Neuromuscular system


Nervous system

The sympathetic and parasympathetic nervous systems are part of the peripheral nervous system. Their role is to transmit information from the brain to the parts of the body that need to adjust what they are doing to prepare for exercise:

  • Sympathetic nervous system prepares the body for exercise and is often referred to as the "flight or fight" response.
  • Parasympathetic nervous system has the opposite effect, relaxing the body and slowing down many high-energy functions- "rest and relax".
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Slow twitch fibres (type I)

  • These fibres have a slower contraction speed than fast twitch fibres
  • Better adapted to lower intensity exercise such as long-distance running.
  • They produce most of their energy (ATP) aerobically (using oxygen) 
  • Therefore hace specific characteristics that allow them to use oxygen more effectively 
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Fast twitch fibres (type II)

  • Fast contraction speed and can generate a greater force of contraction
  • However, fatigue quickly and are used for short, intense bursts of effort
  • Produce most of their energy anaerobically

Type IIa - fast oxidative glycolytic fibres are most resistant to fatigue and are used for events such as the 1500m in athletics where a long burst of effort is needed

Type IIx - fast glycolytic fibres fatigue quicker than type IIa and are used for highly expolsive events such as the 100m where a quick, short burst of energy is needed.

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Characteristics of Type I

  • Contraction speed (m/sec)- Slow (110)
  • Motor neurone size- Small
  • Force produced- Low
  • Fatigability- Low
  • Capillary density- High
  • Aerobic capacity- Very high
  • Anaerobic capacity- Low
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Characteristics of Type IIa

  • Contraction speed (m/sec)- Fast (50)
  • Motor neurone size- Large
  • Force produced- High
  • Fatigability- Medium
  • Capillary density- Medium
  • Aerobic capacity- Medium
  • Anaerobic capacity- High
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Characteristics of Type IIx

  • Contraction speed (m/sec)- Fast (50)
  • Motor neurone size- Large
  • Force produced- High
  • Fatigability- High
  • Capillary density- Low
  • Aerobic capacity- Low 
  • Anaerobic capacity- Very high
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Functional and Structural characteristics

Functional Chracteristics (what a fibre does)

  • Contration speed 
  • Motor neurone conduction capacity
  • Force produced 
  • Fatigability
  • Aerobic capacity
  • Anaerobic capacity 

Structural Chracteristics (make-up of the fibre)

  • Motor neurone size 
  • Mitochondrial density
  • Myoglobin content 
  • Capillary density
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Motor Unit

Motor Unit- a motor neurone and its muscle fibres 

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 which end in the neuromuscular junction on the muscle fibre.

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All or none law

All or none law- where a sequence of impulses has to be sufficient intensity to stimulate all of the muscle fibres in the motor unit in order for all of them to contract. If not, none of them contract.

A minimum amount of stimulation is needed, called a threshold, is requried to start a contraction. 

If the sequence of impulses are equal/more= all of the muscle fibres will contract

If the sequence of impulses are less= no contraction

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Strength of contraction

  • Wave summation- where there is a repeated nerve impulse with no time to relax, so a smooth, sustained contraction occurs rather than twitches.

The greater the frequency, the greater the tension developed by the muscles. This is wave summation, where repeated activation of a motor neurone stimulating a given muscle fibre results in a greater force of contraction.

  • Tetanic contraction- a sustained powerful muscle contraction caused by a series of fast repeating stiumli. 

Each time the impluse reaches the muscle cells, calcium is released (which causes the muscle to contract). If there is repeated impulses with no time to relax, this will result in a build up of calcium in the muscle cells. This produces a forceful, sustained, smooth contraction.

  • Spatial summation- when the strength of contraction changes by altering the number and size of the muscles motor units.

This occurs when impulses are recieved at the same time at different places on the neurone which add up to fire the neurone. Involves the recruitment of bigger motor units and fast twitch fibres to develop more force. Activation is staggered, which equals a sustained contraction as some motor units are contracting as others are relaxing, which delays fatigue.

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Proprioceptive neurimuscular facilitation (PNF)

PNF- an advanced stretching technique, which is a type of flexibility training to increase range of motion.

CRAC- contract-relax-antagonist-contract.

In PNF, muscle action has to be controlled in order for movement to be effective. Proprioceptors are sensory organs in the muscles, tendons and joints that inform the body of the extent of movement that has taken place. 

Muscle spindles- proprioceptors that lie between the muscle fibres, which detect how far and fast a muscle is being stretched and send a excitory signal to the CNS that produces a stretch reflex.This reflex action causes the muscle to contract to prevent overstrecthing, reducing risk of injury. 

Golgi tendons- found between the muscle fibres and tendons, which detect levels of tension in a muscle. When the muscle is contracted isometrically in PNF, they sense the increase in muscle tension and send inhibitory signals to the brain, which allows the antagonist muscle to relax and lengthen. This is called autogenic inhibition

Muscle spindles= length of muscle Golgi tendons= load and force applied to muscle

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PNF in practice

  • Individual perfroms a passive strecth with the help of a partner and exetends the leg until tension is felt. This strecth is detected by the muscle spindles. If the muscle is being strecthed to far, a reflex should occur
  • The individual then isometrically contracts the muscle for 10 seconds by pushing their leg against their partner who provides enough resistance to hold their leg in a stationary position. The golgi tendons are activated during the isometrical contraction and the inhibitory signals send overide the excitory signals (from the muscle spindles) to delay the stretch reflex.
  • As the leg is passively strecthed again, the golgi tendons are responsible for the antagonist muscle relaxing, which means the leg stretches further. This process is repeated until no more gains are possible.
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