3.1.1.4 - 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 our skeletal muscles within the body
• Works involuntarily

Question 2

What is the neuromuscular system?

Answer 2

Where the nervous system and the muscles work together to allow movement. (through nerves)

Question 3

Why do changes in the neuromuscular system occur before, during and after exercise?

Answer 3

These changes prepare the body for exercise and also allow for the changing demands of different intensities of exercise.

Question 4

What is the role of the sympathetic and parasympathetic nervous systems? (part of the peripheral nervous system)

Answer 4

To transmit information from the brain to the parts of the body that need to adjust what they are doing to prepare for and recover from exercise.

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

Parasympathetic system → Opposite effect - relaxes the body and slows down many high energy functions - often referred to as ‘rest and relax’.

Question 5

What are the 3 main types of muscle fibre?

Answer 5

• slow oxidative (type 1 - also known as slow twitch)
• fast oxidative glycolytic (type 2a)
• fast glycolytic (type 2x)

Question 6

What are slow twitch fibres and what do they do?

Answer 6

• Fibres that contract against low resistances for extended periods of time
• Produce most of their energy aerobically and therefore have specific characteristics that allow them to use oxygen more effectively.
• Equipped to resist fatigue - preferred muscle fibre type for endurance athletes.

Question 7

Structural characteristics of slow twitch fibres?

Answer 7

High density of capillaries
High myoglobin quantity
Large triglyceride storage space
Small glycogen and phosphocreatine storage space
High mitochondrial density

Question 8

Functional characteristics of slow twitch muscle fibres?

Answer 8

High aerobic capabilities
High fatigue resistance
Slow contractile speed
Low anaerobic capabilities

Question 9

What are fast oxidative glycolytic (Type 2a) and what do they do?

Answer 9

• Share characteristics with both slow oxidative as well as fast glycolytic ones
• Have structural properties required for both aerobic and anaerobic respiration so acts as the middle ground (in terms of contractile force/speed and resistance to fatigue)
• Good for games players due to their versatility as well as 1500m runners

Question 10

Structural characteristics of fast oxidative glycolytic fibres?

Answer 10

Large fibre size
Large glycogen and phosphocreatine storage space
Medium capillary density
Medium mitochondrial density
Medium triglyceride storage space

Question 11

Functional characteristics of fast oxidative glycolytic fibres?

Answer 11

Fast contractile speed
Medium contractile force
Medium fatigue resistance
High anaerobic capabilities
Medium aerobic capabilities

Question 12

What are fast glycolytic (Type 2x) muscle fibres and what do they do?

Answer 12

• Have greatest anaerobic capabilities
• Large and plentiful - generate high amounts of force, very quickly
• Good for explosive sports such as shot put and 100m where quick bursts of energy are required

Question 13

Structural characteristics of fast glycolytic fibres?

Answer 13

Large fibre size
Large glycogen storage space
Large phosphocreatine storage space
Small triglyceride storage space
Low myoglobin quantity

Question 14

Functional characteristics of fast glycolytic fibres?

Answer 14

Fast contractile speed
High contractile force
Low fatigue resistance
High anaerobic capabilities
Low aerobic capabilities

Question 15

How can training effect muscle fibres?

Answer 15

Fibre type is mostly genetically determined, however, it is possible to increase the size of the muscle fibres through training.
Increased size= hypertrophy, resulting in greater muscle strength.

Question 16

How does the neural system control muscular contraction?

Answer 16

The central nervous system sends impulses to muscles.
→ the strength and frequency of the impulses determines speed and quantity of the muscle that contracts
→ impulses known as action potential - when their threshold is reached, chemical processes occur at the neuromuscular junction and the muscle fibres contract
→ each motor neurone has branches that end in the neuromuscular junction on the muscle fibre
→ when central nervous system reduces/stops the frequency and strength of the impulses, action potential drops below the threshold, meaning the fibres cease contracting

Question 17

What is a motor unit?

Answer 17

A motor neurone and it’s muscle fibres

Question 18

What is a motor neurone?

Answer 18

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

Question 19

What is a neuromuscular junction?

Answer 19

Where the motor neurone and muscle fibre meet

Question 20

Key points about motor units?

Answer 20

• Only one type of muscle fibre is found in one motor unit.
• Each muscle is made up of many motor units and they vary in size.
• A small muscle used for fine motor control e.g. muscle controlling eye movement, will only have a few fibres per motor neurone.
• However, a large muscle used for gross motor control such as the quadriceps when the leg is extended, will have motor units with a motor neurone feeding hundreds of fibres.

Question 21

What is the ‘all or none law’?

Answer 21

When the motor neurone stimulates the muscle fibres, either all of them contract or none of them contract.

• it is not possible for a motor unit to partially contract
• so, when action potential threshold reached, all muscle fibres in a motor unit will contract
• if threshold not reached, none contract

Question 22

When are slow twitch motor units used?

Answer 22

Lower intensity

Question 23

When are fast twitch motor units used?

Answer 23

Higher intensity

Question 24

How to increase the strength of contraction?

Answer 24

2 ways:
Wave summation (including tetanic contraction)
Spatial summation

Question 25

What is wave summation?

Answer 25

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

Repeated activation of a motor neurone stimulating a given muscle fibre results in a greater force of contraction.

Question 26

What is a tetanic contraction

Answer 26

A forceful, sustained, smooth contraction which is as a result of wave summation.
e.g. consecutive box jumps

Question 27

What is spatial summation?

Answer 27

Occurs when impulses are received at the same time at different places on the neurone which add up to fire the neurone.
It is the recruitment of additional and bigger motor units within a muscle to develop more force.

Question 28

What is PNF?

Answer 28

Proprioceptive neuromuscular facilitation.

An advanced stretching technique. It is also considered to be one of the most effective forms of flexibility training to increase range of movement.

Question 29

How is PNF used?

Answer 29

There are a few different PNF techniques, but the most practical is the CRAC technique.

C→Contract
R→Relax
A→Antagonist
C→Contract

Question 30

What are proprioceptors?

Answer 30

Sensory organs in the muscles, tendons and joints that inform the body of the extent of movement that has taken place.

Question 31

What proprioceptors are used in PNF?

Answer 31

Muscle Spindles
Golgi Tendon Organs

Question 32

What are muscle spindles ?

Answer 32

Very sensitive proprioceptors that lie between skeletal muscle fibres.

Question 33

How do muscle spindles work?

Answer 33

• Often called stretch receptors as they provide information (excitory signals) to the CNS about how fast and far the muscle is being stretched.
• CNS sends an impulse back to the muscle telling it 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 34

What are golgi tendon organs?

Answer 34

Found between muscle fibre and tendon and detect levels of tension in a muscle.

Question 35

How do golgi tendons work?

Answer 35

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