Anatomy & Physiology - Neuromuscular system Flashcards
At Low intensity what fibre types are recruited:
- Slow twitch motor units
At Higher intensity what fibre types are recruited:
- Fast twitch type 2a motor units
At the Greatest intensity what fibre types are recruited:
- Fast twitch type 2x motor units to produce powerful and fast muscle contractions
Neural control of muscular contraction - CNS:
- 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
What are the impulses called sent from the CNS:
- Action potential
What happens if the Action potential threshold is reached:
- 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
What happens when CNS reduces/ stops frequency + strength of impulse:
- 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
What are muscles fibers grouped into:
- A motor unit
What is a motor unit:
- 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
How many muscle fibers to a motor unit:
- Only 1 type of muscle fiber can be found in one particular motor unit
What do muscle fibers work with for a contraction to occur:
- Muscle fibers work with the nervous system so that a contraction can occur. The motor neurone transmits the nerve impulse to the muscle fiber
What is the Neuromuscular junction:
- Where the motor neurone and the muscle fiber meet
For fine motor skills, what does the CNS engage:
- 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
For gross motor skills, what does the CNS engage:
- 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
What is the ‘All or None law’:
- 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)
The threshold required to start contraction:
- 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.
What is Wave summation:
- Wave summation is where there is a repeated nerve impulse with no time to relax so a smooth, sustained contraction occurs
How wave summation occurs - first impulse:
- 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.
What happens on a second impulse - wave summation:
- 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
When can wave summation be repeated:
- This process can be repeated in short succession, culminating in the gradual increase of a muscle contractile force
What happens if wave summation persists inside a motor unit:
- Eventually there will be no time for any relaxation to occur
What is Tetanic contraction:
- A sustained muscle contraction caused by a series of fast repeating stimuli
How tetanic contraction occurs:
- 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
What does tetanic contraction produce:
- This produces a forceful, sustained, smooth contraction which is referred to as tetanic contraction
What is spatial summation:
- 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
How does spatial summation work:
- 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.
How does the activation of the motor units work - spatial summation:
- Activation of these motor units are staggered, which enables some motor units to contract while others relax, therefore delaying fatigue
What does the recruitment of motor units do - spatial summation:
- It is the recruitment of additional and bigger motor units within a muscle to develop more force
What are slow twitch type 1 muscle fibers:
- 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
What are fast twitch type 2a muscle fibers:
- 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
What are fast twitch type 2x muscle fibers:
- 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
6 Functional characteristics of slow + fast twitch muscle fibers:
1) Contraction speed
2) Motor neurone conduction capacity
3) Force produced
4) Resistance to fatigue
5) Aerobic capacity
6) Anaerobic capacity
5 Structural characteristics of slow + fast twitch muscle fibers:
1) Motor neurone size
2) Mitochondrial density
3) Myoglobin content
4) Capillary density
5) Anaerobic enzymes/ ATPase levels
What are skeletal muscle fibers classification based on:
1) Speed of contraction
2) Metabollic pathway used to make ATP
What is PNF (Proprioceptive neuromuscular facilitation):
- 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)
What are muscle spindles:
- Muscle spindles detect how far and how fast a muscle is being stretched and produce the stretch reflex
How muscle spindles work:
- 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
What happens to the muscle spindles in an antagonistic pair:
- 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
Role of muscle spindle:
- 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
What do Golgi tendon organs do:
- They detect changes in muscular tension
What happens to the Golgi tendon organs in an antagonistic pair:
- 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
Role of the Golgi tendon organs:
- 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
How does PNF positively affect a sport performer:
1) Increases range of motion at joints
2) Increases flexibility
3) Reduces chances of injury (from over stretching muscles)
