach to actin and pull the filaments past each other.
- ATP supplies energy for myosin to detach and reset.
- Repeated cross-bridge cycles shorten sarcomeres while the filaments themselves stay the same length.
Key terms
| Term | Meaning |
|---|---|
| Sarcomere | The unit of a myofibril between two Z discs. |
| Sarcolemma | The cell surface membrane of a muscle fibre. |
| Sarcoplasmic reticulum | The endoplasmic reticulum of a muscle fibre that stores calcium ions. |
| Troponin | A protein on actin that binds calcium and moves tropomyosin. |
| Tropomyosin | A protein on actin that blocks myosin binding sites at rest. |
| Antagonistic pair | Two muscles that pull in opposite directions at a joint. |
| Myoglobin | A red oxygen-storing pigment in muscle. |
| Power stroke | The bending of myosin heads that pulls actin filaments. |
Avoid these mistakes
1
Saying the filaments shorten in contraction — they slide, and only the sarcomere, I band and H zone shorten.
2
Saying muscles push as well as pull — they only pull, so antagonistic pairs are needed.
3
Forgetting that ATP is needed for relaxation — it detaches myosin and pumps calcium back into the sarcoplasmic reticulum.
4
Confusing tendons and ligaments — tendons join muscle to bone and ligaments join bone to bone.
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