Muscle Fibres

Learning Outcomes All are able to apply

knowledge of the fibres to sporting events

Most are able to explain the role of the motor unit in contraction.

Some are able to apply knowledge to a range of sporting activities.

Write up a neat copy of your extended question to be marked

Prepare for Mock exam – Tues 7th October

Bring in file with all Muscle Notes

Homework

Question chain activity to recap muscle fibres.

Complete exam question

Starter Activity

The motor unit is the basic functional unit of skeletal muscle.

The motor unit is the motor nerve (neurone) and the group of muscle fibres that it controls.

Stimulation of one motor neuron causes all the muscle fibres in that motor unit to contract simultaneously.

Each muscle is made up of a number of units. The number recruited varies depending on strength required.

Number of fibres within a motor unit is dependent on control required. Small muscle for fine motor skill may only require

one fibre per motor unit e.g. eye to focus Large muscle for gross skill may need 500 or more

fibres e.g. kicking a football

Motor unit

Motor units are usually made up of the same muscle fibre.

So we see both fast and slow twitch motor units in a muscle.

Motor unit

The innervation (stimulation) of a muscle occurs when a motor neuron transmits a nerve impulse to the muscle fibre.

The all or none law states that if a motor impulse is of sufficient intensity, the motor unit is stimulated and all the muscle fibres within it will contract to their maximum potential.

Either the neurone will fire a response or it won't. There is no partial response.

All or none law

Give handout – diagrams

The force exerted by a muscle is dependent on: Recruitment: the more motor units recruited,

the more muscle fibres that contract, thus increasing the force produced.

Frequency: decreasing the time between impulses so that the muscle fibres do not have time to relax, resulting in a continuous wave of contractions known as wave summation.

Graduation of contraction

Timing: spatial summation – To create a greater force of contraction the brain recruits more and larger motor units.

Use bigger/larger motor units More motor units More and larger units leads to increased strength/more

force in muscles FT units produce more force than ST units.

Graduation of contraction

Resistance training will result in some long term physiological responses to the neuromuscular system: Recruitment of more motor units (trained to

act together) Muscle hypertrophy (due to increases in size of

fibres or hyperplasia – splitting of fibres) Conversion of type 2b to type 2a (delays

fatigue in prolonged training).

Effect of training

Individually explain how the strength of muscle contraction can be varied in relation to a high jumper and a distance runner.

Share this information with a partner between you come up with an agreed answer.

Be prepared to share this information

Plenary Activity

The strength of a muscle contraction can be increased Use bigger/larger motor unitsMore motor unitsMore and larger units leads to increased strength/more force in musclesFT units produce more force than ST units.

All or none lawIf all motor units are stimulated at same time then max force can be appliedHigh jumper – predominantly FT muscle fibresMarathon runner – predominantly ST muscle fibres

Plenary activity

Complete this question in pairs:

How can a performer vary the strength of muscular contractions to ensure that a skill is completed correctly? (4 marks)

Exam Q

A. (Greater the force needed) larger motor units recruitedB. More units recruitedC. Need fast twitch fibres rather than slow twitch fibresD. Multiple unit summation/spatial summationE. All or none law/All or nothing law/or explanationF. Wave summation/frequency of impulse/innervationsG. Motor unit unable to relax/increase the forceH. Tetanus/titanic for powerful contractionI. Muscle spindles detect changes in muscle length/speed of contractionJ. Send information to brain/CNSK. Compares information to long term memory to ensure correct force applied/past experiencesL. Spatial summation – rotating the frequency of the impulse to motor units to delay fatigue

In pairs use your notes to complete a draft version of the extended question.

Extended question