Chapter Eleven: Levers

What makes up the muscular system?

voluntary controlled muscles together

Origin

portion of the muscle that is attached to the bone that remains stationery when contracted

Insertion

portion of the muscle that is attached to the bone that moves when contracted

what is a lever system?

involves a bone (the rigid lever), a joint (the fulcrum), and a muscle (the effort) to move a load, which is the weight or resistance

Lever

rigid structure (bone) that can move around a fixed point (the fulcrum)

What is the fulcrum?

the joint that is moving

What is the effort?

force exerted by muscular contraction, causing movement 

What is load

Weight of the limb or limb+weight of the object, opposing the movement (effort)

When does motion occur?

when the effort applied to the bone of the insertion exceeds the load 

What is mechanical advantage mean?

load is closer to the fulcrum and the effort is farther from the fulcrum

MA: What is the effort required?

relatively small effort to move a large load over a small distance 

What does mechanical disadvantage mean?

load is farther from the fulcrum and effort is applied closer to the fulcrum 

MD: What is the effort required? 

relatively large effort required to move a small load, but at a greater speed 

What determines if a lever operates at a mechanical advantage or disadvantage? 

the relative distance between the fulcrum and load and the point where the effort is applied 

How are levers categorized?

categorized into three types according to the positions of the fulcrum, load, and effort

What are first class levers?

the fulcrum is between the effort and the load

FCL: MA or MD?

can produce a MA or MD depending on whether the effort or load is closer to the fulcrum 

FCL: Provide an example

lever formed by the head resting on the vertebral column 

E: posterior neck muscles

F: atlanto-occipital joint

L: weight of the anterior portion of the skull 

What are second class levers?

the load is between the fulcrum and the effort

SCL: MA or MD?

always produces a MA because the load is always closer to the fulcrum than the effort, but is the most uncommon lever 

SCL: Provide an example

standing up on your toes

F: ball of the foot

L: weight of the body 

E: the contraction of the muscles of the calf 

What are third class levers?

the effort is between the fulcrum and the load, is the most common lever type 

TCL: MA or MD?

always produces a MD because the effort is closer to the fulcrum than the load 

TCL: Provide and example

flexing the forearm

F: elbow joint

E: contraction of the biceps brachii muscle 

L: weight of the hand and forearm