Lever 6zu3j

Bones, ligaments, and muscles are the structures that form levers in the body to create human movement. In our bodies:    

bones act as lever arms ts act as pivots muscles provide the effort forces to move loads load forces are often the weights of the body parts that are moved or forces needed to lift, push or pull things outside our bodies.

the effort and load forces have acted in opposite rotation directions to each other. Forces acting on a lever also have different effects depending how far they are away from the pivot. If a load tries to turn the lever clockwise, the effort tries to turn the lever anticlockwise. Different classes of levers are identified by the way the t and muscles attached to the bone are arranged.Levers are typically labeled as first class, second class, or third class. All three types are found in the body, but most levers in the human body are third class while the less common in the body than second and third is the first one. A first-class lever has the axis (fulcrum) located between the weight (resistance) and the force (figure 1.21a). Non-anatomical examples of a first-class lever are a pair of pliers or scissors and seesaw. First-class levers in the human body are rare. One example is the t between the head and the first vertebra (the atlantooccipital t) (figure 1.21b). The weight (resistance) is the head; the axis is the t, and the muscular action (force) come from any of the posterior muscles attaching to the skull, such as the trapezius. The place where your skull meets the top of your spine is a Class 1 lever. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward.

The pivot is the place where your skull meets the top of your spine. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward. ------ muscles provides the force (effort) to lift

In a second-class lever, the weight (resistance) is located between the axis (fulcrum) and the force (figure 1.22a). The most obvious example is a wheelbarrow, where a weight is placed in the bed of the wheelbarrow between the wheel (axis) and the hands of the person using the wheelbarrow (force). In the human body, an example of a second-class lever is found in the lower leg when someone stands on tiptoes (figure 1.22b). The axis is formed by the metatarsophalangeal ts, the resistance is the weight of the body, and the force is applied to the calcaneus bone (heel) by the gastrocnemius and soleus muscles through the Achilles tendon.

For the Class 2 lever the effort force needed is less than the load forcé. The pivot is at your toe ts and your foot acts as a lever arm. Your calf muscles and achilles tendon provide the effort when the calf muscle contracts. The load is your body weight and is lifted by the effort (muscle contraction).

In a third-class lever, the most common in the human body, force is applied between the resistance (weight) and the axis (fulcrum) (figure 1.23a).

For a Class 3 lever the load is further away from the pivot than the effort. Picture someone using a shovel to pick up an object. The axis is the end of the handle where the person grips with one hand. The other hand, placed somewhere along the shaft of the handle, applies force. At the other end of the shovel (the bed), a resistance (weight) is present. There are numerous thirdclass levers in the human body; one example can be illustrated in the elbow t (figure 1.23b). The t is the axis (fulcrum). The resistance (weight) is the forearm, wrist, and hand. The force is the biceps muscle when the elbow is flexed.