VCE PE Units 1 & 2 Neuromusculoskeletal System Muscle formation, recruitment and contraction

1. VCE PE Units 1 & 2 Neuromusculoskeletal System Muscle formation, recruitment and contraction

2. Key Knowledge and skills

3. Learning Intentions • Strengthen your understanding of the • musculoskeletal system • To learn the characteristics of a motor unit • including how it is controlled

4. Muscle fibre arrangement • Fusiform- Run longitudinally with the tendon. • E.g. Biceps in the arm • Produce low force but can shorten over a long range • Penniform- run at angles to tendon. • Can produce greater force with a higher number of fibers • Divided into 3 groups: • Unipennate (fibers branch out to one side of the tendon) • E.g. Gastrocnemius • Bipennate (Fibers branch out to both sides of the central tendon) • E.g. Quadriceps • Multipennate (fibers branch out repeatedly from a number of tendons) • E.g. Deltoid

5. Muscle fibre arrangement Using what you have learnt, label the following muscle fibre types

6. ANSWERS….

7. Complete text book ‘Thinking Things Through’ Page 16 Questions 1-4

8. The microscopic structure of muscles

9. Neuromuscular Junction A single muscle contraction is initiated by an electrical signal in the CNS (Central Nervous System) that is transmitted along a threadlike axon of a motor unit to a group of skeletal muscle fibres. when the signal reaches the end of a motor unit, it must cross a ‘gap’ before it can stimulate the skeletal muscle fibre to contract. This “gap” is called the neuromuscular junction (NMJ). A chemical know as the neurotransmitter assists in carrying the Electrical signal across to the adjacent muscle fibre. A momentary change in cell voltage then results in action potentials spreading across the skeletal muscle fibre which results in contraction and force production. A stronger stimulus will produce a greater number of action potentials per second and a stronger contraction.

11. Microscopic Structure of a Skeletal Muscle worksheet

12. Nervous control of muscular contractions Motor neurons convey nerve impulses form the brain to muscles A motor neuron and the fibres it controls/stimulates are known as the motor unit Sensory neurons convey nerve impulses from muscles, organs and cells to the brain

13. The all or nothing principles states: It is not until an electrical threshold is surpassed that all of the fibres linked to a motor unit will fire together and maximally. Gross movements requiring major muscle involvement require more motor units than precise/ fine movements Fibres will be recruited according to the activity demand and this is known as preferential recruitment

14. Sliding Filament Theory *How muscles contract *Myofilaments sliding across each other Steps: Electrical impulse sent from brain to the synapse of individual myofibrils [neuromuscular junction] Acetylcholine activates the release of calcium ions This stimulates oar-like projections call ‘Cross-bridges’ to reach out and attach to the actin filaments Cross bridges shorten and pull actin filaments towards the center The muscle contracts http://youtu.be/xhgDbjrrmFg (SFT song) http://youtu.be/0kFmbrRJq4w

15. The effect of muscle contraction on structures of the sarcomere

16. How muscles contract Insert 1.23

17. Thinking Things Through Pg. 22 Questions: 1,2,3,4,5

18. Types of Contraction There are basically three types of muscular contraction, classified by the movement they cause. These are listed below in order of occurrence in everyday activity, from most common to least common: • isotonic (concentric and eccentric) • isometric • isokinetic lsotonic contraction Occurs whenever the muscle length changes through a range of motion or action. When a constant load (weight) is being moved, differences exist in the amount of force applied at various joint angles. Isometric contraction Occur when tension is developed but no change results in the length of the muscle. Isometric contractions hence involve little, if any, change in muscle length while tension is developed. lsokinetic contraction Tension developed is maximal throughout the entire range of motion and is common on hydraulic fitness equipment. The amount of force applied by the machine always equals the amount of force applied by the muscle. http://youtu.be/4qCaiaFwtL0 http://youtu.be/T3OiOJ6-x34

19. Fast & Slow Twitch Fibres Muscles are made up of two different types of fibres: • Red, type I, slow-twitch fibres (ST), best suited to aerobic, endurance work such as triathlons. • White, type II, fast-twitch fibres (FT), best suited to short-duration, high intensity anaerobic work, for example the bursts of power and speed required to sprint. http://youtu.be/0XhSlRkytkE

20. Thinking Things Through Pg. 26 Questions:1-4

21. Fibre Recruitment Theory Recruitment: The progressive activation of a muscle by consecutive activation of motor units i.e. When the muscle is first activated, the earliest motor units to fire will be small in size with progressively larger units recruited as the strength of muscle contraction is increased. To measure the neural activity of muscle you use an Electromyography (EMG). An EMG records both the quality and quantity of electrical activity within a muscle.

22. Factors Affecting Muscle Strength • Fibre arrangement • Muscle fibre recruitment • Muscle fibre type • Speed of contraction • Gender • Age

23. Lab Muscle cross-sectional area V.s strength Pg. 27

24. SAC revision Practical- complete the worksheet