How muscles and bone work together like a simple machine called a lever

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Illustration by Fouad A Saad via Shutterstock.com

Levers

Muscles pulling on bone work like one of the 3 types of lever displayed above. In anatomy a lever consists of bone or tendon [a rigid bar] that pivots at an anatomical structure that acts as a hinge or a point of support [a fulcrum] and moves a weight [load] at one end or at the midpoint of the bar by applying a muscle contraction [force].

Thinking of muscles and bones as a set of levers helps to clarify how an array of angular movements can be accomplished by cells, skeletal muscle fibers, that change only linearly. The angle of muscle fibers relative to the muscle’s tendon assists in converting linear to non-linear movement as does the arrangement of muscle origins and insertion points on bone. Lever arrangements, judicious use of insertions and points of origin and an assortment of muscle sizes result in precise performance.

Check out this video describing the various types of muscle and bone levers in the human body.

Muscles and Levers by Bob Myers

Origins and Insertions

Origin and insertion of a muscle can be thought of as the anchor end [origin] and the most mobile end [insertion] when contraction occurs. The origin is usually the bone with greater mass and stability. Bones at the origin of a muscle are typically those nearer the axis of the skeleton. Bones at muscle insertions are usually lighter and distal.

Insertions are generally connections of muscle by way of tendon to bone. But, sometimes muscle insertions are on soft tissues. For example, the orbicularis oris inserts on the skin around the lips and has its origin on the maxilla and mandible.

Learning the origin and insertion points of various muscles is much easier if bones are well-learned first. Bones appear a bit boring without something attached to them, but it is well worth going back and reviewing the size, shape and location of the larger bones before trying to learn muscle origins and insertions.

Another approach that helps when learning muscle origins and insertions is to keep in mind the shape of the muscle and its tendons. Long thin tendons are likely to attach to lighter, thinner and distal bones. For example, review the tendons of the hands and feet and think about how much the bones of the fingers and toes move. Thicker broader tendons make much better anchors and are found at origins.

Keep in mind as you work with this frustrating aspect of anatomy, that anatomic names are repetitious to a degree from system to system. The names of the muscles correspond in many ways to the names of the bones to which they attach. The names of the arteries, veins and nerves you will learn next also reflect shape and names of the bones and muscles that they pass through.

Do you have questions?

Dr. Reece is always available to answer your questions at DrReece@MedicalScienceNavigator.com. If you found this discussion of muscles, origins, insertions and levers helpful please share it with your followers on social media by clicking on one of the buttons below.

 

Reece-4-S2S14-001Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts and CSO at Serometrix LLC is now CEO at Reece Biomedical Consulting LLC.

Dr. Reece is passionate about helping students, online and in person, pursue careers in life sciences. Her books “Physiology: Custom-Designed Chemistry” (2012), “Inside the Closed World of the Brain” (2015) and upcoming “Step-by-step Guide for Study of Physiology” (2016) are written for those new to life science.

Dr. Reece offers a free 30 minute “how-to-get-started” phone call for students struggling with human anatomy and physiology. Appointments are scheduled by email at DrReece@MedicalScienceNavigator.com.