Module 4: Lecture 5 Flashcards
What are the 2 ways our motor units be controlled?
- Changing the number of fibres
- By changing the activation of the fibres
what is a motor unit made of?
- one motorneuron: cell body sits in the spinal region with the axon splitting into multiple divisions that will interact with a skeletal muscle fibre
- all the myofibres it innervates with it
What is the motor unit recruitment talking about?
this means all of our muscle fibres within a motor unit will be activated when a motor unit is recruited
True or False
The greater the amount of force needed the more motor units will be recruited
True
True or False
A muscle fibre can only have ONE neuromuscular junction and it is only innervated by ONE motor neuron
True
From a microscopic view, What colour are your slow and fast twitch muscle fibres?
slow twitch = dark stain (type 1)
fast twitch = light stain (type 2)
What do we mean when talking about the “size” of a motor unit?
the number of muscle fibres that are innervated with the motor unit
True or False
Very fine motor control movements are going to have very few muscle fibres per motor unit
True
What is the asynchronous recruitment of motor units?
means depending on the amount of force that needs to be generated, you will first recruit some motor units, and then you can recruit additional motor units as needed
Why do we have the asynchronous recruitment of motor units?
to control our motor force and not get tired too easily aka fatigue resistance
- typically we will recruit out type 1 muscle fibres first then out type 2 muscle fibres
What are type 1 muscle fibres?
- slow twitch
- fatigue resistance
- don’t produce much force
What are type 2 muscle fibres?
- fast twitch
- tired easily
- produces lots of force
How does the CNS know which motor units to recruit?
motor units are recruited by size from smallest to largest
- The smallest will be type 1
- The largest will be type 2
What is the Henneman’s size principle?
the theory is that the size of the motor unit will dictate the recruitment principle
- smallest to largest
What are the 3 rules for the orderly recruitment of motor units?
- Minimizes Fatigue (always recruit type 1 first for any given action)
- Allows a finer control of muscle forces
- Simplifies the control of force
What is our whole muscle tension?
number of fibres contracting, whether our motor unit is turned on or off
The frequency of motor neuron activation means we are altering what?
altering the amount of tension the muscle fibres are generating, aka changing the frequency of action potentials
How does changing the frequency of the action potential affect the muscle?
this changes the amount of calcium in the muscle and that will adjust how much force those muscle fibres are generating
What are the 4 factors that influence the extent to which tension can be developed? (3 of which are muscle characteristics)
- Frequency of stimulation
- Length of the fibre at the onset of contraction
- Extent of fatigue
- Thickness of the fibre (number of myofibrils/sarcomeres)
One action potential leads to how many muscle twitches?
1
What is twitch summation?
when a single muscle twitches can summate on top of another
True or False?
The amount of calcium that is released during a single twitch is not sufficient to fully activate all of our thin filaments.
True
What is the name for when we achieve action potentials so frequently that there is no time for our muscles to relax?
tetanus
At the tetanus stage, what is occurring?
- all your thin filaments are activated
- all your cross-bridges are formed
- the motor units are all generating the maximum amount of force it can
What happens when you have the disease of tetanus?
these individual’s muscles are going under full muscle contraction
- neurological condition
- lockjaw
True or False
The motor neruon goes through refractory periods
True
The central nervous system can control muscle force through 2 key mechanisms which are?
- Motor unit recruitment
- through Henneman’s size principle - Motor unit activation rate
- fusion of muscle twitches
- frequency of action potentials
