LEVERS FOR ANATOMY AND PHYSIOLOGY

Levers for anatomy and physiology

Levers

A lever is an easy machine used, in its most basic form, for magnifying the force that can be used on an object. An early lever, furthermore known as the shaded, was used in very old Egypt. It consisted of a long bar pivoted near one end that enabled a person pulling down on the long arm to raise a bucket of water, many times his or her own weight, attached to the short arm. The simplest lever is a crowbar, a long beam of timber or metal. One end of a crowbar is pried under the object to be lifted, and a solid impede is skidded under the bar, close to that end. The point, round which the bar turns, in this case impede is called a Fulcrum. The distance that each end moves is proportional to the extent of the bar from that end to the fulcrum.

Movement in the body is made by a system of levers. These series of levers work simultaneously to produce coordinated action, some by genuine action (dynamic) and other ones by stabilization (static).

Definitions

Lever: Rigid bar that turns about an axis of rotation or a fulcrum (A)

Motive Force (F): effort or effort directed to cause movement against opposition or weight

Resistive Force (R): resists motive force

First Class Lever

axis is put between force and resistance

examples: crowbar, seesaw, scissors

examples in body:

elbow extension

triceps applying force to olecranon (F) in expanding the non-supported forearm (R) at the elbow (A)

flexing muscle

agonist (F) and antagonist (R) muscle groups are simultaneously contracting on either edge of a joint axis (A).

lever characteristics

balanced movement

axis is midway between force and resistance

e.g.: seesaw

speed and variety of motion

axis is close to force

e.g.: elbow extension

force

axis is close to resistance

Second Class Lever

resistance is between axis and force

classic examples: wheelbarrow, nutcracker

complex example: rowing

paddle in water actions as falling axis (A)

boat opposition is resistive force (R)

rower is motive force (F)

relatively few demonstrations in body

planter flexion of foot to lift body up on toes

ball of base (A) serves fulcrum as ankle plantar flexors request force to calcaneus (F) to raise opposition of body at tibial articulation (R) with foot.

entire body during push-up

foot is axis of rotation (A) when answer force of ground impelling against hands (F) elevators heaviness of body's center of gravity (R).

lever characteristics

produces force: large resistance can be moved by a relatively little force

weight machines: more opposition required, smaller inertia, smoother feel.

Third Class Lever

force is put between the axis and resistance

examples:

Tongs: nourishment (R) is sustained by grab on handles (F) while axis is on converse end.

shoveling: dirt on shovel (R) is lifted by force to handle by hand (F) while upper hand on end of shovel handle serves as axis (A)

Rbe obliged: oar is moved through water (R) by dragging on middle of oar ...