Download how do action potentials trigger muscle

Musculoskeletal System
& Movement
What are the types of movement?
What are the different types of muscle tissue and skeletal
systems?
How do muscles exert force at the gross level?
…at the cellular level?
…at the molecular level?
How do action potentials trigger muscle contraction in
skeletal muscle?
How do you quantify muscle activity? (force, work,power)
Cost of transport vs. body size; vs. mode of transport
3 Basic Types of Movement
• Ameboid
• Ciliary Locomotion
• Muscular Movement
Three Types of Muscle
• Smooth
• Cardiac
STRIATED
• Skeletal
– Slow twitch – red
– Fast twitch – white
good for endurance
good for sprints
Slow Twitch vs. Fast Twitch
Figure 46-18
Endoskeleton
Skeletal
Systems
Exoskeleton
Hydrostatic skeleton
Endo
&
Exoskeletons
Anatomy of Skeletal Muscle
Sliding Filaments are the basis of
muscle shortening
Extended
Contracted
Figure 46-21
Myosin
head
Colors indicate
protein subunits
ATP binding site
Actin binding site
Figure 46-22
Conformational Change in Protein (myosin head)
is “molecular motor” for movement
CHANGES IN THE CONFORMATION OF THE MYOSIN HEAD PRODUCE MOVEMENT.
1. ATP bound to myosin head.
Myosin head
of thick filament
Head releases from thin filament.
Actin in thin filament
4. ADP released.
2. ATP hydrolized.
Cycle is ready to
repeat.
Head pivots, binds to
new actin subunit.
3. Pi released. Head pivots,
moves filament (power stroke).
Figure 46-23
Tropomyosin and troponin work together to block the
myosin binding sites on actin.
Myosin head
Troponin
Myosin binding
sites blocked
Tropomyosin
Actin
Calcium ions
Myosin
binding sites
When a calcium ion binds to troponin, the troponintropomyosin complex moves, exposing myosin binding sites.
Myosin binding
site exposed to
myosin head
Calcium ion
Troponin-tropomyosin complex, moved
Figure 46-24
Motor neuron
Muscle cell
HOW DO ACTION POTENTIALS TRIGGER
MUSCLE CONTRACTION?
Motor neuron
Action
potential
1. Action potential
ACh
arrives; acetylcholine
(Ach) is released.
ACh receptor
Action
potentials
2. ACh binds to ACh
receptors on the muscle
cell, triggering depolarization that leads to
action potential.
3. Action potentials
propagate across muscle
cell’s plasma membrane
and into interior of cell via
T tubules.
4. Proteins in T tubules
open Ca2+ channels in
sarcoplasmic reticulum.
5. Ca2+ is released
from sarcoplasmic
reticulum. Sarcomeres
contract when troponin
and tropomyosin move in
response to Ca2+ and
expose actin binding
sites in the thin filaments
(see Figure 46.23).
Thick filaments
(myosin)
Thin filaments Ca2+
(actin)
ions
Figure 46-24a
Motor neuron
Muscle cell
HOW DO ACTION POTENTIALS TRIGGER
MUSCLE CONTRACTION?
Motor neuron
Action
potential
1. Action potential
arrives; acetylcholine
ACh
(ACh) is released.
ACh receptor
Action
potentials
2. ACh binds to ACh
receptors on the muscle
cell, triggering depolarization that leads to
action potential.
Figure 46-24b
Motor neuron
Muscle cell
HOW DO ACTION POTENTIALS TRIGGER
MUSCLE CONTRACTION?
3. Action potentials
propagate across muscle
cell’s plasma membrane
and into interior of cell via
T tubules.
4. Proteins in T tubules
open Ca2+ channels in
sarcoplasmic reticulum.
5. Ca2+ is released
from sarcoplasmic
reticulum. Sarcomeres
contract when troponin
and tropomyosin move in
response to Ca2+ and
expose actin binding
sites in the thin filaments
(see Figure 46.23).
Thick filaments Thin filaments
(myosin)
(actin)
Ca2+
ions
Quantify Performance in terms of
Power (Watts; kcal/min;horsepower)
• 1 Watt = 6.12kg-m/min
• 1 Horsepower = 746 W
• 1 Kcal/min = 69.78 W
(70 Watts is close to the Basal Metabolic Rate for an
average sized human)
1 Kcal/min x 60mins/hr x 24hrs/day = 1440 Kcal/day
Total caloric expenditure = BMR + extra activity
Total Energy Expenditure
(BMR + extra activity)
• Skeletal Muscle tissue - largest consumer of extra calories
• Digestive, cardiovascular, immune can cycle on and off
• (N.B. = muscle is only 25% efficient so putting out 100 W
on a machine requires burning calories at a rate of 400W)
The Cost of Movement
How much force does it take to move 1kg of animal..?...
Body Shape of Swimming Animals
Some comparisons
• Most Cost effective mode of movement
• Largest organisms
• Fastest speeds
– Water:
– Land:
– Air:
50 mph
60 mph
115+ mph