KINESIOL 2Y03 Lecture Notes - Lecture 17: Fiber To The X, Motor Unit, Motor Neuron
MYO – MUSCLE
SARCO – RELATED TO MUSCLE
Motor Unit:
• 3 basic fiber types, one fiber type per motor neuron
• Motor Unit → one neuron can serve many fibers, but each fiber only has a connection
with one motor neuron.
• Depending on where motor units are in the body, itll differ the number of fibers the
fibers
Strength and Muscle Contraction:
• When we send an AP, we get an excitatory response so we always get some sort of
contraction
• When would we change the amount of force or contractions, what are ways that we can
do that.
o The number of motor units that are recruited. More motor units the more
amount of your mass you will be contracting. One motor unit would cause a
slight twitch not a full contraction; if you want more of a contraction you recruit
more motor units. If you have a sub threshold stimulus (how much muscle you
need to contract), you wouldn’t even get any contraction or twitch.
o Threshold stimulus is only one motor unit responds → tension. Small amount of
force reduced. Example; Eye twitch.
o Greater the amount of stimuli or force, the more motor units will respond to it.
You eventually get to the maximal stimulus. Factors that go into the force a
muscle can produce
▪ Why are some people stronger than others?
• Fiber diameters. When we strength train, the number of fibers
doesn’t not change, but how big the fibers become change. And
what are inside the fibers are our columns of contractile tissue →
myofibrils. As we strength train we cause damage in muscles
which stimulus protein synthesis, which will build muscle back
better so next time it wont become damaged. Does this so you
stop causing muscle damage.
▪ Weight resistance → continually change and grow muscle
▪ Amount of contractile protein will dictate our strong a muscle can be or
how much force can be produced
▪ Amount of motor neurons can dictate how strong the muscle is
▪ How frequent the AP are being sent through a motor unit. More
frequent, the longer the muscle stays contracted. When we release
acetylcholine, AP, the SR releases calcium → the calcium is floating
around that needs to be taken away for contraction to stop. Bc calcium
doesn’t have time to be taken away, the contraction will continue until it
is gone.
