VCE PE Units 1 & 2Neuromusculoskeletal System

Muscle formation, recruitment and contraction

Key Knowledge and skills

KEY KNOWLEDGE KEY SKILLS The way the neuromuscular and

musculoskeletal systems work together to bring about movements including major bones, muscles, joints and joint action

The various characteristics of the different muscle types – fibre and arrangement

Isotonic, isokinetic and isometric muscle contractions

The agonist and antagonist relationship as related to reciprocal inhibition and the associated use of stabilisers

The nervous control of muscles including recruitment of motor units, fibres and types of contraction

Correct use of anatomical terms related to major bones, muscles, common joints and their actions that bring about movements.

Participate in and analyse a broad range of movements used in sporting activities and be able to identify key bones, muscles and joint movements associated with those movements.

Explain and discuss how reciprocal inhibition works

Identify the different types of muscle fibres and contractions responsible for a wide range of physical activities performed at varied intensities

Learning Intentions

• Strengthen your understanding of the musculoskeletal system

• To learn the characteristics of a motor unit including how it is controlled

Muscle fibre arrangement

Fusiform- Run longitudinally with the tendon. E.g. Biceps in the armProduce low force but can shorten over a long range

Penniform- run at angles to tendon.Can produce greater force with a higher number of fibersDivided 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

Muscle fibre arrangementUsing what you have learnt, label the following muscle fibre types

ANSWERS….

Complete text book ‘Thinking Things Through’ Page 16

Questions 1-4

The microscopic structure of muscles

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 resultsin contraction and force production.A stronger stimulus will produce a greater number of action potentials per second and a stronger contraction.

Microscopic Structure of a Skeletal Muscle worksheet

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

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

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 filamentsCross bridges shorten and pull actin filaments towards the centerThe muscle contracts

http://youtu.be/xhgDbjrrmFg (SFT song)

http://youtu.be/0kFmbrRJq4w

Sarcomere region

Muscle shortening

Muscle lengthening

A band Unchanged Unchanged

I band Shortens Lengthens

H zone Shortens and disappears

Reappears and lengthens

Z line Unchanged Unchanged

The effect of muscle contraction on structures of the sarcomere

How muscles contract

Insert 1.23

Thinking Things ThroughPg. 22

Questions: 1,2,3,4,5

Types of ContractionThere 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 contractionOccurs 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 contractionOccur 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 contractionTension 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/T3OiOJ6-x34 http://youtu.be/4qCaiaFwtL0

Fast & Slow Twitch FibresMuscles 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.

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Thinking Things ThroughPg. 26

Questions:1-4

Fibre Recruitment TheoryRecruitment: 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 anElectromyography (EMG). An EMG records both the quality andquantity of electrical activity within a muscle.

Factors Affecting Muscle Strength

• Fibre arrangement• Muscle fibre recruitment• Muscle fibre type• Speed of contraction• Gender• Age

LabMuscle cross-sectional area V.s strengthPg. 27

SAC revision

Practical- complete the worksheet