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MUSCLES AS TRANSMISSION LEVERS
Name: _________________________
Background
Muscles are the observable unit of movement in animals. The human body is
composed of over 600 such entities. Each of these muscles contains an origin
(the immovable tapered end towards which the movement occurs), a belly (the
fleshy part of the muscle that shortens during contraction), and the insertion (the
moveable tapered end that moves).
Animal muscle systems function as levers. Any lever has three necessary
components, a moving force, a fulcrum or pivot point, and the load to be moved.
Three classes of levers have been identified based on the relative relationship
between these three components. Each is named and pictured below. Levers
themselves do not do work but are devices that act as transmissions. They
transmit the work done on the lever to work done by the lever.
In the following activity you will become familiar with examples for each of the
three types of levers, some specific examples of muscle system arrangement in
humans, as well as the function of some muscle systems in animals in general.
Questions
1. Identify the class of lever for each of the following situations and make a
sketch of your reasoning.
a. Wheelbarrow
________________
b. Hyper extension of the neck pulling the head up
________________
c. Carrying a loaded shovel
________________
d. Standing on the tip of your toe
________________
e. Teeter Totter
________________
f. Lifting a textbook with your hand and arm
________________
2. How are a muscle and its ligaments, tendons, and bones arranged in general
to form a functional unit (sketch and label).
3. Given that there is a conservation of work (and knowing that you must
remember the two variables that equal work) analyze, deduce, and write a
symbolic equation denoting the relationship between the force of the muscle,
the force of the load, distance of each of these forces from the fulcrum (really
the distance that of movement).
4. Think about a pry bar and identify the class of lever that it represents. Given
that the mechanical advantage of a lever is calculated as being the value by
which the lever increases the force of the muscle, use the equation you
derived in questions 3 to determine the mechanical advantage for the pry bar.
Assume the force of the muscle is “X”. Show your work.
Class ____
Mechanical Advantage _____
5. Think about arm bones and determine where the insertion for the bicep muscle
on the radius and/or ulna. Imagine that the arm is picking up a textbook.
Identify the class of lever that it represents. Determine the mechanical
advantage of for the arm. Assume the force of the muscle is “X”. Show your
work. Compare the mechanical advantage of the arm and the pry bar. What
does this suggest about the evolutionary significance of the arm or what other
type of advantage could there be? (hint: look at the variables in your derived
equation again)
Class ____
Mechanical Advantage _____
6. Think about a mammalian jaw. Sketch and label the two groups of teeth at the
front and rear of the jaw. Based on your new knowledge of the relationship
between force and distance (speed) in levers, why does it make sense that
the two groups of teeth are located where they are instead of the reverse?
7. Think about leg bones and determine the location of the quadriceps femoris
and gastrocnemius insertions. Based on your knowledge of the relationship
between force and distance (speed) in levers, explain which leg movement is
more forceful and which covers more distance or is quicker.