Quiz 1.9 Flashcards
Action Potential
Neurological signal that exceeds the threshold of the cell membrane
Resting -> depolarization -> repolarization -> refractory period -> resting
How AP causes contraction
Depolarization of cell leads to release of Ca –> actin/myosin interaction –> force generated
Hyperpolarization
Delivery of a current that makes the membrane potential more negative; nothing happens
Depolarization
Membrane potential becomes more positive than resting (If membrane potential reaches threshold then an AP occurs)
Action potential
The brief (~1ms) up and down of graph that represents change from negative to positive transmem. potential
EC-Coupling general
Turing electrical signal into contraction/force
Depolarization open Ca channels which leads to sliding muscle filament…
Twitch
Single motor unit active
Why does force increase as successive signals are sent?
More motor units are recruited
Rate coding
Increases of intensity of firing of motor units increase the frequency of action potentials
Increase motor units increases force
Motor unit 1 will recruit #2 when it can’t produce enough force (stair-case)
Motor unit
Motor neuron and the muscle fibers it innervates
*Many nerve endings in one muscle
Recruitment of motor units
MUs receive common neural input and are recruited according to their sizes (slow –> fast)
S type motor neuron
Small, highly excitable, recruited first
type I
FR type motor neuron
“Fatigue resistant”
Big, average excitability, recruited second
Type IIa
FF type motor neuron
“Fatigable”
Very big, low excitability, last recruited
Type IIb
Three principles that are responsible for the magnitude of the force produced by muscles
Force-length relationship
Force-Velocity relationship
Activation (rate coding and Henneman’s size principle)
Muscle tendon unit
Junction between the muscle and the tendon
Forces are generated and transmitted
Tendon function
Transfer force rom contractile elements (muscle) to bone
Series elastic element (SEE)
Elastic material in series with connective tissue
Describes how elastic the tendon is which varies across body
Elasticity and force
More elastic = easier to transfer force to bone
The stiffer the easier to transfer force
Hooke’s law
F = -kx
k –> spring constant
> K means more stiff
x–> displacement
Tendon force-length relationship
See graph
Increase length, increase force applied to tendon to a point and then things start to break down until ultimate failure
Tendon stretch-shorten cycle
As muscle is active, force develops and SEE stretches (Changes shape)
Elastic structures are capable of storing and releasing elastic energy by changing shape
Increase force production due to release of stored energy changing to KE
ex: Achilles lengthens then turns into KE by shortening to push foot off ground
Tendon injury
Tendons mostly tear at body insertion or musculo-tendinous junction
Why are mid tendon tears rare
Visco-elastic nature: high force production increases tendon stiffness
Tendon has greater tensile strength than bone and muscle
Tendon can withstand more force than Bone and muscle so the weakest link becomes the integration point between the tendon and the bone/muscle
