1. To understand the cellular processes for synthesis of ATP.

2. To compare and contrast aerobic and anaerobic processes in the muscle cell.

3. To examine the differences in ATP synthesis among different types of muscle cells

dehydration synthesis

"energy currency"

ATP hydrolysis moving myofilaments & transporting ionsATP

Structure of Adenosine Triphosphate (ATP)

Note: ATP has three phosphate groups. The structure of a phosphate group (Pi) is:

• The bond between the last two phosphate groups is high energy

Regeneration of ATP

1.direct phosphorylation of CP

2.anaerobic glycolysis

3.Oxidative phosphorylation of glycogen, glucose, fat

(1)

(2)

(3)

Metabolism of Skeletal Muscles• Phosphcreatine:• Rapid source of renewal of ATP.• ADP combines with creatine phosphate.• Phosphocreatine concentration (20-40 mM) is 4-8 times

concentration of ATP (5mM).

Sources of Glucose• Two sources of glucose to muscles: 1. Blood glucose. 2. Breakdown of glycogen into glucose within the muscle cell

Anaerobic Pathway: Lactic Acid

glycolysisGlucose Pyruvic

Acid+ 2 ATP2Glycogen

Lactic Acid

glucose

glucoseglycogen lactic acid

pyruvic acid

2

Aerobic Pathway

glucose

glucoseglycogen

myoglobin

pyruvic acid

36

2

O2

O2

H2OCO2

acetyl CoA

Regeneration of ATP

1.direct phosphorylation of CP: 1ATP produced per CP

2.anaerobic glycolysis: 2 ATP per glucose

3.Oxidative phosphorylation of glycogen, glucose, fat; ?? ATP per glucose

glucose

glucose

glycogen

pyruvic acid

lactic acid

acetyl CoA

myoglobin

O2

O2

H2OCO2creatine

White muscle fiber Red muscle fiber

Features of White Muscle FibersCharacteristics of white muscle fibers:1. Large in diameter2. Light in color due to reduced or absent

myoglobin3. Surrounded by only a few capillaries4. Have relatively few mitochondria5. Have a high glycogen content

White muscle fiber

6. Synthesize ATP mainly by glycolysis

Features of Red Muscle Fibers

Characteristics of red muscle fibers:1. Half the diameter of white muscle fibers2. Dark red in color due to a large quantity of

myoglobin3. Surrounded by many capillaries4. Have many mitochondria5. Have a low glycogen content

Red muscle fiber

6. Synthesize ATP mainly by the Krebs cycle and oxidative phosphorylation

Factors Affecting Muscle Tension

Three factors which affect muscle tension in a whole muscle:

1. Frequency of stimulation2. Number of motor units recruited3. Degree of muscle stretch

Contraction of Motor Units1. To examine the components of a motor unit.2. To understand the relationship between motor

unit size and precision of muscle movement.3. To explore the relationship of motor units to

muscle tone.

Types of Muscle Contractions

• Twitch:– Muscle is stimulated with a single electrical shock (above

threshold).

– Quickly contracts and then relaxes.

– Increasing stimulus increases the strength of the twitch (up to maximum).

Latent period

Relaxation

Contraction phase

Relation between force and shortening velocity• Velocity of contraction is maximal when load is zero • Velocity decreases when load increases• Power is maximal at intermediate velocity

Temporal Summation of Two Stimuli

Effect of Time Interval on Second Contraction

Types of Muscle Contractions

• Summation:– If second electrical shock is administered before

complete relaxation of muscle.

Types of Muscle Contractions

• Incomplete tetanus:– Stimulator delivers an increasing frequency of

electrical shocks.– Relaxation period shortens between twitches.– Strength of contraction increases.

• Complete tetanus:– Fusion frequency of stimulation.– No visible relaxation between twitches.– Smooth sustained contraction.

Second & Third Factor Affecting Muscle Tension

Three factors which affect the development of muscle tension:

1. Frequency of Stimulation2. Number of Motor Units Recruited3. Degree of Muscle Stretch

Length-Tension Relationship

Slow- and Fast-Twitch Fibers

• Slow-twitch (type I fibers):– High oxidative capacity:– Resistant to fatigue.– Have rich capillary supply.– Numerous mitochondria and aerobic enzymes.– Use ATP slowly– Red muscle (dark-colored meat of fish and fowl)

Classification of fiber types

1. Tonic fibers: contract slowly, do not produce twitches and AP,

postural muscle and extraocular muscles

2.Three types of twitch (or phasic) fibers

a. slow twitch (or type I) fibers

b. fast twitch oxidative (or type IIa) fibers

c. fast-twitch glycolytic (or type IIb) fibers

Slow- and Fast-Twitch Fibers

• Fast-twitch (type IIa fibers):– Adapted to respire aerobically.– Specialized for repetitive movement– Relatively resistant to fatigue.– Numerous mitochondria and aerobic enzymes – Flight muscles of migratory birds

Slow- and Fast-Twitch Fibers

• Fast-twitch (type IIB fibers):– Adapted to respire anaerobically.– Have large stores of glycogen.– Have few capillaries.– Have few mitochondria.– White breast muscle of domestic fowl.

Ration for different fiber types

Fast-twitch fibers: rapid movement of its limb or fins, use large amount of ATP.

Slow muscles: move slowly, use less amount of energy

Cardiac Muscle

• Contain actin and myosin arranged in sarcomeres.

• Contract via sliding-filament mechanism..

• Adjacent myocardial cells joined by gap junctions.– AP spread through cardiac

muscle through gap junctions.

– Behaves as one unit.– All cells contribute to

contraction.

Cardiac muscle

A small, elongated cell, single nucleus, connected together by gap junction, myogenic (contraction initiated in the muscle fibers themselves).

Contains contractile fibers and conducting fibers (peacemaker fibers)

Initiation and sustain of contraction depend on a signal from pacemaker fibers and spreads as APs through the heart by gap junctions.

Skeletal muscle: short AP with a few milliseconds

Cardiac muscle:

Long AP and long refractory period with several hundred milliseconds

Features of smooth muscle

Lack of sarcomeres & T-tubules (non-striated)

Thick and thin filaments are anchored on dense bodies

Walls of hollow organs

Support visceral functions (not for locomotion and other behavior)

Very slow contraction & prolonged contracted activity

Low energy requirement

Myogenic (single-unit) and neurogenic (multi-unit)

Stretch more than skeletal muscle

Synthesis and secrete proteins (collagen & elastin)

Small spindle-shaped cells, one central located nucleus, diameter 2-10 m, length 100-500 m

Smooth Muscle Contraction• Depends on rise in free intracellular Ca++ .• Ca++ binds with calmodulin.• Ca++ calmodulin complex joins with and activates

myosin light chain kinase.• Myosin heads are phosphorylated.• Myosin head binds with actin.• Relaxation occurs when Ca++ concentration

decreases.

Calmodulin

Ca2+

Ca2+ -calmodulin

Inactive myosin kinase Active myosin kinase

Pi

Phosphorylated myosin(can bind with actin)

Inactive myosin

ATP

ADP

Fig. 8-30, p.351

Caldesmon inhibits myosin-actin binding in smooth muscle.

Remove caldesmon by Ca 2+-Calmodulin or phosphorylation

1. Binding Ca 2+ to myosin light chain

2. Phyosphorylation of myosin light chain by Ca2+-calmodulin or PKC