Describe the structure of a motor neurone.

A motor neurone has a cell body and dendrites that receive signals. A long axon insulated by a myelin sheath carries impulses to the motor end plates on the muscle fibres.

What is an action potential?

An action potential is an electrical impulse that travels along the axon of a motor neurone. The impulse is produced when the neurone's membrane depolarises.

What role does a neurotransmitter play at the neuromuscular junction?

The neurotransmitter acetylcholine is released into the synaptic cleft when an impulse arrives. Acetylcholine crosses the cleft and triggers an action potential in the muscle fibres.

State the all or none law.

Once the threshold stimulus is reached, every fibre in the motor unit contracts fully. A stimulus below the threshold produces no contraction at all.

OCR A-Level Physical Education H555

Skeletal and Muscular Systems

Topic overview Shoulder, elbow and wrist joints and muscles Hip, knee and ankle joints and muscles Planes of movement, muscle roles and contractions Analysing movement in sporting actions Motor units and muscle fibre types

The Cardiovascular System

Topic overview Heart rate, stroke volume and cardiac output at rest The cardiac cycle and conduction system Cardiac responses to exercise and recovery The vascular shunt mechanism Venous return and heart rate regulation

The Respiratory System

Topic overview Breathing frequency, tidal volume and minute ventilation Mechanics of breathing at rest and in exercise Regulation of breathing Gas exchange at the alveoli and the muscles

Energy for Exercise

Topic overview ATP and coupled reactions The ATP-PC system The glycolytic system The aerobic system The energy continuum and intermittent exercise EPOC and the recovery process

Environmental Effects on Body Systems

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Biomechanical Principles and Levers

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Goal Setting

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Attribution

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Confidence and Self-Efficacy

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Leadership

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Stress Management

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Sport in Pre-Industrial and Industrial Britain

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Sport in the 20th and 21st Centuries

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The Olympic Games and Global Sporting Events

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Drugs in Sport

Topic overview Legal supplements and illegal doping Why elite performers dope Consequences of doping for society, sport and performers Strategies against doping

Violence and Gambling in Sport

Topic overview Causes of player and spectator violence Implications of violence in sport Preventing violence among players and spectators Match fixing, bribery and illegal betting

Commercialisation and the Media

Topic overview What drives the commercialisation of sport Impacts of commercialisation Television, radio, press and internet coverage Positive and negative effects of the media Sport as a commodity and the golden triangle

Routes to Sporting Excellence

Topic overview From talent identification to elite performance Schools, clubs and universities in elite success UK Sport and the national institutes Drop-out from elite programmes

Modern Technology in Sport

Topic overview Technology and elite performance Technology and general participation Technology and fair outcomes Technology and entertainment

Skeletal and Muscular Systems

Motor units and muscle fibre types

3 things to know
Component 01

Overview

Motor units and the control they give, the motor neurone, action potentials and neurotransmitters at the neuromuscular junction, the all or none law, and slow oxidative, fast oxidative glycolytic and fast glycolytic fibres with their order of recruitment.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is a motor unit, and how does its size relate to the control it gives?

Key term

What is a motor unit?

Key term

How does the size of a motor unit relate to the control it gives?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a motor unit?
Model answer
A motor unit is a single motor neurone and all the muscle fibres it stimulates. The motor unit is the working unit of muscle contraction.
2
How does the size of a motor unit relate to the control it gives?
Model answer
A small motor unit supplies only a few fibres and allows fine control, as in the fingers. A large motor unit supplies many fibres for powerful movements, as in the quadriceps.
3
Describe the structure of a motor neurone.
Model answer
A motor neurone has a cell body and dendrites that receive signals. A long axon insulated by a myelin sheath carries impulses to the motor end plates on the muscle fibres.
4
What is an action potential?
Model answer
An action potential is an electrical impulse that travels along the axon of a motor neurone. The impulse is produced when the neurone's membrane depolarises.
5
What role does a neurotransmitter play at the neuromuscular junction?
Model answer
The neurotransmitter acetylcholine is released into the synaptic cleft when an impulse arrives. Acetylcholine crosses the cleft and triggers an action potential in the muscle fibres.
6
State the all or none law.
Model answer
Once the threshold stimulus is reached, every fibre in the motor unit contracts fully. A stimulus below the threshold produces no contraction at all.

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