Download Chapter 8b

dehydration
synthesis
ATP
ATP hydrolysis
moving myofilaments &
transporting ions
"energy
currency"
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
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)
1.direct phosphorylation of CP
2.anaerobic glycolysis
3.Oxidative phosphorylation of
glycogen, glucose, fat
(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
Glycogen
Glucose
glycolysis
2 Pyruvic + 2 ATP
Acid
Lactic Acid
glucose
glycogen
glucose
lactic acid
pyruvic acid
2
Anaerobic Pathway: Lactic Acid
Aerobic Pathway
glucose
glycogen
O2
glucose
pyruvic acid
acetyl CoA
2
myoglobin
36
O2
CO2
H2O
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
O2
glucose
lactic acid
glycogen
pyruvic acid
acetyl CoA
O2
myoglobin
creatine
CO2
H2O
White muscle fiber
Red muscle fiber
White muscle fiber
Features of White Muscle Fibers
Characteristics of white muscle fibers:
1. Large in diameter
2. Light in color due to reduced or absent
myoglobin
3. Surrounded by only a few capillaries
4. Have relatively few mitochondria
5. Have a high glycogen content
6. Synthesize ATP mainly by glycolysis
Red muscle fiber
Features of Red Muscle Fibers
Characteristics of red muscle fibers:
1. Half the diameter of white muscle fibers
2. Dark red in color due to a large quantity of
myoglobin
3. Surrounded by many capillaries
4. Have many mitochondria
5. Have a low glycogen content
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 stimulation
2. Number of motor units recruited
3. Degree of muscle stretch
Contraction of Motor Units
1. 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
Relaxation
Latent period
Contraction phase
• 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).
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 Stimulation
2. Number of Motor Units Recruited
3. 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 slidingfilament 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 mm,
length 100-500 mm
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.
Ca2+
Calmodulin
Ca2+ -calmodulin
Inactive myosin kinase
Active myosin kinase
ATP
ADP
Pi
Inactive myosin
Phosphorylated myosin
(can bind with actin)
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