Musculoskeletal Organ Level Muscle Physiology

Front 1

What determines the distance a muscle can shorten?

Back 1

The number of sarcomeres in series

Front 2

What determines the strength/power that muscle can generate?

Back 2

The number of sarcomeres in parallel

Front 3

What is the term for the longer delay in onset and time to peak response because it must first take up slack before shortening occurs?

Back 3

Series Elastic Element

(rubber band example, once the tension exceends the mass, the mass moves)

Front 4

What happens to the time delay when you place a heavier load?

Back 4

The delays are greater with a heavier load

Front 5

What happens if the load is increased to greater than the muscle can develop tension?

Back 5

No distance will be moved and you have an isometric contraction

Front 6

What muscle fibers are used for antigravity, prolonged use, and slow fatigue?

Back 6

Slow twitch

Front 7

T/F
Fast twitch fibers have a lot of mitochondria

Back 7

False

Front 8

T/F
Fast twitch fibers have a lot of Glycogen

Back 8

True

Front 9

T/F
Fast twitch fibers have a lot of myoglobin

Back 9

False
White muscle has little myoglobin

Front 10

What determines the maximum velocity of the contraction of a muscle fiber?

Back 10

Myosin cross-bridging determines velocity

Front 11

What is the rate of myosin cross-bridging in intermediate fibers?

Back 11

Fast

(which also means the maximum velocity is fast as well)

Front 12

What is the mitichondria content of intermediate and slow twitch fibers?

Back 12

A lot of Mitochondria

Front 13

How is it that Fast twitch fibers are large, while slow twitch fibers are small?

Back 13

It has to do with surface area. Slow twitch fibers need large surface area so they are slim muscle fibers. The increased surface area to volume ratio allows oxidative phosphorylation to occur.

Front 14

What is the glycogen content of slow twitch fibers?

Back 14

Low glycogen content

Front 15

What is the myoglobin content of intermediate and slow muscle fibers?

Back 15

High - thus the red hue

Front 16

What is the ATP source to power muscle contraction for Fast twitch fibers?

Back 16

Glycolysis (makes ATP fast & is anaerobic)

Front 17

What is the ATP source to power muscle contraction for intermediate twitch muscle fibers?

Back 17

Oxidative phosphorylation

Front 18

What is the ATP source to power muscle contraction for Slow twitch muscle fibers?

Back 18

Oxidative Phosphorylation

Front 19

What determines the duration of a contraction for a single twitch?

Back 19

Duration is linked to rate of return of Ca++ into the sarcoplasmic reticulum

Front 20

What muscle has the longest duration of contraction for a single twitch?

a) occular
b) gastrocnemius
c) soleus

Back 20

Soleus has the longest duration

occular is for rapid eye movement
gastrocnemius is for running/jumping
soleus is for antigravity support

Front 21

T/F
The less discrete you need to be, the longer an individual twitch will tend to be.

Back 21

True

so, discrete motion like quick movement of the eye has a very short duration

Front 22

What stage of muscle contraction is the action potential complete?

Back 22

The muscle action potential is complete before tension begins to increase

Front 23

At what point does active cross-bridging occur in a muscle twitch?

Back 23

Active cross-bridging occurs while intracellular Ca++ is elevated

Front 24

What happens to twitch tension with regard to Ca++?

Back 24

Twitch tension lags behind Ca++ elevation as the series elastic element is tightened

(so the muscle cell is still providing tension on the load even though calcium is no longer elevated)

Front 25

What happens to the series elastic element as the Ca++ falls?

Back 25

The series elastic element maintains tension even as Ca++ falls (like pulling on a rubber band to lift a weight)

Front 26

What is the optimum length of a single sarcomere for maximal cross-bridging?

Back 26

Lo = 2 micrometers

Front 27

T/F
Depending on the extent a muscle is stretched prior to contraction determines how strongly it can contract.

Back 27

True

Front 28

What state of contraction are our muscles at during rest?

Back 28

near Lo=2microns
maximum cross-bridging

Front 29

How can we increase the strength of contraction?

Back 29

1) Summation of contractions
2) Recruitment of motor units

Front 30

How does the muscle AP relate to the Ca++ levels?

Back 30

The muscle AP is brief compared to the duration of the Ca++ and the constant pulses keep the Ca++ levels high.

Front 31

How does the recruitment of motor units increase contractile strength?

Back 31

Start firing additional alpha motor neurons to activate the muscle fibers they innervate

Front 32

What makes muscle contraction smooth during recruitment of motor units?

Back 32

Asynchronous activation

(without this, muscle contraction would be a ratcheting motion)

Front 33

What composes a motor unit?

Back 33

one axon and all of the muscle fibers it innervates

Front 34

T/F
There is a single motor unit in a single muscle.

Back 34

False
There are many motor units in a single muscle

Front 35

T/F
A single axon can innervate multiple motor cells

Back 35

True

Front 36

T/F
A single muscle cell is innervated by only one alpha motor neuron

Back 36

True

Front 37

Is there summation in individual skeletal muscle fibers?

Back 37

No because we only have one axon innervating them

Front 38

Which muscles have the largest motor units?

Back 38

Antigravity muscles

Front 39

What muscles have the smallest motor units?

Back 39

Eye muscles