Skeletal Lever Systems Flashcards
how are muscles able to generate a force
Muscles made of many long thin fibres. When stimulated by electrical impulses from the CNS, the muscle contracts briefly - exert a force.
The maximum tension (force) a muscle can produce is ….
is proportional to the cross sectional area of the muscle at its widest point
when is maximum tension achieved
when muscle is stimulated in its relaxed state
maximum tension of most muscles
30-40 N/cm2
when does maximum tension decrease significantly
significantly if the muscle is elongated or shortened.
what does joint articulation usually involve
Joint articulation usually involves using groups of muscles (i.e. normal muscle action and antagonistic muscle action
line of action of a fusiform
straight line joining the point of insertion of muscle w/ origin
line of action of pennate muscles
like a feather
in direction of fibres - diagonally
pennate muscles can produce what kind of lines of action and what does that allow?
Such muscles (multipennate or combinations of pennate or bipennate) can produce oblique (& many) different lines of action. (This allows total muscle force to be minimized
lever
apply one force and gives a different force
how do levers operate
thru application of moments and torques
longer r is the more torque is applied more leverage
moment or torque
a force which causes some rotational motion about a fixed point.
statics
the study of forces acting on an object which is in Equilibrium, i.e. bridges, bones and limbs, etc.
a rigid body is in equilibrium when 2 conditions are met.
net force = 0
net torque = 0
torque
the quantity which indicates the ability of a force to cause rotation, i.e
torque formula
P (pivot) = rFsin0
(radius?/distance)
F = force applied
when is the torque largest
The torque is largest when the force F is applied PERPENDICULAR to the direction of r.
how to reduce the applied torque
This distance should be minimized to reduce the applied torque, i.e. a much lower torque required to be produced by the back muscles
mechanical advantage
measure of efficiency
a ratio of the load force to the applied force
levers are examples of ..
simple machines where a force (Fa) is applied to lift or balance a load force (Fl).
scale of mechanical advantage
can be >1 or <1 depending on whether the lever is efficient or not
3 classes of lever
Class I
Class II
Class III
Class I lever
FULCRUM is between load(Fl) and applied force(Fa)/effort
both forces need to be in the same direction otherwise it is a propellors
Class II lever
Fl is between the fulcrum and Fa
Fa Fl fulcrum
Class III lever
Fa is between fulcrum and Fl
Fl Fa fulcrum
mechanical advantage of Class I lever is
more, less or equal to 1
mechanical advantage of Class II lever is
always greater than 1
applied force is always further out - always efficient
mechanical advantage of Class III lever is
always less than 1 - always inefficient
