1.3 - The neuromuscular system

Question 1

What does the autonomic nervous system do?

Answer 1

Regulates the function of our internal organs such as the heart and also controls some of the skeletal muscles within the body.

Question 2

Does the autonomic nervous system work voluntary or involuntary?

Answer 2

Involuntary.

Question 3

What is the movement of muscles controlled by during exercise?

Answer 3

The brain via nerves.

Question 4

What is the neuromuscular system?

Answer 4

Where the nervous system and the muscles work together to allow movement.

Question 5

When do changes in the neuromuscular system take place?

Answer 5

Before, during and after exercise.

Question 6

Why are there changes in the neuromuscular system before, during and after exercise?

Answer 6

To prepare the body for exercise and allow for the changing demands of different intensities of exercise.

Question 7

What do the sympathetic and parasympathetic systems make up part of?

Answer 7

The peripheral nervous system.

Question 8

In terms of the neuromuscular system, what is the role of the sympathetic system?

Answer 8

Prepares the body for exercise and is often referred to as the ‘fight or flight’ response.

Question 9

In terms of the neuromuscular system, what is the role of the parasympathetic system?

Answer 9

Has the opposite effect of the sympathetic system and relaxes the body and slows down many high energy functions. Often explained by the phrase ‘rest and relax’.

Question 10

What are the 3 types of muscle fibre?

Answer 10

• Slow oxidative (type I) (slow twitch).
• Fast oxidative glycolytic (type IIa) (fast twitch).
• Fast glycolytic (type IIx) (fast twitch).

Question 11

What does the mixture of fibres in a persons muscle depend on?

Answer 11

Endurance athletes have more slow twitch muscle fibres in the legs and sprinters will generally have more fast twitch muscle fibres in the legs. Postural muscles usually have a greater proportion of slow twitch fibres as they are involved with maintaining body position over a long period of time.

Question 12

Describe the structure/adaptations of slow twitch fibres (type I):

Answer 12

• Slower contraction speed than fast twitch fibres.
• Better adapted for lower intensity exercise such as long distance running.
• Produce most of their energy aerobically so have specific characteristics that allow them to use oxygen more effectively.

Question 13

Describe the general structure/adaptations of fast twitch fibres (type II):

Answer 13

• Much faster contraction speed than slow twitch fibres.
• Can generate a much greater force of contraction than slow twitch fibres.
• Fatigue very quickly.
• Used for short, intense bursts of effort.
• Produce most of their energy anaerobically.

Question 14

What are the differences between type IIa and IIx fast twitch muscle fibres?

Answer 14

IIa) More resistant to fatigue, used for events such as the 1500m in athletics where a longer burst of energy is needed.

IIx) Fatigue much quicker than type IIa, used for highly explosive events such as the 100m in athletics where a quick, short burst of energy is needed.

Question 15

Define aerobic:

Answer 15

‘With oxygen’. Exercise that is at a low to medium intensity where the oxygen demand of the muscles can be met.

Question 16

Define anaerobic:

Answer 16

‘Without oxygen’. Exercise at high intensity such as sprinting where the demand for oxygen by the muscles is so high that it cannot be met.

Question 17

What is the contraction speed (metres per second) for the 3 types of muscle fibres?

Answer 17

I) Slow (110)
IIa) Fast (50)
IIx) Fast (50)

Question 18

What is the motor neurone size of the 3 types of muscle fibres like?

Answer 18

I) small
IIa) large
IIx) large

Question 19

What is the motor neurone conduction capacity of the 3 types of muscle fibres like?

Answer 19

I) Slow
IIa) Fast
IIx) Fast

Question 20

What is the force produced by the 3 types of muscle fibres like?

Answer 20

I) low
IIa) high
IIx) high

Question 21

What is the fatigability of the 3 types of muscle fibres like?

Answer 21

I) low
IIa) medium
IIx) high

Question 22

What is the mitochondrial density of the 3 types of muscle fibres like?

Answer 22

I) high
IIa) medium
IIx) low

Question 23

What is the myoglobin content of the 3 types of muscle fibres like?

Answer 23

I) high
IIa) medium
IIx) low

Question 24

What is the capillary density of the 3 types of muscle fibres like?

Answer 24

I) high
IIa) medium
IIx) low

Question 25

What is the aerobic capacity of the 3 types of muscle fibres like?

Answer 25

I) very high
IIa) medium
IIx) low

Question 26

What is the anaerobic capacity of the 3 types of muscle fibres like?

Answer 26

I) low
IIa) high
IIx) very high

Question 27

What is the myosin ATPase/glycolytic enzyme activity like in the 3 types of muscle fibres?

Answer 27

I) low
IIa) high
IIx) very high

Question 28

What is hypertrophy?

Answer 28

Where the muscle has become bigger and stronger.

Question 29

How do fibre types appear to be determined?

Answer 29

Genetically.

Question 30

How can you increase the size of muscle fibres?

Answer 30

Through training.

Question 31

What is a motor unit?

Answer 31

A motor neurone and its muscle fibres.

Question 32

What are motor neurones?

Answer 32

Nerve cells which transmit the brain’s instructions as electrical impulses to the muscles.

Question 33

What is a neuromuscular junction?

Answer 33

Where the motor neurone and the muscle fibre meet.

Question 34

How many types of muscle fibre can be found in one particular motor unit?

Answer 34

1

Question 35

How do the muscle fibres work with the nervous system and what does this result in?

Answer 35

The motor neurone transmits the nerve impulse to the muscle fibre and each motor neurone has branches that end in the neuromuscular junction on the muscle fibre. They work together so that contraction can occur.

Question 36

What is the difference in terms of muscle fibres between different size muscles?

Answer 36

Small muscle used for fine motor control = motor units with only a few fibres per motor neurone.

Large muscle used for gross motor control = motor units with a motor neurone feeding hundreds of fibres.

Question 37

What is the all or none law?

Answer 37

Where a sequence of impulses has to be of efficient intensity to stimulate all of the muscle fibres in a motor unit in order for them to contract. If not, none of them contract.

So, if the sequence of impulses is equal to or more than the threshold required to start the contraction, then all of the muscle fibres in the motor unit with contract.

If the sequence of impulses is less than the threshold required, then no muscle action will occur.

Question 38

What is wave summation?

Answer 38

Where there is a repeated nerve impulse with no time to relax so a smooth, sustained contraction occurs, rather than twitches.

Question 39

What is a tetanic contraction?

Answer 39

A sustained muscle contraction caused by a series of fast repeating stimuli.

Question 40

In terms of wave summation,

The greater the frequency of stimuli…

Answer 40

the greater the tension developed by the muscle.

Question 41

In the neuromuscular system, what happens each time the nerve impulse reaches the muscle cell?

Answer 41

Calcium is released.

Question 42

What mineral needs to be present for a muscle to contract?

Answer 42

Calcium.

Question 43

What happens if there are repeated nerve impulses with no time to relax and what will this produce?

Answer 43

Calcium will build up in the muscle cell producing a forceful, sustained, smooth contraction which is referred to as a tetanic contraction.

Question 44

What is spatial summation?

Answer 44

When the strength of a contraction changes by altering the number and size of the muscle’s motor units.

It is the recruitment of additional and bigger motor units within a muscle to develop more force.

Question 45

When does spatial summation occur?

Answer 45

When impulses are received at the same time at different places on the neurone which add up to fire the neurone.

Question 46

What is PNF (proprioceptive neuromuscular facilitation)?

Answer 46

An advanced stretching technique and is considered to be one of the most effective forms of flexibility training for increasing range of motion.

Question 47

What is an example of a PNF (proprioceptive neuromuscular facilitation) technique?

Answer 47

The most practical is the CRAC technique (contract-relax-antagonist-contract).

Question 48

What are 2 types of proprioceptors?

Answer 48

Muscle spindles

Golgi tendon organs

Question 49

What are muscle spindles?

Answer 49

Very sensitive proprioceptors that lie between skeletal muscle fibres. They are often called stretch receptors.

Question 50

What do muscle spindles do and then what happens next?

Answer 50

Detect how far and how fast a muscle is being stretched and produce the stretch reflex. They provide this information (excitory signals) to the central nervous system.

The central nervous system then sends an impulse back to the muscle to contract, which triggers the stretch reflex. This reflex action that causes the muscle to contract to prevent over-stretching reduces the risk of injury.

Question 51

Where are golgi tendon organs found and what do they do?

Answer 51

Found between the muscle fibre and tendon.

They detect levels of tension in a muscle and are activated when there is tension in a muscle.

When the muscle is contracted isometrically in PNF, the sense the increase in muscle tension and send inhibitory signals to the brain which allows the antagonist muscle to relax and lengthen. This is known as autogenic inhibition.

Question 52

What is an isometric contraction?

Answer 52

Where there is tension in a muscle but no visible movement.

Question 53

What is autogenic inhibition?

Answer 53

Where there is a sudden relaxation of the muscle in response to high tension. The receptors involved in this process are golgi tendon organs.

Question 54

How is the CRAC technique carried out?

Answer 54

Individual performs a passive stretch with the help of a partner and extends until tension is felt. This stretch is detected by the muscle spindles. If the leg is being stretched too far, then a stretch reflex should occur.

Individual then isometrically contracts the muscle for at least 10s by pushing against the partner who supplies just enough resistance to hold the stretching limb in a stationary position.

As the leg is lifted again, the golgi tendon organs are responsible for the antagonist muscle relaxing, which means the leg stretches further. This process can be repeated until no more gains are possible.

Question 55

What are golgi tendon organs sensitive to and what does this mean?

Answer 55

They are sensitive to tension developed in a muscle, and during an isometric contraction they are activated and the inhibitory signal they send override the excitory signals from the muscle spindles, therefore delaying the stretch reflex.