BIOD43H3 Lecture Notes - Lecture 4: Sarcomere
BIOD43 Lecture 4 Notes: Muscle Structure Part II
How Fiber Type Relates to Function
• Isometric contractions generate force without changing the length of the muscle.
• The maximum force occurs when there is zero length change, and zero work done
• At 1/3 of its contraction velocity the most power is generated
• In red muscles, which work during steady swimming for fish shown in lecture slide
contraction velocity is about 1 length change per second.
• In the white muscles, activated during fish escape response there are 5 length changes per
second, which is much more compared to the red muscle.
• The most power is generated at about 40% of maximum shortening velocity, however
muscle is most efficient at less than 40% of maximum shortening velocity.
• It is important to note that during escape (white muscle activation) efficiency is not
considered, the fishes body is more concerned with avoiding danger and staying alive
Extracellular Recordings (EMG’s)
• Record local electrical potentials via probes that stick on skin that present voltage
difference waves of AP
• Extracellular recordings show that there is progressive recruitment of more and
more motor units
• First at a slow-swim electrodes are recorded to be in the fish anterior (front) red
muscle
• As fish swims faster, red muscles are still active, however white muscle in the
posterior of the fish are fired
Fiber Arrangements
• Pennate fiber arrangements reduce fore transmission along primary contraction axis,
shortening is lost due to perpendicular direction. About 13% of force is lost off to the
sides.
• Sarcomere length varies within animals, some have long, while others have shorter.
• A fiber composed of 6 short sarcomeres, is able to shorten faster than 4 longer
sarcomeres of the same total length. This is because the shorter sarcomeres can fit more,
and therefore, shorten more at same speed
Muscle Mechanical Power
• Joints act as levers
• Closer to fulcrum= stronger force
• For this reason, it is easier for a person to lift their full body weight via calf rises than it is
to do bicep curls with about 25 lbs for 3 reps. Not because muscle in the calf are stronger
than bicep muscles, but because calf sarcomere shorten at a shorter difference.
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Document Summary
Biod43 lecture 4 notes: muscle structure part ii. In red muscles, which work during steady swimming for fish shown in lecture slide contraction velocity is about 1 length change per second. It is important to note that during escape (white muscle activation) efficiency is not considered, the fishes body is more concerned with avoiding danger and staying alive. Fiber arrangements: pennate fiber arrangements reduce fore transmission along primary contraction axis, shortening is lost due to perpendicular direction. This is because the shorter sarcomeres can fit more, and therefore, shorten more at same speed. Stresses and strains: stress ask the question how strong is something? , which measures the breaking stress, extensibility ask the question how much can it stretch without breaking? ex. When landing the cross- section area of bones are not strong enough: stiffness (e)= high slope means lots of force is needed to get something un-stiff.
