Quiz 1.9

Question 1

Action Potential

Answer 1

Neurological signal that exceeds the threshold of the cell membrane
Resting -> depolarization -> repolarization -> refractory period -> resting

Question 2

How AP causes contraction

Answer 2

Depolarization of cell leads to release of Ca –> actin/myosin interaction –> force generated

Question 3

Hyperpolarization

Answer 3

Delivery of a current that makes the membrane potential more negative; nothing happens

Question 4

Depolarization

Answer 4

Membrane potential becomes more positive than resting (If membrane potential reaches threshold then an AP occurs)

Question 5

Action potential

Answer 5

The brief (~1ms) up and down of graph that represents change from negative to positive transmem. potential

Question 6

EC-Coupling general

Answer 6

Turing electrical signal into contraction/force
Depolarization open Ca channels which leads to sliding muscle filament…

Question 7

Twitch

Answer 7

Single motor unit active

Question 8

Why does force increase as successive signals are sent?

Answer 8

More motor units are recruited

Question 9

Rate coding

Answer 9

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)

Question 10

Motor unit

Answer 10

Motor neuron and the muscle fibers it innervates
*Many nerve endings in one muscle

Question 11

Recruitment of motor units

Answer 11

MUs receive common neural input and are recruited according to their sizes (slow –> fast)

Question 12

S type motor neuron

Answer 12

Small, highly excitable, recruited first
type I

Question 13

FR type motor neuron

Answer 13

“Fatigue resistant”
Big, average excitability, recruited second
Type IIa

Question 14

FF type motor neuron

Answer 14

“Fatigable”
Very big, low excitability, last recruited
Type IIb

Question 15

Three principles that are responsible for the magnitude of the force produced by muscles

Answer 15

Force-length relationship
Force-Velocity relationship
Activation (rate coding and Henneman’s size principle)

Question 16

Muscle tendon unit

Answer 16

Junction between the muscle and the tendon
Forces are generated and transmitted

Question 17

Tendon function

Answer 17

Transfer force rom contractile elements (muscle) to bone

Question 18

Series elastic element (SEE)

Answer 18

Elastic material in series with connective tissue
Describes how elastic the tendon is which varies across body

Question 19

Elasticity and force

Answer 19

More elastic = easier to transfer force to bone
The stiffer the easier to transfer force

Question 20

Hooke’s law

Answer 20

F = -kx
k –> spring constant
> K means more stiff
x–> displacement

Question 21

Tendon force-length relationship

Answer 21

See graph
Increase length, increase force applied to tendon to a point and then things start to break down until ultimate failure

Question 22

Tendon stretch-shorten cycle

Answer 22

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

Question 23

Tendon injury

Answer 23

Tendons mostly tear at body insertion or musculo-tendinous junction

Question 24

Why are mid tendon tears rare

Answer 24

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