Announcements

1
Announcements

• Muscle lectures Chapter 10 (400-419)
• If you missed last class, check out CD on reserve
• Sliding filament theory
• Goes through all of the players and how they
  interact in contraction
• REALLY WORTH IT!
• Exams done will hand back at end of class
• Next exam is Nov 4 (2.5 weeks!!!)
• This is a change from the syllabus!!!

2
In class exercise

• A) Use your knowledge of the bind-swing-release
  mechanism to answer the following question If
  ATP is no longer available once contraction has
  started, in which position will the thick
  (myosin-based) and thin (actin-based) filament be
  frozen?
• B) Now consider the sequence by which
  contraction is initiated and ended, as shown in
  the video. If ATP is no longer available, what
  other process that controls the interaction of
  thick and thin filaments will be affected?
• C) Muscles enter a state called rigor mortis
  about 10 minutes after death. They do not have
  to have been contracted at the time of death.
  Why might this happen?

3

• Tension is the force produced by a muscle in
  opposition to an externally applied force.
  Imagine two hypothetical sarcomeres. In
  sarcomere A, each thin filament forms one
  cross-bridge with its neighboring thick filament
  in sarcomere B, each thin filament forms ten
  cross-bridges with its neighboring thick
  filament. Which can generate greater tension?
• What general principle about muscle tension is
  demonstrated by this hypothetical example?
• Using this principle, plot the tension that can
  be produced by each of the sarcomeres shown below
  on the axes provided below. Jot down a brief
  explanation of why you plotted the relation as
  you did.

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(No Transcript)
5
Rigor Mortis

• After death, membranes become more permeable to
  Ca ions
• Intracellular calcium promotes myosin binding
• ATP depletion means Actin/myosin cant disengage
• Muscles stay locked until they start to decay

6
Tension Force
Sarcomere state
Tension produced
Overstretched muscle No myosin binding
Maximal myosin binding
Interference from thin filaments
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Mechanics

• Terminology
• Force Tension
• Imparts acceleration to an object (Force Mass
  X Accel.)
• Units Newtons
• (force needed to accelerate 1 kg 1 m/s2)
• Work
• Force Distance (Newton meters)
• No distance, no work
• Distance determined by length of contraction,
  levers
• Power
• How quickly work can be done
• Watts Newton (m/s)

Muscles trade off Force and Power!
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Force cross bridges

• Most vertebrate muscles have a predictable
  sarcomere length (2.5 mm)
• Muscles also have a maximal density of myosin
  cross bridges per unit length
• Therefore, force per cross sectional area of
  muscle has a maximum ( 4-5 kg force/cm2)

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What about ants?
Can carry objects many times their body mass
10
Are ants stronger?

• Ants (and many other insects) can carry objects
  greater than their own weight with ease
• However, their muscles are not inherently
  stronger than those of vertebrates (4-5 kg
  force/cm2)
• Their ally is SIZE

Muscle force surface area Length2 Body
weight volume Length3 Muscle force/body
weight Length-1
Strength/Size Scales as surface area to volume!
Small animals have greater strength relative to
their body mass than big animals
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Force vs. Power (speed)

• Depends on amount of cross bridges
• Depends on length and configuration of sarcomeres

E.g. shellfish attachment muscles Resist high
force Very long sarcomeres (10 times that of
typical vertebrate)
All of these pullers pull 1 cm/sec
1 cm/sec
E.g. squid tentacles Shoot out in 1/40th sec. Low
force / high speed Sarcomeres short
3 cm/sec
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Muscle fibers

• Tonic fibers (red)
• Important in postural muscles, esp. in reptiles,
  birds.
• Slow kinetics of contraction and calcium pumping
• Have small nerves with multiple contact points to
  fiber
• Slow signal conduction
• Graded response to stimulation
• Twitch fibers (white)
• Used in rapid movements or responses
• Rapid kinetics of contraction and calcium pumping
• Have big nerves with single contact point to
  fiber
• Fast signal conduction velocity
• Threshold, all or nothing response
• Twitch fibers have several types!

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Different types of Twitch fibers
Slow twitch (Type I)
Fast twitch (Type II)
These operate more slowly
These operate more quickly
How are they fueled?
How are they fueled?
Oxidative (IIa)
Glycolytic (IIb)
Oxidative
Aerobic metabolism
Aerobic metabolism
Anaerobic metabolism
Intermediate
Fastest
Slowest
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Red versus white
Red Lots of mitochondria Lots of myoglobin Lots
of capillaries
White Fewer mitochondria Less myoglobin Fewer
capillaries
Aerobic metabolism
Anaerobic metabolism
Why have Anaerobic Fibers???
Fewer contractile elements
More contractile elements
More power Less efficient Faster to fatigue
Less power More efficient Slower to fatigue
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Twitch (fast) Fibers

• Slow twitch (Type I)
• Very aerobic
• Low fatigue
• Mammalian postural muscles, fish swimming muscles
• Fast twitch oxidative (Type IIa)
• Aerobic
• Somewhat resistant to fatigue
• Used in repetitive, fast locomotion
• Running, flying
• Fast twitch glycolytic (Type IIb)
• Anaerobic
• High power output
• Fatigues easily
• Sprinting, leaping, evasion or attack

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Muscles have multiple fiber types

• These images look at the same muscle with
  different techniques

• This muscle is more likely to be involved in
  sprinting

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Aerobic vs. anaerobic

• In humans, takes 1-2 minutes of exercise before
  oxygen supply catches up with ATP demand
• How?
• Heart rate increases (increases blood pressure
  flow)
• Breathing rate increases
• However, reach peak anaerobic capacity more
  quickly
• Can use anaerobic and aerobic metabolism
  simultaneously
• Oxygen debt is generated
• Can pay it off after activity

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Anaerobic metabolism at the onset of exercise
Lactate is cleared aerobically - requires O2
Even animals that rely on aerobic metabolism need
to use anaerobic metabolism to get started -
oxygen delivery needs to catch up
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ATP supply to muscles

• Muscles have very little stored ATP (2 seconds
  of sprinting worth)
• High energy phosphate is stored (short term) as
  CrP (Creatine phosphate) --- 3-6X amt ATP
• Highly reversible reaction
• ATP Creatine ADP Creatine
  Phosphate
• Very responsive to changes in cellular conditions
• Prevent inhibitory effects on metabolism of too
  much ATP!

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Anaerobic metabolism and ectotherms

• Ectotherms tend to be sprinters
• Lower capacity for oxygen exchange
• Lower resting metabolic rate lower active
  metabolic rate
• (metabolic scope never more than 10)
• Rely on anerobic metabolism for burst activity
• Counterexamples Tuna swimming muscle
• Anaerobic metabolism is less temperature
  dependent!
• Q10 1.1 1.3 vs. 2-3 for aerobic metabolism
• Important for poikilothermic animals!

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Ectotherms sprint and exhaust
This trout sprinted for 15 minutes Required 8
- 24 hours to clear lactate!
lactate
Lactate is cleared aerobically aerobic
capability is limited in ectotherms!
Were exhausted!
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Metabolism and thermal biology
Endotherms tend to rely on aerobic metabolism
Achieve much higher rates of sustainable
metabolism
Have higher resting metabolic rates
Ectotherms tend to rely on anaerobic metabolism
Have lower rates of sustainable metabolism
Have lower resting metabolic rates
Sprinters that take off and exhaust quickly
Are really fast (lots of power)
Metabolism is less temperature dependent
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Exam 1 Grades
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Handy grade interpretation guide

• 85 Doing great
• 75 Doing well
• 65 Doing OK
• 55 In the D range, try to improve on next
  exam
• Under 55 Please come see me before next exam.