Anatomy & Physiology - Neuromuscular system

Question 1

At Low intensity what fibre types are recruited:

Answer 1

• Slow twitch motor units

Question 2

At Higher intensity what fibre types are recruited:

Answer 2

• Fast twitch type 2a motor units

Question 3

At the Greatest intensity what fibre types are recruited:

Answer 3

• Fast twitch type 2x motor units to produce powerful and fast muscle contractions

Question 4

Neural control of muscular contraction - CNS:

Answer 4

• The central nervous system sends impulses to muscles. The strength and frequency of these impulses determines the quantity of muscles that contracts, and the speed in which it contracts

Question 5

What are the impulses called sent from the CNS:

Answer 5

• Action potential

Question 6

What happens if the Action potential threshold is reached:

Answer 6

• When the AP threshold of a muscle is reached by the incoming impulses, chemical processes occur at the neuromuscular junction and the muscle fibers contract, sliding over one and other, shortening the muscle and causing the bones they are attached to move as well

Question 7

What happens when CNS reduces/ stops frequency + strength of impulse:

Answer 7

• When the CNS reduces of stops the frequency and strength of the impulse, the Action potential will drop bellow the required threshold once more, and the fibers will cease contracting

Question 8

What are muscles fibers grouped into:

Answer 8

• A motor unit

Question 9

What is a motor unit:

Answer 9

• A motor unit consists of a motor neuron and it’s muscle fibers. A motor unit can include anywhere from 10s of fibers, up to 100s of fibers

Question 10

How many muscle fibers to a motor unit:

Answer 10

• Only 1 type of muscle fiber can be found in one particular motor unit

Question 11

What do muscle fibers work with for a contraction to occur:

Answer 11

• Muscle fibers work with the nervous system so that a contraction can occur. The motor neurone transmits the nerve impulse to the muscle fiber

Question 12

What is the Neuromuscular junction:

Answer 12

• Where the motor neurone and the muscle fiber meet

Question 13

For fine motor skills, what does the CNS engage:

Answer 13

• The CNS engages small motor units that can be used in conjunction with other small motor units to create the most accurate amount of force for the desired action. A small muscle that is used for for fine motor control E.g. the muscles controlling eye movements will have motor units that have only a few fibers per motor neurone

Question 14

For gross motor skills, what does the CNS engage:

Answer 14

• The CNS engages larger motor units with greater contractile force potential. 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 fibers

Question 15

What is the ‘All or None law’:

Answer 15

• Once the motor neurone stimulates the muscle fibers either all of them contract or none of them contract. It is not possible for a motor neuron to partially contract (All or none law)

Question 16

The threshold required to start contraction:

Answer 16

• If the sequence of impulses is equal to or more than the threshold then all muscle fibers in a motor unit will contract. However, if the sequence of impulses is less than the threshold then no muscle action will occur.

Question 17

What is Wave summation:

Answer 17

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

Question 18

How wave summation occurs - first impulse:

Answer 18

• Following the arrival of a sufficient impulse to overcome the threshold of a muscle fiber, full contraction occurs, followed by a period of relaxation wherein the fiber and its chemical process can reset to its resting form.

Question 19

What happens on a second impulse - wave summation:

Answer 19

• If a second impulse of sufficient action potential were to arrive before the relaxation phase completes, then a new contraction will occur with greater force as it has started with pre-existing tension left in the muscle from the previous contraction

Question 20

When can wave summation be repeated:

Answer 20

• This process can be repeated in short succession, culminating in the gradual increase of a muscle contractile force

Question 21

What happens if wave summation persists inside a motor unit:

Answer 21

• Eventually there will be no time for any relaxation to occur

Question 22

What is Tetanic contraction:

Answer 22

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

Question 23

How tetanic contraction occurs:

Answer 23

• Instead the frequency of impulses arriving at the muscle merge into one of constant innervation.
• At this point the muscle will remain in a state of maximal contraction and tension until a time of rest or fatigue

Question 24

What does tetanic contraction produce:

Answer 24

• This produces a forceful, sustained, smooth contraction which is referred to as tetanic contraction

Question 25

What is spatial summation:

Answer 25

• When the strength of a contraction changes by alerting the number of size of motor units. This occurs when impulses are received at the same time at different places o the neuron

Question 26

How does spatial summation work:

Answer 26

• The impulses add up to build up the strength of the action potential, until such a time that it reaches the threshold required to excite the muscle and contraction occurs.

Question 27

How does the activation of the motor units work - spatial summation:

Answer 27

• Activation of these motor units are staggered, which enables some motor units to contract while others relax, therefore delaying fatigue

Question 28

What does the recruitment of motor units do - spatial summation:

Answer 28

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

Question 29

What are slow twitch type 1 muscle fibers:

Answer 29

• Type of muscle fiber that is high in mitochondria, myoglobin and capillaries which produce a small amount of force over a long period of time. They produce most of their energy (ATP) aerobically and therefore allow them to use OXYGEN more effectively

Question 30

What are fast twitch type 2a muscle fibers:

Answer 30

• A type of muscle fiber that have a fast contraction time but also have more resistance to fatigue and so can be used for both aerobic and anaerobic exercise

Question 31

What are fast twitch type 2x muscle fibers:

Answer 31

• A type of muscle fiber rich in phosphocreatine (PC) which are used for highly explosive events where producing a maximal force (energy) over a short period of time is essential

Question 32

6 Functional characteristics of slow + fast twitch muscle fibers:

Answer 32

1) Contraction speed

2) Motor neurone conduction capacity

3) Force produced

4) Resistance to fatigue

5) Aerobic capacity

6) Anaerobic capacity

Question 33

5 Structural characteristics of slow + fast twitch muscle fibers:

Answer 33

1) Motor neurone size

2) Mitochondrial density

3) Myoglobin content

4) Capillary density

5) Anaerobic enzymes/ ATPase levels

Question 34

What are skeletal muscle fibers classification based on:

Answer 34

1) Speed of contraction

2) Metabollic pathway used to make ATP

Question 35

What is PNF (Proprioceptive neuromuscular facilitation):

Answer 35

• PNF is an advanced stretching technique. It is also considered to be one of the most effective forms of flexibility training for increasing range of movement. There are a few different PNF techniques but the most practical is CRAC (Contract relax agonist contract)

Question 36

What are muscle spindles:

Answer 36

• Muscle spindles detect how far and how fast a muscle is being stretched and produce the stretch reflex

Question 37

How muscle spindles work:

Answer 37

• The 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 38

What happens to the muscle spindles in an antagonistic pair:

Answer 38

• The returning impulse may be split between the 2 muscles, half causes the contraction of the muscle under tension, the other stimulates the relaxation of the antagonist

Question 39

Role of muscle spindle:

Answer 39

• Detect how far and fast a muscle is stretched or an increase in muscle length
• Sends a message to the nervous system
• During PNF the muscle spindles will initiate a stretch reflex/ muscle contraction
• This can prevent over stretching

Question 40

What do Golgi tendon organs do:

Answer 40

• They detect changes in muscular tension

Question 41

What happens to the Golgi tendon organs in an antagonistic pair:

Answer 41

• 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 known as autogenic inhibition

Question 42

Role of the Golgi tendon organs:

Answer 42

• Golgi tendon organs detect the tension in the muscle (created during the isometric contraction phase)
• Golgi tendon organs send inhibitory signals to allow the antagonist muscle to relax and lengthen (Autogenic inhibition)
• Delays the stretch reflex
• Allowing for greater range of movement

Question 43

How does PNF positively affect a sport performer:

Answer 43

1) Increases range of motion at joints

2) Increases flexibility

3) Reduces chances of injury (from over stretching muscles)