Skeletal And Muscular Systems

Question 1

Compare isotonic and isometric muscle contractions. (2)

Answer 1

Isotonic contraction causes a change in length of muscle.
Isometric contraction there is no change in muscle length.

Question 2

Concentric / eccentric

Answer 2

In concentric contractions the muscle shortens
In eccentric contractions the muscle lengthens

Question 3

Describe the structure of a motor unit (1)

Answer 3

Consists of a motor neurone and a number of muscle fibres

Question 4

What is the “all or none law”? (1)

Answer 4

When stimulated all the fibres within a motor unit contract completely or not at all

Question 5

What is the effect of stimulating more motor units (1)

Answer 5

Increases force of contraction

Question 6

Explain how a motor unit is stimulated to cause muscular contraction. (4)

Answer 6

-Nerve impulse from CNS travels down from motor neurone
- Action Potential
- Release of sodium causes depolarisation
- at neuromuscular junction neurotransmitter is secreted
- impulse crosses synaptic cleft to muscle fibres
- if the impulse is above threshold, all muscle fibres will contract or not at all

Question 7

Explain how a motor unit is stimulated to cause muscular contraction. (4)

Answer 7

-Nerve impulse from CNS travels down from motor neurone
- Action Potential
- Release of sodium causes depolarisation
- at neuromuscular junction neurotransmitter is secreted
- impulse crosses synaptic cleft to muscle fibres
- if the impulse is above threshold, all muscle fibres will contract or not at all

Question 8

Explain, using sporting examples, how the predominance of each muscle fibre type in performers may impact on their performance. (3)

Answer 8

Slow twitch for endurance .
E.g. footballer can last 90 minutes without fatigue
Fast oxidative glycolytic for muscular endurance.
E.g. gymnast can complete a strenuous floor routine without tiring
Fast glycolytic twitch for power.
E.g. High jumper can produce explosive strength needed to jump over bar.
Mix of fibre types would benefit a games player, providing a combination of speed, muscular endurance and stamina

Question 9

Explain the recruitment of muscle fibre types during exercise of differing intensities. (4)

Answer 9

Slow oxidative fibres (T1) recruited for aerobic work. eg marathon / long distance
becauseslow oxidative fibres have high fatigue resistance and high aerobic capacity
becausethey have high density of mitochondria and a high myoglobin content
Fast oxidative glycolytic fibres (2a) recruited during high intensity exercise. eg team sports / 400m / 800m
becausefast oxidative glycolytic have high force of contraction andmoderate fatigue resistance
becauselarge neuron and moderate myoglobin store
Fast glycolytic fibres (2b) recruited during very high intensity. eg. shot put / 100m / sprint for ball
becausefast glycolytic have fast speed and high force of contraction
becauseFG fibres have high phosphocreatine store and large neurons
Slow oxidative fibres are recruited first then as intensity increases, fast oxidative glycolytic fibres and finally fast glycolytic fibres are subsequently recruited.