Whole Muscle Contraction

What are the two elements that contribute to muscular tension....in the physical sense.

Elastic Element & Contractile Element

True or False All muscles can sustain their contracted state for roughly an equal amount of time

False

True or False Isometric contractions generate work

False, Work is Force x distance. No length change means no work done.

What are the two ways that muscle contractions can summate?

Frequency and Multi-fiber summation

What is frequency summation?

Frequency summation occurs when the signals to contract are received faster than the muscle can fully relax.

What happens if the frequency of contraction signals in faster than the myocytes ability to resequester calcium back into the SR?

Frequency summation, or tetany, will occur.

The majority of increased muscle strength during training or exercise comes from Hyperplasia or Hypertrophy?

Hypertrophy, but in extreme circumstances hyperplasia is observed.

Where is Titin found in the body?

In sarcomeres of skeletal muscle

The inflexion point between concentric and eccentric contractions is called what?

Isometric contraction

How does Norepinephrine effect the contractility of cardiac muscle?

It increases peak tension of isometric contractions and in increases the shortening of myocytes in afterload contraction

In pure isometric contraction, Norepinephrine has what effect on peak tension?

It increases peak tension, meaning that the muscle can resist a greater load in an isometric state.

What is preload?

It is the load placed on the muscle before any active contraction

What is after load?

It is the load remaining on muscle that must be overcome to transition from isometric to isotonic contractions.

What is multi fiber summation?

Multifiber summation occurs when multiple motor units are recruited for a movement.

What is concentric contraction?

Muscle contractions that result in the shortening of muscle fibers

What is eccentric muscle contraction?

Muscle fibers contract, but lengthen

By convention, the value of eccentric contraction velocity is what?

Negative, because the muscle is lengthening during contraction and not shortening.

Is there any work being performed during isometric contraction?

No, there is no movement, therefore there is no work being done, however energy is still being consumed to maintain tension.

Stretch, either positive or negative, is called what in terms of muscle contraction?

Preload

When a muscle is fatigued, what occurs in the sarcomere when it receives a stimulatory signal?

The sarcomere is unable to contract or maintain contraction due to lack of energy such glycogen depletion that results an ATP shortage.

What causes tetanus?

The temporal summation of contractile stimuli that occur before the cell has time to return to its relaxed state.

What is the mathematic relationship between muscle load and the velocity of that muscles contraction?

They are inversely proportional

What protein in a sarcomere is responsible for passive tension?

Titin

True or False Extrinsic factors such as temperature can effect the Load-Contraction velocity relationship curve

True

True or False Tension is the same as force

True

True or False There is an optimal resting length of a muscle fiber

True, each muscle fiber has an optimal length in regards to stretch and compression

What is fused tetanus?

When there is no time for the muscle to relax between different stimulation events.

What is unfused tetanus?

When there is partial relaxation of the muscle between successive stimuli.

What is the optimal resting length of a sarcomere?

2.1 to 2.2 microns

What elements of a sarcomere contribute to the active contractile tension in a muscle?

Actin and Myosin

Total isometric tension is the sum of what two forces?

Active and passive tension

What is afterload as it relates to muscle?

Afterload is the amount of force that is required to shorten a myocyte after it has been preloaded with some type of stretch due to weight or fluid volume.

What proteins anchor F-actin and myosin to the Z-disk in a sarcomere?

Alpha Actin directly links F-actin to the Z-disk. Myosin is attached to Titin which then attaches to alpha actin.

How does isometric contraction result in sarcomere shortening, without any change in length of the muscle fiber itself?

As the sarcomere contracts, the elastic elements stretch allowing the muscle to remain the same length

Why does a myofibril that has been compressed below its optimal length generate less force when stimulated?

Because even though there is a lot of myosin-actin overlap, there is not enough space between the Z-disks for the filaments to slide and generate a lot of force.

Why is passive tension only seen in stretched muscle fibers?

Because passive tension is the result of the stretching of elastic fibers such as titin.

Why does a myofibril that has been stretched produce less force when it is stimulated?

Because the stretch of the fiber reduces the amount of myosin-actin overlap. This reduction in interactions results in less for generated

In cardiac muscle, Norepinephrine increases contractility by increasing what?

By increasing the calcium levels in the sarcoplasm

Does skeletal muscle or cardiac muscle have greater passive tension?

Cardiac Muscle

Isometric contractions are characterized by what physical events?

Change in force generation by sarcomeres that results in no change in length of the muscle.

Isotonic contractions are characterized by what physical events?

Change in muscle length due to a constant force generated by sarcomeres

Briefly describe the transition from concentric, to isometric, to eccentric contractions

During concentric contraction the muscle is able to overcome the load. At the inflexion point of isometric contraction, the muscle can balance the force of the load, but cannot overcome it to make it move. During eccentric contraction, the muscle is unable to balance the force of the load and lengthens.

Are greater forces generated during concentric or eccentric contractions?

During eccentric contractions.

What are the three mechanisms by which a muscle can replenish its ATP supply from ADP?

1. Use high energy phosphate of Phosphocreatine to phosphorylate ADP to ATP. 2. Use Glycolysis. 3. Use oxidative phosphorylation.

Are motor neurons of smaller or larger motor units more excitable?

Smaller motor units as they are recruited for lighter loads.

What is happening with the elastic fibers that allows an isotonic contraction?

The elastic fibers inside the sarcomere are already stretched to their max, and so when the myosin-actin complex is stimulated, the muscle must shorten.

How does the length of an unstretched muscle fiber influence its ability to exert a force?

The longer the muscle fiber, the larger the force it can generate due to the increased number of myosin-actin bridges it can form.

On loads that are below the peak isometric tension of a muscle, Norepinephrine has what effect on the myocytes during contraction?

The myocytes are able to contract to shorter lengths duirng the afterload phase of contraction.