Question

Give an example of each class of lever in the human body. (i.e. class I, II, and III) Fully describe the action of the muscle-bone-joint system. A tendon attached to the radius in your arm provides a greater force upward than the weight of an object in your hand when you are lifting an object by just your forearm (like doing curls in weight-lifting, using only your elbow as a pivot point). Please explain why.

Answer 1

Answer:

Bones, ligaments, and muscles are the structures that form levers in the body to create human movement. In simple terms, a joint (where two or more bones join together) forms the axis (or fulcrum), and the muscles crossing the joint apply the force to move a weight or resistance. 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.

A first-class lever(Class-I) has the axis (fulcrum) located between the weight (resistance) and the force.A first-class lever has the axis (fulcrum) located between the weight (resistance) and the force.The weight (resistance) is the head, the axis is the joint, and the muscular action (force) come from any of the posterior muscles attaching to the skull, such as the trapezius.

In a second-class lever(class-II), the weight (resistance) is located between the axis (fulcrum) and the force.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.The axis is formed by the metatarsophalangeal joints, 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.

In a third-class lever(class-III), the most common in the human body, force is applied between the resistance (weight) and the axis (fulcrum).There are numerous third-class levers in the human body; one example can be illustrated in the elbow joint.The joint is the axis (fulcrum). The resistance (weight) is the forearm, wrist, and hand. The force is the biceps muscle when the elbow is flexed.

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Musculoskeletal system is made up of muscles, tendons, ligaments, bones, cartilage, joints and bursae. Our muscles work with the nervous system to contract when stimulated with impulses (messages through the receptor arc) from motor nerves. The muscles are attached to the bones with ligaments. Our skeletal system is made mostly of bones and cartilage. Bones attach to bones with cartilage or ligaments. Bursae are small fluid filled at friction points near joints to protect ligaments and tendons from rubbing against bare bones.

The skeletal system serves as a framework for tissues and organs to attach themselves to. This system acts as a protective structure for vital organs. Major examples of this are the brain being protected by the skull and the lungs being protected by the rib cage.Located in long bones are two distinctions of bone marrow (yellow and red). The yellow marrow has fatty connective tissue and is found in the marrow cavity. During starvation, the body uses the fat in yellow marrow for energy.The red marrow of some bones is an important site for blood cell production.
Another function of bones is the storage of certain minerals. Calcium and phosphorus are among the main minerals being stored. The importance of this storage "device" helps to regulate mineral balance in the bloodstream.
There are three types of muscles—cardiac, skeletal, and smooth. Smooth muscles are used to control the flow of substances within the lumens of hollow organs, and are not consciously controlled. Skeletal and cardiac muscles have striations that are visible under a microscope due to the components within their cells. Only skeletal and smooth muscles are part of the musculoskeletal system and only the skeletal muscles can move the body. Cardiac muscles are found in the heart and are used only to circulate blood; like the smooth muscles, these muscles are not under conscious control. Skeletal muscles are attached to bones and arranged in opposing groups around joints.
Muscle contraction is stimulated by the motor neuron sending a message to the muscles from the somatic nervous system. Depolarization of the motor neuron results in neurotransmitters being released from the nerve terminal.
Joints: There are two divisions of joints, diarthroses which allow extensive mobility between two or more articular heads, and false joints or synarthroses, joints that are immovable, that allow little or no movement and are predominantly fibrous. Synovial joints, joints that are not directly joined, are lubricated by a solution called synovial fluid that is produced by the synovial membranes. This fluid lowers the friction between the articular surfaces and is kept within an articular capsule, binding the joint with its taut tissue.

From our head to our toes, our bones provide support for our bodies and help form our shape.Together, our bones, muscles, and joints — along with tendons, ligaments, and cartilage — form our musculoskeletal system and enable us to do everyday physical activities.

Answer 2

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