Degree of muscle stretch (The Effect of Sarcomere Length on Tension)

Change the strength of stimulus The stimulus intensity increases , more and

more motor units are stimulated, and thus the strength of muscle contraction increases

Effects of frequency of Stimulation

Twitch and Treppe Contractions

Muscle stimulation at variable frequencies low frequency (up to 10 stimuli/sec)-

each stimulus produces an identical twitch response moderate frequency (between 10-20

stimuli/sec) each twitch has time to recover but develops more

tension than the one before (treppe phenomenon) calcium was not completely put back into SR

Incomplete and Complete Tetanus

Higher frequency stimulation (20-40 stimuli/second) generates gradually more strength of contraction each stimuli arrives before last one recovers

temporal summation or wave summation

Maximum frequency stimulation (40-50 stimuli/second) muscle has no time to relax at all twitches fuse into smooth, prolonged contraction called complete

tetanus

TREPPE

ALL PHASES OF MUSCLE CONTRACTIONARE PRESENT AND HAVE NOT BEEN ALTERED.

TEMPORAL (wave) SUMMATION

IF TWO IDENTICAL STIMULI ARE

DELIEVERED TO A

MUSCLE IN RAPID

SUCCESSION, THE

SECOND CONTRACTION

WILL SUMMATE

WITH THE FIRST. THE RELAXATION PHASE HAS BEEN SHORTENED.

INCOMPLETE TETANUS

IF THE STIMULUS

STRENGTH IS HELD

CONSTANT AND THE

MUSCLE IS STIMULATED AT AN

INCREASINGLY FASTER

RATE, INCOMPLETE

TETANI RESULTS.

COMPLETE TETANUS

WHEN ALL EVIDENCE OF MUSCLE RELAXATION DISAPPEARS AND THE CONTRACTIONS FUSE INTO A SMOOTH, SUSTAINED CONTRACTION, COMPLETE TETANUS RESULTS.

Fatigue

Fatigue is defined as the decrease in muscular activity due to repeated stimuli. When stimuli are applied repeatedly, after some time, the muscle does not show any response to the stimulus. This due to built up of acidic compound which affect protein functioning, lack of ATP and ionic imbalances

Functions of ATP in Skeletal Muscle Contraction1. Hydrolysis of ATP by myosin

- energizes the cross-bridges, providing energy for force generation.

2. Binding of ATP to myosin - dissociates cross-bridges bound to actin.

3. Energizes Ca pumps that actively transport Ca back into the sarcoplasmic reticulum- Lowers cytosolic Ca level leading to relaxation

4. Runs the Na+-K+ pump in the sarcolemma- maintains the resting membrane potential of the

sarcolemma

Muscle Metabolism

ATP: Compose of Adenine nucleotide, two phosphate groups, attached by high energy phosphate bond

ATP Synthesis

Muscle cells uses three processes to synthesize ATP

1. Hydrolysis of creatine phosphate2. Glycolysis3. Krebs cycle and oxidative

phosphorylation

ATP Synthesis (hydrolysis of creatine phosphate)

Creatine phosphate (CP): Organic

compound in muscle cells serves as source of energy Most rapid method of ATP generation ADP + CP creatine kinase C + ATP The amount of CP is limited and rapidly

depleted Only 1 ATP per CP used CP (creatine phosphate) regenerated

during resting conditions (ATP + C CP + ADP)

ATP Synthesis (Glycolysis) Glucose is the major source of

energy for synthesizing ATP. Glucose available to muscle from two different sources

1. Glucose enter the body directly from the blood

2. Glucose is produced by hydrolysis of glycogen that stored in muscle cells

ATP Synthesis (Glycolysis) Glucose is broken down in glycolysis End product of glycolysis include:2 ATP moleculePyruvic acidIn the absence of O2, pyruvic acid is converted into

lactic acid (the end product of anaerobic pathway)Excess lactic acid builds up and caused muscle fatigue

In the presence of O2, aerobic pathway (Krebs cycle) proceeds, pyruvic acid converted to acetyl CoA

The end products: CO2, H2O and 36 molecule ATP

O2 enter the muscle cells from two sources:

O2 enter the muscle cells directly from the blood

O2 stored in myoglobin, an oxygen binding proteins

Muscle Metabolism: Energy for Contraction

Figure 9.18

Physical ActivitiesPhysical Activities

Basketball players use both systems

Some use mainly aerobic respiration.

Others use mainly anaerobic

respiration.

Most use a combination of the two.

EventPercentage of

Aerobic Respiration

Less than 1%100 m

10%200 m

20%400 m

50%800 m

60%1,500 m

83%5,000 m

95%10,000 m

100%Marathon

Oxygen Debt

Oxygen Dept: The oxygen required to completely oxidized lactic acid formed and to replenish the depleted stores of ATP and creatine phosphate

For a muscle to return to a resting state: Additional oxygen to rebind to myoglobin Lactic acid must be converted to pyruvic

acid which enter krebs cycle producing ATP ATP use to rephosphorylate creatine into CP Glycogen synthesize from glucose

Oxygen DebtOxygen DebtHow do sprinters pay back their

oxygen debt at the end of a race?

Sprinters will continue to breathe more deeply and rapidly for a number of minutes at the end of their race. This will enable them to pay back the oxygen debt, and allow lactic acid levels to fall.

Variations in muscle fiber type

There are two types of muscle cells which differ in size and coloration

White muscle cells Red muscle cells These structural differences relate to

their method of metabolism

Features of white muscle fiber Large in diameter Light in color due to reduced myoglobin Few mitochondria Few capillaries High glycogen content Mainly use glycolysis to synthesize ATP Rapid cross bridge cycling results in fast

contractions Called fast twitch glycolytic fiber Fatigue rapidly due to build up of lactic acid

and depletion of glycogen

Features of red muscle fiber Half diameter of white muscle fiber Dark red in color due to myoglobin Surrounded by many capillaries Numerous mitochondria Low glycogen content Cross bridge occur slowly Called slow twitch oxidative fiber Synthesize ATP by krebs cycle Fatigue resistant