Excitation Contraction One And Two

Front 1

What is the resting membrane potential range?
What is the relative level of intracellular cytoplasmic concentration of Ca in an at rest cell?
Where is Ca located in a resting cell?

Back 1

-80-90 mv

The relative intracellular cytoplasmic Ca level is very low

Ca is stored in the Sarcoplasmic Reticiular (specialized smooth ER)

Front 2

What is a T tubule?
What is a terminal cisternae?
What is a triad?

Back 2

A t tubule is the invagination of the cellular membrane of a muscle cell

The terminal cisternae is an enlarged area of the sarcoplasmic reticulum

A triad is two terminal cisternae surrounding one t tubule

Front 3

How is calcium stored in the SR?

Back 3

It is moved into the sarcoplasmic reticulum against a REALLY high gradient via a Ca ATPase pump

Front 4

What is calsequestrin?

Back 4

Calsequestrin is something inside of the sarcoplasmic reticulum which binds calcium to keep the number of free Calcium to a minimum; because of this, the cellular expenditure of ATP to bring Ca into the SR is reduced

Front 5

How does an action potential propagate into a muscle cell?

Back 5

The action potential will travel down the T Tubule/ the t tubule membrane.

Front 6

Can T Tubules generate an action potential?

Back 6

Yes

Front 7

Which two proteins are essential to let Calcium out of the SR? Where are these proteins located?

Back 7

Ryanodine receptor and DHP receptor

The DHP receptor is on the T Tubule
The Ryanodine Receptor is located on the Terminal Cisternae

Front 8

How does Calcium leave the SR during contraction and where will it go?

Back 8

1. As the Action Potential travels down the T tubule, a conformational change occurs in the DHP receptor.
2. This conformational change in the DHP receptor will cause the Ryanodine receptor to be physically affected (the change in shape of DHP will cause Ryanodine receptor to change.
3. Calcium will be released because of the open state conformational change in the ryanodine receptor
4. Calcium will diffuse into the myofibril area

Front 9

What is another way that DHP and Ryanodine receptors can be opened?

Back 9

DHP can be opened via dihydropurine and ryanodine receptor can be opened by ryanodine.

We don't have these chemical ligands in our body

Front 10

What happens at rest to myosin and binding sites?

Back 10

At rest myosin has a VERY high affinity for active site on Actin; however, the myosin head cannot get to the binding site because it is covered by Tropomyosin

Front 11

Steps of Contraction

Back 11

1. Calcium diffuses into myofibril area
2. Calcium binds to Troponin C which will require four Ca
3. Troponin undergoes a conformational change
4. This conformational change in troponin pulls tropomyosin off of the active sites on actin (myosin head binding sites)
5. The inorganic phosphate on Myosin will dissociate and the myosin head will bind to the active site on Actin
6. ADP will dissociate from Myosin causing the POWERSTROKE (myosin head will rotate on the axis and cause the actin fiber to move, Z lines get closer together)
7. ATP will bind to myosin head and cause it to dissociate
8. The ATP will be hydrolized by MYOSIN ATPase into ADP and inorganic Phosphate
9. This energy will be used to bring myosin head back into an extended position such that crossbriding can occur later
10. This will repeat

Front 12

Do all of the fibers in a muscle contract and relax at the time same?

Back 12

No, doing so would bring major problems to a person.

Front 13

How long will the muscle contraction keep repeating/when will it stop?

Back 13

The steps of muscle contraction will keep going until there is no more action potential being received by the motor end plate OOOOOR mechanical forces prevent further contraction

These steps will also repeat until there is no more Ca in the cytoplasm

Front 14

How is Calcium removed from the cytoplasm after a muscle contraction and what happens to the Calcium on Troponin C?

Back 14

It is removed via a Ca ATPase pump

Calcium will unbind and start coming off of troponin C

Front 15

What happens when Ca starts to come off of the troponin C?

Back 15

This causes a conformational change in the troponin C back to the stage it was at precontraction.

This will cause tropomyosin to be pulled back over Actin Active sites and they will be covered.

Front 16

How does the skeletal muscle obtain it's ATP for muscle contraction?

Back 16

This does not occur via mitochondria, they are on the periphery of the cell.

This occurs through the CrP atp generation system

Front 17

How does the CrP cycle of ATP regeneration work?

Back 17

1. When ADP is released from myosin, It will interact with creatine phosphate
2. CrP will donate it's phosphate to ADP and generate Creatine and ATP
3. This ATP will then be used to dissociate myosin and recock myosin from the actin binding spots
4. Near the mitochrondria, ATP will lose it's phosphate to Cr to make CrP

Front 18

Energy Sources for contracting muscle cell

What is another biproduct of these reactions that we do not want?

Back 18

ALL OF THESE REACTIONS GENERATE SUBSTANIAL AMOUNTS OF HEAT

ATP + H20 = ADP + H3PO4 + 7.3 kcal
CrP + ADP = ATP +creatine

Anaerobic Metabolism - Glucose + 2ATP = 2 Lactic acid + 4 ATP

Aerobic Metabolism - Glucose + 2 ATP = 6 CO2 + 6H20 + 40 ATP

FFA = CO2 + H20 + ATP

Front 19

What's wrong with anaeorobic metabolism for ATP?

Back 19

This generates high amounts of ACID driving the pH very low within a matter of 40 seconds

This metabolism is only good for about 40 sec worth of work

Front 20

What happens when the energy supply is NOT maintained?

Back 20

Muscle Fatigue (doesn't necessary correspond to low energy)

At the NMJ, there can be a depletion of ACh (an issue with those who get seizures)

There will be inadequate ATP, low nutritional state

Front 21

What happens during Rigor Mortis and how long does it take to achieve Rigot Mortis?

Back 21

Cell membrane will depolarize because there is no sodium potassium pump running.

Muscle will under the action but will not dissociate from the actin because there is no more ATP left.

Rigor Mortis will take about Four Minutes: i.e. it will take four minutes to run out of ATP after death.

Front 22

Which protein is associated with the Z disk?

Back 22

Actin, the thin filament

Front 23

Describe the amount of contraction in a long muscle and how it progresses.

Back 23

At first, the contraction is weak; however as time passes it becomes much larger because there will be more myosin binding and firing

Front 24

What happens when muscle is longer than it should be? i.e. muscle fibers are too stretched out?

Back 24

Active Tension in muscle will be low:
There will be less overlap between myosin and actin thereby reducing the number of myosin being bound to the actin. (not enough active actin myosin heads)

The active tension will increase as the muscle contracts and it gets shorter (improvement of strength)

Front 25

What happens when a muscle is too short?

Back 25

The amount of contraction and the amount of shortening due to contraction will be reduced.

This is because the absolute shortest a muscle can become is the length of the thick filament. At this point, Z disks will end up plowing right into the thick filament

Front 26

What is an Isometric Contraction?

Back 26

iso means same, metric means length:
an isometric contraction is when muscle contraction does not show a significant change in length of the sarcomere; however, the muscle develops force:

Imagine putting your hands together and pushing on them

Isometric contractions might cause muscle to bulging but there is no motion.

We will still see CROSSBRIDGE CYCLING, but only nanometers of muscle length change.

Front 27

What do isometrics contractions let you do?

Back 27

The muscle is not doing any external work; HOWEVER, it is enabling me to move against the force of gravity.

Front 28

What is an Isotonic Contraction

Back 28

Isotonic contractions involve a lot of motion
Isotonic contractions involve a significant change in muscle fiber length. (I.E. little change in tension or force)

Myosin is binding and passing over a LOT of actin sites and there is great change in muscle length/motion.

Front 29

How can you tell if there is an isometric or isotonic contraction?

Back 29

If you see that muscle fibers are significantly changing in length, you have an ISOTONIC contraction

Front 30

What makes up the Series Elastic Element

Back 30

SEE: tendons, ligaments, membranes
Tendons and elastic tissue in the muscle actually stretch
During an isometric contraction, you may see a bulge; this bulge is caused by the stress the contraction causes of the series elastic element

Front 31

Series Elastic Element and what happens to it during lifting?

Back 31

1. Stretch in SEL which is isotonic: you will never see the reduction in SEL length and this first step removes the slack caused by SEL
2.Force Generation: isometric contraction (if you are lifting 5 LB then you must generate 5LB of force (this becomes more noticeable with a higher opposing force)
3. Lifting load: Isotonic contraction: after overcoming the force of the object you're lifting, you can engage in isotonic contraction to move the object.

Front 32

What factors affect/change muscle contraction?

Back 32

Length of Muscle
Weight the muscle is attempting to move
When the muscle is affected by the weight (what point in time/object relation)

Front 33

Muscle Length and Tension: what's the relationship?

Back 33

To generate maximal force, muscle should be clamped close to the length that it is in the body normally
Tension is maximal at this point

At lengths longer or shorter than normal, you lose tension
Too much overlap causes an inappropriate overlapping and there will be less myosin and actin interacting. ALSO you will reach a PHYSICAL limit

Front 34

Relationships in muscle length and tension when incorporating the SEL component: Active Tension, Passive Tension, Summation of Tensions EXPLAINED

Back 34

Active Tension: The tension achieved by cross bridging (curve is rounded because of the millions of sarcs in action at the same time and each sarc isn't identical)
Passive Tension: the tension that occurs when the muscle starts becoming too long: this is independent of crossbridging and it is due to SEL. This is greatest when muscle is longest (becomes like a rubberband, recoil due to noncontractile tissue)
Summation: recorded by force transducers

Front 35

How the amount of weight affects muscle contraction?

Back 35

Higher the weight, the longer it will take for that movement to occur.

Hypothetically, velocity of muscle shortening is greatest at lowest load (although the muscle always have to overcome it's own weight and limb weights)

Front 36

"When" the muscle encounters/is affected by the weight? (think preload and afterload)

Back 36

Preload: the load affects the muscle prior to beginning of contraction (briefcase hanging on my hand)
Preload will stretch my muscle out before contraction
Afterload: the load that is affected after the muscle has already began to contract (book being on a desk before it is lifted)

Front 37

How to distinguish between preload and afterload?

Back 37

Is the muscle stretched prior to any lifting?
if yes: then it is preload
if no: then it is afterload
Preload does not become afterload.
Preload makes the muscle longer and weaker than it was before the load or stretch