Muscle Units ans Fibres

Question 1

How does a skeletal muscle contract.

Answer 1

Skeletal muscles contract when stimulated by an electrical impulse sent from the CNS

Question 2

Explain the Motor Unit step by step?

Answer 2

1) Dendrites collect the signals and the axon transmits the signal to the neuromuscular junction

2) The signal travels through the neuromuscular junction till it reaches the end plate, there’s a gap between the end plate and the muscle fibre which is called the synaptic cleft

3) Once an impulse reaches the end plate it stimulates the vesicle to release Ach, which is then secreted across the synaptic cleft

4) If Ach is secreted above a threshold then the action potential will be transmitted into a muscular contraction

Question 3

Explain the All or none Law

Answer 3

If a motor unit receives a stimulus to create an action potential that has reached the threshold, all muscles fibres will contract at the same time with maximum force

If action potential does not reach the threshold, none of the fibres will contract

Question 4

Name all muscle fibre types

Answer 4

• Type 1 : Slow Oxidative
• Type 2a : Fast Oxidative Glycolytic
• Type 2b : Fast Glycolytic

Question 5

Features of Type 1 (Slow Oxidative) Fibre

Answer 5

• Store oxygen in myoglobin and process oxygen in the mitochondria to break down fats and glucose into ATP, (High density of mitochondria and myoglobin, Dense network of capillaries to transport oxygen to cells)
• Aerobic Respiration (withstand fatigue for long periods, small amounts of force in contraction)
• Slow contraction time
• Low Glycolytic capacity
• High Oxidative Capacity

Question 6

Features of Type 2a (Fast Oxidative Glycolytic)

Answer 6

• Structurally designed to produce a large amount of force relatively quickly but are also able to resist fatigue
• Have large neurons which innervate many muscle fibres at once
• Large stores of phosphocreatine which helps main a good anaerobic capacity
• Moderate mitochondrial and myoglobin density ( moderate fatigue resistance )
• High Oxidative Capacity
• Fast Contraction Time
• Suited for lengthy anaerobic exercise
• High Force Production
• High Glycolytic Capacity
• Medium Capillary Density

Question 7

Features of Type 2b (Fast Glycolytic) Fibre

Answer 7

• Exert a large force, have a fast contraction and relaxation time
• Large stores of phosphocreatine, enable immediate energy supply
• Work anaerobically, last a short duration before fatigue
• Large amounts of neurons, help exert a larger force of contraction
• Low oxidative capacity
• Fastest contraction time
• Low resistance to fatigue
• Highest Force Producer
• High Glycolytic Capacity
• Low capillary density