The Neuromuscular System

Pre Task Write down a definition of aerobic and anaerobic respiration, explaining the difference between the two.

Aerobic Exercise AIRobic Performed in the presence of oxygen at a low intensity over a prolonged period of time e.g. marathon running. Slow Twitch Muscle Fibres

Anaerobic Exercise Is performed in the absence of oxygen at a high intensity that can only be sustained for a short period of time due to the build up of lactic acid. E.g. 100m sprint Fast Twitch Muscle Fibres

Key Terms You Should Know Before we start this section Slow Oxidative Muscle Fibres A type of muscle fibre rich in Mitochondria, Myoglobin and capillaries which produces a small amount of force over a long period of time – DOES NOT FATIGUE EASILY Fast Oxidative Glycolytic Fibres Type 2a fibres Fast Glycolytic Muscle Fibres A type of muscle fibre rich in Phosphocreatine which produces a maximal force over a short period of time FATIGUE EASILY Phosphocreatine (PC) High energy compound stored in muscle cell and used as a fuel for very high- intensity energy production (ATP-PC System)

Key Terms You Should Know Before we start this section Mitochondria Structure in sarcoplasm responsible for aerobic energy production Myoglobin A protein in muscle responsible for transporting oxygen to the mitochondria. AEROBIC work/Exercise low intensity, long duration exercise in the presence of oxygen. Performed in the presence of oxygen at a low intensity over a prolonged period of time e.g. marathon running. Suited to - Type one – slow twitch ANAEROBIC Work/Exercise High intensity, short duration exercise in the absence of oxygen. Is performed in the absence of oxygen at a high intensity that can only be sustained for a short period of time due to the build up of lactic acid. E.g. 100m sprint Suited to - Type two – fast twitch

There are three main muscle fibre types Our skeletal muscles contain a mixture of all three types of fibre but not in equal proportions. This mix is mainly genetically determined. The relative proportion of each fibre type varies in the same muscle of different people. For example, an elite endurance athlete will have a greater proportion of slow twitch fibres in their leg muscles compared to an elite sprinter who would have a high level of fast twitch fibres. Also postural muscles tend to have a greater proportion of slow twitch fibres as they are involved in maintaining body position over a long period of time. Slow Oxidative (type 1) - also know as slow twitch Fast Oxidative (Type 2a) - also know as fast twitch type 2a Fast Glycolytic (type 2b) - also know as fast twitch type 2b

Type 1 Slow Twitch Fibres These fibres have a slower contraction speed than fast twitch fibres and are better adapted to lower intensity exercise such as long distance running. They produce most of their energy aerobically (using oxygen) and therefore have specific characteristics that allow them to use oxygen more effectively

Type 1 Slow Twitch Fibres Mitochondria- ATP is produced- cope With prolonged periods of exercise Structure Greater blood flow to the working Muscles more O2- work for longer Red Small Many mitochondria Many capillaries High myoglobin Low glycogen Myoglobin- is found mainly in the muscle tissue, it is a storage site for oxygen, in times of oxygen deprivation oxymyoglobin releases its bound oxygen to help create energy.

Type 1 Slow Twitch Fibres Function They have a slower form of ATPase which is an enzyme that splits, releasing ATP. Contraction- slow Contractile strength- low Fatigue resistance-high Aerobic capacity- high Anaerobic capacity- low Produce a small amount of force over a longer period of time Have the enzymes to break down fats, carbohydrates to Water and CO2- so less lactic Acid and fatigue

Type 1 Slow Twitch Fibres SPORTING EXAMPLE: Marathon Runners (aerobic events) Long distance cycling Highly trained distance runners- 80% of the muscle is made up of slow twitch fibres. You can’t predict how good someone is just from their % of muscle fibres- depends on training, efficiently of CV and respiratory system.

Type 2 Fast Twitch Fibres These fibres have a much faster contraction speed than slow twitch fibres and can create a greater force of contraction. However, they also fatigue very quickly and are used for short, intense bursts of effort. They produce most of their energy anaerobically (without using oxygen). There are two types of fast twitch fibres: Type 2a Type 2b

Type 2a Fast Oxidative Glycolytic (Fog) Fibres Structure Red Moderate mitochondria Moderate capillaries Moderate myoglobin High glycogen Lighter- fast twitch

Type 2a Fast Oxidative Glycolytic (Fog) Fibres Function Contraction- fast Contractile strength- high Fatigue resistance-low Aerobic capacity- low Anaerobic capacity- high Suited to more anaerobic respiration- release energy quickly Produce energy aerobically and anaerobically

Type 2a Fast Oxidative Glycolytic (Fog) Fibres SPORTING EXAMPLE: 800M Runners Invasion Games players

Type 2b Fast Glycolytic (FG) Fibres Structure White Biggest Few mitochondria Few capillaries Low myoglobin High glycogen High Stores of Phosphocreatine (PC)

Type 2b Fast Glycolytic (FG) Fibres Function Produce a large amount of force over a short period of time Contraction- fastest Contractile strength- Highest Fatigue resistance-lowest Aerobic capacity- lowest Anaerobic capacity- highest Energy is released quick but the muscle tires Rely on anaerobic respiration

Type 2b Fast Glycolytic (FG) Fibres SPORTING EXAMPLE: 100 metre sprinter 200M Sprinters Wide receivers (American Football) Any activity requiring speed and power A sprinter has 76% fast twitch fibres compared to 24% slow twitch fibres

Structural Differences of the different types of muscle fibres Characteristic Slow Twitch (Type 1) Fast Oxidative Glycolytic (Type 2a/FOG) Fast Glycolytic (Type 2b/ FG) Fibre size Small Large Number of mitrochondria Moderate Number of capillaries Myogobin content High Low PC stores Glycogen Stores Triglyceride stores Functional Differences Speed of contraction Slow (110) Fast (50) Fastest (50) Force of contraction Highest Resistance to fatigue Lowest Aerobic capacity Anaerobic capacity Activity suited   Marathon 800m 110m Hurdler

The Motor Unit Muscle fibres are groups into motor units. A motor unit consist of a motor neurone and its muscle fibres. Only one type of muscle fibre can be found in on particular motor unit. Muscle fibres work with the nervous system so that a contraction can occur. The motor neurone transmits the nerve impulse to the muscle fibre. Each motor neurone has branches that end in the neuromuscular junction on the muscle fibre.

Key Terms You Should Know Motor Unit A motor neurone and its muscle fibres. Motor Neurones Nerve cells which transmit the brains instructions as electrical impulses to the muscles. Neuromuscular Junction Where the motor neurone and the muscle fibre meet.

Motor Unit Contiued Each muscle is made up of many motor units and they vary in size. A small muscle that is used for fine motor control, for example the muscle controlling eye movements, will have motor units that have only a few fibres per motor neurone. However, a large muscle used for gross motor control, such as the quadriceps when the leg is extended, will have motor units with a motor neurone feeding hundreds of fibres.

This is called the all or none law Once motor neurone stimulates the muscle fibres, either all of them contract or none of them contract. It is not possible for a motor unit to partially contract This is called the all or none law A minimum amount of stimulation called the “threshold” is required to start a contraction. If the sequence of impulses is equal to or more than the threshold, all the muscle fibres in a motor unit will contract. However, if the sequence of impulses is less than the threshold, then no muscle action will occur.

Slow Twitch And Fast Twitch Motor Units Motor units contain the same type of muscle fibre so they are either slow twitch or fast twitch motor units. The brain will recruit slow twitch motor units for low intensity activities such as jogging or long distance swimming. If a great force of contraction is needed, the brain will recruit fast twitch motor units for activates such as sprinting or power lifting.

Breaking Motor Units down Our body tries to be lazy. It tries to get away with only activating one part of the muscle – least tiring part – type 1, if that fails then fast twitch fibres activated. When motor units are activated they activate in the following order: Type 1 Motor Units (MU) FOG IIa Motor Units (MU) FG IIb Motor Units (MU) So when we go to run – Type 1 activated if action needs to be more explosive then… Type 2a recruited, if even more power needed then… Type2B is activated.

Practical example - Gym Scenario You go to lift a heavy bar at the gym – Type 1 activated – If you cannot lift the bar… Type IIa activated. If more strength is needed then… Type IIb recruited to lift the bar. This is why there is a slight delay in us being able to lift the bar as we have to go through type 1 then IIa then eventually type IIb!!

How to increase the strength of contraction A basketball player jumping for a rebound needs to exert as much force as possible to gain the height needed to win the rebound. In order to increase the strength or force exerted by the quadriceps muscles, one of the following needs to occur Wave Summation Where there is a repeated nerve impulse with no time to relax. therefore a smooth sustained contraction occurs rather than twitches For example box jumps (this is often called a tetanic contraction) Spatial Summation When the strengths of the contraction changes by altering the number and size of the muscles motor units For example squatting

Key Terms You Should Know All or none law where a sequence of impulse has to be of sufficient intensity to stimulate all of the muscles fibres in a mot unit in order for them to contract. If not, none of them contract Wave Summation where there is a repeated nerve impulse with no time to relax so a smooth sustained contraction occurs, rather than twitches. Tetanic Contraction A sustained muscle contraction caused by a series of fast repeating stimuli Spatial Summation When the strength of a contraction changes by altering the number and size of the muscles motor units.

PAST EXAM QUESTIONS OLD SYLLABUS MUSCLE FIBRE TYPES

PAST EXAM QUESTION TIME Jan 2009 (1a) Give two ways that a warm up affects the speed and strength of muscular contraction during the sit up (2 Marks) June 2010 (1b) A performer’s mix of fast and slow twitch muscle fibres is genetically determined. How might the mix of muscle fibre types determine the success of a performer? Identify two structural characteristics of muscle fibre types associated with athletes participating in endurance events (5 Marks) June 2012 (1c) A performer’s mix of fast and slow twitch muscle fibres is genetically detemined. (i) Identify three functional characteristics of slow twitch (slow oxidative) muscle fibres. (3 Marks) (ii) Explain how a performer’s mix of muscle fibre types might influence their reasons for choosing to take part in particular types of physical activity. (3 Marks)

ANSWERS

JAN 2009 (1A) Jan 2009 (1a) Give two ways that a warm up affects the speed and strength of muscular contraction during the sit up (2 Marks)

JUNE 2010 (1B) June 2010 (1b) A performer’s mix of fast and slow twitch muscle fibres is genetically determined. How might the mix of muscle fibre types determine the success of a performer? Identify two structural characteristics of muscle fibre types associated with athletes participating in endurance events (5 Marks)

JUNE 2012 (1C) June 2012 (1c) A performer’s mix of fast and slow twitch muscle fibres is genetically detemined. Identify three functional characteristics of slow twitch (slow oxidative) muscle fibres. (3 Marks)

JUNE 2012 (1C) June 2012 (1c) A performer’s mix of fast and slow twitch muscle fibres is genetically detemined. Identify three functional characteristics of slow twitch (slow oxidative) muscle fibres. (3 Marks) (ii) Explain how a performer’s mix of muscle fibre types might influence their reasons for choosing to take part in particular types of physical activity. (3 Marks)