Study Guide 4 - Skeletal Muscle Contraction

Front 1

Describe the sliding filament theory including the role of the cross bridges.

Back 1

A muscle is made to contract at the sarcomeres by the actin filaments sliding past the myosin filaments.

Activities of cross bridges move the actin filaments pass the myosin filaments.

Front 2

Describe the energy source used for a skeletal muscle contraction( enzyme for the reaction).

Back 2

The direct source of energy for the movement of the cross bridges and therefore muscle contraction is the splitting of ATP into ADP + P + energy.

Part of the myosin cross bridge functions as an enzyme for this reaction – that is it functions as an ATPase.

Front 3

Explain the role of the nerve impulse in skeletal muscle contraction.

Back 3

Role of nerve impulse:

As the NERVE IMPULSE MOVES along the SARCOLEMMA and T-TUBULE it CAUSES the RELEASE of Ca++ from the sarcoplasmic reticulum.

Front 4

Explain the role of T-Tubules in a skeletal muscle contraction.

Back 4

Role of T-tubules:

CONDUCTS the nerve impulse INTO the INTERIOR of the FIBER.

Front 5

Explain the role of sarcoplasmic reticulum in a skeletal muscle contraction.

Back 5

Role of sarcoplasmic reticulum:

STOREHOUSE or reservoirs of Ca++ within the muscle fiber.

Front 6

Explain the role of tropomyosin and troponin in a skeletal muscle contraction.

Back 6

Roles of tropomyosin and troponin:

They play a role in REGULATING MUSCLE CONTRCTION as a result of the TROPOMYOSIN BLOCKING or NOT BLOCKING the active sites on the actin filaments.

TROPONIN DETERMINES the POSITION of the TROPOMYOSIN.

Front 7

Explain the role of Calcium(Ca+) in a skeletal muscle contraction.

Back 7

Role of calcium { Ca++}:

By BONDING to the TROPONIN it causes the TROPOMYOSIN to MOVE from its blocking position on the active sites on the actin filaments SO the CROSS BRIDGES CAN ATTACH.

Front 8

Sequence of events occurring during muscular contraction:

Back 8

a. Muscle at rest - cross bridges are not attached to active sites on actin filaments.

b. Nerve impulses sent to muscle fiber and move along sarcolemma and T- tubules.

c. Ca++ 's released from sarcoplasmic reticulum.

d. Ca++ 's bind with the troponin causing tropomyosin to move away from its blocking position and the cross bridges attach to active sites on actin filaments.

e. Myosin acts as an ATPase and splits ATP's.

f. This released energy causes movements of cross bridges.

g. This causes actin filaments to slide past myosin filaments.

h. Removal of Ca++ 's back into the sarcoplasmic reticulum by Ca++ pump mechanism.

i. Tropomyosin moves back to its blocking position.

j. This prevents further interaction between cross bridges and actin filaments.

n. Relaxation occurs.

Front 9

Know the following about energetics of muscle contraction:

a. The FORMATION of creatine phosphate in muscle fibers.

Back 9

At rest a skeletal muscle fiber produces more ATP's than it needs.

Under these conditions it transfer the energy of the ATP's into another high energy compound called creatine phosphate {CP }.

This can be summarized as follows:

ATP + creatine -------> ADP + creatine phosphate

Front 10

Know the following about energetics of muscle contraction:

The UTILIZATION of creatine phosphate in muscle fibers.

Back 10

As ATP's are used up during contraction, new ATP's are generated from CP.

This can be summarized as follows:

ADP + CP -------> ATP + C

creatine phosphokinase (CPK) is the enzyme that catalyzes this reaction.

When muscle fibers are damaged CPK leaks across the sarcolemma into the bloodstream. Thus a high concentration of CPK in blood usually indicates serious muscle damage.)

Front 11

The patterns of ATP production and utilization in the following:

The RESTING skeletal muscle.

Back 11

In resting muscle fibers the demand for ATP's is low.

Also more than enough oxygen is available; so a surplus of ATP's are produced.

These extra ATP's are used to buildup reserves of CP and Glycogen.

(Resting muscle fibers absorb glucose and fatty acids from the bloodstream. The fatty acids are broken down in the mitochondria and ATP 's are generated.These ATP 's are used to convert C to CP and glucose to glycogen.

Front 12

The patterns of ATP production and utilization in the following:

Skeletal muscle at PEAK levels of activity.

Back 12

At peaks levels of activity, the ATP demands are enormous. Oxygen can not diffuse into the fibers fast enough to supply the needed ATP 's by aerobic respiration alone.

At peak activity aerobic respiration (mitochondria) can supply only about one-third of the ATP needed. The rest is produced by glycolysis.(anaerobic respiration)

When glycolysis produces pyruvic acid faster than it can be utilized by the mitochondria, it levels rise in sarcoplasm and is converted to lactic acid.

So a buildup of lactic acid occurs. So at peak levels of activity ATP 's are supplied mainly by glycolysis
(anaerobic respiration).

Front 13

The patterns of ATP production and utilization in the following:

Skeletal muscle at MODERATE levels of activity.

Back 13

At moderate levels of activity the demand for ATP 's increase.

This demand can be met by aerobic respiration (Krebs cycle and electron transport chain).

Oxygen availability is not a limiting factor, it diffuses into the muscle fibers fast enough to supply ATP 's at the rate they are being used. But there is no surplus of ATP 's so no CP or glycogen being formed.

So skeletal muscle at moderate activity relies primarily on aerobic espiration to generate ATP 's.

(Glycogen used up to supply the pyruvic acid for aerobic respiration).

Front 14

2 DRAWBACKS of anaerobic energy production:

Back 14

1. Since lactic acid is produced the ph. within the fibers is lowered which could alter enzyme function and effect the functioning of the muscle fibers, including contracting.

2. Glycolysis is an inefficient means of producing ATP 's.

Front 15

A skeletal MUSCLE fiber is FATIGUED when it no longer contract despite continued neural stimulation.

Back 15

Muscle fatigue

Front 16

Muscle Fatigue:

Causes in muscles contracting at moderate levels.

Back 16

In muscles contracting at moderate levels ATP demands are met by aerobic respiration so fatigue will not occur until glycogen, lipid, and amino acids reserves are depleted.

This type of fatigue affects muscles after hours of exertion such as marathon runner.

This type of prolonged muscle activity can also result in damage to the sarcoplasmic reticulum resulting in an interference of intracellular Ca++ Concentrations.

Front 17

Muscle Fatigue:

Causes in muscles contracting at peak levels.

Back 17

At peak levels when a muscle produces a sudden, intense burst of activity, most of the ATP 's are supplied by glycolysis.

So after a short period of time the rising lactic acid levels lowers the ph. within the muscle fibers.

Because of this the muscle can no longer function normally causing fatigue.
This may occur within seconds to minutes.

Athletes running sprints, such as 100 meter dash, suffer from this type of fatigue.

Front 18

Muscle Fatigue:

Other causes

Back 18

Normal muscle functioning requires the following:

1. substantial energy reserves within the fibers.

2. normal circulatory supply.

3. normal blood oxygen concentrations.

So anything that interferes with 1 or more of these factors could cause premature muscle fatigue.

For example reduced blood flow from tight clothing, a circulatory disorder, or loss of blood slows delivery of oxygen and nutrients, thereby accerlating the buildup of lactic acid and promoting fatigue.

Muscle fatigue becomes pronounced as more fibers within the muscle are affected and can eventually reduce the capabilities of the entire skeletal muscle.

Front 19

Describe the recovery period:

Back 19

When a muscle fiber contracts, the conditions inside the fiber are changed. Energy reserves are consumed, heat is released, and if contraction was at peak levels lactic acid is produced.

During the recovery period conditions within the fibers are returned to normal precontraction levels.

Front 20

What is the time period of a Recovery period?

Back 20

After moderate activity it may take several hours. That is it takes that long to return the conditions in fibers to conditions before contraction.
After sustained activity at higher levels, complete recovery may take a week.

So the length of the recovery period depends on the intensity and length of the muscular activity.

Front 21

Why is ATP required and how is it generated?

Back 21

During the recovery period the muscle fibers rebuild there energy reserves, such ATP 's, CP, and glycogen.

Rebuilding these energy reserves is a synthetic activity that requires ATP.

Since oxygen is available during the recovery period, the ATP 's can be produced by aerobic respiration.

Front 22

Describe lactic recycling and the Cori cycle.

Back 22

a. During strenuous activity skeletal muscles generate ATP through glycolosis under anaerobic conditions. LDH converts the pyruvte produced into lactic acid.

b. During the recovery period, when oxygen is plentiful, lactic acid is coverted back to pyruvic acid. Some of the pyruvic acid is broken down aerobically, by the TCA cycle to produce ATP. The rest is converted back to glucose.

c. The work of lactic acid recycling is divided between the liver and the muscles in the Cori cycle. The liver absorbs the circulating lactic acid and produces glucose for discharge into the bloodstream. Muscle fibers then use the glucose to rebuild their glycogen reserves.

Front 23

Describe oxygen debt.

Back 23

The amount of oxygen needed to restore normal preexercise conditions in the muscle fibers.

Front 24

The major tissues involved in additional oxygen consumption and why?

Back 24

Additional oxygen consumption by the skeletal muscle fibers is necessary to restore ATP 's, CP, and glycogen to there precontraction levels.

Additional oxygen consumption by the liver is necessary to generate the ATP 's to convert excess lactic acid to glucose.

Front 25

Role of myoglobin.

Back 25

Provides oxygen reserves that can be used for contraction.

Front 26

An oxygen - binding pigment found in skeletal and cardiac muscle fibers.
(Most abundant in slow skeletal fibers and cardiac muscle).

Back 26

Myoglobin

Front 27

How is Oxygen Debt quantitatively measured?

Back 27

Oxygen Debt = amount of oxygen that would be needed for total aerobic respiration during the muscle activity minus the amount that is actually used {that is made available to muscle fibers }

Example:
If ran a 100 yd. dash in 12 sec., your body would require about 6 L of oxygen to allow for total aerobic res.However the amount of oxygen that could be actually delivered to and used by your muscles during that 12 sec. interval is 1.2 l.

So:
Oxy. debt = 6 l - 1.2 l = 4.8 l

Front 28

These activities require a SURGE OF POWER but the activity ONLY LASTS A FEW SECONDS. So they rely entirely on the ATP and CP reserves in the muscle.

There is about 10-15 seconds worth.

Back 28

weight lifting, diving, and sprinting

Front 29

These activities are MORE SUBSTAINED but LESS STRENDOUS; but they require the muscles to work at PEAK levels so fueled almost entirely by glycolysis.

Back 29

tennis, soccer, and swimming

Front 30

These activities require ENDURANCE rather than power; so they require the muscles to work at MODERATE levels for a LONG period of time, so fueled mainly by aerobic respiration.

Back 30

marathon running and jogging

Front 31

This DOES NOT PRODUCE active movements, but KEEPS the MUSCLES FIRM, healthy, and ready to respond to stimuli.

Back 31

Muscle tone

Front 32

It consist of the muscle fibers supplied by a nerve fiber by way of its terminial branches. The number of muscles fibers in a MOTOR UNIT may be as many as a several hundred or as few as four. All of the fibers of a MOTOR UNIT contract as a unit.

Back 32

Components of a motor unit.

Front 33

A single stimulus-contraction-relaxation sequence in a muscle fiber. So it’s a response to a single brief threshold stimulus.

Back 33

A muscle twitch

Front 34

3 parts of a muscle twitch:

Hint: LCR

Back 34

Latent period
Contraction period
Relaxation period

Front 35

the time interval between the STIMULUS TO THE MUSCLE and the BEGINNING OF the CONTRACTION. During this time the nerve impulse is spreading along the sarcolemma and T-tubules and the sarcoplasmic reticulum is releasing Ca++. The MUSCLE DOESN'T DEVELOP TENSION during this time because the cross bridge activity hasn’t begun. It lasts about 2 msec.

Back 35

Latent period

Front 36

time when the MUSCLE IS SHORTENING. During this time the CROSS BRIDGE activity is SLIDING the actin by the myosin which CAUSES CONTRACTION of the sarcomeres - which causes contraction of the muscle fibers - which cause contraction of the muscle. It lasts about 15 msec.

Back 36

Contraction period

Front 37

the time when the muscle fiber is RESUMING it’s ORIGINAL LENGTH. During this time Ca++ levels are dropping and Tropomyosin is covering active sites; so CROSS BRIDGE activity is DECLINING and at the sarcomeres the actin is sliding out. It last about 25 msec.

Back 37

Relaxation period

Front 38

If a skeletal muscle is stimulated immediately after the relaxation phase of a muscle twitch, the contraction that occurs will develop _____ _______ than the previous contraction.

Back 38

more force {tension}

Front 39

This increase in force well over the first 30-50 twitches after which the force of the contractions remain constant. This is known as ________ OR the ___________.

Back 39

treppe or the staircase.

Front 40

Twitches in a skeletal muscle do not accomplish anything useful. All normal activities require sustained _________ ____________.

Back 40

muscle contractions.

Front 41

Variations in degree of muscle contraction.

Back 41

graded muscles responses

Front 42

2 ways muscle contractions can be graded:

Back 42

1. Changing the frequency of stimulation.

2. Changing the strength of the stimulus.

Front 43

if 2 IDENTICAL STIMULI are delivered to a muscle in rapid succession, the 2nd contraction will be greater than the first.
This occurs because the muscle is already partially contracted and more Ca++ is being released from sarcoplasmic reticulum due to the 2nd stimulus. So as a result of these 2 factors more cross bridges will be attached to the actin filaments resulting in more shortening of the muscle fiber.

Back 43

Wave summation

Front 44

Muscle responses to frequency of stimulation:

Hint: WS, IT & CT

Back 44

Wave Summation
Incomplete Tetanus
Complete Tetanus

Front 45

occurs when a muscle is stimulated at an DECREASING faster rate, so that the RELAXATION TIME between contractions BECOMES SHORTERand shorter, and the concentration of Ca++ in the sarcoplasm becomes higher and higher, and the degree of summation greater and greater

Back 45

Incomplete tetanus

Front 46

this is obtained by INCREASING the frequency of stimulation until the RELAXATION PHASE is ELIMINATED resulting in a continuous sustained contraction.

Back 46

Complete tetanus

Front 47

occurs when the STRENGTH OF STIMULUS is INCREASED thus causing more motor units in the muscle to contract resulting in a contraction of greater force.

Back 47

Recruitment

Front 48

the MINIMUM STIMULUS that will cause a muscle to contract.

Back 48

Threshold stimulus

Front 49

the STRONGEST STIMULUS that produces increased contractile strength. It represents the point at which all the motor units of the muscle are recruited{all the motor units are contracting}. So increasing the strength of the stimulus beyond this MAXIMUM STIMULUS will not increase the force of the contraction.

Back 49

Maximum stimulus

Front 50

The 4 factors that affect the force of muscle contraction:

Back 50

Number of fibers stimulated
Relative size of the muscle
Series-elastic elements
Degree of muscle stretch

Front 51

The ideal length of a muscle fiber to allow it to contract with the maximum force is when the muscle is slightly stretched and the actin and myosin filaments barely overlap. This permits sliding along nearly the entire length of the actin filaments; so the sarcomeres shorten more therefore the muscle fiber contracts with a greater force

Back 51

Degree of muscle stretch

Front 52

They include the connective tissue coverings of the muscle and the tendons that attach the muscle to the bones. These structures are able to stretch and recoil. The force generated by the contracting myofibrils{ called internal tension} stretches the series-elastic elements and they in turn exert tension on the load. The tension exerted by series-elastic elements is called external tension, and the higher this external tension the greater the force of the contraction. Because of the time required to take up the slack and stretch the series-elastic elements, brief twitch contractions result in an external tension less than the internal tension; but when a muscle is stimulated to tetanus more time is available to stretch the series-elastic elements and the external tension approaches the internal tension. So the more rapidly a muscle is stimulated the greater the force of the contraction.

Back 52

Series-elastic elements

Front 53

The thicker the muscle fibers {larger their diameter} the more tension the muscle develops so the greater the force of the contraction. Exercise can increase the size of the fibers{hyperthophy} by increasing the number of myofibrils in the fibers.

Back 53

Relative size of the muscle

Front 54

The more motor units contracting the greater the force of the contraction.

Back 54

Number of fibers stimulated

Front 55

3 factors that affect the velocity and duration of contraction:

Back 55

Muscle fiber type
Load
Recruitment

Front 56

The more motor units that are contracting, the faster and more prolonged the contraction will be.

Back 56

Recruitment

Front 57

Because muscles are attached to bones , they work against some resistance when they contract.
This resistance is called ______.

The heavier the ______the slower the contraction and the shorter the duration of the contraction.

If the ______ exceeds the muscle’s ability to move it, the speed of contraction is zero and the contraction is isometric.

Back 57

Load

Front 58

2 criteria for classifying muscle fibers

Back 58

1. Speed of contraction

2. Major ways of forming ATP - Fibers rely on aerobic pathways are called oxidative fibers and those that rely on anaerobic glycolysis are called glycolytic fibers.

Front 59

how fast their myosin ATPases split ATP. On this basis there are fast fibers and slow fibers.

Back 59

Speed of contraction

Front 60

Fibers rely on aerobic pathways are called oxidative fibers and those that rely on anaerobic glycolysis are called glycolytic fibers.

Back 60

Major ways of forming ATP

Front 61

On basis of these 2 criteria muscle fibers can be put in 3 categories:

Back 61

Slow oxidative fibers
Fast oxidative fibers
Fast glycolytic fibers

Front 62

Contracts SLOWLY because myosin ATPases are slow.

Depends primarily on aerobic pathway to generate ATP’s - so large number of mitochondria and blood capillaries.

SMALL RED FIBERS - high content of myoglobin

FATUGUE RESISTANT - best suited for endurance activities such as distance running.

Back 62

Slow oxidative fibers

Front 63

Contracts FAST because myosin ATPases are fast.

Depend primarily on aerobic respiration to generate ATP’s -so large number of mitochondria and blood capillaries.

INTERMEDIATE RED TO PINK FIBERS - high content of myoglobin but not as much as slow oxidative fibers.

MODERATELY FATIGUE RESISTANT - best suited for activities such as sprinting and walking.

Back 63

Fast oxidative fibers

Front 64

Contracts FAST because myosin ATPases are fast.

Depends primarily on glycolysis{anaerobic respiration} to generate ATP’s - so has large glycogen reserves and low number of mitochondria and blood vessels.

Large white fibers - large number of myofibrils and low content of myoglobin.

FAST TO FATIGUE fatigable} - best suited for activities that require short term and powerful movements such as hitting a baseball.

Back 64

Fast glycolytic fibers

Front 65

The muscle shortens and moves the load - so the tension developed by the contracting muscle exceeds the load.

The muscle shortens and moves the load - so the tension developed by the contracting muscle exceeds the load.

Back 65

Isotonic contractions :

Front 66

The muscle develops tension but does shorten - the tension is not sufficient to move the load. Muscles contractions that act to maintain posture and to hold joints in stationary position while movements occur at other joints are isometric

Back 66

Isometric contractions: