Neuromuscular

• Name the muscle fibre type in use during an endurance race and identify the physiological characteristics that allow these muscles fibres to work for extended periods of time (3)

  - Type 1 muscle fibres

  - high number of mitochondria

  - high capillary density

  - high myoglobin
• Explain how 4 characteristics of type Iix muscle fibres enable them to be suited to anaerobic physical activities (4)

  - high levels in phosphocreatine allows high rate of contraction

  - high force production allows for an increase in speed of contraction

  - high actin and myosin allows for a faster contraction

  - high stores of PC allows the maintenance of high rate contraction for longer periods of time
• Suggest 3 physiological causes of muscle fatigue (3)

  - build up of lactic acid

  - lack of calcium ions

  - lack of acetylcholine
• Suggest why the muscles concerned in maintaining the trunk posture of the body of a sprinter might be expected to have a larger percentage of slow twitch muscle fibres (2)

  - they have to maintain posture for long period of time

  - it is important for these muscles to not fatigue as easily

  - therefore there is no need for them to have fast twitch fibres which are for powerful contractions
• Explain why fast twitch muscle fibres may build up an oxygen debt during a 400m sprint (3)

  - low capillary density

  - few mitochondria

  - therefore less O2 is supplied because they contain fewer oxidative enzymes
• How can a performer vary the strength of muscular contractions to ensure that a skill is completed correctly (4)

  - recruit larger motor units

  - recruit more motor units

  - use fast twitch muscle fibres rather than slow twitch

  - all or none law
• The strength of a muscle contraction involves the use of motor units. How are motor units used to produce muscle contractions of varying strength in a lift (3)


  - number of motor units used could be varied

  - all or none law

  - size of motor units can be varied
• Explain how training can adjust the recruitment of different fibre types (6)

  - low intensity endurance training will result in recruitment of slow twitch muscle fibres

  - high intensity will recruit more type IIx fibres

  - as the muscles get stronger, fewer fibres are required to produce the force needed

  - high intensity training will increase the rate of fibre recruitment
• Identify and explain the function of the different regions of a motor neurone (6)

  - cell body received stimuli from other neurones

  - via dendrites

  - axon conducts the electrical impulse

  - nodes of Ranvier allows the impulse to jump speeding up the rate of transmission

  - axon terminals transmits neurotransmitters such as acetylcholine
• What is a motor unit (2)

  - a motor unit consists of a block of muscle fibres connected to a motor neurone

  - this connects to the brain via the nervous system
• Why is it that all the muscle fibres attached to a motor neurone will not necessarily contract at the same time (3)

  - motor neurones have different lengths so the impulse takes less time in a shorter one

  - it may not be necessary for all motor units to be stimulates at the same time ( spacial summation)

  - motor units may be relaxing and resting
• The sliding filament hypothesis suggests muscular contraction occurs in the sarcomeres of the muscle fibres. Explain how actin and myosin filaments in the sarcomere bind together causing muscular contraction (4)

  - filaments are unable to bind due to tropomyosin

  - sarcoplasmic reticulum releases calcium ions which bind to troponin

  - this causes he shape of the troponin to change moving the tropomyosin out of the way

  - this exposes the binding site for myosin to attach to actin creating a cross bridge
• How are motor units involved in the process of spatial summation (2)

  - increases strength in muscles

  - use of more and bigger motor units
• Explain how a muscle contracts according to sliding filament theory (4)

  - action potential reaches the motor end plate

  - this causes calcium ions to be released to attach to troponin

  - this causes the tropomyosin to move revealing the actin binding sites

  - myosin attaches to actin forming a cross bridge and pulls on it
• Explain the roles of tropomyosin and troponin during a muscular contraction (4)

  - tropomyosin prevents myosin attaching to actin filaments

  - calcium ions attach to troponin in order to change the shape of the troponin so the tropomyosin binds to the troponin so the myosin binding site are exposed
• What is the effect of stimulating more motor neurones (1)

  increases strength/ force of contraction
• Describe the all or none law


  - when stimulated all the fibres within a motor unit will contract fully or not at all

  - there is no strong or weak contraction
• Compare wave summation and spacial summation firing patterns (4)

  - wave summation gradually increases the force of contraction as the muscle is stimulated again before it can fully relax

  - for example a gymnastics floor routine

  - spacial summation is where the motor units are turned on simultaneously to produce a constant force of contraction to prevent fatigue

  - for example a marathon runner
• Explain two reasons why actin and myosin may stop pulling on one another (4)

  - ATP is depleted

  - this is required to allow the myosin to break the cross bridge and move so without this there is no movement taking place

  - calcium is depleted

  - without calcium the tropomyosin will twist back and block the binding site of the actin preventing movement
• State why it is important to warm up muscle tissue prior to long jumping (2)

  - raises the muscle temperature to:

  --> increase enzyme action

  --> increase ATP conversion
• Describe three changes that occur in muscle cells as a result endurance training (3)

  - increase in muscle size (hypertrophy)

  - increase in number and size of mitochondria

  - increase in myoglobin content
• Examine the chronic adaptations to the cardiovascular system experienced after a sustained period of endurance training (8)

  - increase in cardiac output

  - hypertrophy of the heart

  - increase in blood volume

  - increased stroke volume

  - increase in capillary density allows for better gas exchange

  - increased haemoglobin allows better oxygen carrying capacity

  - increase in gas exchange in blood allows for faster delivery of oxygen

  - decrease incrusting heart rate (bradycardia)